meiosis

Question 1

describe the start cell

Answer 1

diploid (2n) - chromosomes in pairs

Question 2

describe 2 homologous pairs of chromosomes

Answer 2

• same length
• same genes in same order
• centromeres in same position

Question 3

describe prophase 1

Answer 3

• homologous chromosomes associate in pairs “bivalents”
• chromosomes visible because they have condensed
• pair of centrioles at each pole start to form spindle fibers
• nuclear membrane starts to break down
• crossing over may occur between non sister chromatids causing alleles to swap places causing genetic variation - recombinants

Question 4

what does the cell have to go through before meiosis, explain

Answer 4

interphase
- G1: organelles replicate
- S: DNA replication
- G2: energy reserves released
each chromosome becomes 2 genetically identical sister chromatids held at the centromere

Question 5

describe metaphase 1

Answer 5

• chromosomes line up in pairs across equator of cell
• 2 possibilities of cells
• independent assortment occurs if chromosomes = more GV in gamete

Question 6

Describe anaphase 1

Answer 6

-spindle fibers contract
- homologous pairs of chromosomes separate

Question 7

describe telophase 1

Answer 7

• nuclei are now haploid (n) = half the original chromosome number
• chromosomes no longer pairs
• cell divides by cytokinesis

Question 8

why does meiosis 2 have to occur?

Answer 8

the cells at end of telophase 1 are haploid but each chromosome is still twice it’s normal size so it has to go through meiosis 2 to separate the two chromatids

Question 9

describe prophase 2

Answer 9

• nuclear envelope breaks down
• spindle fibers form at each pole

Question 10

describe metaphase 2

Answer 10

• single row of chromosomes across equator
• chromatids no longer identical due to crossing over
• independent assortment

Question 11

describe anaphase 2

Answer 11

• chromatids pulled apart to opposite poles of each individual chromosome
• centimeter divide

Question 12

describe telophase 2

Answer 12

• chromatids assemble at poles
• chromosomes uncoil
• form chromatin again
• nuclear membrane reforms
• nucleolus becomes visible

Question 13

describe second cytokinesis

Answer 13

• end up with 4 haploid gametes
• chromosomes no longer chromatids once they are pulled apart = they elongate again
• genetically different