Topic 13 Genetics Of Development

Question 1

What are homeotic mutants

Answer 1

Mutant where one part of the body is transformed to another part

Ex. Antenaane turned into leg

Question 2

What is the anteropostetier axis

Answer 2

Anterior and posterior ends of the fly

Question 3

What is the fruit fly made up of

Answer 3

Head thorax abdomen

Question 4

What is a morphogen

Answer 4

A molecule whose effects are concentration dependent

This molecule establishes the pattern of tissue development and body plan formation

Question 5

What are hox genes

Answer 5

They are transcription factors that control the identity (arm,leg) of segments in the body

They as well as genes that encode regulators of hox genes make up the toolkit genes

Hox genes are similar throughout diff animal

Question 6

What do morphogen gradients determine

Answer 6

Hox gene expression

Question 7

What is meant by toolkit genes being expressed differently through space and time?

Answer 7

Space: some Expressed in the anterior/posterior

Time: some expressed earlier/later in life

Question 8

What are the five classes of toolkit genes that are involved in regulating the anteroposteir axis in fruit flies

Answer 8

1. Maternal effect genes
2. Gap genes
3. Pair rule genes
4. Segment polarity genes
5. Hox genes

In order of time they are expressed

Question 9

What are maternal effect genes

Answer 9

Genes expressed in the mother, these genes are needed before fertilization

After fertilization the genes are expressed and make a gradient

Determine anterior and posterior axes

The phenotypes of the offspring only depends on the genotype of the egg it came from. If m/m but came from m/+, phenotype is wt

Only expressed in the mother

Question 10

What are names of maternal effect genes, what are they

Answer 10

Bicoid (attached to anterior end of developing egg) nanos (posterior end of developing egg)

They are transcription factors that regulate expression of the next set of genes in the toolbox (gap genes)

Question 11

What are gap genes give example

Answer 11

They divide the embryo into broad regions

Example: kruppel which is expressed in middle of the embryo

If mutated, anterior segments are gone (large gaps in segmentation)

Define regional sections

Question 12

What are pair rule genes give example

Answer 12

Affect alternating pairs of segments (act in more narrow regions than gap genes)

Ex. Hairy or even skipped genes, if mutated every other segment is gone

Define individual segments

Question 13

What are segment polarity genes give example

Answer 13

The keep the individual segments organized.

Ex engrailed or gooseberry

Mutations in gooseberry leads to misorganization of segments (they get flipped) defects in segment polarity

Define organization of individual segments

Question 14

How many hox genes are in drosophila
What it special about them

Answer 14

8

Order of the genes in the chromosome corresponds to the order of the body region they affect

Question 15

How do hox genes control the identity of segments

Answer 15

They are transcription factors so they regulate expression of networks of other genes

They are dna binding protien that bind to cis acting regulatory elements of other genes to activate or repress them

Question 16

How are all of the toolkit genes expressed at diff times

Answer 16

The genes (transcription factors) interact with cis regulatory elements to control expression over time

They all encode transcription factors and turn each other on at the right times

Question 17

What is and example of how maternal affect genes turn on gap genes

Answer 17

Gap genes get regulated by the diff levels of bicoid protein expression

The bicoid protien (once fertilized) binds to three sites upstream of the hunchback (gap gene) promoter to activate expression

The hunch back expression depends on the concentration of bicoid, there’s a certain amount of bicoid that we need to get hunchedback expression

Low bicoid concentration means no protien bind to hunchback which means no hunchback

Question 18

Hox genes and maternal effect genes are

Answer 18

Transcription factors

Question 19

How to tell if something promotes expression

Answer 19

Its concentration is high where the gene is expressed

Repress if it’s concentration is low