NCEA L1 Science: Punnett Squares And Pedigree Chart Explained

Summary

This educational video delves into the fundamentals of genetics, focusing on key concepts like DNA, genes, alleles, and base sequences. It explains how different versions of genes, or alleles, lead to variations in physical traits, using examples like hairline patterns. The video also teaches how to use Punnett squares and pedigree charts to predict genetic outcomes in offspring, with practical examples like albinism in rats. It emphasizes the importance of understanding dominant and recessive alleles, and how they manifest in different genotypes, providing a comprehensive guide for students navigating genetics.

Takeaways

• 🧬 DNA is the double helix structure that contains all genetic information, with specific sections called genes that represent individual traits.
• 🔑 Genes have different versions known as alleles, which are responsible for variations of the same trait due to different base sequences (A, T, C, G).
• 🔠 Dominant alleles are represented by capital letters and are more likely to be expressed, while recessive alleles are in lowercase and only appear when no dominant allele is present.
• 🌟 Understanding the difference between heterozygous (one dominant, one recessive allele) and homozygous (two dominant or two recessive alleles) genotypes is crucial for predicting genetic outcomes.
• 📊 Punnett squares are used to predict the possible genotypes and phenotypes of offspring by combining the alleles of two parents.
• 🐀 The example of rat coloration, where albinism is caused by a recessive allele (small a), illustrates how genetic traits can be analyzed.
• 👨‍👩‍👧‍👦 Pedigree charts help visualize the inheritance of traits within a family tree and are essential for predicting genetic outcomes across generations.
• 🔄 The importance of understanding both forward (from parents to offspring) and backward (from offspring to parents) inheritance to solve genetic problems.
• 📚 The video emphasizes the value of practice with past exam papers for mastering genetics and related statistical analysis.
• 🌐 The instructor encourages students to utilize available resources, like past exams on the instructor's YouTube channel, for better understanding and preparation.

Q & A

What is DNA and what is its significance?

DNA stands for Deoxyribonucleic Acid, and it is the double helix structure that contains all the genetic information. It is crucial as it carries the instructions for the development, functioning, growth, and reproduction of all known living organisms and many viruses.

What is a gene and how does it relate to physical traits?

A gene is a segment of DNA that represents one particular trait or physical characteristic. It is responsible for determining specific features such as eye color or hair type.

What are alleles and how do they contribute to genetic variation?

Alleles are different versions of the same gene, which can result in different expressions of the same trait. They arise due to variations in the base sequence of DNA, leading to genetic diversity.

What is the difference between a dominant and a recessive allele?

A dominant allele is a version of a gene that is expressed when present, even in a single copy. A recessive allele, on the other hand, is only expressed when two copies are inherited. Dominant alleles are usually represented by uppercase letters, while recessive alleles are represented by lowercase letters.

What is meant by the term 'heterozygous' in genetics?

Heterozygous refers to an individual having two different alleles for a particular gene. This means they have one dominant and one recessive allele, resulting in a mix of traits.

How is a Punnett square used in genetics?

A Punnett square is a diagram used to predict the genotypes of offspring based on the genotypes of the parents. It is a simple way to visualize the possible genetic combinations that can occur in a cross.

What is a pedigree chart and how is it used to study genetics?

A pedigree chart is a graphical representation of the inheritance of a particular trait through successive generations of a family. It helps in understanding the pattern of inheritance and predicting the likelihood of a trait appearing in future generations.

Why is it important to understand the difference between genotype and phenotype in genetics?

Genotype refers to the genetic makeup of an individual, including the alleles they carry for specific traits. Phenotype is the observable physical or biochemical characteristics of an individual, which results from the interaction of their genotype and the environment. Understanding this difference is important for predicting how traits will be expressed and inherited.

What is the significance of the term 'homozygous' in the context of genetics?

Homozygous refers to an individual having two identical alleles for a particular gene. This can be either homozygous dominant, where both alleles are dominant, or homozygous recessive, where both alleles are recessive. It is significant because it indicates a higher likelihood of the trait being expressed consistently.

How can one determine the likelihood of an offspring inheriting a specific trait?

The likelihood of an offspring inheriting a specific trait can be determined by analyzing the genotypes of the parents and using tools like Punnett squares or pedigree charts. This allows for the prediction of the probability of different genotypes and phenotypes in the offspring.

