Download Chapter 10: Meiosis

Chapter 10: Meiosis
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Goal: Genetic Mixing!!
I. Sexual vs Asexual Reproduction
A. Asexual: One genetic donor.
1. Produce clone.
2. Disadvantage: No genetic
recombination except for mutations.
Examples: Sea star, plant clippings.
I. Sexual vs Asexual Reproduction
B. Sexual: Offspring product of two genetic
donors.
1. Benefit: Genetic recombination.
2. Product of meiosis.
3. Requires (usually) reduction (diploid to
haploid) to produce gametes.
II. Basic Genetics
A. Vocabulary
1. Gene: A segment of DNA that codes
for a particular trait.
2. Allele: Alternate forms of a gene (can
be more than 2).
II. Basic Genetics
A. Vocabulary
3. Chromosome: A molecule of DNA that
contains many genes.
II. Basic Genetics
4. Homologous Chromosomes: Two
chromosomes with the same traits
(one from paternal donor, one from
maternal donor).
II. Basic Genetics
B. Images
(Y)
(X)
one pair of
duplicated
chromosomes
Fig. 10.3, p. 163
III. Specifics of Meiosis
A. Goal: Produce hapliod gametes with a
random mix of parental alleles.
B. Stages:
1. Meioisis I: The reduction phase
(2n to n)
2. Meiosis II: Basically mitosis (but with
haploid cells)
III. Specifics of Meiosis
C. Meiosis I:
Prophase I: Homologous chromosomes
pair up (form tetrad); Cross over may
occur; other aspects as observed in
mitosis.
Metaphase I: Homologous pairs align at
equator (not sister chromatids).
III. Specifics of Meiosis
C. Meiosis I
Anaphase I: Homologous chromosomes
are moved to opposite poles.
Telophase I: Each nuclei gets one of the
homologous chromosomes (thus
haploid).
III. Specifics of Meiosis
C. Meiosis I:
Cross Over: Chromosomes are ‘sticky’,
so one portion of homolog can get
switched with another, further
increasing genetic variability.
MEIOSIS I
plasma
membrane
newly
forming
microtubules
in the
cytoplasm
PROPHASE I
spindle
equator
(midway
between the
two poles)
one pair of
homologous
chromosomes
METAPHASE I
ANAPHASE I
TELOPHASE I
Fig. 10.4a p. 164
III. Specifics of Meiosis
D. Meiosis II:
Repeat Mitosis
MEIOSIS II
PROPHASE II
METAPHASE II
ANAPHASE II
TELOPHASE II
Fig. 10.4b p. 165
MEIOSIS I
MEIOSIS II
in-text, p. 163
IV. Gametogenesis
A. Sperm formation: Equal distribution of
cytoplasm.
IV. Gametogenesis
B. Oogenesis (egg formation): Unequal
distribution of cytoplasm, resulting in 3
polar bodies and one healthy egg
(usually).
2n
germ cell
germ cell
each chromosome
duplicating during
interphase
n
MEIOSIS I
separation of
homologues
MEIOSIS II
separation of
sister chromatids
gametes
gametes
2n
diploid number
restored at
fertilization
zygote
Fig. 10.11, p. 172