NCEA L1 Science: Punnett Squares And Pedigree Chart Explained
Summary
TLDRThis 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
🧬 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.
🐀 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.
📊 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.
🧐 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.
🐎 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.
🤧 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.
Mindmap
Keywords
💡DNA
💡Gene
💡Alleles
💡Base Sequence
💡Dominant Allele
💡Recessive Allele
💡Heterozygous
💡Homozygous
💡Punnett Square
💡Pedigree Chart
💡Genotype
💡Phenotype
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
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