Topic 1: Chromosomes and Cell Cycles

Question 1

What is the n-value?

Answer 1

number of chromosomes and it’s ploidy

diploid cells carry two sets of genetic information

haploid cells carry one set of genetic information

Question 2

What is the c-value or genome size?

Answer 2

actual amount of DNA in the haploid cell

measured in picograms (c-value) or bp (genome size)

Question 3

What is the number of genes?

Answer 3

function of the DNA in the cell

Question 4

What are homologous pairs?

Answer 4

same genes in the same order

might have different alleles of genes

Question 5

What are the conversion rates of base pairs?

Answer 5

bp = base pairs
kb = kilo base pairs = 1000
Mb = mega = 1 million bps
gb = giga bps = 1 billion bps

Question 6

What is the c-value paradox?

Answer 6

the size of the genome doesn’t tell you anything about the organisms complexity

Question 7

What is non-gene DNA comprised of?

Answer 7

unique sequence DNA: present one or a few times

protein coding genes + families

non-protein coding genes/DNA (code for functional RNAs, e.g. tRNA and rRNA)

repetitive DNA

centromeres: moderately repetitive, tandemly repeating

telomeres: 6 bp repeats, tandem

Question 8

What is moderately repetitive DNA?

Answer 8

150-300 bps

found in many different places in the genome

transposons

Question 9

What is highly repetitive DNA?

Answer 9

less than 10 bps

microsats

Question 10

What are centrosomes?

Answer 10

constricted region of a chromosome where spindle fibers attach

moderately repetitive DNA in heterochromatin form

Question 11

What are telomeres?

Answer 11

repetitive sequence at the end of linear chromosomes

solves end replication problem

provides stability

Question 12

What is the T-loop?

Answer 12

G-rich strand folds over and pairs with a short stretch of DNA

found in mammals, provides stability

Question 13

What is the G0 phase of the cell cycle?

Answer 13

stable, nondividing period of variable length

Question 14

What is the G1 phase of the cell cycle?

Answer 14

growth and development of the cell

G1/S checkpoint

Question 15

What is the S phase of the cell cycle?

Answer 15

synthesis of DNA

Question 16

What is the G2 phase of the cell cycle?

Answer 16

preparation for division

G2/M checkpoint

Question 17

What is prophase in the cell cycle?

Answer 17

chromosomes condense and mitotic spindles form

Question 18

What is prometaphase in the cell cycle?

Answer 18

nuclear envelope disintegrates, and spindle microtubules anchor to kinetochores

Question 19

What is metaphase in the cell cycle?

Answer 19

chromosomes align on the metaphase plate

spindle-assembly checkpoint

Question 20

What is anaphase in the cell cycle?

Answer 20

sister chromatids separate, becoming individual chromosomes that migrate toward spindle poles

Question 21

What is telophase in the cell cycle?

Answer 21

chromosomes arrive at the spindle poles

the nuclear envelope re-forms

condensed chromosomes relax

Question 22

What is cytokinesis in the cell cycle?

Answer 22

cytoplasm divides

cell wall forms in plant cells

Question 23

What are the genetic consequences of the mitotic cell cycle?

Answer 23

produces two cells that are genetically identical (to each other and parent)

new cells contain full complement of chromosomes (2n –> 2n)

each new cell contains half the cytoplasm of parent cell

Question 24

How does the n-value change during the mitotic cell cycle?

Answer 24

2n = 4 in interphase all the way to anaphase where it briefly becomes 2n = 8

returned to 2n = 4 in telophase and cytokinesis

Question 25

How does the c-value change during the mitotic cell cycle?

Answer 25

of DNA strands is 4 until S phase where it doubles to 8 stays at 8 until anaphase where it gradually transitions back to 4 in telophase and cytokinesis

Question 26

What is meiosis?

Answer 26

haploid gametes are produced (2n --> n)

Question 27

What is fertilization?

Answer 27

fusion of two haploid cells (n --> 2n)

Question 28

What is genetic variation?

Answer 28

a consequence of meiosis

Question 29

What is interphase in meiosis?

Answer 29

same as mitosis (G1, S, G2)

Question 30

What is meiosis I?

Answer 30

separation of homologous chromosome pairs reduction division 2n --> n metaphase plate homologs line up

Question 31

What is meiosis II?

Answer 31

separation of sister chromatids equational division n --> n no change in ploidy, same as mitosis

Question 32

What are the three processes that occur in prophase I?

Answer 32

synapsis tetrad crossing over

Question 33

What is synapsis?

Answer 33

close pairing of homologous chromosomes process of the pairing (the verb)

Question 34

What is a tetrad?

Answer 34

the pair of homologous chromosomes connected with each other synaped chromosomes (the noun)

Question 35

What is crossing over?

Answer 35

exchange of genetic material between homologous chromosomes

Question 36

What happens in middle prophase I?

Answer 36

chromosomes condensing centrosomes connecting

Question 37

What happens in late prophase I?

Answer 37

homologs pairing synapsis happens forming tetrads chiasmata form crossing over happens

Question 38

What happens in metaphase I?

Answer 38

tetrads line up on metaphase plate

Question 39

What happens in anaphase I?

Answer 39

separation of homologous chromosomes chromosomes segregate independently (chromosome shuffle)

Question 40

What is interkinesis?

Answer 40

stage between meiosis I and meiosis II

Question 41

How does the separation of sister chromatids and homologous chromosomes occur?

Answer 41

tubulin subunits both separations happen because of spindle action the tubules grow and shrink via polymerization and depolymerization

Question 42

What is cohesion?

Answer 42

ring-like heterotrimer separase cleaves it in anaphase

Question 43

What is the shugoshin?

Answer 43

protects cohesion from separase add to cohesion near centromeres

Question 44

What happens in prophase I?

Answer 44

chromosomes condense homologous chromosomes synapse crossing over takes place the nuclear envelope breaks down the mitotic spindle forms

Question 45

What are the consequences of meiosis and genetic variation?

Answer 45

four cells are produced from each original cell chromosome number: reduced by half, diploid --> haploid, 2n --> n newly formed cells from meiosis are genetically different from one another and from the parental cell genetic variation resulting from independent segregation of chromosomes, there are 4 possible alignments at metaphase I, gives a shuffling of maternal and parental chromosomes genetic variation resulting from recombination via crossing over, shuffling of alleles chiasmata: crossing over event, aka recombination

Question 46

How does the n-value change during meiosis?

Answer 46

is 2n until dropping to n after meiosis I stays n after meiosis II is completed

Question 47

How does the c-value change during meiosis?

Answer 47

of DNA strands doubles during S phase starts declining at the start of meiosis I and eventually decreases to half of what it started with by the end of meiosis II

Question 48

What is the overall process of mitosis?

Answer 48

cell division: yes reduction in chromosome number: no genetic variation produced: no crossing over: no random distribution of maternal and paternal chromosomes: no metaphase: individual chromosomes line up anaphase: chromatids separate

Question 49

What is the overall process of meiosis I?

Answer 49

cell division: yes reduction in chromosome number: yes genetic variation produced: yes crossing over: yes random distribution of maternal and paternal chromosomes: yes metaphase: homologous pairs line up anaphase: homologous chromosomes separate

Question 50

What is the overall process of meiosis II?

Answer 50

cell division: yes reduction in chromosome number: no genetic variation produced: no crossing over: no random distribution of maternal and paternal chromosomes: no metaphase: individual chromosomes line up anaphase: chromatids separate