13 Flashcards
What is meiosis? How is it different from mitosis?
- Cell division of sex organs
- Produces gambetes
Testes produce what?
Ovaries produce what?
Sperm, eggs
What are the 5 properties of mitosis that make it different from meiosis?
- Results in 2 identical daughter cell
- Only 2 division
- No crossing over
- Happens in somatic cells
- No genetic diversity other than mutations
What are the 5 properties of meiosis that make it different from mitosis?
- Results in 4, not 2, DIFFERENT, not identical, daughter cells
- 2 separate cell divisions (Meiosis 1 and Meiosis 2)
- Synapsis results in crossing over
- Independent assortment
- Law of segregation
What is synapsis? What does it result in?
- The pairing of homologous chromosomes
- Results in crossing over
When does independent assortment occur?
Metaphase 1
When does the law of segregation occur?
Anaphase 1 and 2
What are the properties of Diploid cells?
- 2 complete sets of chromosomes
- All cells are diploid other than sex cells
What does 2n mean in 2n=46?
- Diploid
- The number of SETS of chromosomes is 2n
- 46 is the number of chromosomes that it contains
Meaning, if 2n is the number of diploid, n would be the number of haploid. So, if 2n=46, n=23.
How many homologous pairs of chromosomes to humans have?
23
How many chromosomes do humans have in total?
46
How many chromosomes do each of our gametes have?
23
Which cells are haploid?
Sex cells
Which cells are diploid?
All cells except sex cells
what happens in meiosis 1?
Homologous chromosomes are separated into daughter cells
What are the steps of meiosis 1?
- Prophase 1
- Metaphase 1
- Anaphase 1
- Telophase 1
- Cytokinesis
What happens in prophase 1?
- Synapsis
- Crossing over
What is it called when homologous chromosomes pair up?
A tetrad
What happens when a cell forms a tetrad?
It becomes diploid
What happens during crossing over?
Parts of 1 homologous chromosome are swapped with the other chromosome (think of swapping parts on a Lego set from one set to another)
What happens at metaphase 1? There is 1 major event
Homologous chromosomes line up at the metabolic plate independently. This is independent assortment
What is independent assortment?
Homologous chromosomes lining up at the metabolic plate independently
When does Independent assortment occur?
Metaphase 1
What happens at anaphase 1?
Homologous chromosomes split and go to separate daughter cells. This is the law of segregation.
What is the law of segregation?
Homologous chromosomes split and go to separate daughter cells.
What happens at telophase 1?
Cytoplasm splits and two separate cells result with a COMPLETE chromosomes, each having 2 sister chromatids
What happens at prophase 2?
Spindle fibers reform
What happens at metaphase 2?
Chromosome line up at the metabolic plate.
Are the chromosomes identical at metaphase 2? Why it why not?
No, because of Crossing Over at prophase 1
What happens at anaphase 2?
The sister chromatids separate from each other. the law of segregation.
What happens at telophase 2? What state are the cells in now?
- 4 daughter cells are created
- The cells are now haploid (n) because they only have 1 sister chromatid per chromosome.
Does crossing over occur in mitosis?
NO!!
What are the 3 sources of genetic variation?
- Independent assortment
- Crossing over
- Random fertilization
What is the equation for possible number of combinations during independent assortment?
2^n = the number of possibilities. N would be the haploid #.
If n = 25, how many possible combinations are there?
Almost 34,000,000
What is it called when homologous chromosomes swap segments of DNA? (Remember the legos)
Crossing over
What is random fertilization?
Any egg cell can match with any sperm cell
