Chapter 11 meiosis and Sexual Reproduction

Asexual reproduction

One parent produces genetically identical offspring (clones); no gametes are involved (e.g., bacteria, some plants).

Sexual reproduction

Two parents contribute gametes (sperm and egg) that fuse to form a genetically unique zygote.

Gametes

Haploid sex cells (sperm or egg) with 1 set of chromosomes (n).

Zygote

A diploid cell (2n) formed by the fusion of two gametes; first cell of a new organism.

Haploid

One set of chromosomes (gametes)

Diploid

Two sets of chromosomes—one from each parent (somatic cells and zygote).

Meiosis I (Reduction Division)

Prophase I: Homologous chromosomes pair up and cross over; synapsis and formation of tetrads.

Metaphase I: Tetrads align at metaphase plate.

Anaphase I: Homologous chromosomes (not chromatids) are pulled to opposite poles.

Telophase I + Cytokinesis: 2 haploid cells form, each with duplicated chromosomes.

Meiosis II

Prophase II: New spindles form in each haploid cell.

Metaphase II: Chromosomes line up in each cell.

Anaphase II: Sister chromatids are pulled apart.

Telophase II + Cytokinesis: 4 genetically unique haploid cells are produced.

Duplicated chromosome

A chromosome with two sister chromatids.

Tetrad

A pair of homologous chromosomes (4 chromatids total) formed during prophase I.

Allele

Different versions of a gene (e.g., blue vs. brown eyes).

Mutation

A change in the DNA sequence that can create new alleles.

Synaptonemal complex

Protein structure that holds homologs together during synapsis

Synapsis

Synaptonemal complex proteins help each Homologue form a tight pair with its other Homologue

Chiasma

Point where homologous chromosomes cross over

Recombinant chromosomes

Chromosomes that contain new combinations of alleles due to crossing over.

Oogenesis

makes 1 viable egg and 3 polar bodies (die)

Spermatogenesis

Production of sperm in testes; makes 4 functional sperm.

Random Mutations

occur in gametes during DNA Replication

(also occurs in Mitosis) makes different forms of a gene

Crossing over

gives new unique Recombinant Chromosomes

Independent Assortment

at Metaphase I 2^23 possible combinations = 8.39 million genetically unique

gametes from 1 person

Fusion of egg and sperm

creates > 70 trillion genetically distinct combinations of zygotes

Gonads

organs that produce gametes – Ovaries & Testes

Germ Cells

cells in gonads that produce gametes

Pluripotent stem cells

capable of reproducing and becoming any human cell

Differentiated cells

change from one cell type to another by changing their gene expression pattern, becoming more specialized

Embryonic stem cells

pluripotent stem cells in blastocyst

Adult stem cells

In bone marrow, skin, and brain, they can form a limited number of cell types. Red cells are pluripotent stem cells

Fungi life cycles

Can reproduce sexually and asexually

Haploid cells make up tissue of dominant multicellular stage

Algae life cycles

Can reproduce sexually and asexually

Haploid cells make up the tissue of the dominant multicellular stage

could also be like plants life cycle

Plants life cycles

Have both Haploid and Diploid multicellular organisms

Gametophytes: haploid multicellular plants

Sporophyte: diploid multicellular plants