Occasionally, chromosomes fail to separate during called meiosis, leading to dau
ID: 164837 • Letter: O
Question
Occasionally, chromosomes fail to separate during called meiosis, leading to daughter cells that have an abnormal number of chromosomes This phenomenon is called nondisjunction. crossing over. pleiotropy. chromosome inactivation. In a healthy male, how many sperm cells would be expected to form from 400 primary spermatocytes? 400 secondary spermatocytes? (a) 800; (b) 800 (a) 1600; (b) 1600 (a) 1600; (b) 800 (a) 400; (b) 400 (a) 400; (b) 800 In a healthy female, how many secondary oocytes would be expected to form from 100 primary oocytes? How many first polar bodies would be expected from 100 primary oocytes? 200; 50 100; 50 200; 200 100; 100 50; 50 The sex of birds, some insects, and other organisms is determined by a ZW chromosomal arrangement in which the males have like sex chromosomes (ZZ) and females are ZW (similar to XY in humans) Assume that a recessive lethal allele on the Z chromosome causes death of an embryo in birds. What sex ratio would result in the offspring if a cross wore made between a male heterozygous for the lethal allele and a normal female? 4:1 male to female 2; 1 male to female 3:1 male to female 1.2 male to female 1: 1 male to female A recessive gene for red-green color blindness is located on the X chromosome in humans. Assume that a woman with normal vision (her father is color-blind) marries a color-blind male. What is the likelihood that this couple's first son will be color-blind? 0% 25% 50% 75% 100%Explanation / Answer
18. The phenonmenon is called non-disjunction. Epistasis is the modification of the effect of a gene by a gene present in a different locus. Crossing over is the exchange of information between homologus chromosomes. Pleiotropy is when a gene affects unrelated genes. Chromosome inactivation occurs in one X of the two X chromosomes in female mammals for silencing.
19. Each primary spermatocyte gives rise to 4 sperm cells, and each secondary spermatocyte gives rise to 2 sperm cells. Therefore the number of sperm produced will be 400 x 4 = 1600, and 400 x 2 = 800, meaning option C is the correct option.
20. Each primary oocyte gives rise to one first primary polar body and one secondary oocyte. Therefore 100 primary oocytes will give rise to 100 secondary oocytes and 100 first polar bodies, meaning option D is the correct option.
21. Assuming the male gametes are Z and Z', and the female gametes are Z and W, the possible genotypes for the embryos are ZZ (male), ZW (female), ZZ' (carrier male) and Z'W (affected female). As the gene is recessive, the female Z'W will not survive. Therefore the ratio will be 2:1 male to female (option B).
22. The cross is XX (normal mother) with X'Y (color blind father). The only way a male offspring can be concieved is if the father contributes the Y chromosome, which means the defective X chromosome is not transmitted. The mother can only contribute X chromosome, which the son cannot have color blindness. Therefore the chance of color blindness is zero in the male offspring (option A).
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