Download must have half the number of chromosomes

7.2 Meiosis
The function of meiosis is to produce eggs and
sperm for sexual reproduction. (sex cells)
1. Egg and sperm cells must have half the
number of chromosomes as the parent cell
so that when put together they will have the
same number of chromosomes as the parent
cells. (23 vs. 46 in our body cells.)
2. Egg and sperm cells are NOT genetically
identical to the parent cell like you see in
mitosis.
3. Although you may look more
like one parent than the
other, you receive the same
amount of genetic
information from each.
4. Chromosomes similar in
shape, length and gene
arrangement are called
homologous chromosomes.
Summary of Meiosis
First, the genetic material must be
replicated so that each daughter cell
can be given the appropriate amount of
genetic information. This occurs in
Interphase.
Second, the genetic material must be
divided twice so that each of the four
daughter cells gets a set of information.
Interphase  PMAT  PMAT  Interphase
Atypical Meiosis (7.9) FYI
Errors occurring during cell divisions may
not harm an organism… but if something
goes wrong during meiosis of
reproductive cells, the resulting embryo
is in serious trouble since all of its cells
will be affected.
Nondisjunctive Disorders
(failure to separate)
Is an error that occurs when two homologous
chromosomes move to the same pole during
meiosis.
… the resulting sex cell may have 22 or 24
chromosomes.
… Therefore, the resulting zygote may have 45
or 47 chromosomes rather than 46.
In general, people with Down Syndrome have an
extra chromosome in pair 21 (trisonomy 21).
Children may have mental disabilities and
some muscular weakness.
Most common with elderly mothers.
Klinefelter Syndrome: The
child is a male, but at
puberty he begins
producing high levels of
female sex hormone and
can not father children.
(1 in every 1000 births.)
Turner Syndrome: Females
with T.S. do not mature
sexually and are shorter
in height. (1 in every
10000 births)
Both caused by nondisjunction.
Turner Syndrome also can occur when
nondisjunction happens during meiosis
forming the human females gametes.