Chapter 11: Meiosis and Sexual Reproduction

Meiosis

A type of cell division that reduces the chromosome number by half, resulting in the formation of haploid cells from diploid cells.

Homologous chromosomes

Chromosome pairs, one from each parent, that are similar in shape, size, and genetic content.

Diploid number

The total number of chromosomes in a somatic cell, represented as 2n.

Haploid number

The number of chromosomes in a gamete, represented as n.

Synapsis

The pairing of two homologous chromosomes during meiosis.

Crossing-over

The exchange of genetic material between homologous chromosomes during meiosis.

Tetrad

A structure containing four chromatids formed during synapsis in meiosis.

Chiasma

The point at which homologous chromosomes exchange genetic material during crossing-over.

Interkinesis

The phase between meiosis I and meiosis II, where the cell prepares for the second division.

Meiosis I

The first division of meiosis, where homologous chromosomes are separated.

Meiosis II

The second division of meiosis, where sister chromatids are separated.

Interphase

The phase of the cell cycle where the cell prepares for division, including DNA replication.

Mitosis

A type of cell division that results in two genetically identical daughter cells.

Sexual reproduction

A reproductive process that involves the fusion of two haploid cells to form a diploid cell, introducing genetic variation.

Asexual reproduction

A reproductive process that produces genetically identical offspring from a single parent.

Advantage of asexual reproduction

Rapid reproduction without the need for a mate.

Disadvantage of asexual reproduction

Lack of genetic variation, making populations susceptible to disease.

Advantage of sexual reproduction

Increased genetic variation, enhancing adaptability and survival.

Disadvantage of sexual reproduction

Requires finding a mate and is generally slower than asexual reproduction.

Life cycle of plants and animals

Meiosis occurs during the formation of gametes in the reproductive organs of plants and animals.

Zygote

The diploid cell formed by the fusion of two haploid gametes during fertilization.

alternation of generations

life-cycle type in which the diploid and haploid stages alternate

chiasmata

(singular, chiasma) the structure that forms at the crossover points after genetic material is exchanged

cohesin

proteins that form a complex that seals sister chromatids together at their centromeres until anaphase II of meiosis

crossover

exchange of genetic material between nonsister chromatids resulting in chromosomes that incorporate genes from both parents of the organism

diploid

cell, nucleus, or organism containing two sets of chromosomes (2n)

fertilization

union of two haploid cells from two individual organisms

gamete

haploid reproductive cell or sex cell (sperm, pollen grain, or egg)

gametophyte

a multicellular haploid life-cycle stage that produces gametes

germ cells

specialized cell line that produces gametes, such as eggs or sperm

haploid

cell, nucleus, or organism containing one set of chromosomes (n)

life cycle

the sequence of events in the development of an organism and the production of cells that produce offspring

reduction division

nuclear division that produces daughter nuclei each having one-half as many chromosome sets as the parental nucleus; meiosis I is a reduction division

somatic cell

all the cells of a multicellular organism except the gametes or reproductive cells

spore

haploid cell that can produce a haploid multicellular organism or can fuse with another spore to form a diploid cell

sporophyte

a multicellular diploid life-cycle stage that produces haploid spores by meiosis

synaptonemal complex

protein lattice that forms between homologous chromosomes during prophase I, supporting crossover