Flashcards in MCB Lecture 25 Developmental Genetics Deck (39)
Describe the life cycle of drosophila
What are Homeotic genes?
These are genes responsible for the development of specific body parts
What is Ultrabithorax?
This is a Homeotic gene that results in the haltere being replaced by a second set of wings
What is antennapedia?
This is a gene that when mutated causes feet growing out of the antennae
What are HOX genes
These are Homeobox genes
This is a suite of 8 genes in drosophila
The genes are involved with development of body structures
Describe spatial expression of HOX genes
Different regions express different genes
Describe how segment identity can be determined by HOX mutants
HOX mutants indicate which region is controlled by that gene
What is a homeodomain?
How many are there in drosophila?
This is a protein coded for by a HOX gene
There are 8 in drosophila
What is special about the amino acid sequences in the 8 homeodomain proteins?
Between the 8 homeodomain proteins are consensus sequences that are identical or very similar.
What do the consensus sequences in the homeodomain proteins correlate to?
Three helices that are similar in all the homeodomain proteins
What do the variable regions in the amino acid sequences of the homeodomain proteins correlate to?
This corresponds to the regions of the protein outside the helices. This gives the 8 proteins their different functions
What is the function of homeodomain proteins?
The mediate binding of protein to DNA
Compare HOX genes in drosophila and mice
Number of clusters
Order of genes
Number: dros: 8, mice: 39
Clusters: dros: 2, mice: 4
Order of the genes: same
Why is studying HOX genes in drosophila relevant to humans?
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
Compare HOX genes is drosophila and humans
Number of clusters
Sequence correlating to body map?
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
What is the first step in development of a body plan?
Setting up the axes:
Describe (in order) all the different types of developmental genes
Egg polarity genes
Pair rule genes
Segment polarity genes
Homeotic selector genes
What are egg polarity genes
Give an example
These genes set up the anterior-posterior axis of the egg
What are Gap genes?
Gap genes set up the broad segments
Eg. Krüppel, Hunchback, Giant
What are pair rule genes?
Pair rule genes set up more definite regions
Eg. even skipped, Ftz
What are segment polarity genes?
Definition of segment
Eg. Gooseberry, engrailed
What are homeotic selector genes?
Define segment identity
What are maternal effect genes and why are they relevant to study of development?
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
Describe the phenotype of a homozygous mutant female fly
Why is this so?
Because their mother was not homozygous mutant, so they received the required proteins.
What are the parental genotypes that result in a mutant fly?
The mother must be homozygous mutant to produce a mutant fly
What are the parental phenotypes that lead to normal fly development?
The mother must have at least one functional copy of the gene
Describe the problem of lethality
When studying genes to do with development, any homozygous mutants will probably not be viable
Why are maternal effect mutants useful?
Because they allow us to overcome the problem of lethality and see the affect when developmental genes do not function
Describe cell-cell sequential induction
Which type of gene is involved?
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
Describe the interaction between Egg polarity genes and Gap genes
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
Describe the interaction between egg polarity, gap and pair rule genes
Bicoid, hunchback, Giant and Krüppel are activators and repressors from the Even skipped gene
In a pair rule gene (even skipped) enhancer, how many bicoid binding sites are there?
In a pair rule gene (even skipped) enhancer, how many giant binding sites are there?
In a pair rule gene (even skipped) enhancer, how many Krüppel binding sites are there?
In a pair rule gene (even skipped) enhancer, how many hunchback binding sites are there?
Which genes act as activators on the Even skipped gene enhancer?
Which genes act as repressors on the Even skipped gene enhancer?
Bicoid is a ... regulatory element.
It acts on ... Regulatory elements on ...
It acts on cis elements in the enhancer region of the Eve gene