Outlines

00:00

🧬 Introduction to Genetics and Alleles

The video begins with an introduction to genetics, focusing on DNA and its structure. The presenter explains that DNA contains all genetic information and is composed of genes, each representing a specific trait. Alleles, which are different versions of the same gene, are introduced as the cause for variations in traits. The concept of base sequences, denoted by the ATCG code, is briefly touched upon as the foundation for allele differences. The video then delves into the dominance and recessiveness of alleles, using capital and lowercase letters to represent them, respectively. The presenter uses the example of hair traits to illustrate these genetic principles, explaining how different combinations of alleles can result in different physical appearances.

05:00

🐀 Understanding Albinism in Rats Through Genetics

The second paragraph delves into a specific genetic condition, albinism in rats, which is caused by a recessive allele. The video uses this condition to explain how to determine dominance and recessiveness in genetics. The presenter guides viewers through the process of using pedigree charts and Punnett squares to predict genetic outcomes in offspring. The video explains how to interpret these tools, using the example of albino rats to demonstrate how different genetic combinations can lead to different phenotypes. The importance of understanding these genetic principles is emphasized for predicting the likelihood of certain traits appearing in future generations.

10:02

📊 Analyzing Pedigree Charts for Genetic Inheritance

This section of the video focuses on the practical application of pedigree charts to determine the genotypes of rats. The presenter uses an example to illustrate how to deduce the genetic makeup of rats based on their physical traits and the traits of their offspring. The process involves logical deduction and the use of genetic principles to fill in the missing alleles for each rat in the chart. The video demonstrates how to work through a pedigree chart systematically, using the information provided by the presence of certain traits in the offspring to infer the genotypes of the parents. The presenter encourages viewers to practice this skill as it is crucial for understanding genetic inheritance patterns.

15:05

🧐 Deciphering Genotypes from Phenotypes

The video continues with a deeper exploration of how to determine the genotypes of rats from their observable phenotypes. The presenter uses logic and the principles of dominance and recessiveness to explain why certain genotypes are more likely than others. The discussion includes the use of Punnett squares to predict the possible genetic outcomes of breeding pairs and how to interpret these outcomes to understand the likelihood of certain traits appearing in offspring. The presenter also touches on the importance of probability in genetics, emphasizing that while certain outcomes are more likely, genetic inheritance is not deterministic and can be influenced by chance.

20:06

🐎 Applying Genetic Principles to Different Traits

In this part of the video, the presenter applies the genetic principles discussed earlier to different traits, such as a white patch on horses. The video explains how to identify recessive traits and use them to deduce the genotypes of the animals in a pedigree chart. The presenter walks through the process of filling in the genotypes for each animal, using the information provided by the presence of dominant and recessive traits in the offspring. The video also discusses how to handle cases where the genotype is not immediately clear, emphasizing the importance of logical deduction and the use of genetic principles to make informed guesses.

25:08

🤧 Discussing Photoptic Sneezing and Its Genetic Basis

The final paragraph of the video script discusses the genetic basis of photoptic sneezing, a condition where exposure to bright light causes sneezing. The video uses this trait to illustrate how to apply the principles of dominance and recessiveness to determine the genotypes of individuals in a pedigree chart. The presenter explains how to work backwards from the phenotypes of the offspring to deduce the genotypes of the parents, emphasizing the importance of understanding genetic inheritance patterns. The video concludes with a reminder of the importance of practice and the availability of past examination papers for further study.

Keywords

💡DNA

DNA, or deoxyribonucleic acid, is the hereditary material in humans and almost all other organisms. In the video, DNA is described as the double helix structure containing all genetic information. It is the basis for heredity and variation among organisms. The script explains that genes, which are sections of DNA, determine specific traits or characteristics.

💡Gene

A gene is a segment of DNA that contains instructions for producing a specific protein, which in turn is responsible for a particular trait. The video script uses the example of hairline to illustrate how a gene can have different versions, leading to variations in physical appearance.

💡Alleles

Alleles are different versions of the same gene that can exist at the same locus (position) on a chromosome. They are responsible for the variation in traits within a species. The script discusses how different alleles, such as 'A' and 'a', can lead to different expressions of the same trait, like albinism versus normal pigmentation in rats.

💡Base Sequence

The base sequence refers to the order of nucleotides (adenine [A], thymine [T], cytosine [C], and guanine [G]) in a DNA molecule. This sequence encodes the genetic information. The video explains that different base sequences can result in different alleles, which in turn can affect the physical traits of an organism.

