Download day 1- meiotic process

Meiosis
Objective
-to discover how haploid cells are made
Bellwork
-The Goal of mitosis is to create ___ (a #)
cells that are exactly the ________.
Meiosis sequencing activity
KEY CONCEPT
Gametes have half the
number of chromosomes that
body cells have.
Meiosis and Sexual Reproduction
•All individuals eventually die, therefore:
–Reproduction is required for a population to
survive
•The purpose of an organism?
–To attract a mate and make more copies of
itself and its genes.
•Evolution and reproduction intimately tied
together
• No organism, would be alive today, with
its exact set of genes, unless every
ancestor of that organism successfully
reproduced.
• This includes each of us
• How many ancestors does each of us have?
–
–
–
–
–
2 parents
4 grandparents
8 great-grandparents
1,024 great x 8 grandparents
1,048,576 great x 18 g.prnts.
• You are 1 in a million!
25 years ago (1995)
50 years ago
75 years ago
250 years ago (1756)
500 years ago (1456)
Meiosis terms to remember:
• Haploid (n)- a cell with ½ the normal number of
chromosomes.
– Made by meiosis, not mitosis
– A sex cell
• Sperm or egg
• Diploid (2n)- a cell with the full number of
chromosomes
– A somatic cell
• A non-sex cell (skin, lung, hair, blood, etc…)
• Chromosome- a strand of DNA and protein
which contains your genetic material. A “normal”
human has 46 chromosomes. 23 come from
mom and 23 come from dad to make 23 pairs, or
46 total
Homologous chromosomes
• Your body cells have 23
pairs of chromosomes.
• Each pair is homologous
• For each pair, one
chromosome comes
from each parent.
Homologous shoes
More terms
• Gametes- another word for sex cell
• Zygote-a fertilized egg
• Spermatogenesis- creating sperm in the process
of meiosis
• Oogenesis-creating eggs in the process of
meiosis
Germ cells develop into gametes.
Germ cells are located in the ovaries and
testes.
– Gametes are sex cells: egg and sperm.
– Gametes have DNA that can be passed to
offspring.
body cells
sex cells (sperm)
sex cells (egg)
Body cells are diploid; gametes are haploid.
• Haploid (n) cells have one copy of every
chromosome.
– Gametes are haploid.
– Gametes have 22 autosomes and 1 sex
chromosome. (23 chromosomes total)
• Fertilization is the fusing of the egg and
sperm.
• Diploid (2n) cells have two copies of
every chromosome.
– Body cells are diploid.
– Half the chromosomes come from each
parent.
• Meiosis makes haploid cells from diploid
cells.
– Meiosis occurs in sex cells.
– Meiosis produces gametes.
KEY CONCEPT
double, divide, divide again.
The Basics of meiosis:
1. The cell doubles its chromosomes (just
like in mitosis). You could say the cell is
“4n” here
2. The cell divides (just like in mitosis). 2
cells are made, each is 2n (diploid) now
3. The cell divides again, and the resulting
4 cells are n (haploid)
•
•
In males 4 sperm are made
In females 1 egg and 2 polar bodies are
made. The polar bodies support and protect
the egg (sort of the egg’s body guards), but
will not be released for reproductive
purposes
• Meiosis I and meiosis II each have four
phases, similar to those in mitosis.
• Draw these 2 chromosomes at the bottom of
your paper and labelled them as I tell you to
– Pairs of homologous chromosomes separate in
meiosis I
– Sister chromatids divide in meiosis II.
homologous chromosomes
sister
chromatids
sister
chromatids
Shoe meiosis
Before synthesis –diploid or haploid?
Shoe meiosis
• Meiosis I:
Shoe meiosis
• Meiosis II- diploid or hapolid?:
• Meiosis I occurs after DNA has been
replicated (S phase of interphase)
• Meiosis I divides homologous chromosomes
in four phases. P,M, A, + T
• Meiosis II divides sister chromatids in
four phases.
• DNA is NOT replicated between meiosis
I and meiosis II.
Different forms of meiosis happens
in different genders
Spermatogenesis in
males. 4 sperm are
made
Oogenesis in females.
1 egg is made
Meiosis drawings
• P. 141 (picture) page 135 (description) for
the interphase I and II cells
• P. 174-175 for the rest of the meiosis cells
• Make 2 more cells for telophase so there
is a total of 4