Download 122 lec 04 mult all mitosis meiosis

Announcements
• Problem sets due this week at the
beginning of lab.
• Show your work!
• Write out solutions, helps to think things
through.
• Review study CD that came with text for lab
this week (especially mitosis and meiosis).
Human blood type example
• One locus determines blood type
• Three alleles are common
• Two alleles are dominant to the third
and codominant with each other
Blood type genotypes
• Three alleles present- Ia, Ib, i
– Ia and Ib are codominant
– i is recessive
• Possible genotypes
– IaIa homozygote, Iai heterozygote,
– IbIb homozygote, Ibi heterozygote,
– ii homozygote, Ia Ib heterozygote
Objectives
• Understand inheritance of blood type in humans.
• Know how
– organisms vary in chromosome number among life
stages and among species.
– to tell chromosomes apart
– to figure out which chromosomes are homologues.
• Understand the role of mitosis and meiosis in
asexual and sexual reproduction.
• Distinguish between stages of cell division.
• Recognize how chromosome movement during
meiosis results in Mendel's laws of Segregation
and Independent Assortment.
Blood type phenotypes
• Four phenotypes: A, B, AB, O
• A, B or no substance coats blood cells
• Blood type determined by whether
antibodies react to substance
Eukaryote chromosome structure
• Chromosomes contain DNA & proteins
• made of
– centromere- region to which spindle fibers
attach during mitosis and meiosis
– arms
• region that extends from centromere
• contain genes
1
Figure 12.3 Chromosome duplication and distribution during mitosis
Figure 13.x4 Human male chromosomes
Figure 13.x5 Chromosomes differ in length and position of centromere
Life cycle stages differ in ploidy
• Ploidy = number of copies of each homologue
• Common ploidy levels
– Haploid- one copy (1N)
– Diploid- two copies (2N)
– Polyploid- multiple (>2) copies (3N, 4N, etc)
Figure 13.5 Three sexual life cycles differing in the timing of meiosis and
fertilization (syngamy)
How do organisms differ in
chromosome number?
• Ploidy- how does organism spend most of life?
– Haploid (protists, algae & fungi, moss)
– Diploid (ferns, flowering plants, insects, vertebrates)
– Polyploid (many plants, few animals)
• ‘haploid’ chromosome number
– Humans: 23
– Fruit flies: 4
– Ferns: thousands
2
Figure 13.1 The asexual reproduction of a hydra
Reproduction in eukaryotes
• asexual
– budding or vegetative reproduction
– offspring genetically identical to parent
• sexual
– fusion of two haploid gametes
– different combinations of genes than in
parents
Figure 33.7 The life cycle of the hydrozoan Obelia (Layer 3)
Cell cycles in eukaryotes
• Interphase
– 90% of cell life
– cell growth occurs
– chromosomes are copied but not visible
• Mitotic phase
– nucleus 'dissolves'
– chromosomes condense
– cell divides
– two daughter cells genetically identical to parent
Figure 12.4 The cell cycle
Figure 12-09x Mitosis in an onion root
3
Mitosis
• Occurs throughout life of a multicellular
organism
– development
– growth
– maintenance
• Involved with asexual reproduction
• We define stages (prophase, metaphase,
anaphase, telophase)
Figure 12.5 The stages of mitotic cell division: G2 phase; prophase
Prophase
• Nuclear membrane disappears
• Mitotic spindle forms
– Microtubule organizing centers
(centrosomes) form and migrate to opposite
ends of cell
– Microtubules attach to centromere at
kinetochore
• Duplicated chromosomes (sister
chromatids) move toward center of cell
Figure 12.5 The stages of mitotic cell division : prophase; prometaphase
Figure 12.6 The mitotic spindle at metaphase
Metaphase
• Chromosomes align along metaphase
plate
• Centromeres aligned with each other
• Kinetochores face centrosomes away
from center of the cell
4
Figure 12.5 stages of mitotic cell division: metaphase; anaphase
Anaphase
Sister chromatids are pulled
toward opposite ends of cell
Stages of mitotic cell division : anaphase; telophase and cytokinesis
Telophase
• Nuclear membrane in each daughter
cell starts to form
• Chromosomes elongate
• Cell division occurs
Significance of Meiosis
• Gamete cells formed with one copy of
each chromosome
• Meiotic events cause Mendel's laws
– Segregation- Homologues separate
– Independent assortment- independent
orientation of chromosomes
• Recombination occurs (independent
orientation, crossing over)
Prophase I (longest phase)
• pairing of homologous chromosomes
• paired homologues consist of 4
chromatids (tetrads)
• X-shaped configurations form (chiasmata)
• Crossing over occurs
• chiasmata move to end of chromosome
arms
5
What happens during crossing over?
Metaphase & Anaphase I
• exchange of
segments at
identical
positions along
homologues
• no loss or
addition of
genetic material
• tetrads moved to metaphase plate
• homologues pulled apart into different
daughter cells
• sister chromatids remain attached at
centromeres
• chromosome number is now reduced
Figure 13.7 The stages of meiotic cell division: Meiosis I
Telophase I and Prophase II
• Chromosomes may uncoil as cell
division occurs
• No chromosome duplication occurs
Figure 13.7 The stages of meiotic cell division: Meiosis II
Metaphase II, Anaphase II,
Telophase II
• mitotic division repeated, but now
sister chromatids separate
• genetic material reduced, but not
chromosome number
6