💡Dominant Allele

A dominant allele is a version of a gene that expresses its trait even when only one copy is present in the genotype. In the script, dominant alleles are represented by uppercase letters, and they are said to 'mask' the effect of the recessive allele, which only shows its trait when two copies are present.

💡Recessive Allele

A recessive allele is a version of a gene that only expresses its trait when two copies are present in the genotype. Recessive alleles are represented by lowercase letters in the script and are only visible when there is no dominant allele present to override them.

💡Heterozygous

Heterozygous refers to an individual having two different alleles for a particular gene. In the context of the video, a heterozygous genotype is represented as 'Aa', where 'A' is the dominant allele and 'a' is the recessive allele. The script uses this term to explain scenarios where an individual carries a trait but does not express it.

💡Homozygous

Homozygous means having two identical alleles for a particular gene. The video script explains two types: homozygous dominant ('AA') where both alleles are dominant, and homozygous recessive ('aa') where both alleles are recessive. These terms are crucial for predicting the outcomes in genetic crosses.

💡Punnett Square

A Punnett square is a diagram used to predict the genotypes of offspring in a genetic cross. It is a simple way to determine the possible combinations of alleles that can result from a particular mating. The script demonstrates how to use a Punnett square to predict the likelihood of traits in offspring, such as the color of rats.

💡Pedigree Chart

A pedigree chart is a graphical representation of the inheritance of traits within a family tree. It is used to track the patterns of dominant and recessive alleles through generations. The video script uses pedigree charts to illustrate how to determine the genotypes of individuals based on the traits observed in their offspring.

💡Genotype

The genotype is an individual's complete set of genes, or the specific set of alleles they carry for a particular gene. The video script discusses how to determine the genotype of individuals by analyzing their phenotypes and the phenotypes of their relatives in a pedigree chart.

💡Phenotype

The phenotype is the observable physical or biochemical characteristics of an individual, as determined by both the genotype and the environment. In the script, phenotypes like hairline shape and albinism are used to deduce the underlying genotypes and the presence of dominant or recessive alleles.

Highlights

Introduction to the video's focus on NCAA one sites and genetics variation.

Recap of key genetic terms such as DNA, genes, alleles, and base sequences.

Explanation of how different base sequences lead to different alleles and traits.

Use of capital letters for dominant alleles and lowercase for recessive alleles in genetic notation.

Description of heterozygous and homozygous genotypes and their implications.

Introduction to Punnett squares for predicting genotypes and their ratios in offspring.

Example of using a Punnett square to determine the likelihood of albinism in rats.

Explanation of how to interpret pedigree charts to deduce genetic information.

Step-by-step guide on analyzing a pedigree chart to determine the genotypes of rats.

Discussion on the probability and statistics involved in genetic inheritance.

Practical advice on using logic to solve genetic problems, like solving puzzles.

Application of genetic principles to a real-world example of horse coloration.

How to determine the likelihood of a trait being dominant or recessive from a pedigree chart.

Importance of understanding both forwards and backwards logic in genetic analysis.

The significance of homozygous dominant and heterozygous genotypes in genetic expression.

Advice on practicing with past examination papers for better understanding of genetics.

Encouragement to combine biology with statistics for a comprehensive understanding.

Closing remarks and sign-off, with a reminder to take care and engage with future content.

