Non-Mendelian Inheritance

Gregor Mendel was never able to predict or observe co-dominance in his study of pea plants. Codominance arises if two organisms cross and an offspring in the heterozygous condition expresses the phenotypes of both parents. One example of codominance is observed in people of African descent. People who are heterozygous for the sickle cell genetic trait will have both normal and sickle-shaped red blood cells in their blood stream, which is called sicklecell anemia. The sickle-shaped blood cells limit their ability to transport oxygen and limit the physical activity of anyone suffering from sickle cell anemia.

View A Mutation Story from eMediaVASM to learn how sickle anemia originated from a gene mutation due to Malaria. While you are watching the video clip, pay attention to how the traits of sickle cell are passed from parents to offspring.

Non-Mendelian Inheritance

Not all traits are inherited in a simple dominant/recessive pattern. The expression of some traits seems to be a blend of the contrasting alleles, and with other traits the contrasting alleles are expressed equally. Because the inheritance of these traits does not follow the dominant/recessive pattern described by Gregor Mendel, the inheritance type is referred to as non-Mendelian. In this interactivity, explore how non-Mendelian Inheritance occurs. Click the player button to begin.

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Stephen Hawking and Muscular Dystrophy

Muscular dystrophy is a type of trait called a sex-linked trait. Muscular dystrophy is a disorder that, over time, causes the muscles in your body to weaken, break down and progressively diminish.  It can cause paralysis of every muscle in the body.  Most people with muscular dystrophy do not live long lives and are disabled most of their lives.

Amazingly, Stephen Hawking has lived to be over seventy years old. Hawking is a famous modern-day physicist.  He is an accomplished professor at the University of Cambridge, and he has a neuro-muscular dystrophy that is related to amyotrophic lateral sclerosis (ALS).  When he lost the ability to speak, a voice synthesizer was created to aid in his speech. It is through this synthesizer that Hawking communicates with the world.

 

Pedigree

Genetics in humans cannot be studied by performing controlled crosses. Scientists cannot perform breeding experiments on humans. Instead, geneticists must study the genes in humans and other organisms to collect data on a single trait within a family, or closed gene pool. This data can be used to construct a pedigree, like a family tree. Scientists use this chart to look for patterns of inheritance from one generation to the next. In this interactivity, learn how to analyze a pedigree. Click the player button to begin.

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Polygenic Traits

Many of the traits you have learned about so far are determined by a single pair of alleles. However, there are other traits, like skin color, eye color, height, and fur color, which are determined by multiple pairs of alleles. These traits are called polygenic traits. In this interactivity, learn how many genes determine polygenic traits. Click the player button to begin.

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Environment

Genes are not the only factors that determine the traits of and organism. The environment can also play a role in determining what traits are expressed by an organism. Environmental influences can change or mutate genetic material very easily. Environmental influences can include: chemicals, pollution, organic substances, and UV radiation. These environmental influences can cause mutations in genetic material for good or harm. Chromosomes and DNA can be damaged and/or changed to code for new proteins or other genetic information.

Perhaps the most unusual example of an organism that is affected by its environment is the sea turtle. The temperature of the sand determines the sex of different sea turtles. If the sand is warmer, a female turtle is born. If the sand is cooler, a male turtle is born. Sea turtles are unusual because chromosomes normally determine the sex of an organism.

Non-Mendelian Inheritance Review

Now that you investigated non-Mendelian inheritance, review your knowledge. In this non-graded activity, read each question and select the correct response. Then, click SUBMIT to check your answer. Click the player button to get started.