Cell division and inheritance

Question 1

What are the stages of the cell cycle?

Answer 1

• G1: cellular contents excluding chromosomes replicated
• G0: cell cycle arrest- resting phase or apoptosis
• S: dna replication, each of 46 chromosomes duplicated
• G2: cell double checks duplicated chromosomes for error and changes if needed
• Mitosis
• Cytokinesis

Question 2

What are the stages of mitosis?

Answer 2

• prophase
• prometaphase
• metaphase
• anaphase
• telophase
• cytokinesis (controversial)

Question 3

What happens in prophase?

Answer 3

• Duplicated chromosomes condense and sister chromatids join at centromere
• DNA binding proteins including cohesin and condensin
• cohesin forms rings that hold sister chromatids together
• condensin forms rings that coil the chromosomes into highly compact forms
• the mitotic spindle begins to develop and centrosomes move towards opposite poles, microtubules assemble

Question 4

What happens in prometaphase?

Answer 4

• Nuclear membrane breaks down, forms multiple vesicles
• Spindle microtubules can now directly access genetic material
• Spindle microtubules attach to chromatids (kinetochore of each chromosome)

Question 5

What happens in metaphase?

Answer 5

• Microtubules shuffle chromosomes to form metaphase plate- to line them up
• Once tension becomes balanced chromosomes stop moving (spindle completed)

Question 6

What are the three groups of spindle microtubules and their role?

Answer 6

• Kinetochore microtubule: attach the chromosomes to the spindle pole
• Interpolar microtubule: extend from the spindle pole across the equator, almost to opposite spindle pole
• Astral microtubule: extend from spindle pole to cell membrane

Question 7

What happens during anaphase?

Answer 7

• enzymatic breakdown of cohesin separates chromatids, changes in microtubule length exert pull on chromosomes
1) anaphase A: the kinetochore microtubules shorter and pull chromosomes toward spindle poles
2) anaphase B: astral microtubule anchored to cell membrane pull poles further apart, interpolar microtubules slide past each other and increases pull on chromosomes more

Question 8

What happens during telophase?

Answer 8

• Chromosomes arrive at the cell poles
- vesicles containing fragments of original nuclear membrane form around two new nuclei
• the spindle microtubules depolymerise

Question 9

How does meiosis differ from mitosis?

Answer 9

• two divisions
- meiosis 1- reduction division
- meiosis 2- equatorial division

• similar stages to mitosis however:
- dna replication occurs twice
- nuclear division occurs twice

• results in 4 haploid (n) daughter cells- each contain half the nunver of chromosomes of the diploid (2n) parent cell

• occurs in germline cells only

Question 10

What happens in prophase 1 in meiosis

Answer 10

• Homologous chromosomes pair up
• Synapsis occurs (crossing over), genetic material swaps at chiasmata increasing variation

Question 11

What happens in metaphase 1 and anaphase 1 in meiosis?

Answer 11

(same as mitosis but with following differences:)

• homologous pairs line up on the metaphase plate
• the homologous pairs split, homologous chromosomes are separated to the poles at anaphase, not individual chomatids

Question 12

What happens during telophase 1 in meiosis?

Answer 12

similar to mitosis however cells may not fully separate (species dependent)

• DNA does not decondense prior to entering meiosis 2
• no DNA replication

Question 13

What happens during prophase 2 in meiosis?

Answer 13

• chromosomes condense
• new set of spindle fibres form at right angles to og chromosomes begin moving toward equator of cell
• nuclear envelop disintegrates

Question 14

What happens during metaphase 2, anaphase 2 and telophase 2 in meiosis?

Answer 14

progress as before but result in 4 genetically non identical haploid daughter cells

Question 15

what happens during cytokinesis?

Answer 15

cytoplasm divides

Question 16

Define unit heritance

Answer 16

Hereditary characters are determined by indivisible units of information (alleles of genes)

Question 17

define dominance

Answer 17

alleles occur in pairs in each individual but the effects of one allele may be masked by those of a dominant partner allele

Question 18

define segregation

Answer 18

during formation of gametes, the members of each pair of alleles separate so that each gamete carries only one allele of each pair. alleles pairs are restored at fertilisation

Question 19

define independent assortment

Answer 19

different genes control phenotypic characters and the alleles of different genes re assort independently from
one another

Question 20

What is the ratio monohybrid cross? (BB x bb)

Answer 20

1- all offspring have Bb so same characteristic

Question 21

What is the ratio monohybrid cross?
(Bb x Bb)

Answer 21

3:1

Question 22

what is the ratio in dihybrid cross?
(TtBb x TtBb)

Answer 22

9:3:3:1

Question 23

What happens in x linked dominant inheritance? X^A

Answer 23

• If only mother carries: Half of all children affected regardless of gender
• If only father carries: all daughters affected, all sons unaffected
• If both carries: all daughters affected, 50% sons unaffected

Question 24

What happens in x linked recessive inheritance ? X^a

Answer 24

• only mother: 50% females carrier, 50% females unaffected, 50% males affected

• only father: all females carriers, all males unaffected

• both: 50% females carriers, 50% males affected

Question 25

Who is affected by mitochondrial inheritance?

Answer 25

Only passed down through mothers.

Affected fathers do not pass to offspring

Question 26

What is complete dominance between alleles

Answer 26

Allele completely masks recessive allele in heterozygote

Question 27

what is incomplete/partial dominance in alleles?

Answer 27

Heterozygote phenotype is intermediate between that of two homozygous (eg sickle cell)

Question 28

what is co dominance between alleles?

Answer 28

neither allele is recessive and phenotypes of both alleles are expressed eg blood groups

Question 29

What is penetrance?

Answer 29

the proportion of individuals in a population who carry a specific gene and express the related trait

the relationship between a genotype and phenotype

Question 30

what is expressivity?

Answer 30

the degree to which train expression differs among individuals, unlike penetrance, expressivity describes individual variability, not statistical variability among a population of genotypes