The mutation in sickle-cell anaemia involves the substitution of:
The defect is caused by the substitution of Glutamic acid (Glu) by Valine (Val) at the sixth position of the beta globin chain of the haemoglobin molecule.
Question 42 of 519
📘 CLASS XII
The single base substitution at the sixth codon of the beta globin gene that causes sickle-cell anaemia is:
The substitution of the amino acid in the globin protein results from a single base substitution at the sixth codon of the beta globin gene, changing it from GAG to GUG.
Question 43 of 519
📘 CLASS XII
Phenylketonuria is an inborn error of metabolism inherited as an autosomal recessive trait. It is caused by the lack of an enzyme that converts:
In phenylketonuria, the affected individual lacks an enzyme that converts the amino acid phenylalanine into tyrosine, leading to its accumulation and conversion into phenylpyruvic acid.
Question 44 of 519
📘 CLASS XII
Thalassemia is different from sickle-cell anaemia because it is a:
Thalassemia differs from sickle-cell anaemia in that the former is a quantitative problem of synthesising too few globin molecules, while the latter is a qualitative problem of synthesising an incorrectly functioning globin.
Question 45 of 519
📘 CLASS XII
Failure of segregation of chromatids during the cell division cycle, resulting in the gain or loss of a chromosome, is called:
Failure of segregation of chromatids during the cell division cycle results in the gain or loss of a chromosome(s), a condition called aneuploidy.
Question 46 of 519
📘 CLASS XII
Down’s syndrome is caused by the presence of an additional copy of which chromosome?
The cause of Down’s syndrome is the presence of an additional copy of chromosome number 21 (trisomy of 21). The disorder was first described by Langdon Down in 1866.
Question 47 of 519
📘 CLASS XII
Klinefelter’s syndrome is a genetic disorder caused by:
Klinefelter’s syndrome is caused by the presence of an additional copy of an X-chromosome, resulting in a karyotype of 47, XXY.
Question 48 of 519
📘 CLASS XII
Turner’s syndrome is caused by the absence of one of the X chromosomes, resulting in a karyotype of:
Turner’s syndrome is caused by the absence of one of the X chromosomes, leading to a karyotype of 45 with X0.
Question 49 of 519
📘 CLASS XII
A cross between two tall pea plants resulted in offspring of which some were dwarf. The genotype of the parent plants is:
The appearance of the recessive dwarf phenotype (tt) in the offspring indicates that both parents must have carried the recessive allele (t). Since the parents were tall (dominant phenotype), they must both be heterozygous (Tt). A Tt x Tt cross yields a genotypic ratio of 1:2:1 and a phenotypic ratio of 3:1.
Question 50 of 519
📘 CLASS XII
If a colour-blind man marries a woman who is a carrier for colour blindness, what is the probability that their son will be colour-blind?
The son of a woman who carries the gene has a 50 per cent chance of being colour blind. The man's genotype is XcY and the woman's is XhX. A son receives Y from the father and either Xh or X from the mother, giving a 50% chance of being XhY (colour-blind).
