Contributors to Genetic Variation and Cell Division Check Points Flashcards
Contributors to genetic variation
- independent assortment of homologous chromosomes at the metaphase plate in meiosis I
- random fertilization
- crossing over
Independent assortment of homologous chromosomes means that
there is a 50% chance of 1 arrangement of chromosomes and a 50% chance for the other one
Orientation of homologous chromosomes is random like “ “
a flip of a coin
The number of possible combinations for the gametes is calculated by
2^n, where n = the number of chromosomes in the genome
ex 4 chromosomes = 2^4 or 16 possibilities
in independent assortment, the amount of possible assortments is
1 of 8 million
in random fertilization, the number of possible assortments jumps to
1/64 trillion diploid combinations (zygote)
Crossing over increases variability: true or false
true
How many cell cycle check points are there?
3
Check point 1
after G1
- are there enough nucleotides to make the strand
- checks for DNA replication enzymes
- checks for sufficient nutrients and O2 present for S-phase
Check point 2
After S
- is all the DNA replicated ?
Check point 3
after G2
- are enough organelles present for 2 cells identical to the parental cell or 4 gametes
- are all structural proteins needed present? (tubulin)
- are critical proteins needed for mitosis and meiosis present
Two types of cell cycle control molecules
kinases and cyclins
kinases
enzymes that activate or inactivate proteins by phosphorylating them
cyclins
cycle in concentration throughout the cell cycle
MPF
maturation promoting factor/mitosis promoting factor
MPF is made of what 2 proteins?
cdk2 and cyclin B
MPF functions to
- stimulate chromosome condensation
- stimulate spindle assembly
- stimulates nuclear envelope breakdown
MPF gets inactivated when
cyclin gets degraded
MPF functions in what phases of cell division
Prophase - Metaphase
MPF is no longer function in which phase of cell division
Telophase
APC
Anaphase Promoting Complex
what does APC do
it stimulates the degradation of a protein called securin, tagging it for degradation
losing securin releases a protease named
separase
what does separase do?
separase degrades cohesins to allow for sister chromatid separation during anaphase
APC puts a tag on what to degrade MPF
cyclin, which leads to loss of MPF function
when MPF is gone, what happens
spindle reforms, chromosomes decondense, nuclear envelope forms
