EB19

Question 1

What is Mendalian inheritance

Answer 1

all else being equal the gene frequency will not change, two gene copies from mother and father.
fast majority of genes transmitted this way.

Question 2

What is gene drive

Answer 2

process of preferential inheritance (no longer 50/50)

- lead to spread in population (all else being equal).

Question 3

what kind of genes usually spread by NS and what can by drive

Answer 3

norally by NS only genes that increase survival of carriers

gene drive can increase spread of deleterious genes = selfish genetic elements.

Question 4

What are free ways to drive?

Answer 4

killing competition
over replication
directed towards germline

Question 5

what are 7 examples of killing competition in gene drive

Answer 5

1. T-haplotype in mice
2. Segregation distorter in Drosophila
3. Spore Killer in fungi
4. Driving sex chromosome in dipterans
5. Feminizing X chromosome in Lemmings
6. Cytoplasmic male sterility
7. Androgenesis

Question 6

Describe gene drive of T-haplotype in mice

Answer 6

1. two variants T-haplotype and WT.
2. T-haplotype 90% inheritance through males
3. In heterozygote WT sperm has dysfunctional glagella and or acrosome structure at tend of sperm releasing enzymes preventing penetration and fusion with egg. = most fertilisation by T-haplotype.
4. lethal recessive homozygote so only present at 5% in natural populations

Question 7

what is the T-haplotype

Answer 7

30-40mb on the 17th chromsoome and is inherited as a unit. contains 4 inversions wrt WT preventing recombination between the,

Question 8

how long has the t-haplotype been present in mice

Answer 8

3 million years resisting selection due to preferential inheritance

Question 9

Describe Segregation distorter SD in drosophila

Answer 9

1. Transitted 95-99% in males
2. WT SD heterozygote, WT shows failures in chromatin condensation compared to SD sperm.
   * molec mech unknown.
3. lethal recessive homoxugote SD so present 1-5% in natural populations

Question 10

Describe spore killer in fungi (ascomycete)

Answer 10

1. spore killer heterozygote creates 4 viable containing spore killer and 4 WT inviable spores.

Question 11

describe spore formation in fungi

Answer 11

haploid hyphae mate to make breif diploid which goes through meiosis to make haploid spores, fruiting bodies associated with mating event.
four meiotic products each of which goes through a single mitotis = 8 products.

Question 12

Describe driving sex chromsoome in dipterans

Answer 12

1. Drosophia: Sperm with Y chromosomes chromatin does not undergo proper condensation and is incapacitated
2. Y drive in some mosquito, incapacitates X
   * could potentially eliminate population - no known examples.

Question 13

Describe the feminizing X chromosome in Lemmings

Answer 13

Dominant feminizer causes female development even in presence of Y. X therefore gets 67% transmission.

Question 14

What organisms can cytoplasmic male sterility be found in

Answer 14

descrbed in >140spp. in 20 families inc. plantago lancelota flowers

Question 15

Describe cytplasmic male sterility

Answer 15

mitochondrial mutations convert hermaphrodites to females.

1. mitochondrial only inherited through ovule not pollen
2. pollen production irrelevant to mitocondndiral genes.
3. cytoplasmic (mt genes) cause male sterility`

Question 16

What organisms does androgenesis occur in

Answer 16

cyprus tree, fresh water plant and stick insect.

Question 17

Describe androgenesis

Answer 17

Both copies of the gene are inherited from the father (mother genetics not included), despite the fact the mother is producing the main nutrients.
Sperm/pollen kick out chromosome from egg so progeny only has pollen/sperm genes

Question 18

give 4 examples of over replication driving gene drive

Answer 18

1. transposable elements: Class 1: retrotransposons
2. transposable elements: class 11, DNA transposons
3. Variegated flower transposons
4. rapid spread of P elements in Drosophila

Question 19

What are the three class 1 retrotransposons

Answer 19

LTRs encode reverse transcriptase
LINES encode reverse transcriptase, transcribed by RNAP-11
SINES dont encode RT and transcribed by RNAP11

Question 20

describe replication of retrotranspsosons class 1

Answer 20

e.g. LINE is transcribed from DNA to RNA and then the RNA produced is reverse transcribed to DNA, this copied DNA is then inserted back into the genome at a new position.
allows element to increase in abundance over genome and over generations allowing increase in abundance over time.
e.g. ALU element SINE

Question 21

Describe how DNA class 2 transposons drive

Answer 21

cut and paste mechanism, doesnt involve RNA intermediate, catalysed by tranposase enzymes
Transposase enzyme binds to target site at end of transposable element, dimerises and excises the tranposable element with the tranposase atttached, finds another site of DNA causes staggered cut and inserts new transposon via DNAP and DNA ligase.

