Download Meiosis - Background Info - 20 slides

Aim: How do organisms create
offspring through sexual reproduction?
Aim 2: How are the Chromosomes
Described in Meiosis?
What is Sexual Reproduction?
It involves the joining of two cells to
begin the development of a new
individual.
These special cells are called: Sex Cells
(Gametes)
What are the names of these sex
cells?
Egg cell
(Female)
Sperm Cell (Male)
The joining of a sperm
cell with an egg cell is
called… fertilization
How many chromosomes do we have
in our cells?
Karyotype
We have 46
chromosomes in
each of our body
cells.
We can also say
that we have 23
pairs of
chromosomes
Why do we have 2 of each
chromosome?
We get one chromosome from each parent
Each pair of chromosomes are called:
Homologous Chromosomes
Homologous Chromosomes:
Mom
Eye Color
Dad
B
G
Hair Color B
R
Allele
Gene
Part of a
chromosome
that codes for
a trait
Have genes that code for the same trait,
but may have different versions of that trait
How are chromatids different than
homologous chromosomes?
chromatid
Chromatids are exact
duplicates of each other
chromatid
Homologous
chromosomes have
genes that code for
the same trait, but they
may code for different
versions of that trait
Chromatid vs. Chromosome
When 2 DNA
molecules are joined
together, each is
called a chromatid.
Together they are a
called a duplicated
chromosome.
When DNA is not attached to another one
then that single molecule of DNA is called
an unduplicated chromosome (not a
chromatid).
How many chromosomes do the
offspring have after mitosis?
46X
Mitosis
46X
46X
Daughter cells
have the same
number of
chromosomes
as the original
parent cell.
Do our sex cells have 46
chromosomes?
NO!!!
What would happen if our sex cells did
have 46 chromosomes?
46
+
46
Egg
92
Offspring
Sperm
The offspring would have 92
chromosomes
Sexual Reproduction:
23
23
+
Egg
46
Offspring
A fertilized egg cell is called a
Sperm
Zygote
Characteristics of Sexual Reproduction:
• Creation of a new individual from 2 parents.
• Offspring are not genetically identical to the
parents.
Sex Cells (Gametes)
• Sex Cells are:
SPERM and
EGG
• Sex cells should
have 1/2 the
normal number
of chromosomes
Chromosome Number
• Diploid cells: (2n) normal number of
chromosomes (Body Cells)
• Haploid cells: (n) ½ the normal
number of chromosomes (Sex Cells)
Diploid vs Haploid
Movie Clips
Each 1 min.
Meiosis
The process by which haploid (sex)
cells are produced with half the number
of chromosomes.
What is the end result of meiosis?
46X
Meiosis
23X
23X
23X
23X
Where does meiosis occur?
Gonads – Ovaries
and Testis
Why is meiosis important?
• Maintains the number of
chromosomes from
generation to generation
• Provides genetic
variation
• Only during fertilization
(union of sperm and
egg) is the full (diploid)
set of chromosomes
restored.
Practice Problems: