Unit 2 Mitosis and Meiosis

sexual reproduction

reproduction that results from combining genetic material from two individuals.

meiosis

type of cell division that results in 4 genetically unique haploid daughter cells that each have half the number of chromosomes as the diploid parent cell.

Diploid

A cell containing two full sets of chromosomes In humans: 2n=46.

Haploid

A cell containing a single/ half set of chromosomes. In humans: n=23

Gametes

A haploid male or female germ cell (e.g. sperm and egg)

gene

a section of the DNA (chromosome) that codes for a specific trait (e.g. eye color or hair color) or functional protein

crossing over

when homologous chromosomes exchange segments of DNA during Prophase 1 creating new mixture of parent traits in their offspring

Meiosis I

The first cell division of meiosis when the homologous pairs are split up into two separate cells (two diploid daughter cells)

Meiosis II

The second cell division of meiosis. This is when the sister chromatids are split up into two separate cells (haploid daughter cells)

Mitosis

Produces cells almost genetically identical (only source of genetic variation is random mutation)

Asexual reproduction

Has the advantage of producing offspring in greater numbers, with no partner required

Chromatin

Uncoiled DNA. Present in interphase. Looks like bowl of spaghetti.

Homologous Chromosomes

Carry the same genes at the same locus (location). DNA sequence is not necessarily identical. One of maternal origin and one from paternal origin.

Ex. Chromosome 1 and Chromosome 1

Three phases of interphase

G1,S,G2

Prophase

Chromatin coils up into chromosomes.

Centrioles move to poles.

Spindle fibres and asters form. Nucleus and nucleolus

disappear.

Metaphase

Chromosomes line up at the metaphase plate.

Anaphase

Centromeres divide. Sister chromatids move to opposite poles.

Telophase

Chromatids are totally apart. Cleavage furrow starts to form. Nuclear envelope starts to reform.

Cytokinesis

Cell divides into two. Cell plate forms in plant cells.

Sexual Reproduction

Requires male and female gametes. Much more genetic variation.

Asexual Reproduction

One parent only. (cloning)

Mitosis.

Crossing over

Non sister chromatids of homologous chromosomes may exchange genetic material during prophase I.

Occurs more often in genes that are further apart.

Prophase I

Synapsis - homologous chromosomes (tetrads) pair up.

Crossing over may occur - exchange of genetic material.

Metaphase I

Homologous pairs line up in the middle on the metaphase plate.

Anaphase I

Segregation - Homologous pairs separate to opposite poles.

Telophase I

Chromosomes separate nuclei form.

Prophase II

Two cells are present at the beginning.

Metaphase II

Chromosomes line up in the middle

Anaphase II

Centromeres split. Single chromosomes move apart.

Telophase II

4 nuclei begin to form. Totally apart.

Zygote

sperm + egg

2n