b) Mr and Mrs Connelly are planning to start a family. However, Mr Connelly is c

Question

b) Mr and Mrs Connelly are planning to start a family. However, Mr Connelly is concerned that, as his brother was diagnosed with cystic fibrosis (CF), he may be a CF carrier. Their GP explains how Mr Connelly may carry the faulty CFTR gene using a Punnett square.

Create a Punnett square using to show to Mr Connelly his chances of inheriting the gene from his parents if both of them were CFTR carriers and explain the results of the Punnett square.

c) In a separate Punnett square show possible outcomes for their children if Mr Connelly is a CFTR carrier but his wife is not and explain the results.

Explanation / Answer

Cystic fibrosis is an autosomal recessive form of disease.

Case 1 when both the parents of mr. Connelly are carrier

Posiblee gametes - Ff in both the parents Ff x Ff = F×F, Fxf , Fxf, fxf

Therefore possible combination of alleles in offspring

FF, Ff, Ff, ff

FF - normal (both dominant gene)

Ff - carrier (carries one recessive gene)

f f - cystic fibrosis (carries both recessive gene)

Case 2 if mr. Connelly is the carrier and his wife is not

Possible gametes - Ff for mr. Connelly and FF for his wife. Therefore Ff x FF

Possible combination of alleles in offspring are FxF, Fxf, FxF and Fxf

Hence the combination of alleles are FF, Ff,FF and Ff

FF - normal - non Carrier

Ff - carrier since it has one recessive gene

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