Meiosis

Diploid = 2 full sets of chromosomes (2n); 1 set from mom, 1 set from

dad

• Haploid = 1 full set of chromosomes (n); 1 set that is a combination of

chromosomes from mom and dad

• Karyotype = Diagram that shows the number and visual appearance of the

chromosomes in a cell

• Meiosis = The process of cell division that makes gametes in the gonads

for sexual reproduction

• Sexual reproduction = The fusing of genetic information (gametes) from two parents to

produce offspring that are a genetic mixture of both parents

Fertilization = The actual fusion of egg and sperm to form a zygote

• Homologous chromosomes = Chromosome pairs that have the same types of genes (1

from mom and 1 from dad)

• Sister chromatids = 2 identical copies of the same chromosome

• Somatic cells are body cells that are diploid, meaning

they have full copies of DNA (2 complete sets) in each

cell.

• Gametes are sex cells (egg and sperm) that are

haploid, meaning each cell only has half of the DNA (1

complete set).

• Autosomes are chromosomes that carry traits that make

you who you are.

- Ex. In humans, chromosomes 1-44

• Sex chromosomes are chromosomes that specifically

determine biological sex.

- Ex. In humans, chromosomes 45-46

The purpose of meiosis is to make cells for sexual reproduction, the resulting cells need to have half the amount of DNA, since they will hopefully later fuse during fertilization to make offspring. If the parent cell only divided once, the resulting cells would have the same amount of DNA as the parent cell. Resulting in way to much DNA

Meiosis I = purpose is to separate homologous chromosome pairs, so the result is 2 haploid cells that still have duplicated chromosomes (sister chromatids).

• Meiosis II = purpose is to separate sister chromatids, so the result is 4 haploid daughter cells with unduplicated chromosomes

Significance of crossing over - It creates new combinations of genes, with recombinant DNA that make the child part mom part dad

Interphase: pre S phase, with unduplicated chromosomes

Prophase I: homo. chromos pair up, crossing over may occur

Metaphase I: homo. chromos line up in pairs in middle of cell

Anaphase I: homo. chromo pairs separate

Telophase I: nuclear membranes may reform

Cytokinesis: cytoplasm divides into 2 separate cells

Prophase II: nuclear membrane dissolves, spindle fibers form

Metaphase II: sister chromatids line up in pairs in middle of cell

Anaphase II: sister chromatids separate

Telophase II: sister chromatids pull to oppositeends of the cells, nuclear membranes start to reform

Cytokinesis: cytoplasm divides into 4 separate cells

Meiosis = purpose is to make haploid gametes with half the amount of DNA for sexual reproduction.

Mitosis = purpose is to make identical diploid body cells to the parent cell for growth and repair.

A mistake made in meiosis would be passed on to

potential offspring in an egg or sperm.

A mistake made in mitosis would (most likely) only affect

the parent and could result in cancer, or uncontrolled cell

division.