Meiosis

Question 1

diploid and haploid:

Answer 1

• diploid 2n (2 sets of chromosomes)

- haploid n (one set)

Question 2

somatic cells in humans:

Answer 2

• 23 pairs
• numbered by size
• only X and Y not paired

Question 3

paired chromosomes vs sister chromatids:

Answer 3

• paired homologous duplicated chromosomes: similar but from different parents
• sister chromatids: exact same copy joined by centromere

Question 4

meiosis general pathway:

Answer 4

• 2 cell divisions
• meiosis I and meiosis II
• 4 daughter cells
  which have only half chromosomes of parent (n)

Question 5

meiosis I:

Answer 5

• homologous chromosomes separate

- results in 2 haploid daughter cells w replicated chromosomes

Question 6

meiosis II:

Answer 6

• sister chromatids separate

- results in 4 haploid daughter cells

Question 7

stages of meiosis I:

Answer 7

• prophase I
• metaphase I
• anaphase I
• telophase I
• cytokinesis

Question 8

stages of meiosis II:

Answer 8

• prophase II
• metaphase II
• anaphase II
• telophase II
• cytokinesis

Question 9

daughter cells of meiosis:

Answer 9

• each genetically different from each other/ parent cell

- haploid set of chromosomes

Question 10

result of meiosis I:

Answer 10

• 2 haploid cells

- chromosomes have sister chromatids (replicated)

Question 11

result of meiosis II:

Answer 11

• 4 haploid daughter cells

- un-replicated chromosomes

Question 12

differences btw mitosis and meiosis:

Answer 12

• chiasma: pair of duplicated homologous chromosomes attached
• during metaphase I will line up together
• homologs separated in telophase I
• all different genetic material in 4 daughter haploid cells

Question 13

crossing over:

Answer 13

• recombination
• parents DNA shuffled
• approx 50% from each parent

Question 14

homology:

Answer 14

• similarities in DNA sequences due to common ancestry

- same genes in same regions of chromosome

Question 15

homologous recombination:

Answer 15

• paternal and maternal chromosomes line up
• chiasmata forms at regions of homology
• segments of DNA are exchanged

Question 16

euploid:

Answer 16

having equal number of all chromosomes of haploid set

Question 17

aneuploid:

Answer 17

having different number of chromosomes than is usual

Question 18

when does aneuploid happen:

Answer 18

• error is meiosis
• most cases: miscarriage
• 1 in 160 babies
• 21, 18, 13

Question 19

origins of genetic variation:

Answer 19

• behaviour of chromosomes in meiosis and fertilisation responsible for variation of each generation

Question 20

mechanisms contributing: genetic variation

Answer 20

• independent assortment of chromosomes
• crossing over
• random fertilisation
• mutation (usually harmful)

Question 21

independent assortment of chromosomes:

Answer 21

• each pair of chromosomes sorts maternal/parternal homologues into daughter cells independently of other pairs
• n= 23, 8 million combos

Question 22

crossing over:

Answer 22

• recombinant chromosomes
• early in prophase I
• homologs pair up gene by gene (synapsis)
• homologous portions of non sis chromatids trade places

Question 23

random fertilisation:

Answer 23

• any sperm can fuse with any ovum

- zygote 70 trillion diploid combos

Question 24

autosomes:

Answer 24

• carry same series of genes along their length
• each one may carry slightly altered version (alleles)
• so cells may carry two alleles of same gene

Question 25

cystic fibrosis:

Answer 25

• recessive disease
• mutant allele of gene CFTR, chromosome 7
• normal CFTR protein (wild type) controls movement of chloride ions across membranes of cells in gut/ lungs/ pancreas/ liver
• mutant allele deletion of 1 amino acid:
• excess mucous production blocks ducts (eg. bronchioles)
• most patients die from lung infections

Question 26

cons of sexual reproduction:

Answer 26

• significant investment of time and energy (mating, producing gametes)
• slower than asexual
• risk STDs
• random mixing may have suboptimal results