Question

1. Draw a pedigree for the following family. Carlos and Maria are married and have 3 normal children all boys. They are expecting a 4^th child. Carlos has two normal brothers and an affected sister. Maria has an affected brother and a normal sister. Both of Carlos’ parents are normal, but his paternal grandfather is affected, and his maternal great grandmother is also affected. Maria’s mother is affected and her paternal grandfather is also affected.

Part I is the drawing of the pedigree.

Part II label the genotypes of all the individuals in the pedigree.

Part III what is the probability that Carlos and Maria will have a daughter?

Part IV What is the mode of transmission for this trait?

Part V What is the probability that Carlos and Maria will have an affected child if they have only one more child?

Answer 1

Part I- we can draw pedigree using symbols as:

normal male, affected male, normal female, affected female, sex unspecified

Part II- Consider "A" as normal allele, "a " as affected allele for autosomal recessive trait. Then genotypes of individuals will be. as below. First label all affected individuals as aa

Great grond parents. Grand parent Parent KHI Carlos & Maria. Children.

aa will be genotype for I-2, II-1, II-5, III-4, IV-3, IV-6

I-2-aa (Their children II-3 and II-4 are unaffected, If I-1 had genotype Aa, we can expect either II-2 or II-3 being affected)

So I-1 is AA,

IV-3 having aa genotype must have received 1 recessive allele from each parent so parent ( III-1 and III-2 will be Aa)

IV-6 will receive one allele from each parent so III-3 must be Aa. III-3 will receive a from II-5 but A will come from II-6, so II-6 will be either AA or Aa, Since III-4 is aa, II-6 must be Aa

da bi нки и и 0:44.04 HUE ao Aa AA • Aa A a AA AA Aa AA A a Aa aa

IV-1,2,4 and V-1,2,3 have normal phenotype, but considering pedigree, they can have either Aa or AA as genotype.

V-4 Yet to be born child have possibility of AA, Aa and aa as genotype.

Part III- Sex of child is determined by X or Y gamete received from father (XX) with each gamete having 50% probability. This probability is unaffected by sex of earlier child. So, probability of Carlos and Maria having girl child is 50%.

Part IV-As seen from pedigree, the trait is present in males as well as female. To be inherited as autosomal dominant: trait should manifest in every generation without skipping, every affected child should have affected parent.  While in present pedigree, it is skipping in generation) and affected individual IV-3 have both parent (III-1 and III-2 unaffected). So this trit is not inherited as autosomal dominant.

Y linked trait would manifest in III-1 as inherited from II-1 or in III-3 as inherited from II-5, this is not observed. X linked dominant trait will manifest in male individuals from the affected female line, this is not observed, so it is not a sex linked trait.

So the trait must be autosomal recessive.