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.
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