Download Meiosis Word Notes

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10.4—Meiosis
I.
Chromosome number
A. Homologous chromosomes
1. Chromosomes that each have a corresponding
chromosome from the opposite sex parent
2. Humans have a 23 pairs of homologous
chromosomes
a. 23 from mother
b. 23 from father
c. For a total of 46
B. Diploid Cells
1. Means “two sets”
2. Diploid cells contain:
a. Two complete sets of chromosomes
b. Two complete sets of genes
3. Humans have 46 homologous chromosomes, and
therefore a diploid number of 46
a. 2N = 46
C. Haploid Cells
1. Cells contain a SINGLE set of chromosomes
2. In sexually reproducing organisms
a. Gametes or sex cells are haploid
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b. Contain ½ the number of chromosomes
found in the diploid parent
c. Example: Human
i. 2N = 46
ii. Egg and sperm cells are the gametes
 Each has a N = 23
II.
Phases of Meiosis
A. Meiosis is…
1. Process of reduction division of a diploid cell in
which the number of chromosomes per cell is
cut in half during the separation of homologous
chromosomes
2. Results in the production of 4 haploid cells
(gametes)
B. Consists of two phases
1. Meiosis I
2. Meiosis II
Meiosis I
Interphase I
 DNA replicates
 Chromosomes are replicated
 Cell prepares for meiosis
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**Prophase I **
 Chromosomes pair with its
corresponding homologous
chromosome
o This is called a TETRAD
 Crossing-over occurs here
o Portions of the chromatids in the
tetrad EXCHANGE genetic
material
o One of the main reasons why
life is genetically diverse!
Metaphase I
 Chromosomes line up on the
metaphase plate
 Tetrad attaches to the spindle
fibers at the centromere
Anaphase I
 Spindle fibers pull homologous
chromosomes to opposite ends
of the cell
Telophase I and Cytokinesis
 Nuclear membrane reforms
 Cytoplasm pinches off and 2
haploid daughter cells are
formed
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Meiosis II
Prophase II
 Chromosomes become visible
 Spindle forms
Metaphase II
 Chromosomes line up in the
metaphase plate
 Attach to spindle fibers
Anaphase II
 Spindle fibers pull chromatids to
opposite ends of the cell
Telophase II and Cytokinesis
 Nuclear membrane reforms
 Cytoplasm is pinched off
 4 genetically unique haploid
daughter cells are formed
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III.
Meiosis vs, Meiosis
Mitosis
2N or N
Type of cell at
the beginning
1
Number of
phases
2 identical cells
Result
Meiosis
2N
2
4 genetically different
haploid cells
Used for:
Grow and replace cells
Production of gametes
Asexual reproduction
Sexual reproduction
IV. Gene Linkage
A. Some genes are linked together and therefore,
inherited together
B. These linked genes are called linkage groups
1. Linkage groups are found on the same
chromosome
V.
Gene Maps
A. 1911—Alfred Sturtevant
1. Found the farther apart the gene the more likely
crossing over will occur
2. Gene map
a. Shows the relative location of genes on a
chromosome
b. Used to identify specific genes on a
chromosome
c. Human genome