Transcripts

hi guys welcome to today's video we are

going to look at some ncaa one sites um

looking at the achievement standard um

of genetics variation so

um as a topic such as a you know title

suggests we're going to look at punnett

squares and pedigree charts today but

just just before we do that we're just

going to quickly um recap on some of the

key ideas so that when we refer to

certain

terminologies will make sense

otherwise you know it just

doesn't understand what we're trying to

talk about here so just really quickly

some of the key things that you need to

you need to some of the key definitions

you need to understand um everything so

we started looking at dna and then so

what is the dna you can look up on let's

say i've given my clients some

definitions and

and there's very popular questions like

what is the dna you know the double

helix structure that contains all the

genetic information and then from your

dna

in one section of the dna

is called a jing one gene represents one

particular trait one physical

characteristic but then out of that one

trait you have different versions

um

you have different versions of the same

trait

different versions

and these are coded by what we call

um alleles okay so

when you have different versions why do

i have why do you have different

versions because we have different um

genetic

of the different base sequencing so

that's what that is different

see

different base sequencing

what different base sequence

and what is base sequence that's where

the atcg stuff comes in

um so if we break it down to short so

everyone all of us have dna you know in

our cells and then one section and the

dna is really really big really really

long and if you look at one particular

section that is what we call a gene and

one gene calls for one characteristic

one physical trait but then there are

different versions of that particular

trait let's say for example if you look

at if you

look yourself in the mirror you can look

at your hairline um there's um a very

unique um

trait called with widow's peak so it's

like a v-shaped hairline a lot of people

here like just straight a lot of us like

i i have a v-shaped um hair like so

that's different versions of the same

trait why is that because um for that

particular same gene we have different

alleles okay so why why are they

different because for the same gene they

have different base sequence like say

for example one could be a t c g

t a for example this could be one

particular allele for the other one

could be g c t a t a for example and

both of these

these um

base sequence they called for the same

gene but as you can see they're

different so the results in a different

protein and that that results in a

difficult uh a different physical

appearance

which is the physical trait okay now um

alleles so we kept we use capital

letters for um

with capital letters for the dominant

allele so the dominant allele so because

it normally you know to simplify things

we say the two versions of each gene so

um the one that's more dominant that's

always being displayed is what we call

you know we assign that with a capital

letter and the one with the lower case

is going to be

the recessive allele

now the recessive allele is only going

to display

if there's no dominant allele present

okay so that comes down to like say for

example if i use

capital h lowercase h

um

there's three different combinations of

how it could look like so you know the h

could mean on the hairline example h for

hairline so you could have three

scenarios this when you have one of each

a capital h lowercase h this is what we

call a heterozygous

this is a heterozygous

genotype

and

we have two capital h's this is

homozygous dominant

homo means the same

so homozygous dominant means i have two

dominants

and two slow h's this is also the same

so it's homozygous

recessive

because i have got two recessives now

just remember with the heterozygous you

don't need to say heterozygous dominant

or heterozygous recessive heterogeneous

means different so heterozygous means

one of each okay so

i'm gonna just quickly recap these

because we're gonna need to use these

for later okay um

let's look at some particular questions

okay so the best way to do genetics is

by looking at some questions especially

with punnett squares and pedigree charts

so let's have a look at these okay so um

we're looking at rats in this particular

sample let's highlight the important

part albinism is caused by a recessive

allele small a

so one you get told this and they always

tell you the you know that they always

give you the letters to use they always

tell you which one's possible which

one's dominant which is which one is

recessive some questions that give you

the pedigree charts and ask you to

figure out which one's dominant which is

recessive which we can look at for um

which we can look at in some of the

examples that we got given below okay so

let's just really quickly um link back

to what we've done just now so if we

have an albino rat and

we know it's a

the that particular genotype

the allele that calls for that is a

small a so if you have an ability so

that means the genotype of this

particular rat must be small a small a

okay because there's no other k l

there's no other scenario because you as

soon as you have a capital a

in the genotype the the rat will be

black will be normal okay so that means

this is going to be small a small a when

you have a heterozygous black rat so

heterozygous means one of each so you

have a capital a lower case a so why

does a wrap appear this particular color

um like a normal rat that you see is

because of the

capital a that you get given in the you

know in the equation so this is a very

messy punnett square so this is what

they um

so

in in terms of like this is an older

version of some of the exams but this is

what you kind of get given nowadays

they do it like this

okay so this is what it kind of looks

like nowadays so it's the same exactly

the same thing but

these type of table cushions much less

common now they just give you the

punnett square so how do you do punnett

square you literally just identified the

