Mitosis
What is the point of mitosis?
Replicating somatic cells to produce two identical cells.
What is the point of meiosis?
Produces four haploid cells called gametes from a single diploid cell
failure of chromosomes or chromatids to separate
during anaphase of mitosis, meiosis I, or meiosis II
nondisjunction
A widow's peak hairline is dominant to a straight hairline. Cross a heterozygous widow's peak to a straight hairline.
H = widow's peak
h = straight hairline
Look at key on slide 3
What is the first phase of mitosis? Draw it out
Prophase
- Chromosomes condense
• Centrioles move to opposite ends of the cell
• Their location determines locations of the new cells
• Microtubules start to extend from centrioles
toward nucleus
• Together called the spindle
• Nuclear envelope breaks down
• Microtubules attach to chromosomes or
microtubules from other side
What is the first phases of Meiosis I and II? Draw them out
Prophase I
- Same events as prophase of mitosis BUT...
• Homologous chromosomes pair up
• Crossing over occurs
• Microtubules will attach to homologs, not one
chromatid each
Prophase II
- New spindle forms in each cell
• Chromosomes re-condense
• Unlike mitosis, chromosomes don’t contain identical sister chromatids
• Unlike mitosis, half of each homologous pair is in a different cell
condition where cells have an incorrect number of copies of a particular chromosome
Aneuploidy
Premature grey is hair is dominant over normal hair coloring. Cross a homozygous premature hair person to normal hair person.
G = gray hair
g = normal hair
Look at answer key on slide 4
What is the second phase of mitosis? Draw it out
Metaphase
- Chromosomes line up at metaphase plate
What are the second phases of Meiosis I and II? Draw them out
Metaphase I
- Pairs of homologous chromosomes line up at
metaphase plate
• The line of chromosomes will be half as long as in
mitosis
Metaphase II
- Same as metaphase of mitosis BUT...
• Still, chromatids aren’t identical within
chromosomes
• Still, half of the homologs are in a
separate cell
possession of more than 2 sets of chromosomes
polyploidy
Round pees are dominant to wrinkled pees. What would be the genotype and phenotype of offspring between a homozygous dominant and homozygous recessive individuals?
R = round
r = wrinkled
Check key on slide 5
What is the third phase of mitosis? Draw it out
Anaphase
- Centromeres separate, so sister chromatids
separate
• Microtubules pull the (now) chromosomes apart
What are the third phases of Meiosis I and II? Draw them out
Anaphase I
- Microtubules pull the homologs apart
• Centromeres do not separate yet
Anaphase II
- Same as anaphase of mitosis BUT...
• Chromatids separate, not sister
chromatids
• Because they’re not identical
replicated homologous chromosomes trade segments of DNA
crossing over
In tomatoes, tall vines (T) are dominant to dwarf vines (t), and red fruit (R) is dominant to yellow fruit (r).
A farmer mates a homozygous tall, red tomato plant (TTRR) with a heterozygous tall, red tomato plant (TtRr).
What is the percent chance that the offspring will be dwarf plants with yellow fruit?
What is the last phase of mitosis? Draw it out
Telophase
- Two nuclear envelopes form: one per set of DNA
• Spindle gets broken down
Cytokinesis
Second part of M phase (i.e. cell division) in eukaryotic cell cycle
• Division of cytoplasm
• Animals: cell membrane furrows to pinch the two halves apart
Plants: vesicles from Golgi apparatus move to the center and fuse to form a cell membrane
• Then, contents of the vesicles form a cell plate, which becomes a cell wall
What are the last phases of Meiosis I and II? Draw them out
Telophase and Cytokinesis I
- Same as telophase of mitosis, but cells are now
haploid
• Same type of cytokinesis as after mitosis
Telophase and Cytokinesis II
- Same as telophase of mitosis, BUT...
• Happens in four nuclei, not two
• Same type of cytokinesis as after
mitosis, BUT...
• Happens twice, to result in four cells, not
two
the now intermixed chromosomes separate into two cells, but not all of the “mom’s” chromosomes go to the same side
independent assortment
In guinea pigs, black hair (B) is dominant to brown hair (b) and short hair (H) is dominant to long hair (h).
A black, long-haired guinea pig (Bbhh) is crossed with a brown, short-haired guinea pig (bbHh).
What percentage of the offspring will be black with long hair?
25%