Drosophila Lab 3 + Lab 4 Flashcards
Why Drosophila?
They are small in size and easily handled.
They have short generation time (around 2 week).
It is easy to breed and cheap to maintain them in lab.
They have large number of offsprings.
Their entire genome is sequenced and relatively small.
Embryos grows outside the body and every stage can be studied easily.
What is the life cycle of Drosophila?
Day 0: Females lay eggs, and embryonic development begins immediately after fertilization.
Day 1: Eggs hatch
Day 2: First instar
Day 3: Second instar
Day 4: Third and final instar
Day 7: Larvae enter the roaming stage and pupariation occurs.
Day 11: Eclosion occurs and adult flies emerge from the pupa case.
Other than the formation of sex cells, no further development occurs in the adult stage.
How do we identify the sexes?
SIZE
Females are bigger than males.
SEX COMBS
They are present in males but not in females.
TIP OF THE ABDOMEN
It is more rounded in males than in females.
ABDOMEN COLOR
It is quite darker in males and lighter in females.
How to identify virgins?
Meconium is contained in the gut.
It is seen as dark green or black area.
It consists of undigested materials (embryonic fluids, remains of larval food etc.).
They become sexually mature 8–10 hours after eclosion.
Why do we collect the virgins?
Female Drosophila store sperm after mating and they can fertilize multiple batches of eggs over time.If females have already mated, it becomes impossible to determine whether the offspring result from the intended cross or from earlier, unintended fertilization by another male.
What are some of the important gene classes in Drosophila?
Maternal Effect Genes: Set up the initial body axes (e.g., bicoid, nanos, Toll).
Gap Genes: Divide the embryo into broad regions (e.g., hunchback, krüppel, giant).
Pair-Rule Genes: Establish alternating segments (e.g., even-skipped, fushi tarazu).
Segment Polarity Genes: Refine segmentation and polarity (e.g., engrailed, wingless).
Homeotic Genes: Specify the identity of segments (e.g., Antennapedia, Bithorax).
What are the maternal effect genes?
Maternal effect genes called bicoid (bcd), dorsal (dl), and oskar (osk) provide a gradient of transcription factors that collectively activate gap genes. They establish initial body axes, such as anterior-posterior gradients (e.g., bicoid, nanos)
What are the gap genes
Gap Genes refine the broad regions into more specific areas of the embryo.
Krüppel (kr)
Giant (gt)
Hunchback (hb)
Knirps (kni)
What are the pair-rule genes?
Pair-rule Genes create alternating patterns for the development of parasegments.
Even-skipped (eve)
Fushi tarazu (ftz)
Hairy (h)
Odd-paired (opa)
Runt (run)
Twist (twi)
What are the differences between pair-rule genes and gap genes?
Gap genes define broad regions along the anterior-posterior axis.
Mutations in gap genes result in the loss of large contiguous segments, creating gaps in the body plan.
Pair-rule genes divide the embryo into alternating segments.
Mutations in pair-rule genes lead to the loss of specific alternating segments, resulting in a striped pattern of missing segments.
What are the dark staining in the in situ images of the wild type?
Bicoid mRNA
What is the duration of Drosophila’s life cycle?
A: Approximately 11 days from egg to adult emergence
How do mutations in gap genes affect Drosophila development?
They result in the loss of large contiguous segments, creating gaps in the body plan
Provide examples of pair-rule and gap genes.
Pair-rule: even-skipped (eve), fushi tarazu (ftz). Gap: krüppel (kr), hunchback (hb)
What is observed in in situ hybridization of wild-type Drosophila embryos?
Localization of bicoid mRNA at the anterior end
How can phenotypic differences be studied in Drosophila mutants?
By observing cuticle slides under a light microscope to identify segmental or structural differences
What are the main stages of the Drosophila life cycle?
Egg, larva (3 instars), pupa, and adult
What happens during the larval roaming stage?
Larvae prepare for pupariation by wandering and stopping eating
What are sex combs, and which sex has them?
Small black bristles on the front legs of males
How does the abdomen color and shape differ between male and female Drosophila?
Males have darker, more rounded abdomens, while females have lighter, pointed abdomens
What is meconium, and why is it important in identifying virgin Drosophila?
Meconium is undigested larval material seen as a dark spot in the gut, present in virgins
How do gap genes function during embryonic development?
They refine broad body regions into more specific areas, such as hunchback and krüppel
What are the roles of pair-rule genes in Drosophila segmentation?
They establish alternating segment patterns, such as even-skipped and fushi tarazu
Give examples of gap genes and their mutations.
Examples include hunchback, krüppel, and giant. Mutations lead to the loss of large body sections
Provide examples of pair-rule genes and their effects on segmentation.
Examples include even-skipped and fushi tarazu. Mutations cause missing alternating segments
What role do segment polarity genes play in Drosophila?
They refine individual segments and establish anterior-posterior polarity, e.g., wingless
What are homeotic genes, and how do they specify segment identity?
They determine segment identity, e.g., Antennapedia and Bithorax complexes
What happens when there is a mutation in the Antennapedia or Bithorax gene complexes?
Antennapedia mutations cause leg-like structures on the head; Bithorax mutations change thoracic segment identity
Describe the observable phenotype of a vestigial mutant.
Degenerated or absent wings; vg gene is on chromosome 2
What are the physical characteristics of white, ebony, and yellow mutants?
White: White eyes, X chromosome.
Ebony: Darker body, chromosome 3.
Yellow: Pale body, X chromosome
On which chromosome is the ebony gene located?
3
What equipment is used to examine Drosophila under a microscope?
A stereomicroscope and a paintbrush for handling flies
How are flies anesthetized for examination?
Using diethyl ether
Why is it important to keep culture vials horizontal after introducing flies?
To prevent flies from sticking to the medium while anesthetized
Describe how to set up a monohybrid cross experiment in Drosophila.
Cross one pair of contrasting traits, observe F1 heterozygotes, and calculate F2 ratios
What is the expected phenotypic ratio in a monohybrid cross F2 generation?
3:1 Dominant to recessive
What is the phenotypic ratio of a dihybrid cross involving independent assortment?
9:3:3:1
What is the purpose of removing parental Drosophila from a vial?
To ensure only offspring are present for observation and to avoid confusion with parents during phenotypic analysis.
What safety precaution is important when using ether to anesthetize Drosophila?
Do not overexpose flies to ether to prevent sterilization or death.
What is the phenotypic difference between “ebony” and “wild type” Drosophila?
Ebony flies have a darker body color compared to the gray wild type.
What is the goal of counting F1 and F2 Drosophila generations?
To determine phenotypic ratios and test inheritance patterns using a chi-square test.
What does a chi-square test evaluate in genetics experiments?
The goodness of fit between observed and expected data to confirm hypotheses about inheritance patterns.
How is the chi-square test statistic X ^2 calculated?
X^2 = ∑(O−E)^2/E where O is observed data, and E is expected data.
What is the null hypothesis in a chi-square test for Drosophila crosses?
There is no significant difference between observed and expected phenotypic ratios.
why is it necessary to calculate degrees of freedom in a chi-square test?
To determine the critical value for hypothesis testing based on the number of phenotypic categories.
How do reciprocal crosses help in understanding sex-linked inheritance?
By comparing phenotypic outcomes, they show if traits are linked to sex chromosomes or autosomes.
