Name:
Class:
Date:
# ___ Notes – Meiosis (Ch 11.4)
We get all our DNA from our parents – half of our chromatin is from our
, half from our
. Each half matches with the other half. This means that each parent has one allele for the same gene,
but the alleles don’t necessarily have to be the same (T or t). So your genotype can be TT, Tt, or tt depending
on the alleles you received from each parent. The two chromosomes that contain these alleles are matching, or
h
chromosomes.
Label the following:
Centromere
Chromatid
Chromosome
Homologous chromosomes
Sister chromatids
Tetrad
(Mark the possible alleles)
A cell that has both sets of homologous chromosomes are said to be d
(“di”= two; “ploid” =
chromosome). The diploid number is represented by the symbol
. A diploid cell contains
sets (NOT “copies”; as in DNA replication) of chromosomes/genes.
In Chapter 10, you learned that cell division is called m
, wherein a cell produces two i
daughter cells. In other words, a d
(2n) cell divides and produces two d
(
) cells.
In humans, mitosis occurs in body (somatic) cells, such as those in our skin, lungs, blood, stomach, etc.
Reproductive organs (ovaries in women and testes in men) contain sex cells that undergo a different type
of cell division called m
. Like mitosis, this type of cell division begins with a diploid (
n) cell.
Unlike mitosis, when this cell divides, it produces two unique (non-identical) h
(n) cells. In ovaries,
these haploid sex cells are called e
. In testes, these haploid sex cells are called s
.
Another term for these sex cells is “g
”. Why do gametes contain only 1 complete set of
chromosomes?
Some of the steps in meiosis are similar to mitosis. However, remember that mitosis happens to form
more (somatic)
cells while meiosis happens to form
cells (gametes).
Review: During interphase, the following events occur (in chronological order):
 G
 DNA
(Each diploid cell now has two copies of all the chromosomes as well.)
 Copying of major
, such as centrioles, mitochondria, endoplasmic reticulum, etc.
The Phases of Meiosis:
Meiosis I
 Prophase I
o Spindle fibers start to form
o Chromatin coils up and begins to form
, which pair up into t
(one chromosome from the mother matches up with the corresponding chromosome from the
father)
o C
-over might happen (chromosomes exchange information to make new
combinations of genes; refer to page 324)
 Metaphase I
o h
chromosomes line up (as tetrads) in the center of the cell
o How is this different from mitosis?


Anaphase I:
o t
separate; unlike mitosis, c
do not split
Telophase I (with cytokinesis): reverse of prophase I
o Each cell contains
(how much of?) the genetic info of the original cell
o
new cells are formed. Are they considered diploid or haploid?
o each cell has same number of chromatids as they would have had if the cell underwent mitosis
 BUT, the chromatids are different from the set in the original cell (Why?)
 chromatids are still attached at the centromere
 After Meiosis I, one chromosome looks like this (see left)
 Note that after mitosis, one chromosome looks like this:
Between Meiosis I and Meiosis II: (NTK: This stage is called interkinesis.)
No DNA replication happens in either of the new cells from meiosis I (Why not?)
Meiosis II
 Prophase II:
o S
f
attach to chromosomes
 Metaphase II:
o Chromosomes
in the center of the cell (How does this compare to
mitosis?)
 Anaphase II:
o Sister chromatids separate at the c
as spindle fibers pull them apart
 Telophase II (with cytokinesis):
o Nuclear
begin to appear
o Spindle fibers
o The cytoplasm divides
o
new cells are formed
o each cell is
ploid
o one chromosome looks like this:
before it uncoils to become part of chromatin
Meiosis and Mendel’s Laws:
Which part of meiosis explains Mendel’s law of independent assortment? Be able to explain why.
Which part of meiosis explains Mendel’s law of segregation? Be able to explain why.
Errors in Meiosis:
Nondisjunction

“non” means

“disjunction” means

Definition:

Results in p
with this word?)
- more than the usual number of chromosome sets (How did they come up