Principles Of Inheritance And Variation

In Drosophila, the XXY condition leads to femaleness whereas in human beings, the same condition leads to Klinefelter's syndrome in males. It proves that Y chromosome is active in sex determination in both human beings and Drosophila. This observation highlights the role of the Y chromosome in determining male sex characteristics.

So, the correct option is (A): In human beings Y chromosome is active in sex determination

When genes A and B are linked, the genotype of progeny in a cross between AB/ab and ab/ab would typically result in two different combinations of alleles. This is because linked genes tend to be inherited together more often. So, the correct option is (B): AaBb and aabb

In a female with a XXXX chromosome configuration (also known as tetrasomy X), there can be multiple Barr bodies (inactivated X chromosomes). The number of Barr bodies corresponds to the number of extra X chromosomes beyond the normal XX configuration. So, in the case of XXXX female, there would typically be (C): 3 Barr bodies This indicates that three of the four X chromosomes would be inactivated.

In Mendel's experiments, he found that when he crossed a green-seeded pea plant (homozygous for the green allele, gg) with a yellow-seeded pea plant (homozygous for the yellow allele, GG), all the offspring had yellow seeds. However, when he crossed these yellow-seeded offspring with each other (resulting in a Gg genotype), some of the progeny had green seeds, demonstrating the recessive nature of the green seed color trait.

So, the correct option is (B): Green seed colour

Mendel's work with pea plants demonstrated the principles of inheritance for various traits and these traits are controlled by genes located on four different chromosomes.

So, the correct option is (D): Four

Sickle cell anemia is a genetic disorder caused by a mutation in the hemoglobin gene. While it is a harmful condition in itself and can cause various health problems, individuals with sickle cell trait (heterozygous for the gene) are less susceptible to contracting malaria, a mosquito-borne infectious disease. This is because the sickled red blood cells are less favorable for the malaria parasite's growth and survival. Therefore, in regions where malaria is prevalent, having the sickle cell trait can provide some level of resistance to the disease, which is why it's considered a potential savior from malaria. However, it's essential to note that sickle cell anemia itself is a severe health condition with its own set of complications.

So, the correct option is (B): Sickle cell anaemia

Linked genes are located close to each other on the same chromosome, and they tend to be inherited together as a unit during meiosis because they do not independently assort into different gametes as Mendel's law of independent assortment would suggest. This phenomenon is a result of their physical proximity on the same chromosome and is known as genetic linkage.

So, the correct option is (C): Do not show independent assortment

Down's syndrome is typically caused by the presence of an extra copy of chromosome 21. It is most commonly associated with nondisjunction during meiosis, leading to an extra chromosome 21 in the resulting offspring.
When an affected mother (who has two copies of chromosome 21) and a normal father (who has two copies of chromosome 21) have offspring, the possible combinations of chromosome inheritance are as follows:

1. Normal offspring (2 copies of chromosome 21 from each parent): 25%
2. Offspring with Down's syndrome (3 copies of chromosome 21 from the mother, 1 from the father): 50%
3. Offspring with Down's syndrome (3 copies of chromosome 21 from the father, 1 from the mother): 25%

So, 50% of the offspring produced by an affected mother and a normal father would be affected by Down's syndrome.

Therefore, the correct answer is (C): 50%.

X-rays induce sex-linked recessive lethal mutations: This research, often associated with the work of Hermann J. Muller, did indeed contribute to our understanding of mutations. Muller himself was awarded the Nobel Prize in Physiology or Medicine in 1946 for his work on the effects of X-rays on genes.

So, the correct option is (A): X-rays induce sex-linked recessive lethal mutations