Codominance and Incomplete Dominance: Non-Mendelian Genetics

Summary

This educational video delves into the fascinating world of genetic inheritance, focusing on co-dominance and incomplete dominance. It explains how offspring can exhibit phenotypes that are a mix of their parents' traits, rather than a direct match. Using the example of 'Dots' with different coat colors and textures, the video illustrates the concepts of complete dominance, co-dominance, and incomplete dominance. Real-life examples include the coat patterns of cows and the petal colors of flowers, highlighting the complexity of genetic expressions. The video concludes with formal definitions for each dominance pattern, enhancing viewers' understanding of non-Mendelian genetics.

Takeaways

• 🧬 Offspring can exhibit traits that are a mix of both parents due to gene interactions like co-dominance or incomplete dominance.
• 🐾 Complete dominance is when one allele masks the presence of another, resulting in the expression of only one allele in the phenotype.
• 🌈 Co-dominance occurs when both alleles are dominant and both traits are expressed in the phenotype, such as in the coat color of some animals.
• 🎨 In incomplete dominance, neither allele is completely dominant, and the phenotype is a blend of the two, like the pink color in flowers from red and white parents.
• 🔬 Non-Mendelian traits do not follow simple Mendelian inheritance patterns and can result in unique phenotypes in offspring.
• 🐄 Co-dominance in animals can be seen in cow coat colors, where red and white patches appear in a pattern known as 'roan'.
• 🌹 Examples of incomplete dominance in plants include flowers like tulips, roses, and carnations, where red and white parent flowers can produce pink offspring.
• 👨‍⚕️ In humans, blood type is an example of co-dominance, and hair texture can show incomplete dominance.
• 📚 The video script uses the fictional creatures 'Dots' to illustrate the concepts of dominance, helping to clarify genetic principles.
• 📈 The tutorial provides a clear comparison between complete dominance, co-dominance, and incomplete dominance using coat color as an example.

Q & A

What is the difference between complete dominance and non-Mendelian traits?

Complete dominance is a Mendelian trait where one allele is dominant and masks the presence of the other allele, leading to only one allele being expressed in the phenotype. Non-Mendelian traits, however, do not follow Mendelian genetics rules, and the offspring's phenotype is a mix of both parents rather than matching either one.

What are the three types of dominance mentioned in the script?

The three types of dominance mentioned are complete dominance, co-dominance, and incomplete dominance.

How does the phenotype of an organism with co-dominance differ from one with complete dominance?

In co-dominance, both alleles are expressed in the phenotype, resulting in a combination of traits from both alleles. In complete dominance, only the dominant allele is expressed, and the recessive allele's effect is masked.

What is an example of co-dominance given in the script?

An example of co-dominance in animals is the coat coloring of cows, where a red cow bred with a white cow produces offspring with both red and white patches, known as 'roan'.

How does the petal color in flowers demonstrate incomplete dominance?

In flowers like tulips, roses, carnations, and snapdragons, crossing a red flower with a white flower results in pink offspring, which is a blend of the two parental phenotypes, demonstrating incomplete dominance.

What is the genotype of a hybrid offspring resulting from a blue dot and a yellow dot, according to the script?

The genotype of the hybrid offspring resulting from a blue dot (CB) and a yellow dot (CY) is CB-CY.

What would be the phenotype of the hybrid offspring if coat color showed complete dominance of blue over yellow?

If coat color showed complete dominance of blue over yellow, the phenotype of the hybrid offspring with genotype CB-CY would be blue, as only the blue allele would be expressed.

What would the phenotype be if the dots exhibited co-dominance for coat color?

If the dots exhibited co-dominance for coat color, the phenotype of the hybrid offspring with genotype CB-CY would be a combination of blue and yellow.

How is incomplete dominance different from co-dominance?

In incomplete dominance, neither allele is completely dominant, and the phenotype is a blend of the two parental phenotypes. In co-dominance, both alleles are dominant, and traits from both alleles are expressed together in the phenotype.

What is the formal definition of complete dominance as per the script?

Complete dominance is when one allele is dominant and masks the presence of the other allele, resulting in only one allele being expressed in the phenotype.

What is the formal definition of co-dominance as per the script?

Co-dominance is when both alleles are dominant, and traits from both alleles are expressed together in the phenotype.

What is the formal definition of incomplete dominance as per the script?

Incomplete dominance is when neither allele is completely dominant, and a blend of the two alleles is expressed in the phenotype.

