Sex and Homologous Chromosomes

Vocabulary practice flashcards covering the costs of sexual reproduction, meiosis, karyotypes, homologous chromosomes, alleles, and cellular ploidy.

Sexual Reproduction

A reproductive life cycle in which individuals inherit copies of chromosomes from each parent; chromosome numbers are reduced to one copy per cell via meiosis and later restored to two copies upon fertilization.

Parthenogenesis

A form of reproduction—often called 'virgin birth'—where offspring develop without fertilization by sex cells, occurring naturally in species such as whiptail lizards in the genus Aspidoscelis (formerly Cnemidophorus).

Costs of Sexual Reproduction

Disadvantages associated with sexual reproduction compared to parthenogenesis, including extensive expenditure of time, effort, and resources to find and keep mates, lower rates of gene transmission, and slower population growth.

Meiosis

The cell division process that reduces chromosome number from diploid ($2n$) in adult cells to haploid ($1n$) in gametes (sperm and egg cells).

Mitosis

The cell division process by which a diploid ($2n$) zygote divides and multiplies to develop into a fetus, infant, adolescent, and adult while preserving the diploid chromosome number.

Karyotype

An organized visual image or profile of all the chromosomes present within an individual's cell.

Autosomal Chromosomes

Chromosomes that are not sex-determining chromosomes; typical human cells contain 22 pairs ($44$ individual chromosomes) of them.

Sex Chromosomes

Chromosomes that determine the biological sex of an individual; typical humans possess 1 pair ($2$ chromosomes, such as X and Y).

Homologous Chromosomes

Two chromosomes of the same type that contain the same genes in the same chromosomal locations—one inherited from each biological parent—which are not identical because they may carry different alleles.

Allele

A specific version of a gene defined by its particular DNA sequence, which can alter amino acid sequence, protein structure and function, or gene regulation.

Wildtype Allele

The most common or typical allele of a gene found in a population, often referred to as the 'normal' allele.

Homozygous

A genetic condition in which an individual possesses matching (identical) alleles for a specific gene across both homologous chromosomes.

Heterozygous

A genetic condition in which an individual carries two different alleles for a specific gene across homologous chromosomes.

Ploidy

A term describing the number of copies of each kind of chromosome present within a cell.

Diploid ($2n$)

A cell or organism having two copies of each kind of chromosome, as seen in humans and horses.

Haploid ($n$ or $1n$)

A cell or organism having only one copy of each kind of chromosome, as found in human gametes (sperm and egg) and male honeybees.

Polyploid

An organism or cell containing more than two sets of chromosomes, such as hexaploid wheat ($6n$) or octaploid domestic strawberries ($8n$).