Download MEIOSIS I - Issaquah Connect

AP Bio 02.04.16
Goals:
Meiosis Continued
1.
2.
3.
4.
Homework: (next slide)
AP exam practice question
Notes session
Work on:
Activity 46.1 Production of human gametes
Regular book Chapters 32, 36
Old Book Chapters 45 & 46
FRQ & grid in quiz next week (02.11.16) on Chapter 9
© 2014 Pearson Education, Inc.
Due today:
•
Mitosis & Meiosis Lab Bench activity
Ongoing:
• Chapter 10 reading guide: due 02.08.16
• Mastering Biology Chapter 10 HW: due 02.08.16
New:
• Meiosis POGIL & Human Gamete production (02.08.16)
• Watch/take notes on Double Helix film (quiz on 02.08.16)
• Watch/video guide on Bozeman Science video (02.08.16)
© 2014 Pearson Education, Inc.
Figure 10.8
MEIOSIS I: Separates homologous chromosomes
Prophase I
Metaphase I
Anaphase I
Telophase I and
Cytokinesis
MEIOSIS II: Separates sister chromatids
Prophase II
Metaphase II
Anaphase II
Telophase II and
Cytokinesis
Sister
chromatids
Centromere
(with kinetochore) Sister chromatids
remain attached
Centrosome
(with centriole
Cleavage
pair)
furrow
Chiasmata
Metaphase
Spindle
plate
Sister chromatids
separate
Homologous
chromosomes
separate
Fragments
of nuclear
envelope
Homologous
chromosomes
Microtubule
attached to
kinetochore
© 2014 Pearson Education, Inc.
Haploid
daughter
cells forming
Genetic variation produced in sexual life
cycles contributes to evolution
• Mutations:
– changes in an organism’s DNA
– the original source of genetic diversity
– create different versions of genes called alleles
– Reshuffling of alleles during sexual reproduction
produces genetic variation
© 2014 Pearson Education, Inc.
Origins of Genetic Variation Among Offspring
• Three mechanisms contribute to genetic
variation
– Independent assortment of chromosomes
– Crossing over
– Random fertilization
© 2014 Pearson Education, Inc.
Independent Assortment of Chromosomes
• Homologous pairs of chromosomes orient
randomly at metaphase I of meiosis
• In independent assortment, each pair of
chromosomes sorts maternal and paternal
homologs into daughter cells independently
of the other pairs
© 2014 Pearson Education, Inc.
Figure 10.10-1
Possibility 2
Possibility 1
Two equally probable
arrangements of
chromosomes at
metaphase I
© 2014 Pearson Education, Inc.
Figure 10.10-2
Possibility 2
Possibility 1
Two equally probable
arrangements of
chromosomes at
metaphase I
Metaphase II
© 2014 Pearson Education, Inc.
Figure 10.10-3
Possibility 2
Possibility 1
Two equally probable
arrangements of
chromosomes at
metaphase I
Metaphase II
Daughter
cells
Combination 1 Combination 2
© 2014 Pearson Education, Inc.
Combination 3 Combination 4
Crossing Over
• Produces recombinant chromosomes,
which combine DNA inherited from each
parent
• Crossing over begins very early in prophase I,
as homologous chromosomes pair up gene
by gene
• Formation of chiasmata
© 2014 Pearson Education, Inc.
Figure 10.11-1
Prophase I
of meiosis
Pair of
homologs
© 2014 Pearson Education, Inc.
Nonsister chromatids
held together
during synapsis
Figure 10.11-2
Prophase I
of meiosis
Pair of
homologs
Chiasma
Centromere
TEM
© 2014 Pearson Education, Inc.
Nonsister chromatids
held together
during synapsis
Synapsis and
crossing over
Figure 10.11-3
Prophase I
of meiosis
Pair of
homologs
Chiasma
Nonsister chromatids
held together
during synapsis
Synapsis and
crossing over
Centromere
TEM
Anaphase I
© 2014 Pearson Education, Inc.
Breakdown of
proteins holding sister
chromatid arms together
Figure 10.11-4
Prophase I
of meiosis
Pair of
homologs
Chiasma
Nonsister chromatids
held together
during synapsis
Synapsis and
crossing over
Centromere
TEM
Anaphase I
Anaphase II
© 2014 Pearson Education, Inc.
Breakdown of
proteins holding sister
chromatid arms together
Figure 10.11-5
Prophase I
of meiosis
Pair of
homologs
Chiasma
Nonsister chromatids
held together
during synapsis
Synapsis and
crossing over
Centromere
TEM
Anaphase I
Breakdown of
proteins holding sister
chromatid arms together
Anaphase II
Daughter
cells
Recombinant chromosomes
© 2014 Pearson Education, Inc.
Random Fertilization
• Random fertilization adds to genetic variation
because any sperm can fuse with any ovum
• The fusion of two human gametes =
a zygote with any of about
70 trillion diploid combinations!
….... And that doesn’t even account
for crossing over
=> every zygote is unique
© 2014 Pearson Education, Inc.
The Evolutionary Significance of Genetic
Variation Within Populations
• Enables Descent with modification:
1. Natural selection (non-random)
2. Variability of traits (random)
3. Over-production of offspring
4. Competition
The result is organisms
well-suited for their
environments
© 2014 Pearson Education, Inc.