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Gametes
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Molecular Genetics

Haploid and Diploid

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Humans have a
haploid number of:
In humans, every
haploid
chromosome has a
pair. This is the
diploid number:
When DNA
replicates (is copied)
there are 4n:

n = 23

2n = 46

4n = 92
Chromosomes
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Independent Assortment

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Independent Assortment only applies to genes on
different chromosomes, because it is the
chromosomes that assort independent of each other.
To the right are two
pairs of homologous
chromosomes also
known as a tetrad.
Homologous
chromosomes have
the same genes, but
not necessarily the
same alleles.
Is this n, 2n or 4n?
4n
Meiosis


Gametes are sex
cells, or cells that are
used for fertilization of
new offspring.
Gametes have a
haploid (n) number of
chromosomes or half
the total amount
Somatic Cells are the
normal body cells and
they have a diploid
(2n) number of
chromosomes (one
from mom and one
from dad)
Somatic cells
replenish
themselves with
identical copies with
mitosis.
Gametes are made
from somatic cells
that go through
meiosis.
Meiosis consists of 2
divisions-Meiosis I
and Meiosis II
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A. Prophase 1
Meiosis I
homologous
chromosomes)
 Spindle forms,
centrioles separate,
nuclear envelope
breaks down
B. Metaphase 1
 Tetrads line up at
C. Anaphase I
Meiosis I
 Tetrads form (pairs of
 Tetrads separate and
homologous
chromosomes are
pulled towards
opposite ends of the
cell by the spindle
fibers
 Cell elongates
D. Telophase/Cytokinesis 1
 Nuclear envelope reforms,
the center
spindle fibers break down
 Spindle fibers
 Cell splits into two
connect to
homologous
chromosomes at
centromere
 What is the chromosome
number now? 2n
 Are the cells identical?
no
Meiosis II
E. Prophase II
F. Metaphase II
chromatids present in
pairs (chromosomes)
 Spindle reforms,
centrioles separate
and nuclear envelope
breaks down.
 Sister chromatids gather at
poles, lose shape and
nuclear envelope reforms
 Cytoplasm splits and cell
membrane pinches,
making 4 new cells.
chromatids line
up at the center
of the cell
 Centromeres
connect to
spindle fibers
Male
Each cell contains a
haploid number of
chromosomes and are of
equal size.
 All can be used as
gametes

 Centromeres split
H. Telophase/Cytokinesis II
 Sister
Cytokinesis II
G. Anaphase II
Meiosis II
 In 2 cells, sister
and sister
chromatids get
pulled towards
opposite end of
the cells.
 Cells elongate.
Are all of the cells
the same?
No, they are all
different
Female
Each cell contains a
haploid number of
chromosomes, but one is
much larger than the
other 3
 The large cell can be
used as a gamete, the
other three are useless
polar bodies.
Answer These

If an organisms haploid number is 12, its diploid number is
1. 24
2. 6
 Chromosomes that have all the same genes, but different
alleles are:
1. sister chromatids
2. homologous
 During metaphase II, _________ line up at the center.
1. sister chromatids
2. homologous chromosomes
 How many useable gametes are formed during meiosis in
females?

1. One
2. Four
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