Lesson 9: Incomplete Dominance

Summary

This educational video introduces non-Mendelian inheritance, focusing on incomplete dominance. It explains how traits do not always follow Mendel's laws, leading to phenotypes that are a blend of both parental traits, such as pink flowers from red and white parents. Examples like 4 o'clock flowers and Andalusian chickens illustrate this concept, and the video guides viewers to use Punnett squares to predict genotypic and phenotypic ratios for such inheritance patterns.

Takeaways

• 🌟 The video introduces non-Mendelian inheritance, which includes patterns that do not follow Mendel's laws of inheritance.
• 🔍 It focuses on the concept of incomplete dominance, where the phenotype of the offspring is a blend of the parents' traits.
• 🌺 An example of incomplete dominance is given with flowers, where a cross between red and white flowers results in pink flowers.
• 🐔 The Andalusian chicken is used as another example, where black and white feathered parents produce blue-feathered offspring, illustrating co-dominance.
• 🧬 The video explains that in co-dominance, both alleles are expressed in the phenotype, unlike typical Mendelian dominance.
• 📊 Viewers are expected to use a Punnett square to solve for non-Mendelian inheritance problems by the end of the video.
• 📚 A review of Mendelian inheritance terminologies is prompted, including dominant traits, homozygous, recessive traits, monohybrid cross, heterozygous, and phenotype.
• 🌼 The video script includes a sample problem using a Punnett square to determine the genotypic and phenotypic ratios for flower color crosses.
• 🔢 The genotypic ratio for a cross between a pink and a white flower is 50% heterozygous pink and 50% homozygous recessive white, resulting in a 1:1 ratio.
• 🎨 For a cross between two pink flowers, the genotypic ratio is 25% homozygous dominant red, 50% heterozygous pink, and 25% homozygous recessive white, leading to a 1:2:1 ratio.
• 📈 The phenotypic ratio for the cross between two pink flowers is 25% red, 50% pink, and 25% white, also reflecting a 1:2:1 ratio.
• 👋 The video concludes with an invitation to subscribe for more science educational content.

Q & A

What is non-Mendelian inheritance?

Non-Mendelian inheritance refers to any pattern of inheritance where traits do not segregate according to Mendel's laws, which describe the inheritance of traits linked to single genes on chromosomes in the nucleus.

What are the types of inheritance patterns that fall under non-Mendelian inheritance?

Incomplete dominance, sex-linked traits, and multiple alleles are the patterns of inheritance that fall under non-Mendelian inheritance, although the script focuses only on incomplete dominance.

What is incomplete dominance?

Incomplete dominance is a genetic phenomenon where neither allele is completely dominant over the other, resulting in a phenotype that is a blend of both parental traits.

How does the phenotype of the F1 generation differ in incomplete dominance from Mendelian inheritance?

In incomplete dominance, the F1 generation exhibits a phenotype that is intermediate between the phenotypes of the homozygous dominant and homozygous recessive parents, rather than expressing only the dominant trait as in Mendelian inheritance.

What is an example of incomplete dominance in flowers?

An example of incomplete dominance in flowers is seen in 4 o'clock flowers, where a cross between a homozygous red flower and a homozygous white flower results in pink flowers due to the blending of the red and white alleles.

What is the concept of co-dominance mentioned in the script?

Co-dominance is a genetic phenomenon where both alleles are expressed in the phenotype, neither being completely dominant or recessive. An example given is the Andalusian chicken, where black and white feathers result in blue offspring.

What is the purpose of using a Punnett square in the context of the video?

A Punnett square is used to predict the genotypes and phenotypes of the offspring in a genetic cross, helping to solve for non-Mendelian inheritance patterns such as incomplete dominance.

What is the genotypic ratio in the cross between a pink and a white flower, according to the script?

The genotypic ratio in the cross between a pink and a white flower is 50% heterozygous pink and 50% homozygous recessive white, resulting in a 1:1 ratio.

What is the phenotypic ratio when a pink flower is crossed with another pink flower?

The phenotypic ratio when a pink flower is crossed with another pink flower is 25% red, 50% pink, and 25% white, resulting in a 1:2:1 ratio.

What is the significance of the term 'heterozygous' in genetics?

Heterozygous refers to an individual that has two different alleles for a particular gene, one inherited from each parent. In the context of incomplete dominance, a heterozygous individual will display a phenotype that is intermediate between the two homozygous parents.

What is the definition of 'homozygous dominant' and 'homozygous recessive' as per the script?

Homozygous dominant refers to an individual with two dominant alleles for a trait, while homozygous recessive refers to an individual with two recessive alleles. In the script, these terms are used to describe the parental flowers in a genetic cross.