two alleles and put them one each into

the columns

and then you simply combine them like

say for example this and this goes here

so it's a capital a okay say

this and this goes here so this is a

capital a okay say so this is more is

more a small a so

if we come back to this question it's

literally like all right so if i combine

this a and if we combine with this a so

this is capital a or case a

if we combine this a with this a this is

lowercase a lowercase a um if you

combine this one

with this one this is capital a locus a

and this is lowercase l okay so you get

this exactly the same outcome and just

to

represent um

a punnett square so what do we use upon

a square for a punch square is simply

used to predict

the

genotype and the possibility of getting

different genotypes in the

outcomes of you know these two organisms

having offspring and we can predict the

possibility you know what are the

chances of the baby rats are going to be

normal color or albino and we can figure

out a percentage so if we look at this

particular question this is going to be

if you look at that so these are my four

outcomes i have got two of them i've got

two

big a small ace which is heterozygous i

got two small a small a's which is

hormones i guess i'm recessive so out of

four i have 50 percent two out of four

going to be big a small a which means

they're going to be a normal black color

if i get 250 percent small a small a

which is homozygous recessive that means

i'm going to get that whole below red

okay so

does that mean

let's say for example if these rats were

to reproduce that have four baby rats

are they all going to be 50 50 obviously

not it's just every single chance every

single time um a baby rat an offspring

is being reproduced there's a 50 chance

it's like a coin toss like you know with

humans like boy or girls that you said

you know is is just a flip of a coin and

it just depends on what the coin turns

out to be every single time so you know

in our school we have um you know i've

known siblings with

like a very big family six seven sisters

no brothers in the family probably only

actually there's one brother at the end

and the youngest one's a brother so it's

just a

coin toss every time and just happen to

be girls um for like the first five six

times okay so that's unlikely but it can

happen okay so this is the first

question that i thought would look like

now this is looking at the pedigree

chart this is looking at

um so we need to remember um albino is

small a and then

so albino red is more a this is from the

previous question and normal is just

capital a all right so just remember

that now they have been already a lot of

literature so this is your typical um

what do you call it

pedigree charts okay so you look at the

family tree of the physical traits that

we're looking at and then you can

actually predict what the genotypes are

of the falling rats we can do better we

can do instead of doing four and six

let's do all of them okay let's do all

of them it's good practice and that's

often how i teach my guys when we do

pedigree charts don't just look at the

question

if there's a pedigree chart you have the

glory in front of you can you actually

figure out all of the

um all of the answers all right so let's

come back to the example so albino reds

are small a's okay so that means this

one

must be small x y this one must be

homozygous recessive this one must be

homozygous recessive because they have

to have

a lower case a and another lowercase a

because if they were to have the

dominant capital a they would be normal

okay now all of the other guys let's say

two three five six you know so on so

forth all of them have to have at least

one capital base

okay so you can just literally do that

go above them and write a capital a

above them because they have to have at

least one

okay so it doesn't matter what the other

allele is as long as it got one capital

a that means they would group they would

display this particular phenotype which

is a normal hair color

so how do we decide what the other thing

is so this is where you need to look um

i'm just gonna sorry i'm just gonna

clean this a little bit because

you get the idea all right i know what i

just want to clean it out otherwise it's

gonna look really messy okay so let's

ignore these

all right

let's use a different color

so let's look at

the offspring of

number one

and number two so number one and number

two has three offsprings which is this

guy

this guy

and this guy

okay so let's look at the punnett

squares now

if we were to you know i don't want to

write long explanations i just want you

to understand this so can you see so

this has to have have a capital a and

the other letter has to be a small a

and you probably go how do you know that

how do you know it's not a capital a now

how do you know it's not homozygous

dominant well the species of interest is

going to be this guy the the the

organism of interest is going to be that

guys because these two

parents

you have this fella and this fella they

managed to have

three offsprings and one of them is the

smallest moy

so the only possibility that you can get

a small a small a is that you got one

small a from um

and then you got once more a from that

okay so that means

this

um doesn't tell us the gender but this

parent this um could be mommy or rat or

daddy rat doesn't really matter he has

to have a small a because otherwise

where would the second slow small a come

from

you can't remember from when we inherit

alleles from the parents you get half

from each parent so that means you get

half of capital a as small as more ace

which means you guarantee a small a from

this particular rat but then you have to

get the other a from this rat so that's

why

this

number two so it's going to be a bit

messy again number two has to be

heterozygous because there's no other

option there's no other possibility for

this number four

to inherit this small a

okay so it has to have a capital f so

let's do the partner square if we know

it's capital a is located slowly slow a

small smy then you can see that this is

going to be a a

whole heterozygous homozygous recessive

and that explains it okay and you can

