Download Mitosis and Meiosis Notes

Mitosis and Meiosis
Chromosomes
• Chromosomes are made up of DNA
which carries the cells genetic
information
• Human body cells have 46
chromosomes (in 23 pairs)
• Sex cells (gametes aka egg and
sperm) only have 23 chromosomes
• Before cell division occurs, each
chromosome replicates (or copies
itself)
Sister
Chromatids
Centromere
Cell Growth and Division
Cell Cycle is a series of events that cells go
through as they grow, prepare for division and
divide into two identical daughter cells
Two major stages in a cells life are:
1. Interphase
2. M Phase or cell division
Interphase
Interphase is the phase where the cell grows
and prepares to divide.
Interphase is divided into three phases:
• G1 Phase - growth
• S Phase – replication (copying) chromosomes
• G2 Phase – further growth
* A lot is happening during G1, S and G2 phases!
M Phase
M Phase is cell division which includes two
steps:
1. Mitosis- this is division of the nucleus
2. Cytokinesis – this is division of the cytoplasm
Mitosis
Mitosis is divided into four phases:
1. Prophase – chromosomes condense,
becoming visible; centrioles move to
opposite sides of nucleus; nuclear envelope
dissolves
2. Metaphase – chromosomes line up across
middle of cell
3. Anaphase – sister chromatids split
4. Telophase - sister chromatids move to
opposite sides of cell and new nuclear
envelopes form
Cytokinesis
• Cytokinesis is occurring at the same time as
telophase
• The cell membrane pinches the cytoplasm into
two equal parts.
• Two new daughter cells are now formed and
are genetically identical to the parent cell.
• This is the end of the cell cycle.
MEIOSIS
Meiosis is process where the number of
chromosomes per cell is divided in half by
separating homologous chromosomes in a
diploid cell.
Gametes
are produced by meiosis.
What does all that mean???
• Chromosomes are made up of DNA which
carries the cells genetic information
• Genes are found on the chromosomes.
• Genes are chemical factors that determine
traits. (Ex. Eye color, hair color, height, etc.)
• Different forms of a gene are called alleles
(Ex. Blue or brown eyes, brunette or auburn)
N
* The symbol
represents the number of
chromosomes in a gamete (sex cell)
Homologous chromosome means that each
chromosome that comes from the male has a
corresponding chromosome from the female
Homologous chromosome have DNA segments,
or genes, for the same trait
• Diploid cells have both sets of homologous
chromosomes (one set from momma and one
from the baby’s daddy)
– All cells in your body (except egg and sperm) are
diploid
– These cells are called somatic cells
– 2N
• Haploid cells have half
the number of
chromosomes as their
parent cells
• Gametes (egg and
sperm) are haploid
• Gametes are genetically
different than the parent
cell and one another
• N
N
N
N
2N
N
N
N
Human has 46 chromosomes. How many
chromosomes in human gametes?
23
Pineapple has 25 chromosomes in its gametes.
What is it’s haploid number?
25
A giraffe has a diploid number of 62. What is it’s
haploid number?
31
Draw this!
46
First Step
Replication
• During meiosis, chromosomes are replicated
once in S phase (just like mitosis) into sister
chromatids.
• This occurs so that each of the 46
chromosomes exists as a duplicated sister
chromatid.
Meiosis I
• HOMOLOGUES (1-23) are segregated into
different cells.
• Results in 2 cells that each have 1 copy of each
of the 23 chromosomes (still duplicated from
DNA replication).
Prophase I
Crossing over
• Homologous chromosomes in
the cell pair up alongside each
other lengthwise forming a
tetrad
• Swap bits and pieces of their
chromosomes, shuffling the
genome
• Results in NEW Chromosomes
that did not exist before in the
parent
Meiosis II
• SISTER CHROMATIDS of each of the 23
chromosomes are pulled apart just as they are
in mitosis
• Results in 4 cells that have 1 copy of each of
the 23 chromosomes (now unduplicated
again)
• Now officially haploid
Meiosis occurs in two stages
Meiosis I
• Two cells form with
sets of chromosomes
and alleles that are
different from each
other
Meiosis II
• Cells divide again
without DNA
replication forming four
cells with half the
number of
chromosomes of the
parent cell
Summary of Mitosis/Meiosis
Mitosis
• Results in 2 identical cells that are diploid (2N)
and are exactly like the parent cell
Meiosis
• Results in 4 cells that have half the number of
chromosomes, haploid (N), as the parent cell
and are genetically different from one another
• Genetic Recombination
Meiosis Square Dance
Linked Genes - Genes located closely together
are linked
Crossing over is more likely to occur between
genes that are far apart rather than linked
which are close together.
Polyploidy – The occurrence of one or more
extra chromosomes in an organism.
This is not good in animals but is beneficial in
plants (crop plants are stronger and bigger)