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Trait - any characteristic that can be passed from parent to offspring
Heredity - passing of traits from parent to offspring
Genetics - study of heredity
Gametes are sex cells. Gametes are haploid, thus a gamete has only one gene for a single trait.
Genes
• Tiny part of chromosomes, hereditary material
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Phenotype is the observable character of a cell or an organism; the observable manifestation of
a gene combination.
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• Genotype is the specific set of genes carried by an individual cell or organism.
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Homozygous genotype - gene combination involving 2 dominant or 2 recessive genes (e.g. RR or
rr); also called pure
. This individual would exhibit the dominant phenotype.
In heterozygous phenotypes the diploid organism has one dominant and one recessive gene.
This individual would exhibit the dominant phenotype.
Heterozygous genotype - gene combination of one dominant & one recessive allele (e.g. Rr);
also called hybrid.
This individual would exhibit the recessive phenotype.(hh)
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Dominant is a gene that is always phenotypically expressed —it is observable— if it is present.
Dominant genes are written with an upper case letter.
Recessive is a gene that is only phenotypically expressed when the dominant gene is not
present.
Recessive genes are written with a lower case letter.
Drosophila melanogaster
1. Commonly known as fruit fly or vinegar fly, Drosophila melanogaster is one of the most
prevalent flying insects.
2. The distinguishing physical characteristics of fruit flies are brick-red eyes and brownish
colored body with significant black rings along the length of the abdomen.
3. The sexual dimorphism in this type of flying insect is very distinct; males are smaller
4. An adult fruit fly measures about 3 mm in length
From the estimated 6 - 10 millionth insect species, Drosophila melanogaster is widely
used as a model organism in biology experiments.
5. It is studied as a representing organism of eukaryotes.
6. Be it in evolution, genetics, developmental biology or pathology, fruit fly is used in
several fields of science.
Life Cycle of a Fruit Fly (Drosophila melanogaster)
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In laboratory studies, a new generation of fruit flies can be obtained after every two
weeks.
Besides the small body size, there are only 4 pairs of chromosomes.
The length of developing time (an egg maturing into an adult) varies with respect to the
prevailing temperature, which is a characteristic of all cold-blooded insects.
When kept in room temperature (77° F), a Drosophila egg requires 8.5 days to develop
into an adult; whereas in temperatures higher than this, development time is more
because of heat stress.
The life cycle stages of D. melanogaster along with their associated features are discussed
below:
Egg:
The egg of Drosophila melanogaster is about 0.5 mm.
A female may lay as many as 400 eggs in a favorable egg laying ground .
Within 24 hours of laying, the eggs hatch into 1st instar larvae.
In room temperature conditions, this hatching time is as short as 15 hours.
Larva:
The larval stage of D. consists of three instars.
Within 24 hours of hatching, the larva molts to develop into 2nd instar larva.
Again after 24 hours (i.e., 48 hours after egg hatching), the 2nd instar larva molts and
matures to 3rd instar larva.
During these molting stages, the larva loses its spiracles, mouth and hooks.
Pupa:
After 4 days of voracious feeding, the 3rd instar larva encapsulates itself inside a hard
and dark-colored puparium.
It is in this pupal stage, where the metamorphosis of D. melanogaster takes place, giving
rise to wings and legs.
In room temperature condition, the duration of metamorphosis lasts for 4 days.
Adult:
The adult D. melanogaster emerges through the operculum of the puparium.
And within 8 - 12 hours of emergence, the female fly is receptive.
Then, it mates with the male Drosophila for about 30 minutes, during which the male
inseminates a few hundreds of sperms in the female fly.
The female Drosophila stores the sperms and uses them latter for laying eggs.
Since the maturation time of fruit flies differs with temperature fluctuation, it is
obvious that their life span or longevity also varies with the surrounding
environmental conditions. In general, the lifespan of Drosophila lasts for several
weeks. And, considering the ease of breeding and caring, scientists all over the
world agree that fruit flies will remain to be the most versatile model organism in
biological science.
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Drosophila melanogaster.
These are flies exhibiting standard/normal characteristics. Wild-type flies have red eyes, a
grayish body, and long, full wings. All mutants deviate, with respect to one or more
characteristics, from wild-type flies.
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Monohybrid cross