This set of Tough Cytogenetics Questions and Answers focuses on “Sex Influenced Traits and Sex Limited Traits”.
1. The sex influenced traits are present in _______________________
b) Sex chromosome
c) Mitochondrial chromosome
d) These are epigenetic traits
Explanation: Sex influenced traits are present in the autosomes. They are not present in the sex chromosome; although their expression is dependent on the sex of the individual.
2. Sex influenced traits are only related to females.
Explanation: Sex influenced trait effects both males and females. They can be more expressed in male or female depending on the nature of the trait.
3. If A is a sex influenced trait that is more expressed in males, then which of the following is false?
a) Only male having a homozygous recessive form of this gene will not express it
b) No female will express the gene
c) The gene is autosomal
d) Heterozygous female will not express this gene
Explanation: If the sex influenced trait is more expressed in men then it acts as a dominant trait in men. And at the same time, it acts as a recessive trait in female. The female with homozygous form of this trait will thus express it, and men lacking any copy of it in case of recessive homozygote will not express it.
4. If present of horn in a breed of sheep is due to the presence of h+ allele which is sex influenced and more expressed in male, choose the off one out.
a) Female with h+ h+
b) Male with h+ h+
c) Female with h h+
d) Male with h h+
Explanation: This sex influenced trait is dominant for male and recessive for female. Out of the given options only heterozygous female will not express this trait making it the off one.
5. Patterned baldness is a sex influenced trait more expressed in a male. If b+ is normal allele making non-bald phenotype and b is mutant leading to bald phenotype, for a cross between a bald mother and normal father, what is the probability of a bald son?
Explanation: Baldness is a sex influenced trait, so the mother is certainly b/b and the father is b+,b+. So, the son will get at least one baldness allele from the mother. Heterozygous male expresses the sex influenced trait; hence the son will definitely be bald.
6. Homozygous bald gene, a sex influenced gene, is equally expressed in men and women.
Explanation: It is true that the sex influenced trait is expressed in females in homozygous condition, but the expression is not the same as that in male. In females the expression is much delayed under the influence of hormones.
7. Choose the odd one out on the basis of sex influence.
a) Cleft palate
b) Club foot
Explanation: All the mentioned options are sex influenced traits. Cleft palate, Club foot and Gout are dominant for males while osteoporosis is dominant for females.
8. What will be the phenotype and genotype of a daughter born to bald mother and non-bald father?
a) b+/b+ non-bald
b) b+/b+ bald
c) b/b+ non-bald
d) b/b+ bald
Explanation: Baldness is a dominant gene for a male. A bald mother is thus homozygous for the allele; at least one baldness gene will thus pass to offspring from her. The father is normal so he must lack any baldness allele and a normal gene will pass from him. Hence daughter is a heterozygote and normal.
9. Which one of the following will not be expressed in female even in homozygous form?
a) Cock feathering
b) Cleft palate
d) Color blindness
Explanation: Cock feathering is a sex limited trait which is expressed only on one sex depending. Even if the other sex is homozygous for it, the phenotype will not be expressed unless there is serious hormonal change.
10. If a bull doesn’t express the milking factor, where m+ is normal and m is a mutant gene, its genotype is?
d) Can’t be specified
Explanation: Milking factor is a sex influenced trait that is only expressed in females i.e. cows. Bulls will never express these genes irrespective of their phenotype. Hence, their genotype can’t be specified.
11. Appearance of cock feather in chicken is ________________
a) X linked
b) Y linked
c) Sex influenced
d) Sex limited
Explanation: This gene is located in the autosome so it’s not X or Y linked. Cock feathering will not be seen in hen even when it is homozygous, hence it’s not sex influenced. Thus, it is sex limited trait.
12. Sex influenced genes will not occur in ________________
a) Homologous autosome
b) Homologous part of sex chromosome
c) Short arm of human Y chromosome
d) On autosomes of male
Explanation: Short arm of human Y chromosome is not homologous to X chromosome. Thus, genes there will show Y linkage. Sex influenced genes don’t show linkage and are not exclusive to X or Y chromosomes, so it will not be present there.
Sanfoundry Global Education & Learning Series – Cytogenetics.
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