In Morgan's dihybrid cross in Drosophila, the F2 ratio deviated significantly from 9:3:3:1 because the two genes studied were:
Morgan observed that when two genes in a dihybrid cross were situated on the same chromosome, the proportion of parental gene combinations was much higher than non-parental types. This physical association, or linkage, caused the F2 ratio to deviate from the 9:3:3:1 ratio expected for independently assorting genes.
Question 72 of 519
📘 CLASS XII
Which of the following traits in humans is a classic example of polygenic inheritance?
Human skin colour is a classic example of a polygenic trait. Such traits are generally controlled by three or more genes, and the phenotype is spread across a gradient rather than having distinct alternate forms.
Question 73 of 519
📘 CLASS XII
If a heterozygous tall pea plant (Tt) is crossed with a homozygous dwarf plant (tt), what percentage of the progeny will be dwarf?
This is a test cross. The heterozygous tall plant (Tt) produces two types of gametes (T and t) in equal proportion. The dwarf plant (tt) produces only one type (t). The offspring will have genotypes Tt and tt in a 1:1 ratio, meaning 50% will be phenotypically dwarf.
Question 74 of 519
📘 CLASS XII
The two alleles of a gene pair are located on:
An important thing to remember is that chromosomes as well as genes occur in pairs. The two alleles of a gene pair are located on homologous sites on homologous chromosomes.
Question 75 of 519
📘 CLASS XII
The chromosomal condition in a male honey bee (drone) is:
In the haplodiploid system of honey bees, females are diploid (32 chromosomes) and males are haploid, having 16 chromosomes, as they develop from unfertilised eggs via parthenogenesis.
Question 76 of 519
📘 CLASS XII
In the Punnett square, the possible gametes are written on:
The Punnett Square is a graphical representation to calculate the probability of offspring genotypes. The possible gametes are written on two sides, usually the top row and left columns.
Question 77 of 519
📘 CLASS XII
Besides recombination, what is the other phenomenon that leads to variation in DNA?
In addition to recombination, mutation is another phenomenon that leads to variation in DNA. It is defined as an alteration of DNA sequences.
Question 78 of 519
📘 CLASS XII
In a pedigree, mating between relatives (consanguineous mating) is represented by:
According to the standard symbols used in human pedigree analysis, mating between relatives (consanguineous mating) is represented by a double horizontal line connecting the male (square) and female (circle).
Question 79 of 519
📘 CLASS XII
Why is it extremely rare for a female to be haemophilic?
The possibility of a female becoming haemophilic is extremely rare because for this to happen, her mother has to be at least a carrier and her father should be haemophilic, a condition which is often unviable in the later stages of life.
Question 80 of 519
📘 CLASS XII
The shape of red blood cells changes to an elongated sickle-like structure in sickle-cell anaemia under what condition?
In sickle-cell anaemia, the mutant haemoglobin molecule undergoes polymerisation under low oxygen tension, causing the change in the shape of the RBC from biconcave disc to an elongated sickle-like structure.
