Transcript ppt

Chapter 13
Meiosis and Sexual Life Cycles
13.2
Asexual reproduction: Single individual is sole parent, passes copies of
all its genes to its offspring (exact copies, or clones, of the parent)
Offspring resembles their
parents more than they do
less closely related individuals
of the same species
13.1
Sexual reproduction: Two parents give rise to offspring that have
unique combinations of genes inherited from the two parents
(offspring varies genetically from their siblings and their parents).
Genetics:
The study of heredity
and hereditary
variation
13.3.
Human karyotype.
A display of condensed
chromosomes displayed
in pairs
13.4. Chromosomes in a cell
with a diploid number of 6
(2n=6) or 3 homologous pair.
Each of the 6 chromosomes
consist of 2 sister chromatids,
joined at the centromere.
locus
Fig. 13.5.
Human life cycle
Fertilization and
meiosis must alternate
in all sexual life cycles
13.6. Three types of sexual life cycles.
Note alternation of meiosis and fertilization
Concept 13.3:
Meiosis reduces the number of chromosome
sets from diploid to haploid
• Like mitosis, meiosis is preceded by the
replication of chromosomes
• Meiosis takes place in two sets of cell
divisions, called meiosis I and meiosis II
• The two cell divisions result in four daughter
cells, rather than the two daughter cells in
mitosis
• Each daughter cell has only half as many
chromosomes as the parent cell
13.7. Overview of meiosis.
How meiosis reduces the
number of chromosomes.
Meiosis takes place in two sets
of cell divisions, called meiosis I
and meiosis II.
The two cell divisions result
in four daughter cells, rather
than the two daughter cells
in mitosis.
Each daughter cell has only half
as many chromosomes as the
parent cell.
13.8a. The meiotic division of an animal cell.
Synapsis
Crossing over
Interkinesis
13.8b. The meiotic division of an animal cell.
Differences
between mitosis
and meiosis II?
13.9. Comparison of meiosis and mitosis.
13.9. Comparison of meiosis and mitosis.
13.10. Independent assortment of homologous chromosomes in meiosis.
13.11.
The results of
crossing over
during meiosis.
13.12.
The results of
crossing over
during meiosis.
13.12.
The results of
crossing over
during meiosis.
13.12.
The results of
crossing over
during meiosis.
13.12.
The results of
crossing over
during meiosis.
Example question
• A cell has a diploid chromosome number of 2n = 4.
We will designate these four as chromosomes A,
B, C, and D. If meiosis occurred WITH the
formation of homologous pairs AC and BD, and the
chromosomes were then distributed randomly
between the resulting cells, how many gametes
could be formed?
A)
B)
C)
D)
E)
6
3
4
2
5
(AB, AC, AD, BC, BD, and CD)
(AB, BC, and CD)
(AB, AD, BC, and CD)
(AB and CD)
(AB, AC, AD, BC, and CD)
15.13. Meiotic non-disjunction
Aneuploidy
15.14. Alteration of chromosome structure
Chapter 13 Review (see p.260-261)
• 13.1. Offspring acquire genes from
parents by inheriting chromosomes.
• 13.2. Fertilization and meiosis alternate in
sexual life cycles.
• 13.3. Meiosis reduces the number of
chromosome sets from diploid to haploid.
• 13.4. Genetic variation produced in sexual
life cycles contributes to evolution.