1. People with albinism have little pigment in their skin, hair, and eyes. The g
ID: 2925694 • Letter: 1
Question
1. People with albinism have little pigment in their skin, hair, and eyes. The gene that governs albinism has two forms (called alleles), which we denote a and A. Each person has a pair of these genes, one inherited from each parent. A child inherits one of each parent's two alleles, independently with probability 0.5. Albinism is a recessive trait, so a person is albino only if the inherited pair is aa. a) Beth's parents are not albino but she has an albino brother. This implies that both of Beth's parents have type Aa. Why? b) Which of the types aa, Aa, AA could a child of Beth's parents have? What is the probability of each type? c) Beth is not albino. What are the conditional probabilities for Beth's possible genetic types, given this fact? d) Suppose that Beth marries Bob, who is albino (ie. his genetic type must be ca). What is the conditional probability that a child of of a non-albino child if Beth is type AA? Beth and Bob is non-albino if Beth has type Aa? What is the conditional probalbilityExplanation / Answer
1. In order for someone to be able to have an albino child of albinism but not be albino, the must have type Aa. (aa would be full albino) (must have at least one a to possibly have a child with someone who also has at least one a)
2. Let's make a chart.
......A ......... a
A | AA | aA |
a | Aa | aa |
(left side represents parent 1 top repesents parent 2. Each parent gives an allele to the child, and in the boxes show the possible combinations)
There is 1 AA out of the 4 combinations in the chart: 1/4 chance of AA
There are 2Aa (aA is the same as Aa) : 1/2 chance of Aa
There is 1 aa: 1/4 chance of aa
3. Beth must have either AA, or Aa to not be albino.
From the chart, 3/4 are either AA or Aa (aa is the only one that makes an albino, so she can have everything in the chart but aa). Thus, the probablility of not being albino with 2 parents as carries is 3/4.
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