Question

11) In a triploid cell with 4 chromosome triplets (3n = 12), how many sister chromatids will be found in a nucleus at prophase of mitosis? A) 12 B) 24 C) 6 D) 36 12) In birds, sex is determined by a ZW chromosome scheme. Malos aro ZZ and females are ZW. A recessive lethal allele that causes death of the embryo is sometimes present on the Z chromosome in pigeons. What would be the sex ratio in the offspring of a cross between a male that is heterozygous for the lethal allele and a normal female? A) 2:1 male to female B) 1:2 male to female C) 1:1 male to female D) 3:1 male to female 13) Crossing over of chromosomes normally takes place during which of the following processes? A) prophase of meiosis II only B) prophase of meiosis I only C) prophase of meiosis only D) both B and C 14) In human blood types, Rh positive is a trait that shows simple dominance over Rh negative. A woman who has blood type B positive has a daughter who is type o positive and a son who is type A negative. Which of the following phenotypes is possible for the father? A) A negative B) O negative C) B positive D) AB negative 16) Phenylketonuria is an inherited disease caused by a recessive autosomal allele. If a woman and her husband are both carriers, what is the probability that their first child is a phenotypically normal girl, but carries the recessive disease allele? A) 1/4 B) 3/4 C) 1/2 D) 3/8
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Answer 1

11. 24

During prophase of mitosis, there will be 12 chromosomes. Each chromosome will have two sister chromatids. So there will be 24 sister chromatids in total.

12. A

ZW × ZaZ (Za is lethal allele)

Gametes	Za	Z
Z	ZaZ male normal carrier of a	ZZ normal male
W	ZaW lethal female	ZW normal female

Ratio = 2 males : 1 female

(We will not count the lethal one)

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