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Class Notes
Meiosis
Chapter 10: p. 270-276
Questions/Main Idea:
Name: _______________________________________
Period:_______________________________________
Date: _______________________________________
Notes:
What controls each
characteristic or “trait” in an
organism?
What is a gene?
Gene-
How many genes are on each of your chromosomes?
What are homologous
chromosomes?
Homologous chromosomes-
How many chromosomes do humans have?
What is the difference
between haploid and diploid
cells?
Haploid –
Diploid --
What are gametes?
What is meiosis?
meiosis-
What does meiosis produce?
What happens in interphase,
before meiosis?
For each of the following
stages of mitosis, describe
what happens, and draw a
diagram:
PROPHASE I
METAPHASE I
ANAPHASE I
TELOPHASE I
PROPHASE II
METAPHASE II
ANAPHASE II
TELOPHASE II
What is the end result of
meiosis?
What type of cell division do
cells use in asexual
reproduction?
What is the importance of
meiosis in terms of sexual
reproduction?
Compare mitosis and meiosis.
Class Notes
Meiosis
Chapter 10: p. 270-276
Questions/Main Idea:
Name: _______________________________________
Period:_______________________________________
Date: _______________________________________
Notes:
What controls each characteristic or “trait” in an
organism?
The instructions for each trait are located in genes, which are segments of DNA on a
chromosome.
What is a gene?
Gene- A gene is a segment of DNA that controls the production of one particular
protein. (one gene = instructions for one protein)
How many genes are on each of your chromosomes? Each chromosome contains
hundreds of genes
What are homologous chromosomes?
Homologous chromosomes- a pair of matching chromosomes, one from each parent,
that carries genes for the same traits.
How many chromosomes do humans have? 46 chromosomes, or 23 pairs (one from
mom and one from dad for each of the 23 pairs)
What is the difference between haploid and
diploid cells?
Haploid – refers to having half the number of chromosomes as a normal cell. (one
copy of each chromosome) (“n” refers to the number of chromosomes in a cell – for
humans, n = 23)
Diploid – refers to having 2 copies of each chromosome (one from mom and one from
dad) (“2n” = 46)
What are gametes?
Gametes are sex cells (eggs and sperm). They contain half the number of chromosomes
of a normal cell
What is meiosis?
meiosis- a type of cell division that reduces the number of chromosomes by half
What does meiosis produce? Gametes or sex cells.
What happens in interphase, before meiosis?
For each of the following stages of mitosis,
describe what happens, and draw a diagram:
PROPHASE I
METAPHASE I
ANAPHASE I
Cells carry out normal cell function (metabolism) and replicate DNA



Homologous chromosomes pair up
Crossing over occurs! (this is important!! – pieces of the homologous
chromosome pairs switch places. This allows the exchange of genetic
information)
Spindles form


Spindle fibers attach to centromeres
Homologous pairs of chromosomes line up together at the equator

Homologous chromosomes separate and move to either side of the cell. (NOT
sister chromatids – the entire chromosome!)
The cell goes from diploid to haploid (chromosome number is reduced from 2n
to n)

TELOPHASE I



PROPHASE II
Homologous chromosomes (consisting of 2 sister chromatids) reach the cell’s
opposite poles. Each pole contains only one of the original pair of homologous
chromosomes)
The sister chromatids that are still attached might not be identical to each
other because of the crossing over, or exchange of genetic information that
occurred in Prophase I
Chromosomes relax or uncoil in the 2 new nuclei. Cytokinesis occurs and the
cell does NOT enter interphase, or replicate its DNA again
***The following stages occur in BOTH of the cells that resulted in the division in
Meiosis I)
Spindle forms and chromosomes condense.
METAPHASE II
Chromosomes line up at the equator
ANAPHASE II
Centromeres split and sister chromatids move to opposite poles
TELOPHASE II
Nuclei form around the 4 chromosomes
What is the end result of meiosis?
The result of meiosis is 4 genetically different haploid cells
What type of cell division do cells use in asexual
reproduction?
Mitosis – end result is 2 identical haploid gametes
What is the importance of meiosis in terms of
sexual reproduction?
Meiosis provides genetic variation. The 4 resulting haploid cells are all genetically
different because of crossing over and random assortment. When sperm and egg join
to form a new organism, there is genetic variability.
Compare mitosis and meiosis.
Mitosis – 2 genetically identical diploid body cells
Meiosis – 4 genetically different haploid sex cells