Concept 13.2: Fertilization and meiosis alternate in sexual life cycles

Flashcards from Concept 13.2 of Pearson's Campbell Biology, Twelfth Edition.

Life cycle

The generation-to-generation sequence of stages in the reproductive history of an organism

• Chromosmal behavior is related to this in organisms

Karyotype

An ordered display of the pairs of chromosomes from a cell

• Humans display 23 pairs

Homologous chromosomes (homologs)

The two chromosomes in each pair of chromosomes

• Each has the same length, centromere position, and staining pattern with one set of chromosomes from each parent cell for inherited characteristics

Sex chromosomes

Chromosomes that determine the sex of the individual

• X and Y in humans

  • Females have a homologous pair of X chromosomes

  • Males have one X and one Y chromosome

Autosomes

The remaining pairs of chromosomes that do not determine sex

Diploid cell (2n)

A cell with two sets of chromosomes

• Is 46 in humans, representing two half-sets

Chromosome replication

The replication of each chromosome into two identical sister chromatids

Haploid cell (n)

A cell that contains a single set of chromosomes

• Includes gametes (sperm and eggs)

• Is 23 in humans, representing one half-set with a single sex chromosome

  • Eggs (ovum) have a single X chromosome

  • Sperm have either an X or Y chromosome

Fertilization

The union of gametes (sperm and egg) to create a zygote

Zygote

A fertilized egg with one set of chromosomes from each parent

• Produces somatic cells by mitosis and develops into an adult

• Often the only diploid stage in most fungi and some protists with no multicellular diploid stage; these grow by mitosis into haploid multicellular organisms

Meiosis

Type of cell reproduction that creates gametes

• Found in the ovaries and testes in humans

• Results in one set of chromosomes in each gamete (n) as only diploid cells can undergo this

• Alternates with fertilization to maintain chromosome number

Gametes

Reproductive cells produced by meiosis that undergo no further cell division before fertilization

• Often the only haploid cells in most animals

• Fuse to form a diploid zygote that then divides by mitosis to a multicellular organism

Alternation of generations

A life cycle exhibited by plants and some algae that include both a diploid and haploid multicellular stage

Sporophyte

A diploid organism that makes haploid spores by meiosis

Gametophyte

A haploid organism that grew from a spore by mitosis that then makes haploid gametes by mitosis

• Fertilization of these gametes results in a diploid sporophyte