Lecture 5

Question 1

Drosophila melanogaster is a segmented animal, T or F

Answer 1

T

Question 2

The genome of Drosophila has been sequenced, T or F

Answer 2

T

Question 3

Drosophila can regulate their own body temperature, T or F

Answer 3

F – they cannot

Question 4

What two temperatures are stocks of Drosophila kept

Answer 4

18 and 25°C

Question 5

Which temperature stocks tend to have a lifecycle of around 10 days

Answer 5

25°C stocks

Question 6

Which temperature stocks tend to have a longer life cycle of upwards of 21 days

Answer 6

18°C stocks

Question 7

How much time elapses from laying of a fertilised Drosophila egg to hatching

Answer 7

24 hours

Question 8

Briefly outline Thomas Hunt-Morgan’s contribution to Drosophila research

Answer 8

Hunt-Morgan noticed a white-eyed fly in his lab one day. He bred this fly with wild type flies to investigate the phenotypes produced

Question 9

What was Sturtevants contribution to Drosophila research

Answer 9

Constructed the first genetic map and arranged it in a linear order

Question 10

Bridges showed that chromosomes must contains genes, T or F

Answer 10

T

Question 11

Muller showed that radiowaves caused mutations and chromosomal rearrangements, T or F

Answer 11

F – he showed that X-rays caused mutations

Question 12

Outline Nusslein-Volhard and Wischuas contribution to Drosophila research

Answer 12

Carried out a saturation mutagenesis to identify genes in Drosophila involved in development and patterning. This was an absolutely massive screen and lead to the identification of 139 complementation groups

Question 13

Describe the general arrangement of the Drosophila genome

Answer 13

4 chromosomes consisting of 3 autosomes and 1 sex chromosome. Roughly 17,000-18,000 genes, 14,000 of which code for proteins

Question 14

What was seen as a result of alignment of homologous sequences of genes between Drosophila and other organisms

Answer 14

The protein encoding exons were almost perfectly conserved. The non-coding introns were seen to only be randomly conserved and showed differences between organisms most likely due to not being under any selection pressures. Regulatory sequences in the genes also showed high levels of conservation between species

Question 15

Drosophila can produce 200 progeny in less than 2 weeks, T or F

Answer 15

T

Question 16

Put these Drosophila courtship processes in order, orientation, licking, attempted copulation, tapping, wing vibration

Answer 16

Orientation, tapping, wing vibration, licking, attempted copulation

Question 17

Female Drosophila mate several times in their life cycle while males mate only once, T or F

Answer 17

F – vice versa

Question 18

The strongest Drosophila reproducible behaviour is genetically encoded, T or F

Answer 18

T

Question 19

Outline spermatogenesis in Drosophila

Answer 19

The testes located within the abdomen on the male contain hub cells. These cells secrete factors such as unpaired which maintains stem cell fates in the cells adjacent to the hub. Unpaired is a JAK/STAT ligand and its signalling decreases with distance from the hub. Cells further away from the hub differentiate due to decreased levels of unpaired signalling. These cells divide and give rise to 64 sperm cells

Question 20

What is remarkable about sperm produced by male Drosophila

Answer 20

Spermatids are 25x the length of the adult Drosophila body

Question 21

Explain the interplay between the sexual evolution of male and female Drosophila

Answer 21

The sperm produced by male Drosophila is coated in a sex peptide. This binds to receptors in the brain of female Drosophila and prevents them from being able to respond to subsequent courtship dances by other males. This increases the likelihood of the males passing on their genetic information. However, females evolved the ability to repress the effects of the sex peptide. This caused the males to evolve and produce larger and larger sperm coated in more and more sex peptide to try and increase the females inability to respond to other courtship dances.

Question 22

Outline the process of oogenesis in Drosophila

Answer 22

Stem cells are maintained at one end of the bundled linear structures that make up the ovaries. Cells in the ovaries undergo 4 incomplete cytoblast mitotic divisions. Most cells become nurse cells which undergo endoreduplication making multiple copies of the genome and expressing a huge amount mRNA that supplies the oocyte with the genetic information to synthesise proteins etc. The cells that go on to form oocytes do so by undergoing meiosis to produce cells containing mostly cytoplasm.

Question 23

What is meant by cytoplasmic dumping and how does this occur

Answer 23

The nurse cells that supply the developing oocyte contain massive amounts of genetic information and are transcribing a vast amount of mRNA. This mRNA is then deposited through ring canals into the cytoplasm of the oocyte so that it can synthesise useful products.

Question 24

Explain how polytene chromosomes are produced and what they represent

Answer 24

Polytene chromosomes are chromosomes stained for polymerase activity. Bands represent regions of the genome where there is little activity. Interband regions contain puffs which represent extremely active and transcribed genes.

Question 25

Explain how some polarity is established in the oocyte even before fertilisation

Answer 25

Some of the factors deposited by the nurse cells through cytoplasmic dumping become localised (i.e. through gravity and other mechanisms). This localisation of factors accounts for the inherent polarity of Drosophila oocytes

Question 26

Describe some of the features of the Drosophila egg

Answer 26

Chorion acts as the eggshell surrounding the embryo. The vitelline membrane lies beneath the chorion and provides waterproofing. The micropyle located at one end of the egg is the opening through which sperm enter.

Question 27

Describe what is meant by a syncytial blastoderm and how this is achieved in the Drosophila embryo

Answer 27

Syncytium is a multinucleate cell. This is achieved in Drosophila through nuclei duplication in the centre and then migration to the periphery. After 14 rounds of nuclei duplication and after they have relocated to the edges of the embryo the cell membrane moves in and encapsulated the nuclei creating a cellular blastoderm.

Question 28

What happens to the cells that are retained in the centre of the embryo before cellularisation

Answer 28

These become pole cells and give rise to the gametes and gonads of the adult organisms