Unit 3: Meiosis Flashcards
What does ploidy mean ?
The number of sets of chromosomes in a cell
What does haploid mean ?
One set of chromosomes in a cell
What does diploid mean ?
Two sets of chromosomes in a cell
What is the haploid number (n) ?
The number of chromosomes in a gamete (a haploid sperm or egg cell)
If haploid cells are n what does that make diploid and tetraploid cells ?
Diploid = 2n
Tetraploid = 4n
What is a germ cell ?
Cells that will give rise ultimately to mature sperm and eggs
What are somatic cells ?
Cells of the body that do not transmit information to the next generation
What type of cells does meiosis occur in ?
Germ cells
What are the 4 stages of Meiosis 1 ?
1) Prophase 1
2) Metaphase 1
3) Anaphase 1
4) Telophase 1 and cytokinesis
What happens in prophase 1 ?
- Chromsomes condense
- Nuclear envelope breaks down
- Crossing over occurs
What happens in metaphase 1 ?
- Pairs of homologous chromosomes move to the equator of the cell
What happens in anaphase 1 ?
- Homologous chromosomes move to opposite poles of the cell
What happens in telophase 1 and cytokinesis ?
- Chromsomes gather at poles of the cell
- Cytoplasm divides
What are the 4 stages of meiosis 2 ?
1) Prophase 2
2) Metaphase 2
3) Anaphase 2
4) Telophase 2 and cytokinesis
What are the 5 phases of prophase 1 ?
1) Leptotene
2) Zygotene
3) Pachytene
4) Diplotene
5) Diakinesis
What happens during leptotene ?
- Duplicated chromosomes start to condense
- Nuclear envelope breaks down
What happens during zygotene ?
- Bivalent forms
- Synapsis begins (synaptonemal complex forms)
What happens during pachytene ?
- Synapsis is complete
- Crossing over occurs
What happens during diplotene ?
- Chiasma is viable
- Synaptonemal complex disappears
What happens during diakinesis ?
- Nuclear envelope fragments
- Bivalent ready for metaphase
What is homologous recombination ?
The exchange of identical DNA sequences between similar or identical DNA molecules
What is a chiasma ?
The point where 2 homologous chromosomes or chromatids exchange genetic material
What is synapsis ?
Where homologous chromosomes pair up closely along their lengths
What is crossover ?
Where homologous chromosomes exchange pieces of genetic material
Explain the process of meiotic recombination (3)
1) Before the first mitotic division homologous chromosomes pair up
2) Chiasma forms, chromosomes swap bits of their arms
3) New ‘recombinant’ chromosomes formed each with different combinations of alleles to the parental chromosomes
What are the 2 products of meiosis 2 ?
- Parental
- Recombinants
How can position of chromosomes affect recombination ?
Genes that are in close proximity on a chromosome are less likely to be broken up by recombination
