The Role Of Sexual Reproduction In Variation
And Evolution
A) Important Terms
- Phenotype: Appearance of a trait. Ex. Blue eyes
- Genotype: The gene make up of an organism for
a specific trait.
- Asexual Reproduction: Reproduction that
involves only one parent and produces a new
organism that is an exact copy of the parent.
- Diploid: Two sets of each chromosome.
- Sexual Reproduction: Reproduction that requires
two parents. Each contribute genes to the
offspring it is a blend of the features of both
parents.
- Haploid: One set of each chromosome.
(Gametes)
- Mitosis: (Normal Cell Division) Type of cell
division in which two daughter cells receive the
exact chromosome and genetic make-up of the
parent cell. This occurs during growth and
repair.
- Meiosis: (Reduction division). The # of
chromosomes are cut in half during the process so
that when two meiotic cells are joined, the # of
chromosomes is a full and complete (diploid).
Produces four daughter haploid cells (23
chromosomes). Example: producing haploid eggs
and haploid sperm cells.
IT OCCURS ONLY IN THE
REPRODUCTIVE SYSTEM.
- Cross-over: exchange of genetic material
between two sister chromosomes. Vastly increases
the variation in gametes.
- Population: A group of members of the same
species living together in the same area who can
potentially and usually breed with each other.
B) Role of Sexual Reproduction
Sexual Reproduction Variation  Evolution
- If there was no sexual reproduction many
organisms could still reproduce asexually, but
they would be identical to their parents.
- No Sex = No variation = No favored traits.
- If mitosis were used instead of meiosis in sexual
reproduction there would be too many
chromosomes in the new cells.
Diploid X
2n
Diploid = Tetraploid
2n
4n
(Abnormal)
Example : 46 + 46 = 92
- Meiosis produces gametes with ½ the DNA
(chromosomes)
Haploid X Haploid
n
n
Example :
= Diploid
2n
(Normal)
23 + 23 = 46 (normal)
- Meiosis produces 4 gametes all-different. Crossover factor also helps to increase diversity.
- Meiosis only results in Reshuffling of existing
genes. It can only cause organisms to evolve to
some point.
- Mutations to DNA (genes) also play an
important role in changing the genotype 
phenotype.