Meiosis and Sexual Life Cycles Vocabulary

Vocabulary terms and definitions from the lecture notes on Meiosis and Sexual Life Cycles, covering reproductive stages, chromosome types, and mechanisms of genetic variation.

Genetics

The scientific study of heredity and variation.

Heredity

The transmission of traits from one generation to the next.

Variation

Demonstrated by the differences in appearance that offspring show from parents and siblings.

Genes

The units of heredity made up of segments of DNA, passed to the next generation via reproductive cells.

Gametes

Reproductive cells (sperm and eggs) used to pass genes to the next generation.

Somatic cells

Any cell in a multi-cellular organism other than the gamete or its precursor.

Locus

A specific location on a certain chromosome where a gene is found.

Homologous Chromosomes

A pair of chromosomes that have the same size, same genetic loci, and same location of their centromere.

Sex chromosomes

The $X$ and $Y$ chromosomes that determine the sex of an individual; females have a homologous pair ($XX$) and males have one of each ($XY$).

Haploid (n)

A cell containing a single set of chromosomes; in humans, $n = 23$.

Autosomes

The remaining $22$ pairs of chromosomes in the human genome that are not sex chromosomes.

Diploid (2n)

A cell having two sets of chromosomes; in humans, the diploid number is $46$ ($2n = 46$).

Asexual Reproduction

Reproduction involving mitosis only, producing exact genetic copies (clones) of the single parent organism with no genetic variation.

Clones

Exact genetic copies produced from a single parent organism through asexual reproduction.

Sexual Life Cycle

A generation-to-generation sequence of stages involving a diploid stage, meiosis to produce a haploid stage, and fusion of haploid cells to restore the diploid state.

Fertilization

The union of haploid gametes (sperm and egg) to produce a diploid zygote.

Zygote

A diploid cell produced by the fusion of two haploid gametes, which then develops into an adult via mitosis.

Alternation of generations

A life cycle exhibited by plants and some algae that includes both diploid and haploid multicellular stages.

Spores

Haploid reproductive cells in plants that grow via mitosis to give rise to a gametophyte.

Gametophyte

The multicellular haploid generation in the plant life cycle that gives rise to gametes.

Sporophyte

The multicellular diploid generation in the plant life cycle that gives rise to spores by meiosis.

Meiosis

A type of cell division that reduces the number of chromosome sets from diploid to haploid, resulting in four genetically distinct daughter cells.

Meiosis I

The first round of meiotic division characterized by the separation of homologous chromosomes.

Meiosis II

The second round of meiotic division, which is essentially the same as mitosis and involves the separation of sister chromatids.

Synapsis

The pairing of two homologous chromosomes gene by gene during Prophase I of meiosis.

Tetrad

A structure consisting of four chromatids (a pair of homologous chromosomes) formed during synapsis.

Crossing Over

An event in Prophase I where homologous portions of two non-sister chromatids trade places, producing recombinant chromosomes.

Cohesins

Protein complexes that form a ring-like structure to encircle chromatids, holding sister chromatids together and regulating their separation.

Independent Assortment of Chromosomes

The mechanism by which each pair of homologous chromosomes sorts maternal and paternal homologs into daughter cells independently of other pairs during Metaphase I.

Recombinant chromosomes

Chromosomes that carry DNA inherited from both parents, produced by the process of crossing over.

Chiasma

The crossed region where two homologous chromosomes are physically joined during crossing over.

Random Fertilization

The mechanism contributing to genetic variation where any sperm can fuse with any ovum, creating a unique genetic identity for each zygote.