Non-Mendelian Genetics - Online Tutor, Practice Problems & Exam Prep

Polygenic inheritance involves multiple genes influencing a single phenotypic trait, such as human height, which is affected by over 180 genes. In contrast, pleiotropy occurs when a single gene impacts multiple traits, exemplified by Marfan syndrome, where one gene mutation affects various body systems. Multifactorial characters are influenced by both genetic and environmental factors, as seen in hydrangea flower color, which varies with soil pH. Understanding these concepts is crucial for grasping the complexity of genetic inheritance and trait expression.

Polygenic Inheritance

In this video, we're going to talk about some non-Mendelian genetics or genetics that is not described by Gregor Mendel's laws. And we're going to start off by talking about polygenic inheritance. And so it turns out that most inherited traits are actually polygenic. And so what exactly does it mean for traits to be polygenic? Well, polygenic traits, as their name implies with the poly root, which means many, and the genic root here, which of course is referring to genes. These are going to be single phenotypic traits that are affected by multiple genes. And again, you can see that within the root polygenic. Poly meaning many or multiple, and genic of course referring to the genes. And so polygenic traits are single phenotypic traits affected by multiple genes. And so, if we take a look at our image down below over here on the left-hand side, notice we're showing you a representation of a polygenic trait. One single phenotypic trait affected by multiple genes, gene A, gene B, gene C, and gene D over here. And so when you have many genes affecting one trait, that is what's referred to as a polygenic trait. Now, a classic example of a polygenic trait is human height, which is controlled by well over 180 genes. And so when you take a look at this image down below, you can see that we have different human heights, one at 6 feet 5 inches, 6 feet, 5 feet 5 inches, and one at 5 feet. And again, human height is controlled by well over 180 genes. And so, that makes it a polygenic trait since it's a single trait, a single human height is a single trait that's affected by multiple genes. And that, of course, is going to be much more complicated than the simple Mendelian genetics that we've talked about in our previous lesson videos. And so now that we've described polygenic inheritance, we'll be able to compare this to pleiotropy in our next video. So I'll see you all there.

Which of the following phenotypes is an example of polygenic inheritance?

• A. White or purple flower color in pea plants.
• B. Yellow or green pea color in pea plants.
• C. The ABO blood groups in humans.
• D. Skin pigmentation in humans.

Pleiotropy

So now that we've introduced polygenic inheritance in our last lesson video, in this video we're going to introduce pleiotropy. Pleiotropy is practically the opposite of polygenic, and that's because polygenic means multiple genes affecting one trait. However, pleiotropy is when a single gene has effects on multiple different phenotypic traits. If we take a look at our image down below here on the left-hand side, we're showing you a representation of pleiotropy. Pleiotropy is when just one single gene has impacts or effects on multiple different traits, such as traits A, B, C, and D. Pleiotropy is one gene affecting many traits. A classic example of pleiotropy is Marfan syndrome, where a mutation of just one single gene, the FBN1 gene, will limit the body's ability to build connective tissue and lead to a wide variety of phenotypic traits being affected. Some Marfan syndrome phenotypes include having a tall and slender body, long arms, legs, and fingers, a curved spine, crooked or crowded teeth, heart disease and heart murmurs, and eye conditions or vision loss. We have one single gene, this FBN1 gene, which if a mutation occurs there are effects or impacts in the body, the arms, the legs, the fingers, the spine, the teeth, the heart, and the eyes which might seem unrelated but are all traced back to this one particular gene. All of these different traits that you see here are all impacted by just one gene.

This concludes our introduction to pleiotropy and we'll be able to get some practice applying these concepts as we move forward. So, I'll see you all in our next video.

A pleiotropic genetic disorder typically has what characteristics?

• A. A single gene is mutated resulting in the change of one phenotypic trait.
• B. A single gene is mutated resulting in the change of many phenotypic traits.
• C. Many genes are mutated resulting in the change of one phenotypic trait.
• D. Many genes are mutated resulting in the change of many phenotypic traits.

