Cell cycle (meiosis)

Question 1

contain two slightly different copies,
or homologs, of each chromosome, one from
each parent

Answer 1

diploids

Question 2

carrying only a single copy of each
chromosome → gametes

Answer 2

haploid

Question 3

sperm and egg fuse →

Answer 3

zygote

Question 4

reduces the chromosome number by
half

Answer 4

Meiosis

Question 5

duplication of chromosomes

Answer 5

S phase

Question 6

_ successive rounds of chromosome
segregation

Answer 6

two

Question 7

segregate the homologs

Answer 7

meiosis I

Question 8

duplicated paternal and maternal
homologs pair up alongside each other

Answer 8

pair of homologs

Question 9

no further DNA replication;
the sister chromatids pulled apart and
segregated

Answer 9

meiosis II

Question 10

produces four haploid daughter cell
(either maternal or paternal copy)

Answer 10

meiosis II

Question 11

homologs ____each other and
associate ____in order for the
maternal and paternal homologs to be
bi-oriented on the first meiotic spindle

Answer 11

recognize
physically

Question 12

prolonged period; homologs begin
pairing (interactions between pairing
sites)

Answer 12

meiotic prophase (prophase I)

Question 13

four-chromatid structure

Answer 13

bivalent

Question 14

homolog pairs are then locked together
by

Answer 14

homologous recombination

Question 15

the DNA of a chromatid
crosses over to become continuous with
the DNA of a homologous chromatid

Answer 15

crossovers

Question 16

paired homologs are brought into close
______, with their structural axes (axial cores)

Answer 16

juxtaposition

Question 17

assembles on
a double
-strand break in a chromatid,
binds the matching DNA sequence in
the nearby homolog and helps reel in
this partner

Answer 17

recombination complex

Question 18

followed by synapsis

Answer 18

presynaptic alignment

Question 19

axial core of a homolog becomes tightly linked to the axial core of its partner by a closely packed array of transverse filaments

Answer 19

synapsis

Question 20

bridges the gap

Answer 20

synaptonemal complex

Question 21

morphological changes that occur during homolog pairing are the basis
for dividing meiotic prophase into five sequential stages

Answer 21

leptotene, zygotene,
pachytene, diplotene, and diakinesis

Question 22

homologs condense and pair and genetic recombination begins

Answer 22

leptotene

Question 23

synaptonemal complex begins to assemble at sites where the homologs are
closely associated and recombination events are occurring

Answer 23

zygotene

Question 24

assembly process is complete, and the homologs are synapsed along their
entire lengths

Answer 24

pachytene

Question 25

disassembly of the synaptonemal complexes and the concomitant
condensation and shortening of the chromosomes

Answer 25

diplotene

Question 26

segregation of homologs

Answer 26

diakinesis

Question 27

individual crossover events between nonsister chromatids can be seen
as inter-homolog connections called

Answer 27

chiasmata

Question 28

three features of meiosis I that
distinguish it from mitosis

Answer 28

1st: both sister kinetochores in a homolog
must attach stably to the same spindle
pole

2nd: crossovers generate a strong
physical linkage between homologs,
allowing their bi-orientation at the
equator of the spindle

3rd: cohesion is removed in anaphase I
only from chromosome arms and not
from the regions near the centromeres,
where the kinetochores are located

Question 29

Cohesins near the centromeres are protected from separase in meiosis I by
a kinetochore-associated protein called

Answer 29

shugoshin

Question 30

acts by recruiting a protein phosphatase that
removes phosphates from centromeric cohesins.

Answer 30

Shugoshin

Question 31

functions of crossing-over in meiosis

Answer 31

• helps hold homologs together so that they
  are properly segregated to the two
  daughter nuclei produced by meiosis I
• contributes to the genetic diversification
  of the gametes that are eventually
  produced

Question 32

highly regulated

Answer 32

crossing-over

Question 33

each pair of human homologs is linked
by about how many crossovers

Answer 33

two or three

Question 34

DNA is accessible

Answer 34

hot spots

Question 35

heterochromatin regions
(centromeres and telomeres)

Answer 35

cold spots

Question 36

How mamy crossover forms between the
members of each homolog pair

Answer 36

at least one crossover f

Question 37

the presence of
one crossover event inhibits another from
forming close by

Answer 37

crossover interference

Question 38

mistakes can occur in allocating the chromosomes during

Answer 38

meiosis

Question 39

Mistakes are especially common in human female meiosis, which arrests for years after ____: meiosis I is completed only at_____

Answer 39

diplotene
ovulation

Question 40

chromosome
segregation errors during egg development are the most common cause of both

Answer 40

spontaneous abortion (miscarriage) and mental retardation in humans

Question 41

when homologs fail to separate; some of the
resulting haploid gametes lack a particular chromosome, while
others have more than one copy of it

Answer 41

nondisjunction

Question 42

caused by an extra copy of chromosome 21

Answer 42

Down syndrome