Outlines

00:00

🌟 Introduction to Non-Mendelian Inheritance

This paragraph introduces the concept of non-Mendelian inheritance, contrasting it with Mendel's laws of inheritance which describe the inheritance of traits linked to single genes. Non-Mendelian inheritance includes patterns where traits do not segregate according to Mendel's laws. The video focuses on incomplete dominance, a phenomenon where the dominant allele does not completely mask the recessive allele, resulting in a phenotype that is a blend of both. The paragraph sets the stage for the educational content, asking viewers to recall and define key genetic terms such as dominant traits, homozygous, recessive traits, monohybrid cross, heterozygous, and phenotype.

🌸 Exploring Incomplete Dominance

This section delves into the specifics of incomplete dominance, using the example of flower color in plants to illustrate the concept. It explains that when a homozygous dominant and a homozygous recessive flower are crossed, the resulting F1 generation exhibits a phenotype that is intermediate to the two parents, such as pink flowers from a red and white cross. The paragraph further clarifies the concept with additional examples, such as the Andalusian chicken, where the offspring of black and white feathered parents have blue feathers, demonstrating co-dominance where both alleles are expressed. The video script guides viewers to understand how to solve for non-Mendelian inheritance patterns using a Punnett square.

📊 Applying Punnett Square to Incomplete Dominance

The final part of the script provides a practical application of the Punnett square to predict the genotypic and phenotypic ratios in crosses involving incomplete dominance. Two sample problems are presented: one cross between a pink and a white flower, resulting in a 1:1 ratio of heterozygous pink to homozygous recessive white; and another cross between two pink flowers, leading to a 1:2:1 ratio of homozygous dominant red, heterozygous pink, and homozygous recessive white. The paragraph concludes with the expected phenotypic ratios, which mirror the genotypic ratios, reinforcing the understanding of incomplete dominance and its observable outcomes in genetic crosses.

Keywords

💡Non-Mendelian Inheritance

Non-Mendelian inheritance refers to genetic patterns that do not follow Mendel's laws, which typically involve single-gene inheritance on chromosomes. This concept is central to the video's theme as it introduces the idea that not all traits segregate according to Mendel's principles. Examples given in the script include incomplete dominance, sex-linked traits, and multiple alleles, although the focus is on incomplete dominance.

💡Incomplete Dominance

Incomplete dominance is a type of non-Mendelian inheritance where the dominant allele does not completely mask the recessive allele, resulting in a phenotype that is a blend of both parental traits. The video uses the example of a pink flower resulting from the cross between a red and a white flower, illustrating how the offspring's phenotype is a combination of both parental traits rather than a clear dominance of one over the other.

💡Punnett Square

A Punnett square is a diagram used to predict the genotypes and phenotypes of offspring from a particular cross. It is a key tool in understanding non-Mendelian inheritance patterns, as demonstrated in the video when solving for the genotypic and phenotypic ratios in various crosses involving incomplete dominance.

💡Dominant Traits

Dominant traits are those that are expressed when at least one dominant allele is present. In the context of the video, the script discusses how, in Mendelian inheritance, a dominant trait would be expressed over a recessive one. However, the concept of incomplete dominance challenges this by showing that dominance is not always complete.

💡Homozygous

Homozygous refers to an individual having two identical alleles for a particular gene. In the video, the script describes a homozygous dominant and a homozygous recessive flower being crossed, which is a fundamental concept in understanding how traits are passed on genetically.

💡Recessive Traits

Recessive traits are those that are only expressed when two recessive alleles are present. The video explains that in Mendelian inheritance, recessive traits are typically masked by dominant ones, but in the case of incomplete dominance, the recessive trait contributes to the phenotype of the offspring.

💡Monohybrid Cross

A monohybrid cross is a type of genetic cross that involves a single pair of contrasting traits. The video script uses this term to discuss the inheritance patterns of traits linked to single genes, which is foundational knowledge for understanding more complex genetic concepts like incomplete dominance.

💡Heterozygous

Heterozygous describes an individual with two different alleles for a trait. The video script explains that in the case of incomplete dominance, a heterozygous individual (e.g., a pink flower) is the result of the cross between a homozygous dominant and a homogous recessive individual.

💡Phenotype

Phenotype refers to the observable characteristics of an organism, which result from the interaction of its genotype with the environment. The video script uses the term to discuss how different genetic crosses can result in different phenotypes, such as the pink flowers in the example of incomplete dominance.

💡Genotype

Genotype is the genetic makeup of an individual, describing the specific set of genes inherited. The video script discusses genotypes in the context of predicting the outcomes of genetic crosses, such as the 1:2:1 ratio in the cross between two pink flowers.

