MEIOSISSx

Cell Reproduction

Meiosis

• The form of cell division by which gametes (Sex cells), with half the number of chromosomes, are produced.

• Diploid (2n) haploid (n)

• Meiosis is used for sexual reproduction.

• Two divisions (meiosis I and meiosis II) 4 cells are produced at the end of meiosis.

100 % of original DNA 50 % of original DNA

2n=46

humansex cell

diploid (2n)

n=23

n=23

meiosis I

n=23

n=23

n=23

n=23

sperm

haploid (n)

meiosis II

Fertilization

• The fusion of a sperm and egg to form a zygote.• A zygote is a fertilized egg

n=23egg

sperm n=23

2n=46zygote

Homologous Chromosomes

• Pair of chromosomes (mother’s and father’s) that are similar in shape and size.

• Homologous pairs carry genes controlling the same inherited traits (eye color, hair color, nose shape, etc.)

• Humans have 23 pairs of homologous chromosomes (46 total chromosomes)

a. 22 pairs of autosomes (body structures)

b. 1 pair of sex chromosomes (Determine gender)

Homologous Chromosomes

Paternal Maternal

eye coloreye color

hair color

hair color

Humans have 23 Sets of Homologous ChromosomesEach Homologous set is made up of 2 Homologues.

Homologue

Homologue

Sex Chromosomes

XX chromosome - female XY chromosome - male

In Humans the “Sex

Chromosomes” are the 23rd set

Crossing Over

• Crossing over (variation) may occur between chromosomes.

• Crossing over: pieces of nonsister chromatids break and reattach to the other chromatid.

Crossing Over = variation

nonsister chromatids

chiasmata: site of crossing over

variation

Tetrad