Topic:
Meiosis
Notes
Name: ___________________________ Date:____________
Objective: SWBAT understand gametes are produced through the process of
meiosis.
Questions:
How many
chromosomes does
each human cell
have?
What are
homologous
chromosomes?
- Gene- piece of DNA that controls a trait
- Chromosome- DNA wrapped around protein, condensed into an X shape in
the nucleus of eukaryotic cells.
- Each human somatic (body) cell has 23 pairs of chromosome (46 total).
- Each cell has 22 pairs of autosomal chromosomes (44 total).
- Each cell has 1 pair of sex chromosomes (2 total).
o Females are XX
o Males are XY
Homologous Chromosomes= pair of
chromosomes that match up (one from
male parent and one from the female
parent). Each chromosome has the same
genes on it.
What is the
Diploid (2N) = A cell that contains both
difference between sets of homologous chromosomes (one
diploid and
from dad and one from mom).
haploid?
- All somatic cells in the body are
diploid, such as skin cell, liver cell,
etc.
Haploid (1N) = A cell that contains one set of homologous chromosomes.
- The gametes (sex cells) of the parents are the only haploid (N) cells.
What is Meiosis?
Meiosis- production of gametes
- The number of chromosomes is reduced to half the number of chromosomes
in the diploid cell.
What are the parts
of Meiosis?
Meiosis I= Interphase (G1, S, G2), PMAT, Cytokinesis
- Produces 2 cells, then divides again
Meiosis II= PMAT, Cytokinesis
- Produces 4 total cells
- No interphase- in order to cut the number of chromosomes in half
STOP- turn to
Why is it necessary for the process of meiosis to reduce the chromosome number
your elbow partner making the gametes haploid?
and discuss (be
ready to share)
If each parent were to contribute a complete set of chromosomes to their offspring
every time we reproduced, our number of chromosomes would double.
Why is crossing
over important?
Crossing over= two homologous chromosomes line up and exchange pieces of the
DNA.
- Occurs during Meiosis I as the chromosomes are
close together
- The chromosomes exchange alleles and produce new
combinations. Two haploid cells are produced.
- Each chromosome pairs with its corresponding
homologous chromosome to form a tetrad.
What is the end
result of Meiosis?
Meiosis produces 4 genetically different haploid cells
How is Meiosis
Males= sperm, through spermatogenesis.
different for males Females= eggs, through oogenesis.
and females?
- In females, the meiotic division is uneven.
- Only 1 cell gets the majority of the cytoplasm, which will be the only usable
gamete.
- The other 3 cells are known as polar bodies, which will dissolve and be
reabsorbed by the body.
STOP- turn to
Why is it necessary for females to go through the process of Meiosis, if they are
your elbow partner going to only make one viable egg?
and discuss (be
ready to share)
The “good” egg needs to get the cytoplasm and nutrients from the polar bodies and
the cells still need to have half the chromosomes.
What is the
Comparing Mitosis and Meiosis
difference between
Mitosis and
Mitosis
Meiosis?
One Division
Two Diploid daughter cells (2N) are
produced.
Cells are identical to parent cells
Associated with growth, replacing cells,
and asexual reproduction.
Summary:
Meiosis
Two divisions
Four Haploid daughter cells (1N) are
produced.
Daughter cells are not identical to
parent cells.
Associated with sexual reproduction.