Download Aim: How do organisms create offspring through sexual reproduction?

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.
Special cells = Gametes
Female cells = Egg
Male cells = Sperm
Joining of sperm & egg cell = 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-the number and appearance of chromosomes
in the nucleus of a eukaryotic cell.
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 Dad
Eye Color
Hair Color
B
G
B
R
Gene
Part of a
chromosome
that codes
For a trait
Have genes that code for the same trait, but
may have different types 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 types
of that trait
How many chromosomes do the offspring
have after mitosis?
46X
Mitosis
46X
46X
Do our sex cells have 46
chromosomes?
NO!!!
What would happen if our sex cells did
have 46 chromosomes?
46
+
Sperm
46
92
Egg
Offspring
The offspring would have 92 chromosomes!
TOO MANY!!!
Sexual Reproduction:
Zygote
23
+
23
Egg
46
Offspring
Sperm
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
a) Diploid cells: (2n) normal number of
chromosomes (Body Cells)
b) Haploid cells: (n) ½ the normal
number of chromosomes (Sex Cells)
Diploid vs Haploid
________
________
Meiosis
•The process by which haploid (sex)
cells are produced with half the number
of chromosomes.
Meiosis has 2 Cell Divisions
1st Cell Division
2nd Cell Division
1 Diploid cell
4 Haploid Cells
What is the end result of meiosis in humans?
46X
Meiosis
23X
23X
23X 23X
End Results of Meiosis:
• Four Cells are made (gametes).
which have the haploid or monoploid
number of chromosomes (half).
• All of the cells are DIFFERENT from
each other.
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: