(l) Give the genotype of the parents shown is generation I and of the son and daughter generation II. 
(2) Give the the genotype of the daughter shown in generation III.
(3) ​Is the trait used linked or autosomal? Justify your answer. 

Dear Student,
I) Let us take  both the parents as carriers for this disease. The  genotype of carrier parents will be Aa and Aa. The cross between them can be depicted as:

Parents                  Aa                            x                      Aa          
                         (Carrier man)                            (carrier woman)

Gametes           A, a                                                     A,  a

Progeny                     AA              Aa             Aa            aa
                          (Unaffected)    (Carrier)    (Carrier)  (Affected)

Therefore, the genotype of parents is Aa and the affected daughter in II generation is aa.

II) The genotype of daughter in second generation is Aa and hence is a carrier of the disorder, the genotype of her parents being aa and AA.
III). The trait is autosomal recessive trait. For example: Sickle cell anaemia is a recessive autosomal disorder; both the mother and father must carry at least one allele for the trait in order for son or daughter to be sickle cell victim. Typically, the parents of affected individuals are not affected but are gene carriers. With each pregnancy of carrier parents there is a 25 percent chance that any given offspring will inherit the condition and there fore will have the phenotype. There is one in two or 50% chance that the offspring will inherit one copy of the disease allele and will be a carrier. There is one in four or 25% chance the offspring will inherit no copies of the disease allele and will not express the phenotype or be a carrier. This individual would not be at risk for passing the disorder to his offspring.

 Ss represent Carrier
SS represent Normal
ss represent sickle cell anaemia

In this pedigree chart male and the female parent are unaffected or normal. In order to predict their genotypes we have to look at the second generation, as we do not know whether the parents are carrier (Ss) or unaffected. In the second generation we can see that among the four children one male child is affected (ss). In autosomal recessive disorder, we know that if the offspring has the sickle cell disease the parents should have atleast one allele of the trait. One female child in the second generation is unaffected and has the genotype (ss). The other two children son and daughter are carriers and have the genotype (Ss). This means that the parents in the first generation  are carriers and have the genotype (Ss). In the second generation we can see that affected man (ss) marries a unaffected women (SS). They have four children; 2 daughters and 2 sons who are carriers (Ss)


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