1-Meiosis

Question 1

where does it occur

Answer 1

• occurs in the gonads
  
  • germline cells (not somatic cells)
    
    • eggs and sperm

Question 2

goals of meiosis

Answer 2

• to produce 4 progeny cells (gametes—eggs and sperm)
• with exactly half the number of chromosomes as the parent cells (2n to n)
• with genetic differences (gametes have unique genotypes)

Question 3

interphase

Answer 3

prior to the start of meiosis, the cell goes through an interphase period, in which the DNA replicates, and the cell is checked to make sure that it is ready to divide

Question 4

Prophase I

Answer 4

synapsis happens
- homologous chromosomes come together
- become tightly associated along their lengths

Question 5

Synapsis

Answer 5

The pairing of two chromosomes that occurs during meiosis

Question 6

Late prophase I

Answer 6

crossing over and recombination happens!!

Question 7

difference between crossing-over and recombination

Answer 7

crossing-over is a process
Recombination is the outcome

Question 8

crossing-over

Answer 8

• specialized protein deliberately break the DNA molecules at the same location in 2 non-sister chromatids of homologous chromosomes
• during DNA repair, rather than joining the broken segment back to the chromatid to which it was originally attached, the broken segment is segment is joined to the chromatid of the other homolog
• results in the exchange of genetic material between non-sister chromatids

Question 9

Recombinant chromatids:

Answer 9

chromatid with a combination of maternal AND paternal alleles

Question 10

non-recombinant chromatids:

Answer 10

chromatid with alleles from ONLY the maternal or paternal side

Question 11

CHIASMA (pl. chiasmata)

Answer 11

• contact point between non-sister chromatids
• the sites of DNA breakage
• EVIDENCE!!! that crossing-over has occurred
• in Prophase I, protein complex breaks down and homologs chromosomes start to separate from each other
• BUT!! are held together at the chiasma until Anaphase I

Question 12

metaphase I

Answer 12

• linked homologous pairs line up on either side of the metaphase plate
• their spatial arrangement (which side of metaphse plate) is random and independent of other homologous pairs

Question 13

independent assortment of homologous chromosomes

Answer 13

random arrangement of chromosomes at the metaphase plate, important for genetic variation

Question 14

the possible number of alignments at the metaphase plate formula

Answer 14

2^n, where n=number of chromosomal pairs

Question 15

Anaphase I

Answer 15

• spindle fibres (microtubules contract
• homologous chromosomes separate and move towards poles

Question 16

Telophase I and Cytokinesis I

Answer 16

• nuclear envelope may reform, forming 2 nuclei!!
• Cytokinesis—creates two cells
• the cells are now haploid!!!
  
  • one of each chromosome type
  • combination of maternal and paternal chromosomes
• sister chromatids still attached at centromere

meiosis 1 is compelte

Question 17

MEIOSIS II

Answer 17

• very similar to mitosis!!
  
  • sister chromatids are separating
• but now… the cell is haploid! (if the parent cell was diploid)

Question 18

end product of Meiosis II

Answer 18

• 4 haploid daughter cells
• half the genetic content of the parent cell
• genetically different from each other!!

Question 19

number of possible gamete genotypes formula

Answer 19

2^n
n=number of heterozygous pairs (genes not linked, or linked but crossing over can occur)

Question 20

what affects the probability of crossing-over

Answer 20

• physical distance between genes affects the probability of crossing over
• genes that are far apart = lots of opportunities for crossing-over
• genes that are close together are less likely to cross over
• scientists cannot predict where and when crossing-over will occur

frequency of parental genotypes > increased likelihood of crossing-over

Question 21

sources of GENETIC VARIATION

Answer 21

Crossing-over and recombination
independent assortment of homologous chromosomes
random fusion of eggs and sperm