Download Meiosis - Willimon-PHS

All Detentions due by Monday OR REFERRAL!!!!
For a species to continue to exist.
 Cell division resulting in chromosome numbers being
reduced by half
 This is achieved because there are two division
 The result:
 production of gametes
23
23
23
46
46
23
 sex cells
 made in meiosis
 Gametes are haploid (n), which means they only
have one set of chromosomes (23 in humans)
 The gametes made in the testes by males are
called sperm
 The gametes made in the ovaries by females are
called eggs
 Somatic cells are the BODY cells that are made in
mitosis
 Somatic cells are diploid (2n), which means they have
two homologous sets of chromosomes
 HUMAN HAVE 46
Total Chromosome #
Diploid
38
20
46
200
78
What is the haploid # for humans?
matching
Chromosomes
>>Two sets
>>Homologous pairs =
One from father
&
One from mother
To increase genetic diversity
through crossing over and
independent assortment
 Homologous chromosomes
contain different versions of
the same genes from each
parent
 Alleles are different
variations of one gene
 Hair Color:
 Blonde, brown, brunette,
auburn, red
 Crossing over creates
genetic diversity
 Tetrads exchange
sections of chromosomes
 This forms four new
chromatids
 Chromosome pairs are randomly lined up and
separated
 Creates: More genetic diversity!
 You can make trillions of sperm and never make the same one
twice!
 Homologous chromosomes pair up
 Crossing over occurs
 In metaphase I, the tetrads are
lined up in the middle
 In anaphase I, the homologous
chromosomes
separate and are pulled toward
opposite poles
 Independent assortment
creates new combinations of
chromosomes/traits
 Separate the homologous pairs
 Meiosis II is very similar to mitosis
 Separate the sister chromtids
 Four daughter cells, called
gametes
 The gametes are haploid (1n)
 The gametes are genetically
different
 In fertilization haploid
gametes combine to form a
new diploid (2n) set of genes
 Mitosis and meiosis have several key differences:
The chromosome number is reduced by half in meiosis, but
not in mitosis
2. Mitosis produces two identical daughter cells, but meiosis
produces four different cells
1.
Meiosis
# Daughter Cells
# Chromosomes
Genes
Type of Cell
Created
# of Sets of
genes (n)
Mitosis
Daughter Cells
Chromosomes
Genes
Type of Cells
Sets of genes
Meiosis
Mitosis
4
2
Meiosis
Mitosis
Daughter Cells
4
2
Chromosomes
23
46
Genes
Type of Cells
Sets of genes
Meiosis
Mitosis
Daughter Cells
4
2
Chromosomes
23
46
Genes
unique
identical
Type of Cells
Sets of genes
Meiosis
Mitosis
Daughter Cells
4
2
Chromosomes
23
46
Genes
unique
identical
Type of Cells
gametes
Somatic cells
Sets of genes
Haploid (1N)
Diploid (2N)
 Your cells will have two sets of chromosomes (a total of
8)
 In first meiotic division your will show crossing over
and independent assortment
 Then turn you paper over and show a second meiotic
division that demonstration a different crossing over
event and a different independent assortment.
 Start with your cell in prophase (remember that the
first division skips telophase and proceeds to