A single gene exhibiting multiple phenotypic expressions is known as a:
Instances where a single gene can exhibit multiple phenotypic expression are known as pleiotropy, and the gene is called a pleiotropic gene.
Question 22 of 519
📘 CLASS XII
The human disease phenylketonuria, caused by a mutation in a single gene, results in mental retardation and changes in hair and skin pigmentation. This is an example of:
Phenylketonuria is an example of pleiotropy. The disease is caused by a single gene mutation that affects the enzyme phenylalanine hydroxylase, leading to multiple phenotypic expressions like mental retardation and reduced pigmentation.
Question 23 of 519
📘 CLASS XII
Who first traced a specific nuclear structure through spermatogenesis in insects, which was later identified as the X chromosome?
Henking (1891) traced a specific nuclear structure in a few insects and observed that 50% of sperm received it. He named it the X body, which was later identified as a chromosome.
Question 24 of 519
📘 CLASS XII
In the XO type of sex determination, such as in grasshoppers, males have:
Grasshopper is an example of XO type of sex determination in which the males have only one X-chromosome besides the autosomes, whereas females have a pair of X-chromosomes.
Question 25 of 519
📘 CLASS XII
In humans and Drosophila, the XY type of sex determination means that males are:
In humans and Drosophila, males have one X and one Y chromosome (XY) and are heterogametic, producing two different types of gametes. Females have two X chromosomes (XX) and are homogametic.
Question 26 of 519
📘 CLASS XII
In birds, the mechanism of sex determination involves:
In birds, females produce two different types of gametes in terms of sex chromosomes, which is called female heterogamety. The female has one Z and one W chromosome, while the male has a pair of Z-chromosomes.
Question 27 of 519
📘 CLASS XII
In humans, the sex of a child is determined by:
Females produce only one type of ovum with an X-chromosome. Males produce two types of sperm, 50% with X and 50% with Y. Therefore, it is the genetic makeup of the sperm that determines the sex of the child.
Question 28 of 519
📘 CLASS XII
The sex determination system in honey bees is called:
The sex determination in honey bees is based on the number of sets of chromosomes an individual receives. This is called the haplodiploid sex-determination system.
Question 29 of 519
📘 CLASS XII
In honey bees, a male (drone) develops from:
An unfertilised egg develops as a male (drone) by means of parthenogenesis. This means that males have half the number of chromosomes (haploid, 16) than that of a female (diploid, 32).
Question 30 of 519
📘 CLASS XII
A phenomenon which results in the alteration of DNA sequences and consequently changes the genotype and phenotype is:
Mutation is a phenomenon which results in alteration of DNA sequences and consequently results in changes in the genotype and the phenotype of an organism. It is a source of variation in DNA, in addition to recombination.
