19/ developmental genetics 2

Question 1

how many pairs of chromosomes do drosophila have

Answer 1

4 - X,Y, 2, 3, 4

Question 2

Drosophila development timescales

Answer 2

• 0 days after fertilisation - embryonic development
• 1 day after fertilisation - hatching, larva
• 5 days - pupation, pupa
• 9 days - metamorphosis, adult

Question 3

segmentation genes: which are maternal effect genes and which are zygotic genes

Answer 3

• maternal effect: polarity genes (bicoid, nanos)
• zygotic: segmentation genes (gap genes, pair-rule genes, segment polarity genes), homeotic genes

Question 4

maternal effect genes - surprising outcome fertile/sterile example

Answer 4

• GCL - fertile wt, gcl - sterile mutant
• if female is gcl/gcl all her offspring are sterile, doesn’t matter what offspring genotype is
• doesn’t fit with mendelian genetics

Question 5

`how is anterior - posterior polarity determined in the oocyte

Answer 5

• transferred from egg chamber
• differences in cytoplasmic density of oocyte before fertilisation determine polarity
• nurse cells generate certain maternal transcripts that are transported to the unfertilised oocyte

Question 6

bicoid and nanos - maternal genes egg polarity

Answer 6

• bicoid - anterior pole
• nanos - posterior

Question 7

mutations in bicoid and nanos

Answer 7

• bicoid - doesnt make head and thorax (anterior structures)
• nanos - no abdomen segments (posterior structure)

Question 8

when does translation of bicoid and nanos occur

Answer 8

after fertilisation

Question 9

mutations in homeotic genes

Answer 9

• homeotic genes control where body features are
• mutations are conversions of one body part to another, not deletions of the segment
• 2 pairs of wings - 3rd thoracic segment replaced by 2nd, bithorax mutant
• antenna replaced by legs - antennapedia mutant

Question 10

homeotic genes are homeodomain transcription factors - elaborate

Answer 10

• homeotic genes contain 180bp homeobox sequence
• encodes 60aa homedomain DNA binding domain
• regulate genes that specify tissue/organ primordia
• not all homeobox containing genes are homeotic genes and vice versa

Question 11

what human condition does mutations in HoxD13 give rise to

Answer 11

• syndactyly
• 2 or more digits fused together

Question 12

homeotic mutations in plants

Answer 12

• wt: sepals, petal, stamen, carpel
• apetala1: carpels, stamen
• pistillata: sepals, carpels
• agamous: sepals, petals
• in each mutant only 2 organs remained , mutation in 1 homeotic gene causes transformation of 2 organ types - conversion not deletion

Question 13

how many hox clusters do mice and humans have

Answer 13

• 4
• Hox A-D

Question 14

how are homeotic genes grouped in drosophila

Answer 14

• arranged in 2 clusters, collectively the Hom-C cluster
• antennapedia and bithorax