even prove it if i do big a big a small

a small a can you see that there's

absolutely no chance

that you get a um you get an albino rat

out in the outcome absolutely no chance

okay so by doing that we figured out

we figured out all of um all of the ones

above so we know there's a small a small

this is big a small a

um this is small a small a this is

number five is big a small a number six

is being big a small a because the only

possibility

for the offspring to have a

normal hair color is because they got

the the capital a from you know number

two and then they got the other small a

from number one okay so we figured out

the five and six so you have if you

actually look at us number four number

six we actually have finished the

question

now let's do a little bit better let's

do more because it's all about

understanding you're not here just to

get

um if you if you want more answers just

go on to the nzq website and read that

but that's not what you're here for

you're here for for the understanding

because you can always memorize how to

write but then especially drawing

lockdowns you probably want someone to

explain to you all right let's look at

number seven if we look at number seven

so again number six and number seven

want to reproduce number 12 and number

13. now number 12 again number 12 is muy

smoy so that means number six has to

have a small a and number seven has to

have a small a but we know number seven

is a normal hair color so it has also

have to have a capital a so it's to do

with logic it's like i love doing

pedigree chances like solving puzzles

and you can't just look top down you

have to sometimes look backwards from

bottom up and to determine what type of

genotypes we're looking at okay so

number seven is capital a's um small a

now for number 13 we actually don't know

because if you do the punnett squares

of these two parents oops

you can see there are

three possible genotypes so the ones

highlighted that i'm highlighting right

now they will all

can become number 13 which can be the

genotype so it could be capital a

capital a or capital a small a

so either homozygous dominant or

heterozygous we don't know and how could

we not get that rat you know pick um

select that rat and then you know get it

to reproduce and then look at the future

generations okay now if you look at

number three number three we don't know

it could be the capital a capital a it

could be

it could be capital a small

because if you look at 8 9 10 11

these guys

would have to be capital a's

small as capital a small a capital a is

more in capital a small and then you go

how do you know that we look at the

parents we look at number four has to be

big small asthma and remember

these number 8 9 10 11 they have to

inherit one allele from each parent so

that means it's a hundred percent chance

you get a small a from the number four

react and then you got a big a from the

number three rat okay because why do you

get that because they look normal okay

so they have to have a capital a so this

is why they have to have a capital a and

they have to have a small a you know

just using logics okay

now

look at this um

so rat three was not an offspring so

we're looking at round number three so

this is

um

we kind of jumped ahead with the

question so if we look at the chart here

let me just wrap this out

if you look at the chart here and then

we go all right what is possibility

number three so we know number four

so we know number four right oops we

know red number four has to be small x

moy we know rat number three could be

composite big a small a or big a big a

because all of their children

all offsprings

all of their

all of their offsprings

are

biggest moy you know with the reasons

that we talked about here so if you look

at the question state the possible

genotype it could be this

or it could be this why because it's

normal it's a normal color so that means

it has to have a dominant trait and we

don't know what the other one is because

if we can't look at this genotype we can

only look at the physical structure

explain why both phenotype genotypes are

possible because if you actually look at

the possibility

um so this these are the two

possibilities

and then they have to mate with the

smaller small uh small a

and then if you actually complete the uh

the punnett squares

you can see

there is a so for this one

there's a hundred percent chance v gas y

and what does that mean so this is a

genotype

and the phenotype is their hair color

which is the normal black color and then

if you look at this this is fifty

percent genotype is going to be two out

of four gonna be big a small fifty

percent is going to be small a small

okay so that means there's a 50 chance

they'll be normal but then there's a 50

percent chance they are albino

okay so which one um which one but one

is more likely so this is more likely so

that means it's more likely for the for

number three to be capital ace which is

homozygous dominant but it is still

possible for rat number three to be

heterozygous because like i just

mentioned with the examples it could be

you know if you know any family or

friends they have siblings and you know

three or four siblings and they're all

of the same gender

you know it could just be by chance and

it has to happen in this case as well

yes it could be a heterozygous rat but

then you know just by chance 50 of time

boom boom boom hit the four times in a

row and then you've got four reds and

the normal so

what we could do um to be more certain

about the genotype of rat number three

get that to keep mating with rat number

four okay because the moment

you see

that one of them is more a small uh one

of them is albino boom you know that the

parent is heterozygous

okay and if you after like a few five

more rats 10 more rats baby rats that

were born

and there's still no albino rats and

it's very likely that it's going to be

kept away captain okay homozygous

dominant so it's to do with probability

and that's why it is important if you're

interested in taking biology

statistics is often a very very

important subject to take alongside

biology because you get a lot of data