Multifactorial Characters

In this video, we're going to introduce multifactorial characters. Multifactorial characters are inherited features or phenotypes that are influenced by many types of factors, and these factors include genetic factors such as alleles, but also environmental factors such as, for example, the temperature or the pH. In our example below, we're going to take a look at the effects of the environment, specifically the pH of the soil on flower color phenotypes of these specific flowers called hydrangea. The hydrangea flower color is impacted by the pH of the soil. Not only is it impacted by genetic factors, but it's also again impacted by environmental factors such as the pH of the soil. When the pH is acidic, these flowers tend to have a bluish type of phenotype. However, when the soil pH is more basic, then the flowers take on a more pinkish type of phenotype. Here, you can see that multifactorial characters are going to be influenced by many types of factors, genetic factors but also environmental factors as well. This here concludes our introduction to multifactorial characters, and we'll be able to get some practice as we move forward throughout our course. So, I'll see you all in our next video.

Hydrangea plants of the same genotype are planted in a large flower garden. Some of the plants produce blue flowers and others pink flowers. This can be best explained by which of the following?

• A. The knowledge that multiple alleles are involved.
• B. The allele for blue hydrangea is completely dominant over the allele for pink hydrangea.
• C. The alleles are codominant.
• D. Environmental factors such as soil pH affect the phenotype of flower color.

A phenotype is controlled by gene A and gene B. Gene B controls the expression of gene A. This is an example of _____.

• A. Incomplete Dominance.
• B. Epistasis.
• C. Codominance.
• D. Multifactorial characters.
• E. Alleles.

Here’s what students ask on this topic:

What is polygenic inheritance and how does it differ from Mendelian inheritance?

Polygenic inheritance involves multiple genes influencing a single phenotypic trait. For example, human height is controlled by over 180 genes. This is different from Mendelian inheritance, where traits are determined by a single gene with two alleles, following Gregor Mendel's laws of segregation and independent assortment. In polygenic inheritance, the combined effect of many genes results in a continuous range of phenotypes, such as varying heights, rather than discrete categories. This complexity makes polygenic traits more variable and less predictable compared to Mendelian traits.

What is pleiotropy and can you provide an example?

Pleiotropy occurs when a single gene affects multiple phenotypic traits. A classic example is Marfan syndrome, caused by a mutation in the FBN1 gene. This single gene mutation impacts various body systems, leading to traits such as a tall and slender body, long limbs, curved spine, crowded teeth, heart issues, and vision problems. These diverse effects arise because the FBN1 gene plays a crucial role in the formation of connective tissue, which is essential in multiple parts of the body.

How do environmental factors influence multifactorial characters?

Multifactorial characters are influenced by both genetic and environmental factors. For instance, the color of hydrangea flowers is affected by the pH of the soil. In acidic soil, hydrangeas tend to have a bluish color, while in basic soil, they appear pink. This demonstrates that environmental conditions, such as soil pH, can significantly impact phenotypic traits, alongside genetic factors. Understanding multifactorial characters requires considering the interplay between genes and the environment.

Can you explain the concept of polygenic traits with an example?

Polygenic traits are single phenotypic traits influenced by multiple genes. A well-known example is human height, which is controlled by over 180 genes. Each gene contributes a small amount to the overall height, resulting in a continuous range of heights in the population. This is in contrast to Mendelian traits, which are typically influenced by a single gene with two alleles, leading to distinct phenotypic categories. Polygenic traits exhibit more variation and complexity due to the involvement of many genes.

What are multifactorial characters and how do they differ from polygenic traits?

Multifactorial characters are phenotypic traits influenced by both genetic and environmental factors. For example, the color of hydrangea flowers is determined by genetic factors and the pH of the soil. In contrast, polygenic traits are influenced solely by multiple genes without considering environmental factors. While both involve multiple influences, multifactorial characters highlight the interaction between genes and the environment, whereas polygenic traits focus on the combined effect of several genes on a single trait.