Hereditary and Variation MCQs for NEET — Botany Questions with Answers

Cri-du-chat syndrome is caused by a deletion of a portion of the short arm of chromosome 5. The syndrome gets its name from the characteristic cry of affected infants, which resembles the mewing of a cat. This deletion results in various developmental issues and physical abnormalities.

In hexaploid wheat (Triticum aestivum), the haploid number (n) of chromosomes is 21. The basic chromosome number (X) is 7. This is because hexaploid wheat has six sets of chromosomes (2n = 6x = 42). Hence, n = 21 and X = 7.

Inheritance of skin colour in humans is an example of polygenic inheritance. This means that multiple genes are involved in determining skin colour. Each gene may have several alleles that contribute to the final phenotype, resulting in a wide range of skin tones.

When a heterozygous yellow-seeded plant (Yy) is crossed with a green-seeded plant (yy), the offspring (F₁ generation) can be YY (yellow), Yy (yellow), or yy (green). The ratio of yellow to green seeds can be determined using a Punnett square. The expected ratio is 1:1, meaning 50% yellow and 50% green seeded plants.

The ABO blood grouping system is named so because type 'O' blood has neither A nor B antigens on the surface of the red blood cells (RBCs). This is why it is referred to as 'O,' indicating the absence of these antigens.

Mendel's law of dominance does not explain the phenomenon where alleles do not show any blending and both characters recover as such in the F₂ generation. This is explained by the law of segregation, which states that allele pairs separate randomly, so that each gamete receives one allele of each pair.

A test cross is used to determine the genotype of a plant showing a dominant phenotype. In a test cross, the individual with the dominant phenotype (but unknown genotype) is crossed with an individual that is homozygous recessive for the trait in question. If any offspring display the recessive phenotype, the dominant phenotype parent must be heterozygous. If all offspring display the dominant phenotype, the parent is likely homozygous dominant.

Mutations can be induced using gamma radiations. Gamma rays are a form of ionizing radiation which have high energy and the ability to penetrate tissues, causing changes in the DNA sequence, leading to mutations. This method is commonly used in genetic studies to create mutations and study their effects.

A test cross involves crossing the F₁ hybrid with a double recessive genotype. This type of cross helps to determine the genotype of the F₁ hybrid by analyzing the phenotypes of the offspring. If the F₁ hybrid is heterozygous, the offspring will show a 1:1 ratio of dominant to recessive traits.

A normal human female child has two X chromosomes (XX). The presence of two X chromosomes ensures the development of female characteristics. Hence, the zygotic condition leading to the birth of a normal human female child is having two X chromosomes.