Sexual Reproduction and Meiosis

These flashcards cover the key vocabulary and concepts for Chapter 9, including the mechanisms of meiosis, genetic variation, and chromosomal disorders resulting from nondisjunction.

Ploidy

The number of complete sets of chromosomes in a cell; for example, animals are mostly diploid while asexually reproducing organisms are haploid.

Diploid

Cells or organisms containing two homologous sets of chromosomes ($2n$), with one set inherited from each parent.

Haploid

Cells or organisms containing only a single set of chromosomes ($1n$), typical of asexually reproducing organisms and gametes.

Homologous chromosomes

Pairs of chromosomes that are the same size, have the same centromere position, and carry the same genes, though they may have different alleles.

Alleles

Variations or different versions of a single gene.

Somatic cells

All body cells except for gametes; these cells are diploid ($2n$) and divide via mitosis.

Gametes

Sex cells (sperm and egg cells) that are haploid ($1n$) and genetically unique, produced through meiosis.

Mitosis

Somatic cell division that produces two genetically identical daughter cells for the purpose of growth and repair.

Meiosis

Sex cell division in germ cells where DNA replicates once but the nucleus divides twice, yielding four genetically unique haploid gametes.

Fertilization

The process where a haploid sperm ($1n$) fuses with a haploid egg ($1n$) to form a diploid zygote ($2n$).

Zygote

A single-cell fertilized egg that contains $46$ chromosomes in $23$ pairs in humans.

Germ cells

Specialized cells that undergo meiosis to produce haploid gametes.

Interphase

The phase of the cell cycle preceding division where the cell grows and copies its DNA; it includes $G1$, $S$ (DNA synthesis), and $G2$ stages.

Crossing-over

Also known as recombination; a process during Prophase I where homologous chromosome pairs exchange genetic material, giving rise to greater allele variations.

Recombinant chromatid

A chromatid produced by the process of crossing over that contains a new combination of maternal and paternal genetic information.

Random assortment

Also known as independent assortment; the process during Metaphase I where homologous chromosome pairs align independently and randomly at the metaphase plate.

Random fertilization

A source of genetic diversity where any sperm can fuse with any egg, resulting in approximately $2^{23}$ combinations per gamete and about $1$ in $70$ trillion total possible combinations.

Monozygotic twins

Identical twins formed from a single zygote that splits into two embryos.

Dizygotic twins

Fraternal twins formed when two separate eggs are fertilized by two different sperm, resulting in two distinct zygotes.

Nondisjunction

An error in meiosis, most common in Meiosis I, where chromosomes fail to separate properly, leading to gametes with extra or missing chromosomes.

Aneuploidy

A condition characterized by an atypical chromosome number, such as having one extra ($n+1$) or one missing ($n-1$) chromosome.

Monosomic

A type of aneuploidy where a cell is missing a chromosome, represented as ($n-1$).

Trisomic

A type of aneuploidy where a cell has an extra chromosome, represented as ($n+1$); examples include Trisomy 21 and Trisomy 18.

Turner syndrome

A sex chromosome abnormality with the genotype XO, occurring in approximately $1$ in $2000$ females, characterized by short stature and infertility.

Klinefelter syndrome

A sex chromosome abnormality with the genotype XXY, occurring in approximately $1$ in $750$ males, characterized by tall stature and breast development.

Polyploidy

A condition where an organism has extra complete sets of chromosomes (e.g., $3n$, $4n$, $8n$). While fatal in humans, it is common and often beneficial in plants like bananas and strawberries.