Meiosis, Recombination, and Chromosomal Variations - Vocabulary Flashcards

Vocabulary flashcards covering key concepts from the lecture notes on meiosis, recombination, and chromosomal variations.

Homologous chromosomes

Pairs of chromosomes that carry the same genes in the same order but may have different alleles; they pair during meiosis I to allow recombination and segregation.

Sister chromatids

Two identical copies of a chromosome created during DNA replication; held at the centromere until separation in meiosis II or mitosis.

Crossing over

Exchange of genetic material between non-sister chromatids of homologous chromosomes during prophase I, producing recombinant chromatids.

Recombination

Process by which crossing over between homologous chromosomes creates new allele combinations and breaks linkage.

Tetrad

Structure formed by paired homologous chromosomes (each with two sister chromatids) during prophase I.

Meiosis I

First division of meiosis; homologous chromosomes separate, reducing chromosome number; crossing over occurs in prophase I.

Meiosis II

Second division; sister chromatids separate; results in four haploid gametes.

Nondisjunction

Failure of homologous chromosomes or sister chromatids to separate properly, leading to abnormal chromosome numbers.

Aneuploidy

Abnormal chromosome number in a cell (e.g., monosomy, trisomy) often due to nondisjunction.

Trisomy 21

Three copies of chromosome 21; cause of Down syndrome; individuals can survive.

Polar body

Small cell produced during female meiosis as a byproduct of unequal cytokinesis; usually degenerates.

Primary oocyte

Diploid germ cell in females formed before birth; arrested in prophase I until ovulation.

Secondary oocyte

Large cell produced after meiosis I, arrested in metaphase II until fertilization; becomes fertilized egg.

Unequal cytokinesis

Cytokinesis during meiosis I in oogenesis yields a large secondary oocyte and a small polar body.

Pseudoautosomal region

Regions on X and Y chromosomes where recombination occurs, behaving like autosomal pairing.

Sex chromosomes

Chromosomes determining sex (X and Y) and their pairing and segregation during meiosis.

G-banding

Chromosome staining technique producing dark and light bands to identify regions and locate genes.

Translocation

Structural chromosomal rearrangement where a segment from one chromosome is transferred to another chromosome.

Gene duplication

An extra copy of a chromosome segment or gene; can occur in various organisms; may lead to extra gene products.

Linkage

Genes located close on the same chromosome tend to be inherited together unless recombination separates them.

Haploid

A cell with a single set of chromosomes.

Diploid

A cell with two sets of chromosomes.