10 Genetics (HL)

Question 1

In which stage of interphase is DNA replicated?

Answer 1

S phase
Producing two identical sister chromatids

Question 2

When are sister chromatids separated (meiosis)?

Answer 2

Meiosis II

Question 3

When are homologous chromosomes separated (meiosis)?

Answer 3

Meiosis I

Question 4

What are the stages of Meiosis I?

Answer 4

Prophase I - chromosomes condense, nuclear membrane dissolves and crossing over occurs
Metaphase I - spindle fibres from centrosomes connect to bivalents (at centromere) and allign them in the middle of the cell
Anaphase I - spindle fibres contract and split the bivalent, homologous chromosomes are moved to opposite poles
Telophase I - chromosomes decondense, nuclear membrane may reform, cell divides to form two haploid daughter cells

Question 5

What are the stages of Meiosis II?

Answer 5

Prophase II - chromosomes condense, nuclear membrane dissolves centrosome move to perpendicular from before
Metaphase II - spindle fibres attach to centromere and line up chromosome on the equator
Anaphase II - spindle fibres contract, separating sister chromatids which move to the poles
Telophase II - chromosomes decondense, nuclear membrane reforms, cells divide into 4 haploid daughter cells

Question 6

Define chiasmata

Answer 6

X shaped points of attachment between two non-sister chromatids - crossing over

Question 7

When does crossing over occur (meiosis)?

Answer 7

Prophase I

Question 8

What name is given to a daughter chromosome which underwent crossing over?

Answer 8

Recombinant

Question 9

Define linked genes

Answer 9

Genes whose loci are on the same chromosome and hence don’t independently assort

Question 10

How may the linked genes (AaBb) be represented?

Answer 10

AB
ab

Question 11

Define recombinants of linked genes

Answer 11

Combination of linked genes not found in parents

Question 12

What is the expected ratio for a dihybrid cross of unlinked traits?

Answer 12

9:3:3:1

Question 13

Define monogenic traits

Answer 13

Characteristics controlled by a single gene loci (tend to be discrete)

Question 14

Define polygenetic traits

Answer 14

Characteristics controlled by more than two gene loci (tend to be continuous)

Question 15

Which 5 processes can lead to a change in allele frequency in a population?

Answer 15

Mutation
Gene flow (immigration/emigration)
Sexual reproduction
Genetic drift (chance/random event)
Natural selection (environmental pressure)

Question 16

Define genetic drift

Answer 16

When a change in the composition of a gene pool occurs due to a random event or by chance

Question 17

What are the two mechanisms by which population change may occur?

Answer 17

Population bottlenecks and the founder effect

Question 18

What is a population bottleneck?

Answer 18

When an event reduces the population by an order of magnitude (~>50%)
The smaller population has less genetic variability and will be subject to a higher level of genetic drift

Question 19

What is the founder effect?

Answer 19

When a small group breaks away from a larger group to colonise a new territory
There will be less genetic variation in this founder group and thus higher genetic drift

Question 20

What are the three types of selection?

Answer 20

Stabilising
Directional
Disruptive

Question 21

Describe stabilising selection

Answer 21

Where an intermediate phenotype is favoured at expense of both phenotypic extremes (removal of extremes)
Operates when env conditions are stable and comp is low

Question 22

Describe a stabilising selection distribution curve

Answer 22

Gets thinned and taller from the middle out

Question 23

Describe directional selection

Answer 23

Where one phenotypic extreme is selected at the cost of the other in response to gradual or sustained environmental change (usually followed by stabilising selection)

Question 24

Describe a directional selection distribution curve

Answer 24

Shifts either far right or left

Question 25

Describe disruptive selection

Answer 25

Both phenotypic extremes are selected for at the expense of the intermediate when fluctuating conditions favour the presence of two phenotypes
Can eventually lead to speciation

Question 26

Describe a disruptive selection distribution curve

Answer 26

Central distribution decreases for two peaks on either side of it

Question 27

What are the two types of reproductive barriers?

Answer 27

Prezygotic isolation
Postzygotic isolation

Question 28

Give examples of prezygotic isolation

Answer 28

Temporal
Behavioural
Geographical/ecological
Mechanical

Question 29

Give examples of postzygotic isolation

Answer 29

Inviability
Infertility
Breakdown is hybrid organisms

Question 30

What are the two types of speciation?

Answer 30

Allopatric (geographical isolation)
Sympatric (reproductive isolation)

Question 31

What is the most common cause of sympatric speciation?

Answer 31

Meiotic failure that makes reproduction no longer viable (plants may still clone despite this and therefore this is more common amongst plants)

Question 32

What are the two methods for speciation?

Answer 32

Phyletic gradualism
Punctuated equilibrium

Question 33

Describe phyletic gradualism

Answer 33

Speciation occurs uniformly, steadily and gradually (many intermediate forms)

Question 34

Describe punctuated equilibrium

Answer 34

Species remain stable for long periods before undergoing rapid change (speciation)
Sudden big changes