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Autosomal Recessive Traits

There are five characteristics of autosomal recessive traits; males and females are equally likely to be affected, the disease is often found in siblings, offspring of an affected person is a carrier, if a child is born to two carriers and is not affected they are ⅔ likely to be a carrier, and two carriers have a 25% chance of having an affected child. These characteristics can easily be explained by using Punnett squares and some examples.

 

Two carriers b
B BB Bb
b Bb bb

 

Affected and carrier b b
B Bb Bb
b bb bb

 

Autosomal refers to 22 chromosome pairs, every person has 23 including their sex chromosome. This means that no matter the gender of a person they can carry an autosomal recessive trait. Above is a punnett square of two carrier parents. The parents have a 50% chance of having a heterozygous child like themselves, a 25% chance of having a homozygous dominant child that doesn’t carry the recessive trait, and a 25% chance of having a homozygous recessive child that does not carry the dominant trait. In the second punnett square there is an affected parent and a carrier parent. There is a 50% chance of having a child who is a carrier, and a 50% chance of having a child that it affected. Essentially the trait will be always be passed on to the offspring. This brings me to the next characteristic, siblings often carry the trait. In both punnett squares there is a high probability of the recessive trait being passed on, even if the parents are unaffected and a carrier there is still a 50% chance of having a child that is a carrier of the recessive trait.

In the Dragon Genetics Lab done in class there is a list of dominant and recessive traits. The trait for wings in dragons is labelled as dominant, while having no wings is a recessive trait. Dragons are usually seen with wings, this gives them the advantage of flight. Dragons who do not have wings are more likely to perish, they will likely have a harder time finding food and competing with other dragons. Having no wings is a lethal allele, and in a heterozygous pair there is a 25% chance of producing offspring with the lethal alleles of no wings.

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