and you need to analyze the data and

stats to teach you really well in that

regard okay so let's look at a few more

um so this is another condition

um so this is to do with horses having a

white patch on the head on the body of

horses very very common so in horses

let's look at this um

buddhism is a dominant trait which is

capital h normal is recessive okay so

let's remember that now when we look at

the chart normal is shaded and then

these guys are you know not filled in so

that means which one is recessive the

normal color is recessive so that means

normal is recessive so don't even think

about it just go small h small h small h

small h small h small h small h small h

and this is how you can analyze you can

probably see i don't even have the

questions like this is just a pedigree

chart i don't even know what the

question is asking you to do but if you

can do these steps you can answer any

question they give you because you

already solved all the species general

genotypes

and you know anything else you would

have answered any possible question the

examine the examiner could have thrown

at you okay so just remember look for

the recessive trait look for the

recessive um trade here and then you can

literally just put homozygous recessive

the small letters for these ones here so

let's decide number one number one must

be homo must be heterozygous

why is that because all of the children

are small ages

okay so that means it has to have

now because it's the it's it has the is

the the pipeline so that means the the

pi volt so they have to have a capital h

then it has to have a lowercase h

because thus gives you that's given from

here and the small h's the small h's

from five six seven eight

tells you that how did they get the

small h they inherited from both parents

okay so that's why number one is capital

h lowercase h if you look at number

three number four so um same thing this

has to have a capital h this has to have

capital h

yeah so

regardless of what the other one is they

have to have at least one capital letter

because they are showing the dominant

trait because they you know they told

you they are pipeled and that's why they

have to have at least one capital h's

and then you can look at the children

number 10 number 11 number 12 are those

small h's so that what does that mean

they would have inherited the small h

from each parent

okay so that means

you get one of the small h's from each

parent that's why number three and

number four are heterozygous okay so if

you look at um

um if you look at number nine number

nine is hard to decide um but these um

these offsprings here they have to be

capital h lowercase h capital you know

they have to be heterozygous why is that

because number eight number eight is

normal so it has to have small h small h

so this is where the small h come from

because you remember you inherit one

allele from each parent so they have to

get the h

from number eight you know the small h

because it's my other option you got 100

gonna get that number nine is going to

be

it's going to be capital h plus

something else could be h h could be h

capital h uh heterozygous could be

homozygous dominant

but it doesn't matter because this these

um offsprings are pi volt so that means

they would have inherited the positive

the big h okay so that's there you go

that's how you can

answer the questions let's do one more

before we wrap it up um photic sneezing

so

i'm not we're not interested in the

water conditioners we're looking at this

um sneezing is dominant

to unaffected okay so

just look here so what's unaffected i

always go with the recessive trait

because that's going to make your life a

lot easier unaffected is

unaffected are these guys so straight

away small a small a

you know

these things that i think these people

sorry these people are all going to be

homozygous recessive

okay regardless and if we apply the same

thinking if we got

number

five six seven or being homozygous

receptive that means numbered so that

means their parents again if you've got

two small a's that means their parents

must must have a small a each

so we got the small a's from this parent

then that means we have to have the

small a from number two okay so you know

they have to have one big calculators

each because they are displaying that

trait and we can just figure out what

the other one is and then if you look at

number three number four

if you look at the children number eight

is showing small asmoy so same thing

would have got this from one of each

parent so that means number four will be

heterozygous as well and that means this

is going to be smoke heterozygous

histozygous heterozygous and you may go

how do you know that because if you look

at you know who are they children of

number 9 10 11 are children of number

three and number four and then you can

you know work backwards you can

you know this is how they can they have

to in

they have to inherit

the small a once more a from parent

number three and then they because they

are affected so they would have got the

they would have got the dominant trait

as well okay so number 12 is also so if

you look at number 11 number twelve

number eleven we know it's going to be

big smoy number 12 is going to be

capital a for sure but we don't know

what the other one is but then if you

look at number 14 number 14 has kept a

small a small a that means you would

have got a small a from each parent so

this is not a question mark this is

going to be heterozygous okay so

hopefully that does make sense it does

take quite a bit of practice that's why

it's all um it's actually good that you

are watching these um because you can

always re-watch um the explanation and

the best way to have a go at it is to go

through the past year's examination

papers which i'm aiming to finish um

relatively soon but you have the

2018-2019 exams available on my youtube

channel so

feel free to browse through the playlist

and find

the particular exams and just make sure

that you can produce something similar

in

in november or december i can't remember

when the exams are okay so hopefully

this has been helpful and

look after yourself and i'll see you

guys next time bye