Download Meiosis II

* One pair of chromosomes come from mother and
father.
Diploid = a cell with two of each kind of
chromosome (2n).
- supports info that organisms have two alleles for
each trait.
Haploid = a cell with one of each kind of
chromosome (n)
- supports that parents give one allele to offspring.
* two chromosomes of each pair in a 2n cell
help determine what organism looks like, these
are called homologous chromosomes.
- genes arrange in same order on chromosomes,
but there are different alleles for the same gene.
A
a
b
B
P. 270 in book
* Offers another form of cell division that allows
offspring to have same # of chromosomes as parents.
• Meiosis = cell division process which produces
gametes containing half the number of chromosomes
as a parent’s body cell.
* consists of two divisions: Meiosis I & II
male gametes = sperm
female gametes = eggs
zygote forms when sperm fertilizes egg (2n)
1. Interphase
- start with diploid cell (2n)
- chromosome replication
occurs
2. Prophase I
- homologous chromosomes
come together and form a fourpart structure called a tetrad,
two homologous chromosomes
w/ 2 sister chromatids.
- packed so tightly together that
chromosomes exchange genetic
material. Process is called
crossing over.
- crossing over can occur in any
location on chromosome and at
several locations at the same time
* average of 2-3 crossovers per
homologous chromosome.
* Gives new combinations of
alleles in chromosome!
3. Metaphase I
- homologous chromosomes
line up at equator side by side
as tetrads instead of
independently (in mitosis)
4. Anaphase I
- homologous
chromosomes with
2 chromatids
separate and move
to opposite ends of
cell.
Early
Anaphase
Late
Anaphase
5. Telophase I
- reverse order of prophase I
Meiosis II
* Needs to occur because each chromosome is still diploid!!
- final product is 4 haploid cells
Meiosis
video
Prophase II
Metaphase II
Anaphase II
Telophase II
* reassortment of chromosomes and
genetic information by crossing over or
independent segregation of homologous
chromosomes.
- major source of variation in organisms
and species.
Ex. Humans have 23 gametes
223 = 70,000,000,000,000 diff. Kinds of
sperm or eggs