Download 6.2 Process of Meiosis

6.2 Process of Meiosis
KEY CONCEPT
Gametes have half the number of chromosomes
that body cells have.
6.2 Process of Meiosis
You have body cells and gametes.
• Body cells are also called somatic cells.
• Gametes are sex cells: egg and sperm.
– Gametes have DNA that can be passed to offspring.
body cells
sex cells (sperm)
sex cells (egg)
6.2 Process of Meiosis
Your cells have autosomes and sex chromosomes.
• Your body cells have 23 pairs of
chromosomes.
• Chromosome pairs #1-22 are
homologous chromosomes
autosomes.
• Sex chromosomes, X and Y, determine
gender in mammals.
– Homologous pairs of chromosomes
have the same structure.
sister
sister
– Homologous chromosomes are
chromatids
chromatids
similar but not identical.
– For each homologous pair, one
chromosome comes from each
parent.
6.2 Process of Meiosis
• Haploid (n) cells have one copy of every chromosome.
– Gametes are haploid
– The production of gametes is called gametogenesis
Genesis = formation
6.2 Process of Meiosis
Body cells are diploid; gametes are haploid.
• Fertilization occurs when gametes fuse during sexual
reproduction
• Diploid (2n) cells have two copies of every
chromosome.
– Somatic cells are diploid.
– Half the chromosomes come from each parent.
6.2 Process of Meiosis
Check for understanding
• Which type of cell is haploid?
a. Skin cell
b. Sperm cell
c. Somatic cell
d. Liver cell
6.2 Process of Meiosis
Check for understanding
The fusion of gametes is called
A. Fertilization.
B. Reassortment.
C. Meiosis.
D. Gametogenesis.
6.2 Process of Meiosis
• Meiosis makes haploid cells from diploid cells.
– Meiosis occurs in
reproductive germ cells
(testes & ovaries)
– Meiosis produces gametes
with half the # of
chromosomes as the parent
cell.
– Unlike the daughter cells of
Mitosis, the daughter cells
and parent cells are NOT
IDENTICAL
6.2 Process of Meiosis
Cells go through two rounds (Meiosis I & Meiosis II) of
division in meiosis.
• Meiosis I and meiosis II each have 4 phases, similar to those in
mitosis
Meiosis I
– Meiosis I occurs after DNA has been replicated.
– Pairs of homologous chromosomes separate in four phases
(just like in Mitosis-same names of stages)
6.2 Process of Meiosis
Meiosis I: Prophase I, Metaphase I, Anaphase I, Telophase I
6.2 Process of Meiosis
• Meiosis II divides sister chromatids* in four phases.
• DNA is not replicated between meiosis I and
meiosis II.
• *remember a sister chromatid = copy of same DNA
6.2 Process of Meiosis
• Meiosis differs from mitosis in significant ways.
– Meiosis has two cell divisions while mitosis has one.
– In mitosis, homologous chromosomes never pair up.
– Meiosis results in haploid cells; mitosis results in diploid
cells.