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S x. MEIOSIS. 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.

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meiosis

S

x

MEIOSIS

Cell Reproduction

meiosis1
Meiosis
  • The form of cell divisionby 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

slide3

n=23

human

sex cell

sperm

n=23

n=23

2n=46

haploid (n)

n=23

n=23

diploid (2n)

n=23

meiosis I

meiosis II

fertilization

sperm

n=23

n=23

egg

2n=46

zygote

Fertilization
  • The fusion of a sperm and egg to form a zygote.
  • A zygote is a fertilized egg
homologous chromosomes
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 chromosomes1

eye color

eye color

hair color

hair color

Paternal

Maternal

Homologous Chromosomes
humans have 23 sets of homologous chromosomes each homologous set is made up of 2 homologues
Humans have 23 Sets of Homologous ChromosomesEach Homologous set is made up of 2 Homologues.

Homologue

Homologue

sex chromosomes
Sex Chromosomes

In Humans the “Sex Chromosomes” are the 23rd set

XX chromosome - female

XY chromosome - male

crossing over
Crossing Over
  • Crossing over (variation) may occur between chromosomes.
  • Crossing over: pieces of nonsisterchromatids break and reattach to the other chromatid.
crossing over variation

Tetrad

nonsister chromatids

chiasmata: site of crossing over

Crossing Over = variation

variation