Cell Cycle and Chromosomes

During oogenesis in mammals, the second meiotic division occurs during fertilisation.

Aneuploidy occurs when nondisjunction at a single chromosome results in an abnormal number of chromosomes.

Ectopic recombination involves unequal crossing over. In ectopic recombination, crossing over occurs between non-homologous chromosomes during meiosis. Duplication occurs at the site of exchange.

Deletion of a small piece of chromosome 22 causes DiGeorge syndrome.

A fusion gene is a hybrid gene formed from two previously separate genes. It can occur as a result of translocation, interstitial deletion and chromosomal inversion.

Chromosomal inversions can be seen in heterozygous condition of polytene chromosomes. Small inversions in most species remain undetected. Polytene chromosomes are exploited for observing inversions.

Meiosis generates maximum genetic variation through two key mechanisms: crossing over during prophase I (recombination between homologous chromosomes) and independent assortment of chromosomes during metaphase I. While polyploidy, mutations, and chromosomal aberrations can introduce variation, they are less frequent and more drastic changes compared to the regular, systematic variation produced by meiosis.

Total number of chromosomes in pea plant is 7 pairs (14).

A chromosomal abnormality in male due to trisomy of sex chromosome is Klinefelter's syndrome.

ZW-ZZ type of sex determination is found in birds.

Telocentric chromosomes have the centromere positioned at the very tip (telos = end), creating a chromosome with only one arm. This contrasts with acrocentric (near the tip), metacentric (middle), and sub-metacentric (off-center).

Metacentric chromosomes have the centromere positioned near or at the center, dividing the chromosome into two arms of roughly equal length. The prefix 'meta-' means middle or central, distinguishing it from other centromere positions.

Human somatic (body) cells are diploid, containing 46 chromosomes (23 pairs - one set from each parent). Gametes (sperm and egg) are haploid with 23 chromosomes. Option B (44) is close but incorrect, while option D (92) would be the total if counting all chromosomes without pairing, but the standard count is 46.

Males have XY and females have XX. Hence, this is the correct answer.

23^rd pair of chromosomes is different in males and females and this distinguishes the males from the females. Males have XY chromosomes and female have XX chromosomes. So, option (C) is correct.