Cell Cycle and Chromosomes

Holandric genes are located exclusively on the Y chromosome and are transmitted directly from father to son. Unlike sex-linked genes on the X chromosome, these Y-specific genes have no homologous counterpart. Options A, B, and C are incorrect: mutagenes induce mutations, sex-linked genes reside on X chromosomes, and allosomal genes refer to all sex chromosomes generally.

Meiosis I occurs when primary spermatocytes (2n, 4C) divide to form secondary spermatocytes (n, 2C). This is the reduction division that halves the chromosome number. Meiosis II then converts secondary spermatocytes to spermatids.

Down syndrome (DS or DNS), also known as trisomy 21, is a genetic disorder caused by the presence of all or part of a third copy of chromosome 21.

Barr body is a small, densely staining structure in the cell nuclei of females, consisting of a condensed, inactive X chromosome. It is regarded as diagnostic of genetic femaleness.

The gene which is responsible for the condition is carried on the X chromosome and this is the reason why many more men are affected than women.

Alleles are each of two or more alternative forms of a gene that arise by mutation and are found at the same place on a chromosome. 

G₁, S, G₂ and M are the sub-divisions in the cell cycle.

Histone synthesis is tightly coupled to DNA replication. Most histone production occurs during S phase when chromosomal DNA is being duplicated. New histones are needed immediately to package the newly synthesized DNA into nucleosomes. G0 is quiescent, G1 is pre-replication, and G2 is post-replication.

While humans and chimpanzees share approximately 98-99% of their DNA, their chromosome numbers differ. Humans have 46 chromosomes (23 pairs), while chimpanzees have 48 chromosomes (24 pairs). This difference is due to a fusion event in human chromosome 2, which formed from two separate ancestral chromosomes that remain distinct in chimpanzees.

This is false. Central zone is a small group of fast dividing cells.

Human males have 46 chromosomes total, written as 44 + XY. This represents 44 autosomes (22 pairs) plus XY sex chromosomes. Option A (44 + XX) is female, Option B has wrong autosomal count, and Option D (23 + XY) doesn't represent the full chromosome complement.

Gametes (sperm and egg cells) are universally haploid, containing only one set of chromosomes (n). This halving occurs through meiosis. The haploid state ensures that when two gametes fuse during fertilization, the zygote restores the diploid chromosome number (2n), maintaining species consistency across generations.

Mendel's 'factors' - the hereditary units that controlled traits in his pea plants - are now known as genes. Mendel discovered and described these units without any knowledge of DNA, chromosomes, or molecular biology. His 'factors' correspond exactly to what we now understand as genes: segments of DNA that code for specific traits.

Karyotyping is the technique of arranging chromosomes according to their size, shape, and banding pattern. It helps identify chromosomal abnormalities. Prototype refers to original type, phenotype to observable traits, and nucleotype is not a standard term.