T13 Flashcards
Why is reproduction important ?
It ensures that there are more individuals (varied) which allows for evolution.
What differs from asexual and sexual reproduction?
You need two parents.
What is the type of cell involved in sexual reproduction ?
Gametes (small for male and big for female)
T or F : Twins are genetically identical.
T
What organisms almost entierly does sexual reproduction ?
Eukaryotes.
What helps assign sex ?
Anatomy, gomads, gametes, chromosomes.
Are gametes haploid or diploid ?
Haploid
Are gametes similar genetically ?
No, they are genetically different
What is the product of mitosis ?
Four daughter cells, haploid, genetically different.
What do we call the cells that produce gametes ?
Germ cells
Why do we produce gametes that are haploid ?
The number of chromosomes would keep increasing.
Why produce gametes that are genetically different?
Genetically diverse = evolution
Evolution through variation
More people = more variation
What comes before meiosis ?
Interphase (G0, S, G1)
Is there any pause between Meiosis 1 and Meiosis 2 ?
No
What do we have at the end of interphase ?
46 chromosomes and centrosomes that have been duplicated.
What do we have at the end of S phase ?
Diploid # (2n) of chromosomes : 2(23) = 46
Number of pairs of sister chromatids : 46
Number of chromatids : 92
Specifically explain Prophase 1.
-Chromatin condenses into chromosomes.
-Centrosomes continue separating and moving to opposite poles.
-The nuclear enveloppe starts disappearing.
-Homologous pairs group and form tetrads.
Synapsis : non-sister chromatids of a homologous pair are held together by protein at a specific region (chiasma/chiasmata).
Crossing over : non-sister chromatids exchange genetic material with equivalent part of a chromatid from the other homologous chromosome.
Explain metaphase 1.
Spindle fibers move tetrads to cell midline.
Tetrads line up
Assortment
What is assortment ?
When the tetrads (homologous pairs) orients independently at the the midline
Where does the most variation occur ?
Prophase 1 and Anaphase 1 (through crossing over/synapsis and assortment)
Explain Anaphase 1.
Tetrads separate but sister chromatids stay together.
Each side of the cell has one set of chromosomes (random mix)
Which one is on top matters.
Explain Telophase 1 and Cytokinesis.
- Chromosomes are drawn to opposite ends of the cell.
- Nuclear envelope reforms.
- The chromosomes starts to loosen back into chromatin.
- Each nucleus contains 1 set of chromosomes (haploid).
Sister-chromatids need to be separated.
How much time passes by between Telophase 1/Cytokinesis and Prophase 2 ?
None.
Explain Prophase 2.
Centrosomes have been duplicated, chromatin into chromosomes, nuclear envelop disappears