💡Co-Dominance

Co-dominance is a genetic phenomenon where two different alleles are both expressed in the phenotype. The video script mentions this in relation to blood typing and the Andalusian chicken example, where the offspring's phenotype is a combination of both parental traits, neither of which is completely dominant.

Highlights

Introduction to non-Mendelian inheritance, a concept where traits do not follow Mendel's laws.

Mendel's laws describe inheritance of traits linked to single genes in the nucleus.

In non-Mendelian inheritance, traits like incomplete dominance, sex-linked traits, and multiple alleles are observed.

Incomplete dominance is the focus of the video, where the dominant allele does not completely mask the recessive allele.

The video expects viewers to use a Punnett square to solve for non-Mendelian inheritance by the end.

Review of Mendelian inheritance terminologies such as dominant traits, homozygous, recessive traits, etc.

A homozygous dominant and homozygous recessive flower cross results in an unexpected pink flower in the F1 generation.

Explanation of incomplete dominance using the example of 4 o'clock flowers, where red and white blend to produce pink.

Andalusian chicken example where black and white feathers result in blue offspring, illustrating co-dominance.

Blood typing as another example of co-dominance in genetics.

Using a Punnett square to determine the genotypic and phenotypic ratios in non-Mendelian inheritance.

Cross between a pink and white flower resulting in a 1:1 ratio of heterozygous pink to homozygous recessive white.

Cross between two pink flowers resulting in a 1:2:1 ratio of homozygous dominant red to heterozygous pink to homozygous recessive white.

Phenotypic ratio in the cross of two pink flowers is 1:2:1 for red, pink, and white flowers respectively.

Encouragement to subscribe for more science educational videos.

Transcripts

[Music]

hello students

welcome back to our science video i will

introduce to you a new concept in

genetics

which is the counterpart of mendelian

inheritance

this topic is non-mendelian inheritance

it is any pattern of inheritance in

which traits do not segregate

in accordance with mendel's laws these

laws describe

the inheritance of traits linked to

single genes on chromosomes

in the nucleus incomplete dominance

sex-linked traits and multiple alleles

are the pattern of inheritance under

this law

but for today's topic we will only cover

incomplete dominance

at the end of this video viewers are

expected to

use the punnett square to solve for

non-mendelian inheritance

but before we start with our lesson

let's review or recall first

some of the terminologies we discussed

about mendelian inheritance

in the comment section below type your

answer for the definition or meaning of

each word

based on our discussion in mendelian

inheritance

the following words are dominant traits

homozygous dominant recessive traits

monohybrid cross heterozygous

and phenotype

to start this lesson let's analyze the

given picture

based on the picture there is a

homozygous dominant thread

and a homozygous recessive white flower

being crossed in the p

generation in mandela inheritance the

phenotype in the f1 generation should be

read

following the idea of law of dominance

wherein

the presence of one dominant allele will

express a dominant trait

but in this picture the offspring in the

f1 generation is a pink flower

and more pink flowers are produced in

the f2 generation

this concept in genetics reveals the

concept of

incomplete dominance

what is incomplete dominance

one allele doesn't completely mass the

other resulting somewhere in between

it only means that the dominant allele

did not completely mass

or cover the other allele that result in

the combination of both alleles

as an example in 4 o'clock flowers

neither red or white is dominant when a

homozygous red flower

mixed with the homozygous white flower

the alleles blend in the hybrid

to produce pink flowers

[Music]

another example is in andalusian chicken

neither black or white are dominant the

offspring of a black feathered chicken

and a white feathered chicken are blue

this concept in genetics

is co-dominance wherein both dominant

alleles

are expressed another example of

co-dominance

is in the blood typing this topic

will be discussed more

in multiple alleles

let's try to solve sample problems and

determine the pinot peak and genotypic

ratio

using the punnett square

[Music]

show the cross between a pink and a

white flower

the possible pinot types and genotypes

of the cross are the following

pink white pink

and white based on the punnett square

the genotypes are 50 percent

heterozygous pink

and 50 homozygous recessive white that

gives ones to one ratio

while for the pinot types we have fifty

percent pink

and fifty percent white that also gives

one is to one ratio

show the cross between a pink and

another pink flower

the possible pinot types and genotypes

of the cross are the following

red pink another pink

and white based on the punnett square

the genotypes are 25

homozygous dominant red 50 percent

heterozygous pink

and 25 percent homozygous recessive

white that gives one

to two is to one ratio while for the

phenotypes

we have 25 red 50

pink and 25 percent white that also

gives ones to two is to one ratio

thank you for watching do not forget to

subscribe for more science educational

videos