C, either the phenotype A-Bb or the genotype AABER Athi -3 gANELII d. either the

Question

C, either the phenotype A-Bb or the genotype AABER Athi -3 gANELII d. either the phenotype 4-B- or the genotvoe gbe A-85.39 · PROBABILITY AND GENETIC COUNSELING In many genetic counseling situations, the counselor will prepare a pedigree for the family or families seeking advice. Insofar as possible, the counselor will determine the phenotype and the genotype for each person in the pedigree with respect to the trait in question (e.g albinism). The counselor can then apply probability principles to determine the probability that a child having a particular abnor- mality will be produced among the offspring of a certain marriage. To illustrate the application of these concepts, consider the pedigree shown in Figure 3.1.For the purposes of this problem your instructor will indicate which members of the pedigree express the genetic abnormality.) Unless there is evidence to the contrary, assume that individuals who have mar- ried into this family do not carry the recessive gene for the trait For a specific example, you might assume that four members of this pedigree are albinos: the woman in the first generation, her third daughter (the mother of individuals 9, 10, and 11D, and indi- viduals 6 and 12 in the third generation. Now, assume that you are a genetic counselor and that indi viduals 1 and 10 in the third generation of this pedigree come to you and ask, "What is the probability that if we marry and have a family, an albino child will be bom to us?" First, the counselor must determine the probability that individuals 1 and 10 are heterozygous carriers of the recessive gene for albinism. The counselor must also consider the probablity of two heterozygous carriers producing a homozygous recessive child. First of all, the mother of individual 1 must be heterozygous (Cc) because her mother is an albino (cc). One can further assume, because al 1 is homozygous normal (CO. Thus, there is no evidence to the contrary, that male Ap 16 17 FIGURE 3.1. Human pedigree showing four generations Circles represent females, squares rep resent males

Explanation / Answer

According to the information, the possible genotypes of the individuals can be found as below:

Answer a: 4 *5 : The genotype can be either AA or Aa (since homozygous aa are affected and both parents are heterozygous) only and hence probability of being albino is 0.

Answer b: 6*10: The homozygous aa individual 6 will mate with heterozygous individual 10 Aa, thus the probability of albino progeny will be 1/4.

Answer c: 7*14: Considering the genotype of individual 7 to be AA and that of 14 to be Aa (inherited from homozygous mother), the probability of having albino offspring will be only 1/4.

Answer d: 2*10: The genotype of individual 2 will be AA and that of 10 will be Aa, thus the probability of having an albino offspring will be only 1/4.

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