Transcript Cell Division

Asexual vs. Sexual Reproduction
Asexual:
-single individual is sole parent and passes ALL
genes to offspring
-offspring are genetically identical to parent’s
-results in a clone…rarely a genetic difference
will occur as a result of a mutation which can
lead to cancer
Sexual Reproduction
• -two parents give rise to offspring
• -each person passes on half of its genes to
its offspring
• -offspring have a unique combination of
genes inherited from both parents
• -results in greater genetic variation;
offspring vary genetically from their
siblings and parents
Meiosis creates genetic variation
• -Recall mitosis produces two daughter cells
genetically identical to parent and to each
other.
• Meiosis will produce FOUR daughter cells
genetically different from parent and each
other.
Sexual Reproduction Varies in
Meiosis By…
• -Independent assortment- random alignment and
each chromosome orients independently of other
pairs
• -Random Fertilization- An egg cell is 1 of 8
million possibilities and a sperm cell is also 1 of 8
million possibilities…thus, a zygote can have 1 of
64 trillion different combinations
• -Crossing Over- (we’ll get to this at the end)
Crossing Over
Crossing Over Cont…
• -occurs when homologous portions of two
nonsister chromosomes trade places
• -produces chromosomes that contain genes
from both parents
• -in humans, average of 2-3 crossovers per
chromosome pair
Intro Sex Cell Division: Meiosis
Meiosis is cell division
of sex cells
to form egg and sperm
Meiosis vocabulary
1. Meiosis - a two stage cell division in which
the chromosome number is halved. It
forms four different gametes (sex cells)
Meiosis I and Meiosis II
2. Gamete - the reproductive cell
(egg or sperm)
Meiosis vocabulary cont.
3. Haploid – “half” (as in when the human cell has
only 23 single chromosomes (gamete cells)
(n=23)
4. Diploid – “two” (as in when the human cell has
23 pairs of chromosomes (2n =46)
5. “homologous” chromosomes- same size,
centromere pairing, and staining pattern
Vocab Cont…
• 6. somatic cell- any cell other than sperm or
egg
• 7. autosome- a chromosome (recall:
threadlike structure in eukaryote made of
DNA + protein) that is NOT a sex
chromosome
• 8. zygote- diploid cell that results from
union of two haploid gametes
Meiosis Steps
1. Pre-Meiosis - Interphase
2. Meiosis I - Prophase I
- Metaphase I
- Anaphase I
- Telophase I
3. Meiosis II - Prophase II
- Metaphase II
- Anaphase II
- Telophase II
4. Post-Meiosis - Cytokinesis
Why is Meiosis important?
• All gametes must be haploid
(n = 23 chromosomes)
Egg (n=23)
+ Sperm (n=23)
offspring (2n=46) normal
Pre-Meiosis: Interphase
46 chromosomes ----> 92 chromosomes
diploid
1. copy Chromosomes
2. copy centriole
No Interphase
between
Meiosis I and Meiosis II
Chromosome Vocab
• SYNAPSIS
Chiasma
Cytokinesis
In males, cytokinesis makes four equal cells
that develop heads and tails = sperm
In females, cytokinesis is unequal; one cell gets
most of the cytoplasm to become the mature
egg, while the other three (called polar bodies)
are not involved.
Cytokinesis
In Males,
In females,
cytokinesis
makes four
equal cells
that
develop
heads and
tails =
sperm
cytokinesis is
unequal;
one cell gets
most of the
cytoplasm to
become the
mature egg,
the other
three (polar
bodies)
usually die
Variety of Sexual Life Cycles
• -in animals, gametes are the only haploid
cells
• -in fungi, the organism in normally haploid
and the only diploid stage is the zygote
(meiosis follows immediately)
• -plants (and some algae)- called
“alternation of generations”… (see
following diagram)
Ch 14 WarmUp
1. What is the difference between an allele and a gene?
2. Briefly define the following terms:
a. homozygous
b. heterozygous
c. phenotype
d. Genotype
3. What is the difference between pleiotrophy and epistasis?
4. Describe the following disorders: Cystic Fibrosis, TaySachs, Sickle Cell Anemia, Achondroplasia, and
Huntington’s disease.