Meiosis in Animals - Exercise 13. Objectives -Understand meiosis and know where it occurs. -Know why meiosis is so important. -Be able to explain the phases of meiosis I & meiosis II. -Be able to show meiosis using peptides (simulation ) .
Meiosis in Animals - Exercise 13
-Understand meiosis and know where it occurs.
-Know why meiosis is so important.
-Be able to explain the phases of meiosis I & meiosis II.
-Be able to show meiosis using peptides (simulation).
-Know at what three phases rearrangement takes place in meiosis.
Most multicellular organism, as well as many unicellular
organism, produce sexually. They utilize specialized SEX cells
called GAMETES. All other types of cells are collectively called
SOMATIC cells. In most organisms, there are two
morphologically distinct types of gametes the EGG cell, and the
Meiosis I used in animals to generate (egg and sperm). It is
required for animals to do sexual reproduction. The main
function of meiosis is to reduce the chromosome number in
half. In many ways meiosis is very similar to mitosis, the stages
are the same in general terms and Meiosis II is identical to
mitosis. Chromosome number of nucleus is reduce by one half
from diploid to haploid and chromosome gene carried are
shuffled or recombined so daughter cell has unique array of
genes. 2 round of chromosome separation occurs in gonads. Ovaries
Since sexual reproduction involves the combining of chromosomes from two
different cells, and since the number of chromosomes per cell remains
constant within members of a species from generation to generation, there
must be a reduction of chromosomes number in each generation to offset
the increase at fertilization. In a normal somatic cell of an organism, there
are actually two complete sets of chromosomes. For each chromosome,
there is a “, and other morphological characters. These two
chromosomes apartner” chromosome which is identical in terms of length,
location of kinetochorelso contain genes for the same characteristics, although not
necessarily for the same form of the characteristic (i.e body size – one gene
may specify tall, the other gene may specify short, but both genes specify body
size). Such chromosomes are said to be HOMOLOGOUS, and one of each of them
was provided by each parent. A cell that has two complete sets of chromosomes
is said to be DIPLOID or to contain the 2N number of chromosomes. A cell that
has only one complete set of chromosomes is HAPLOID and contains the N
number of chromosomes. In animals, normally somatic cells are diploid, while
normal gametes are haploid.
Significant Events in the stages of Meiosis
The process of meiosis, like that of mitosis, is a
continuous sequence of events that have been
arbitrarily divided into stages for convenience. Since
there are two rounds of chromosomes separation,
The two divisions are called MEIOSIS I and MEIOSIS
II. Each division stage is further separated into
prophase, metaphase, anaphase, and telophase
followed by the appropriate Roman numeral (e.g.,
prophase I). Prophase I is a very long, complicated
process, and it too is subdivided into several substages.
The process of MEIOSIS is modified version of the mitotic
cell division process. During meiosis, two highly
significant consequences occur: (a) the chromosome
number of the nucleus is reduced by one half from the
diploid (2N) to the haploid (N) number, and (b) the
chromosomes (and thus the genes that they carry) are
shuffled or recombined so that each daughter cell has a
unique array of genes. It is this latter effect that causes
no individuals (except identical twins) to be exactly alike.
As in mitosis, meiosis is preceded in the cell cycle by
chromosome duplication; however, in meiosis there are
two rounds of chromosomes separation or two cell
divisions called meiosis I and meiosis II. In animals, the
meiotic process occurs in the gonads. The gonads are
called the OVARIES in females and TESTES in males.
Synapsis and crossing over
Tetrads n the metaphase plate
Separation of homologues
Summary of Meioses II
-Each new cell has ½ the amount of DNA as the original parent
-Each has only one copy of each chromosomes (haploid)
-These cells will become either egg or sperm cells.
Three mechanisms contribute to genetic variation:
2. Crossing Over
3. Random fertilization
Simulation of Meiosis
EVOLUTIONARY SIGNIFICANCE OF
GENETIC VARIATION (MEIOSIS)
2 genetically identical diploid cells
Diploid cell with duplicated chromosomes
4 genetically different haploid cells
Haploid gametes (n = 23)
(2n = 46)
adults (2n = 46)
Animal Life Cycle
a) Which meiotic division is the reduction division?
a) During which stage of meiosis does synapsis occur?
b) Does synapsis occur during mitosis? If so, when?
a) During which stage of meiosis does synapsis occur? Prophase I
b) Does synapsis occur during mitosis? If so, when? No
no homolgous pairs. The cells going through meiosis II are haploid.
There’s no homologus pairs to line up.
-A synapsed homologous pair of chromosomes
-4 sister chromtides of a particular n chromosome.
a) Crossing over
b) Independent assortment
c) Union of different gametes (unique fertilization)