Transcript Introduction to Meiosis

Aim: How do organisms create
offspring through sexual
reproduction?
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?
We have 46 chromosomes
in each our body cells.
We can also say that we
have 23 pairs of
chromosomes
Karyotype
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 B
Dad
G
Hair Color B
R
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?
Chromatids are exact
duplicates of each other
Homologous chromosomes
have genes that code for
the same trait, but they may
code for different versions
of that trait (ex. Blue or
brown eyes)
How many chromosomes do the
offspring have after mitosis?
46
Mitosis
46
46
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
Sperm
46
Offspring
A fertilized egg cell is called a Zygote
Characteristics of Sexual Reproduction:
1) Is the creation of a new individual from 2 parents.
2) Offspring are not genetically identical to the parents.
Sex Cells (Gametes)
• Sex Cells:
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: (n) ½ the normal
number of chromosomes (Sex
Cells)
Meiosis
•The process by which haploid (sex) cells
are produced with half the number of
chromosomes.
What is the end result of meiosis?
46
Meiosis
23
23
23
23
Where does meiosis
occur?
Gonads – Ovaries
and Testis
Why is meiosis important?
• Maintains the proper number
of chromosomes from
generation to generation
• During fertilization, (union of
sperm and egg) the full
(diploid) set of chromosomes
restored.
• Provides genetic variation
Practice Problems: