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GN: Types of Inheritance Lesson

I Get It From My Mama

As discussed previously, the genotype (genetic makeup) can determine the phenotype (outward, physical appearance).

There are a few different ways that these alleles can interact to produce a phenotype for a gene. These are called inheritance patterns.

Uppercase A and lowercase a, A says "Let me handle this I'm the dominant one in this relationship"

Can you guess which inheritance pattern is described in the above picture?

If you said “Complete Dominance”, you are correct.

4 Types of Inheritance

There are four types of inheritance that you are expected to understand:

  1. Complete dominance
  2. Incomplete dominance
  3. Co-dominance
  4. Sex-linked

The presentation below will help you learn about each type of inheritance.

Did you notice that when females are heterozygous for a sex-linked trait they are called "carriers?"

Other Types of Inheritance

Other Types of Inheritance

Polygenic
Inheritance

Pleiotropy
Inheritance

Sex Influenced Traits
A person with a green eye Sickled red blood cell next to a normal red blood cell Man with balding head

To get our feet wet with Genetics, so far we have been using traits that are controlled by one gene in most of our practice problems. The reality, however, is that most human characteristics are controlled by several genes, which is polygenic inheritance.

Skin and eye color, both polygenic traits, are each the product of additive effects of 3-6 genes. Each gene would lay down a certain amount of a pigment called melanin. The more of the genes that are expressed, the darker the color produced. Human height is also a polygenic trait.

Pleiotropy, on the other hand, is quite the opposite of polygenic inheritance. In pleiotropy, one gene results in multiple (seemingly unrelated) phenotypes. Often these are congenital (present at birth) diseases, such as sickle cell anemia or phenylketonuria (or PKU). In the case of sickle cell anemia, one gene mutation can cause anemia, lack of blood supply to vital organs, pain, brain damage, and even paralysis, in addition to many other symptoms. A sickled red blood cell is misshapen, unable to do its job to carry oxygen, and is quickly broken down by the body.

Sex-influenced traits are located on autosomes but express themselves differently in the sexes because of sex hormones. Pattern baldness is an example. Females may carry the genes but estrogen helps them avoid losing hair as early and completely as males. Sex-influenced traits should not be confused with sex-linked traits.

Inheritance Challenge and Before You Go

Practice Time! Use the knowledge you learned from the lesson to complete the practice activities below.

 

Before You Go - You Need To Know

The following key points are from the explore section of the lesson. You must know the following information before moving to the next lesson. This is just a summary of the key points.

 

  1. What are the 4 types of inheritance patterns?
    • Complete dominance
    • Incomplete dominance
    • Co-dominance
    • Sex-linked
  2. What is an example of each of the types of inheritance patterns?
    • Complete dominance: pea plant color (yellow color will mask the green color)
    • Incomplete dominance: crossing a red flower and a white flower to result in pink flowers
    • Co-dominance (multiple alleles): blood types *when both alleles of a gene are always expressed.
    • Sex-linked: when a trait is located on the X chromosome, like color-blindness and hemophilia. Women can be carriers of a sex-linked trait, but not show the trait, because they have two X chromosomes
  3. What are lethal alleles?
    • When a genetic defect causes a 100% mortality rate. An example is Huntington’s Disease and Achondroplasia

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