Question

Follow-Up Questions 1. Your brother has an autosomal recessive disorder, while you are unaffected. Neither one of your parents is affected. Explain how this is possible. 2. Using the above situation, what is the probability that you carry the recessive allele? 3. A couple wants to have a child, but the mother has a brother who is affected by cystic fibrosis. They seek out the advice of a genetic counselor at their local hospital to determine what, if any, chance they have of producing an offspring who has cystic fibrosis. During the discussion, the counselor finds out that the husband's sister had cystic fibrosis as well. Build a pedigree to explain the genotypes of the father's parents, the father's sister, the mother's parents, and the mother's brother. Is it possible, based on the pedigree analysis, for the couple to have a child affected by cystic fibrosis? Construct a Punnett square to support your answer.

Answer 1

Autosomal Recessive disorder ---- these are the disorders which are linked with the autosomses or the non-sex chromosomes. As they are recessive in nature so they are expressed only when recessive allele is received from both the parents.

Ans 1 -- as given in question, brother has Autosomal Recessive disorder and I (you) is unaffected and parents too are unaffected.

As brother is affected with disease, he is Homozygous recessive --- dd ( d = recessive allele)

I or you is not affected so can be = DD or Dd (D = dominant allele)

As parents are unaffected, so they be DD or Dd. As unaffected parents have affected child then it shows that the parents are heterozygous i.e. Dd.

	D	d
D	DD	Dd
d	Dd	dd

Phenotye = 3:1

3 = unaffected (2= heterozygous and 1= Homozygous)

1= affected

If any one or both parents are Homozygous then they can't have an affected child.

So, both the parents are heterozygous i.e. Dd.

ans 2) from the above conclusion, the probability that I or you carry the recessive allele is

As parents are heterozygous and 2/4 offspring are carrier of disease as concluded above.

Probability of recessive allele = 2/4 or 1/2.

Or 2/4 * 100 = 50%

ans 3) cystic fibrosis is an Autosomal Recessive disorder so it will be expressed in an individual if it is Homozygous recessive (dd).

Pedigree of the given condition is given in image below

Brother (cc) mother it Husband (c) / (father) ((c) Lister . (cc) M odnottami on affected throt Child Cce) to Mother and father can be homozygous or heterzygous dominant (2/4 or 4/2 probability). Only heterozygous, parents would have an affected child, From Generation 1 → Pm and Pe in a stalo generation 2 is 2/4 or 1/2. exige e Using Product law, liferans apm = 2 9 P p = 16 Hollu est 2 w a (2) . ( 24 ) 1 - 4 - 4 P= Probability of mother P = Probability of father genotype genotype.

Punnett Square for child to be affected

​​​​​​Parents are carrier for the disease as analysed from Pedigree from the given information. So have genotype Cc. C = dominant --- unaffected

c = recessive --- affected

	C	c
C	CC	Cc
c	Cc	cc

Only 1/4 child will be affected, 2/4 or 1/2 are carriers but are not affected individuals and 1/4 are unaffected and are not carrier of disease too.

Yes, it is possible that the couple have an affected child.

Thank you...

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