#1 Use the pedigree in the attachment to answer the following question #1: The p

Question

#1 Use the pedigree in the attachment to answer the following question #1: The pedigree shows an inheritance pattern for congenital cataract, a mutant phenotype in humans. The black circles and black squares represent the individuals showing symptoms. What type of genetic disorder is this?

Autosomal dominant

Autosomal recessive

Sex-linked dominant

Sex-linked recessive

#2 Morgan demonstrated that white eye color in Drosophila is carried recessively on the X chromosome (recall that females are XX and males are XY). Which of the following best describes the offspring of a heterozygous (carrier) female and a white-eyed male?

Half of the daughters have red eyes and all sons have red eyes

Half of the daughters have white eyes and all sons have white eyes

Half of the daughters and sons have white eyes

All daughters have white eyes and half of the sons have red eyes

Autosomal dominant

Autosomal recessive

Sex-linked dominant

Sex-linked recessive

Explanation / Answer

Question 1:

Answer is ”A. Autosomal dominant”.

First we will check if it is dominant or recessive.

Recessive disease will occur only if the individual has two mutant alleles.

If it is recessive II1 and II2 should have both alleles mutated. So, all of their off springs should also have both mutated alleles and be symptomatic. However, III1 (their off spring) is asymptomatic. This suggests that this is not recessive trait. Then it should be dominant. Individual showing dominat trait can be heterozygous for mutation. Most likely, II1 and II2 are heterozygous for mutation.

Now we will check if it is sex linked or autosomal.

Females have the disease. O, it is not Y-linked.

If it is X linked, III2 should have the disease. She inherits one X chromosome from her father (Ii4). He has only one X chromosome and it carries mutated allele. However, III2 is asymptomatic. Therefore, the inheritance is not X-linked. So, it must be autosomal.

Question 2:

Answer is “C. Half of the daughters and sons have white eyes”.

Heterozygous (carrier) female has one X chromosome with white allele and another without it.

Mother provides X chromosome to male off springs while father provides Y chromosome. Mother produces gametes with and without white allele equally. So, half of their male offsprings have white eye.

Father p

A white-eyed male has chromosome with white allele.

Father provides X chromosome with white allele to all his daughters. But, only half of gametes from mother have white allele. For a female fly to have white eye, there should be two white alleles (white is recessive). So, half of female offsprings will have white eye.

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