MCB Lecture 25 Developmental Genetics

Question 0

What are Homeotic genes?

Answer 0

These are genes responsible for the development of specific body parts

Question 1

Describe the life cycle of drosophila

Answer 1

Egg
Embryogenesis
Larva
1st-3rd Instar
Moulting

Pupation
Adult

Question 2

What is Ultrabithorax?

Answer 2

This is a Homeotic gene that results in the haltere being replaced by a second set of wings

Question 3

What is antennapedia?

Answer 3

This is a gene that when mutated causes feet growing out of the antennae

Question 4

What are HOX genes

Answer 4

These are Homeobox genes
This is a suite of 8 genes in drosophila

The genes are involved with development of body structures

Question 5

Describe spatial expression of HOX genes

Answer 5

Different regions express different genes

Question 6

Describe how segment identity can be determined by HOX mutants

Answer 6

HOX mutants indicate which region is controlled by that gene

Question 7

What is a homeodomain?

How many are there in drosophila?

Answer 7

This is a protein coded for by a HOX gene

There are 8 in drosophila

Question 8

What is special about the amino acid sequences in the 8 homeodomain proteins?

Answer 8

Between the 8 homeodomain proteins are consensus sequences that are identical or very similar.

Question 9

What do the consensus sequences in the homeodomain proteins correlate to?

Answer 9

Three helices that are similar in all the homeodomain proteins

Question 10

What do the variable regions in the amino acid sequences of the homeodomain proteins correlate to?

Answer 10

This corresponds to the regions of the protein outside the helices. This gives the 8 proteins their different functions

Question 11

What is the function of homeodomain proteins?

Answer 11

The mediate binding of protein to DNA

Question 12

Compare HOX genes in drosophila and mice

Number
Number of clusters
Order of genes

Answer 12

Number: dros: 8, mice: 39
Clusters: dros: 2, mice: 4
Order of the genes: same

Question 13

Why is studying HOX genes in drosophila relevant to humans?

Answer 13

It is relevant because there has been much conservation of the genes from flies to humans

Things we find out about flies can been applied to human development

Question 14

Compare HOX genes is drosophila and humans

Number of clusters
Gene duplications
Sequence correlating to body map?

Answer 14

Number of clusters: humans have many more
Gene duplication: only in humans; accounts for new functions
The mapping (order of genes to order in body plan) is seen in both flies and humans

Question 15

What is the first step in development of a body plan?

Answer 15

Setting up the axes:
Posterior-anterior
Dorsal-ventral

Question 16

Describe (in order) all the different types of developmental genes

Answer 16

Egg polarity genes
Gap genes
Pair rule genes
Segment polarity genes
Homeotic selector genes

Question 17

What are egg polarity genes

Give an example

Answer 17

These genes set up the anterior-posterior axis of the egg

Bicoid

Question 18

What are Gap genes?

Give examples

Answer 18

Gap genes set up the broad segments

Eg. Krüppel, Hunchback, Giant

Question 19

What are pair rule genes?

Give examples

Answer 19

Pair rule genes set up more definite regions

Eg. even skipped, Ftz

Question 20

What are segment polarity genes?

Give examples

Answer 20

Definition of segment

Eg. Gooseberry, engrailed

Question 21

What are homeotic selector genes?

Answer 21

Define segment identity

Question 22

What are maternal effect genes and why are they relevant to study of development?

Answer 22

Maternal effect genes are genes in the mother that affect only the offspring.

This individual’s genotype does not affect their own genotype, but the offspring’s

They are relevant because they solve the problem of lethality

Question 23

Describe the phenotype of a homozygous mutant female fly

Why is this so?

Answer 23

Normal.

Because their mother was not homozygous mutant, so they received the required proteins.

Question 24

What are the parental genotypes that result in a mutant fly? | Why?

Answer 24

The mother must be homozygous mutant to produce a mutant fly

Question 25

What are the parental phenotypes that lead to normal fly development?

Answer 25

The mother must have at least one functional copy of the gene

Question 26

Describe the problem of lethality

Answer 26

When studying genes to do with development, any homozygous mutants will probably not be viable

Question 27

Why are maternal effect mutants useful?

Answer 27

Because they allow us to overcome the problem of lethality and see the affect when developmental genes do not function

Question 28

Describe cell-cell sequential induction Which type of gene is involved?

Answer 28

B -> A The influence of B on A creates another region C C influences A and B These influences create areas D and E Segment polarity genes and HOX genes

Question 29

Describe the interaction between Egg polarity genes and Gap genes

Answer 29

The nurse cells set up the bicoid gradient from anterior to posterior end Bicoid is an activator for Hunchback (gap). So, high concentration of bicoid at the anterior end corresponds high concentration of hunchback at the anterior end

Question 30

Describe the interaction between egg polarity, gap and pair rule genes

Answer 30

Bicoid, hunchback, Giant and Krüppel are activators and repressors from the Even skipped gene

Question 31

In a pair rule gene (even skipped) enhancer, how many bicoid binding sites are there?

Answer 31

5

Question 32

In a pair rule gene (even skipped) enhancer, how many giant binding sites are there?

Answer 32

3

Question 33

In a pair rule gene (even skipped) enhancer, how many Krüppel binding sites are there?

Answer 33

3

Question 34

In a pair rule gene (even skipped) enhancer, how many hunchback binding sites are there?

Answer 34

1

Question 35

Which genes act as activators on the Even skipped gene enhancer?

Answer 35

Bicoid | Hunchback

Question 36

Which genes act as repressors on the Even skipped gene enhancer?

Answer 36

Krüppel | Giant

Question 37

Bicoid is a ... regulatory element. | It acts on ... Regulatory elements on ...

Answer 37

Trans acting It acts on cis elements in the enhancer region of the Eve gene

Question 38

Name a maternal effect gene Which genes HOX genes are zygotic?

Answer 38

Maternal effect: bicoid Zygotic: Krüppel, even-skipped, gooseberry