c. can never occur in females. 36. If a characteristic is sex-linked, it a. occu
ID: 223062 • Letter: C
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c. can never occur in females. 36. If a characteristic is sex-linked, it a. occurs most commonly in males. d. is always fatal. b. occurs only in females. 37. The sex of an offspring is determined by c. both parents. a. the mother. d. the offspring. b, the father. and a red-eyed male Drosophila. 38. Consider a cross between a white-eyed female Drosophila proportion of the What proportion ofthe female offspring would be expected to be white-eyed? What male offspring would be expected to be white-eyed? c. all; none a. none; all d. none: 25% b, 50%; 50% 39 Which pair of genes in Figure 6.2 would be most likely to be inherited together? e E gene B FIG. 6.2 c. A and D a. A and B b, A and C d. A and EExplanation / Answer
36. If a characteristic is sex-linked it most commonly occurs in males.
In general genes on sex chromosomes are described as sex linked genes controlling characters known as sex linked characters. Since in mammals males have XY sex chromosomes and females have XX chromosomes, males are heterogamtic and females are homogametic. Also most of the genes are present on X chromomosomes and only few on Y chromosome. Thus males have single copy of every sex-linked gene on single X chromosome and show its expression. For example if a boy gets X chromosome from mother who is heamophilic, the boy will be affected but if a girl gets both heamophilic X chromosomes from both parents only then she can become heamophillic otherwie only a carrier.
37. The sex of an offspring is determined by FATHER in case of mammals having XX( females) and XY(males) sex chromosomes. Some species (including humans) have a gene SRY on the Y chromosome that determines maleness.Human sex is determined by the presence or absence of a Y chromosome with a functional SRY gene. Once the SRY gene is activated, cells create testosterone and anti-müllerian hormone which typically ensures the development of a single, male reproductive system.
In Drosophila sex is determined by the balance(ratio) between of autosomal alleles that favour maleness and alleles on the X chromosomes that favour femaleness.
There are some cases of environmental sex determinatioin also
38. If white eyed female is crossed with red eyed male, in F1we get red eyed female and white eyed male. on crossing these we get following results
25% white eyed females
25% red eyed female
50% white eyed male.
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