Genetics Please show your working and how you came up with answer. A small expla

Question

Genetics

Please show your working and how you came up with answer. A small explanation would be greatly appreciated also.

5. In a particular human family, John and his mother both have brachydactyly (a rare autosomal dominant disorder causing short fingers). John's father has Huntington disease (another rare autosomal dominant disorder). John's wife is phenotypically normal and is pregnant. Two-thirds of people who inherit the Huntington allele (HD) show symptoms by age 50. John in 50 and has no symptoms. Brachydactyly is 90% penetrant. Al What are the genotypes of John's parents? (1 mark) BJ What are the possible genotypes for John? (1 mark) C] What is the probability that the child will express both brachydactyly and Huntington disease by age 50 if the two genes are not linked? (1 mark) DI If these two loci are 20mu apart how will it change your answer to part [C]? (2 marks)

Explanation / Answer

both are autosomal dominant diseases, so the genotypes that show the condition are as follows:

• BB- Bractydactyly

• Bb- Bractydactyly

• bb- Normal

• HH- Huntington

• Hh- Huntington

• hh- Normal

Thus, the most probable genotypes of “Mr. J” parents are as follows

Father of Mr. J ----------------------x ------------------ mother of Mr. J

Genotype Hh bb----------------------------- Genotype hh BB

Mr. J-----------------hh Bb

Mr

Father of Mr. J

Genotype: Hh bb

Huntington affected

mother of Mr. J

Genotype: hh BB

Bractydactyly affected

Mr. J-----------------hh Bb

Mr. J-----------------hh Bb

The probability of child with Bractydactyly =1/2

Penetrance =90%

=(1/2 )* (90%)=0.45

The probability of child with huntingchorea age of 50 years=1/6 *1/2 *2/3 =0.056

Both phenotypes =0.45 x 0.056 =0.025 ---------answer

===========================================================

Mr

Father of Mr. J

Genotype: Hh bb

Huntington affected

mother of Mr. J

Genotype: hh BB

Bractydactyly affected

Mr. J-----------------hh Bb

Mr. J-----------------hh Bb

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