Outlines

00:00

🧬 Understanding Gene Interactions: Co-Dominance and Incomplete Dominance

This paragraph introduces the concepts of co-dominance and incomplete dominance in genetics, explaining how they result in offspring that display a combination of traits from both parents rather than a single dominant trait. The video uses the example of 'Dots,' hypothetical creatures with large or small sizes and fluffy or smooth coats, to illustrate complete dominance. It then contrasts this with non-Mendelian traits, where offspring phenotypes are unique combinations of parental traits. The paragraph sets the stage for a detailed exploration of dominance patterns by discussing the breeding of blue and yellow 'Dots' and the potential outcomes for their offspring's coat colors based on different dominance scenarios.

Keywords

💡Co-dominance

Co-dominance is a genetic phenomenon where both alleles of a gene are expressed in the phenotype of an organism. This is in contrast to complete dominance, where only one allele is expressed. In the context of the video, co-dominance is exemplified by the coat color of certain animals, such as cows, which when bred with another cow of a different color, can result in offspring displaying patches of both colors, known as 'roan'. This concept is crucial for understanding how traits can be expressed in offspring that are a combination of both parents' traits.

💡Incomplete Dominance

Incomplete dominance, also known as partial dominance, is a genetic condition where the phenotype of the heterozygote is a blend of the phenotypes of the homozygotes. This is different from complete dominance, where one allele completely masks the effect of the other. The video uses the example of flower petal color to illustrate this concept, where crossing a red flower with a white flower results in pink offspring, showing a mix of both parental traits. This keyword is central to the video's theme of explaining how genetic traits can manifest in unique ways in offspring.

💡Complete Dominance

Complete dominance is a genetic principle where one allele is expressed in the phenotype while the other allele is masked. This is the simplest form of dominance where the dominant allele's trait is always visible in the presence of a recessive allele. In the video, complete dominance is discussed in the context of 'Dots', hypothetical creatures where a large allele would always result in a large size, regardless of the presence of a small allele. This concept is foundational to understanding the basic patterns of trait inheritance.

💡Alleles

Alleles are different forms of a gene that can arise by mutation and are found at the same place on a chromosome. They determine different expressions of the same trait. In the video, alleles are used to explain how traits like size and coat texture in 'Dots' are inherited. The concept of alleles is essential for understanding the genetic mechanisms behind the expression of traits in organisms.

💡Phenotype

Phenotype refers to the observable physical or biochemical characteristics of an organism, as determined by both genetic makeup and environmental influences. The video discusses how different genetic combinations, or genotypes, result in different phenotypes, such as the color and texture of 'Dots'. Understanding phenotypes is key to grasping how genetic traits are expressed in living organisms.

💡Genotype

Genotype is the genetic constitution of an organism, referring to the specific set of genes inherited from its parents. In the video, genotypes are used to predict the potential phenotypes of offspring from different parental combinations. For instance, a 'Dot' with a genotype of CB-CB would have a blue phenotype. Genotype is a fundamental concept in genetics that helps explain the inheritance of traits.

💡Mendelian Genetics

Mendelian Genetics is a branch of genetics that deals with the inheritance of traits from one generation to another, based on the principles formulated by Gregor Mendel. The video mentions that many traits do not follow Mendelian patterns, which are typically characterized by clear dominant and recessive traits. Instead, traits can be expressed in more complex ways, such as co-dominance and incomplete dominance, which are discussed in the video.

💡Non-Mendelian Traits

Non-Mendelian Traits are those that do not follow the simple patterns of inheritance described by Mendel's laws. These traits often involve multiple genes or are influenced by environmental factors. The video explains that while traits like the size and texture of 'Dots' might follow Mendelian genetics, other traits, like coat color in certain animals, do not and instead show co-dominance or incomplete dominance.

💡Hybrid Offspring

Hybrid offspring are the result of breeding between two genetically distinct individuals, often leading to a combination of traits from both parents. In the video, the concept is used to explain how the offspring of a blue and yellow 'Dot' could have a genotype of CB-CY, leading to a phenotype that is a blend of both colors if incomplete dominance is at play. This term is central to understanding how new combinations of traits can arise in offspring.

💡Roan

Roan is a specific coat color pattern observed in some animals, such as cows, where the coat has patches of two different colors. This pattern is an example of co-dominance, as discussed in the video, where both red and white alleles are expressed in the offspring's phenotype. Roan is used as a real-life example to illustrate the concept of co-dominance in the video.

💡Blood Type

Blood type is used in the video as an example of co-dominance in humans. It refers to the presence of specific antigens on the surface of red blood cells, which are determined by genetic factors. The video explains that blood type is an example where neither allele is completely dominant, and the phenotype can be a combination of traits from both alleles, such as AB blood type, which is a result of having both A and B alleles.

Highlights

Offspring may not resemble their parents due to gene interactions like co-dominance or incomplete dominance.

Co-dominance and incomplete dominance are types of gene interactions that result in unique offspring phenotypes.

Complete dominance is when one allele masks the presence of another, as seen in the size and texture of 'Dots'.

