Meiosis Flashcards
How many stages of Meiosis are there? What are they?
- Meiosis I and Meiosis II
What happens before Meiosis I?
All chromosomes duplicate
What happens to the nuclear membrane during Prophase I?
It breaks down
What happens w/ the spindle fibers during Prophase I?
They start to form
What happens in Prophase I with the replicated chromosomes?
Each replicated chromosome joins with its pair to form a group of four sister chromatids
What is the group of chromosomes formed in Prophase I called?
A tetrad
What is the pairing process that forms tetrads in Prophase I called?
Synapsis
What may happen to the homologous chromosomes while the chromosomes are in tetrad formation?
Twist around each other and exchange segments of chromosomes
What is the segment exchange between chromosomes during synapsis called?
crossing over
What happens to the chromosomes during Metaphase I?
They line up in the center of the cell in tetrad formation
What happens to the spindle fibers during Metaphase I? Where?
They attach to the tetrads at their centromeres
What is disjunction?
When the homologous pairs separate and move to opposite sides of the cell.
When does disjunction happen?
Anaphase I
The two cells that result from Meiosis I are diploid or haploid?
Haploid
Why does the cell need to divide again after Meiosis I?
Because the chromosomes are each still double stranded.
What happens during Telophase I and Cytokinesis?
The cell divides into two new, haploid cells
How many chromosomes do the two cells that resulted from Meiosis I have?
Half the number of chromosomes as the original
What happens during Prophase II?
Each daughter cell forms spindle fibers and the chromosomes move toward the middle of the cell
What happens during Metaphase II?
The chromosomes line up in the center, one by one, of both daughter cells and the spindle fibers attach to their centromeres
What happens during Anaphase II?
The two chromatids separate, each becoming a single stranded chromosome and they move to opposite sides of the cell
What happens to the nuclear membrane during Telophase II/Cytokinesis?
It reforms
What happens to the cells during Telophase II/Cytokinesis?
They divide, forming 4 haploid cells
What happens to the chromosomes during Telophase II/Cytokinesis?
They change back to chromatin
Where do gametes develop?
The gonads
What are the female gonads and gametes?
Ovaries, and egg cells, or ova
What are the male gonads and gametes?
Testes, sperm
What is gametogenesis?
the process by which gametes develop in the gonads
What is oogenesis?
the process of ovum formation which occurs in the ovaries
What is a hermaphrodite?
Organisms in which there is no separate male or female gender. they have both testes and ovaries
Examples of hermaphrodite organisms
Earthworms, snails, and other slow moving organisms
Do hermaphrodites self fertilize?
No-they will exchange sperm and use the other’s to fertilize their own eggs
How does oogenesis begin?
With oogonia, a type of diploid cells
What do the oogonia develop into? When?
Cells called primary oocytes. prenatally
What stage are the primary oocytes in at time of birth?
Prophase of meiosis I. They then enter a resting phase.
What happens after a female goes through puberty to the primary oocytes?
It completes Meiosis I once a month
What does Meiosis I of the primary oocyte form every month?
Two cells, a polar body and secondary oocyte.
What is the polar body that resulted from Meiosis I of the primary oocyte?
a small, nonfunctional cell
Which of the two resulting cells of female Meiosis I (the polar body and secondary oocyte) is larger? What did this result in?
The secondary oocyte. It therefore receives most of the cytoplasm.
What occurs at fertilization?
Meiosis II
What happens when Meiosis II occurs to the secondary oocyte?
The secondary oocyte divides into an ootid and a polar body.
What may happen to the polar body that resulted from Meiosis II of the secondary oocyte?
It may split into 2 polar bodies
What happens to the female polar bodies?
They die
What happens to the ootid?
It grows into a mature egg
What is spermatogenesis?
process of forming sperm that occurs in the testes
What does spermatogenesis begin with?
Spermatogonia (diploid cells that a man is born with)
What happens to the spermatogonia throughout the life of a male?
They divide by mitosis to form more of them
What happens to some spermatogonia?
They enlarge, become primary spermatocytes
What happens to the primary spermatocytes?
They go through meiosis I, form 2 cells of equal sizes called secondary spermatocytes?
What happens to each secondary spermatocyte?
It goes through meiosis II to form four equal sized cells called spermatids
What happens to spermatids?
They grow tails and become sperm cells
What’s the difference in chromosome number between mitosis and meiosis?
Diploid for mitosis, haploid meiosis
What’s the difference in chromosome distribution between mitosis and meiosis?
mitosis-daughter cells have same number and type as parent cells. meiosis-daughter cells have 1 chromosome from each homologous pair and each chromosome is different due to crossing over
What’s the difference in function of cells produced between mitosis and meiosis?
mitosis-additional body cells for growth, and for unicellular or simple multicellular organisms, it’s a form of asexual reproduction. meiosis produces gametes.
Homologous chromosomes
one of a pair of chromosomes that match up at meiosis
