Master Chromosome Forms with Picmonic for Pre-Health

A chromosome is the condensed form of chromatin. Chromatin is DNA wound around histones. Humans expectedly have 23 pairs of chromosomes: 22 numbered pairs called autosomes and one pair of sex chromosomes labeled X and Y.

Sister chromatids consist of one chromatid and a replicated copy connected at the centromere. They are typically homozygous with similar traits but may have slight differences due to mutation or crossing over (meiosis I). They only exist during cell reproduction and division. During mitosis and meiosis II, sister chromatids are pulled apart into separate daughter cells.

Homologous recombination occurs during meiosis when genetic material from the egg and sperm are recombined, forming paired or homologous chromosomes. The homologous chromosome pairs code for the same genes at similar loci but have allelic variance as one chromosome is from the mother and the other from the father. During meiosis I, crossing over is an important point after recombination when the homologous chromosome synapses and exchanges genetic information, leading to variation of similar ancestral traits among offspring.

The tetrad is formed by two chromosomes (each chromosome consisting of two sister chromatids) grouped together. It only occurs in meiosis I, as homologous chromosomes do not synapse in mitosis or meiosis II.