Non-Mendelian traits don't follow Mendelian Genetics rules, leading to offspring phenotypes that are distinct from their parents.

There are three types of dominance: complete, co-dominance, and incomplete dominance.

Coat color is used as an example to compare different types of dominance.

Offspring with genotype CB-CB would express only blue color due to complete dominance.

Offspring with genotype CY-CY would express only yellow color due to complete dominance.

Hybrid offspring with genotype CB-CY could show interesting trait combinations.

Co-dominance in coat color would result in a hybrid phenotype that is both blue and yellow.

Incomplete dominance in coat color would result in a green phenotype, a blend of blue and yellow.

Co-dominance in real-life examples includes coat coloring in cows, resulting in 'roan' patterns.

Human blood type is an example of co-dominance in humans.

Incomplete dominance in flowers results in pink offspring from red and white parent flowers.

Hair texture in humans can show incomplete dominance.

Complete Dominance is defined as one allele being dominant and masking the other.

Co-Dominance is defined as both alleles being dominant and both traits being expressed.

Incomplete Dominance is defined as neither allele being completely dominant, resulting in a blend of traits.

The tutorial encourages subscribing to the channel for more educational content.

The presenter also shares diagrams and study aids on Instagram.

Transcripts

Have you ever wondered why some offspring don’t resemble either of their parents,

but rather look like a mix of the two?

This is often due to gene interactions called co-dominance or incomplete dominance.

Today we’ll review what they are, a couple of examples, and then finish out by writing

some definitions for each type of dominance.

In some of the previous videos, we used made up creatures known as “Dots”.

Dots can be either large or small, and can have a fluffy or a smooth coat.

The large and fluffy alleles were dominant over the small and smooth alleles.

Therefore, a dot that had one copy of the large allele would still be large in size, and one copy of the fluffy allele would be fluffy in texture.

We would call this complete dominance.

However, many traits don’t follow the rules of Mendelian Genetics.

Instead, the offspring has its own phenotype, rather than matching either of their parents.

We call them non-mendelian traits.

There are three types of dominance that you should be familiar with; complete

dominance, co-dominance and incomplete dominance.

It’s easiest to compare them if we use coat color as an example.

We’re going to breed two dots together; a blue dot and a yellow dot, and see what

the resulting genotypes and phenotypes for their offspring could be.

Assume that the blue parent is contributing only blue alleles and the yellow parent is

contributing only yellow alleles.

We’ll use the letter C for “color” and the exponent will tell us which variety of

coat color we’re discussing.

If the offspring of these two dots had the genotype, CB- CB, it’s not hard to imagine what color it would

be.

Since we only have the blue alleles in the genotype, the phenotype in all three cases

would be blue.

Similarly, if the genotype is CY-CY, we only have yellow

alleles in the genotype. Because of this, only the yellow alleles will be expressed in the phenotype.

But what about hybrid organisms?

The genotype for the hybrid offspring is going to be CB-CY.

The genotype for the hybrid offspring is going to be CB-CY, and this is often where we see really

interesting trait combinations pop up.

If the coat color trait showed complete dominance of blue over yellow, the resulting hybrid

offspring would be blue.

Only the blue allele from the genotype would be expressed in the phenotype.

If, however, coat color followed patterns of co-dominance, the hybrid phenotype would

be both blue and yellow.

Traits from both alleles are present together in the phenotype.

If dots followed patterns of incomplete dominance, the hybrid offspring phenotype would be a

blend of the two parental phenotypes.

Rather than having a blue phenotype or a yellow phenotype, the offspring would have a green

phenotype.

In this case, neither of the two alleles is completely dominant.

Let’s check out a couple of real-life examples of co-dominance and incomplete dominance.

Co-dominance:

Some animals, such as cows, show a pattern of co-dominance in their coat coloring.

If a red cow is bred with a white cow, hybrid offspring will have both red and white patches

on their coats in a pattern known as “roan”.

Examples of co-dominance in humans include blood type.

Incomplete dominance: Many kinds of flowers show incomplete dominance in terms of their

petal color.

If a red flower is crossed with a white flower, the resulting offspring will be pink.

Tulips, roses, carnations and snapdragons are common examples.

Humans can also show incomplete dominance in terms of hair texture.

To finish up, let’s write out formal definitions for each pattern of dominance.

Complete Dominance: One allele is dominant and it masks the presence of the other allele.

Only one allele is expressed in the phenotype.

Co-Dominance: Both alleles are dominant, and traits from both alleles are expressed in

the phenotype.

Incomplete Dominance: Neither allele is completely dominant, a blend of the two alleles is expressed

in the phenotype

Allright, that’s it for now!

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and checking out some of my other videos.

I also post a lot of diagrams and study aids to Instagram.

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