Question 22

how do DNA class 2 tranpososons increase in copy no.

Answer 22

Preferentially right after replication, tranposase is activated, cuts out transposon and inserts it inot unreplicated DNA ahead of the replication fork.
So DNA replication, means sister chromatid get an extra copy.
preferential movement from replicated to non-replicated means replication fork moves through it twice, increasing copy no.

Question 23

give an exmplae of DNA class 2 tranpososon

Answer 23

AC element in maize

Question 24

Given an example of a common transposon

Answer 24

variegated flowers

• element is inserted into pigment gene of the flower, if it jumps out during development, the flower can restore pigment production.
• when it jumps out and how active it is gives different patterns.

Question 25

describe the spread of the P element in drosophia

Answer 25

rapid spread of P elements; transposable element within drosophila during the 20th century P elements managed to spread through D melanogaster populations more recently collected more likely to have p element.

Question 26

what effect does p element have on drosophila

Answer 26

high p element activity creates vestigal ovaries and testes leading to sterility. viability of a population decreases with no. of p elements.

Question 27

what do site occupancy profiles of p elements show and how are they foWa

Answer 27

polytene chromosomes in the salivary gland can be probed to show where P elements are on the chromosome. 1. natural populations show p element is scattered along chromsoome, expect this if they are causing harm. 2. however sigh at tip of chromosome has been found in high frequency whichi suggests natural selection: found to be a mutant that acts as a suppressor of P element activity. Defective P element suppresses activity of WT P-element.

Question 28

What are the two examples of drive via gonotaxis *directing to germline

Answer 28

1. Knobs of Maize | 2. B chromosome in rye

Question 29

what is gonotaxis

Answer 29

In the zygote not all cells will be passed on, e.g. become germ cells. some will be somatic, gonataxis preferentially move to cell that will become germ rather than somatic

Question 30

describe knobs of maize drive

Answer 30

1. Chromosome 10 have knobs causing dark staining. 2. when cell undergoes meiosis to make ovules. heterozygote have AB10 *abnormal with knob and WT 3. crossing over occurs between the two sets of chromatids, so normal knob is swapped with abnormal. 4. at the first meiotic division the knob has centromeric activity and attached to spindle, so chromosome with knob is closer to pole. 5. second division sister chromatids are cut in two. 6. four meiotic cells produced, outside ones typically have knobs, typically only 1 is viable and in vast maj. of plants one on the outside is chosen to be the ovule.

Question 31

Describe formation of sperm cells in Rye

Answer 31

1. meiosis makes haploid meotic products in males which are all viable 2. in pollen grain products go through mitosis again, one cell becomes pollen tube (somatic) other gives rise to generative nucleus to make two sperm cells: one fertilises to make embryo and one makes endosperm.

Question 32

describe B-chromosome drive in Rye

Answer 32

1. B chromosome found in some individuals (non-essential may be absent or multiple copies) 2. first mitosis in pollen grain, chromatids at cell dvision stick together and preferentially go towards pole giving rise to generative nucleus (not tube nucleus). 3. transmitted two copies in next generation as opposed to one copy. 4. allows increase in abundance in the next generation.

Question 33

What is drive most effective in

Answer 33

outcrossed sexually reproducing populations, less effective in inbred selfing populations in inbred species, normally only 1% as common as they would normally be, so takes 100x as long to spread through a population.

Question 34

what is the B chromosome in British plants

Answer 34

more common in outcrossed than mixed and selfing, mixed species have a slightly higher percentage of B chromosome than selfing.

Question 35

What effect do selfish genes have on host genes

Answer 35

many have a cost against host genes. so the spread of these genes selects for other genes that suppress the selfish gene *in nature often find suppressors for many selfish genes. e.g. in drosophila driving x chromosome.