Chapter 7-1. Drosophila and Genetics
Recommended Post : 【Biology】 Chapter 7. Genes and Genetics
1. Wild-type Male and Female Drosophila Structure
3. Drosophila Salivary Gland Chromosomes
1. Wild-type Male and Female Drosophila Structure
⑴ Structure 1. Head
① Has a pair of antennae.
② Has a pair of red eyes: Compound eyes, unlike human eyes.
⑵ Structure 2. Thorax
① Divided into three parts.
② Each segment has a pair of legs.
③ A pair of halteres is attached to the second thoracic segment.
④ Third thoracic segment has vestigial halteres called halters.
⑤ Halters help in maintaining balance during flight.
⑶ Structure 3. Abdomen
⑷ Sexual Dimorphism
① Males have a structure called sexcomb on the first leg.
② The posterior part of the male abdomen is black, unlike females.
2. Drosophila Mutants
⑴ White Eye Mutant (w, white)
Figure. 1. White Eye Mutant]
① Discovered by Morgan in 1910 through natural variation.
② Type 1. w1 mutant allele
○ First mutant allele discovered.
○ Obtained through natural variation.
○ Protein produced from this gene is involved in synthesizing pigment granules on the eye membrane.
○ Located at the 3C2 position of the third chromosome.
③ Type 2. w118 mutant allele
○ Obtained through natural variation.
○ Protein produced from this gene is involved in synthesizing pigment granules on the eye membrane.
○ More commonly used than w1 allele.
○ Located at the 3C2 position of the third chromosome.
⑵ Bar Eye Mutant (B, bar)
Figure. 2. Bar Eye Mutant]
① Discovered by Tice in 1914 through X-ray.
② Located on the X chromosome.
○ Position: 16A1-2 on the third chromosome.
③ Normal gene duplicated, leading to the development of bar eye phenotype.
○ Wild-type males have around 740 individual facets per eye, while females have around 780.
○ Bar-eyed mutants have around 90 facets in males and around 70 facets in homozygous females.
⑶ Vestigial Wing Sepia Eye Mutant (vg se, vestigial sepia)
Figure. 3. Vestigial Wing Sepia Eye Mutant]
① Double mutant.
② Component 1. Vestigial wing gene
○ Discovered by Morgan and Bridge in 1919 through natural variation.
○ Located on the second chromosome: Position 49D2-E1 on the third chromosome.
○ Inherited in a recessive manner.
○ Mainly involved in wing margin development.
○ Drosophila primarily exhibits wing spreading in the vestigial form.
○ At temperatures above 29°C, wings become elongated.
③ Component 2. Sepia eye gene
○ Discovered by Wallace in 1923 through natural variation.
○ Located on the second chromosome.
○ Inherited in a recessive manner.
○ Encodes an enzyme that converts red pigment granules into other intermediate products.
○ Newly emerged flies show brown color but darken with age.
⑷ Antennapedia Ebony Mutant (Antp e, antennapedia ebony)
Figure. 4. Antennapedia Ebony Mutant]
① Double mutant.
② Component 1. Antennapedia leg gene
○ First discovered by Abbot using X-ray.
○ Later discovered by Green through natural variation (commonly used).
○ Located on the third chromosome: Position 85B1-2 on the third chromosome.
○ Inherited in a dominant manner.
○ Essential homeotic gene for development, determining leg formation from thorax.
○ Homeosis or homeotic transformation occurs.
③ Component 2. Ebony body gene
○ Discovered by Wallace in 1923 through natural variation.
○ Located on the third chromosome: Position 93D2-6 on the third chromosome.
○ Inherited in a dominant manner.
○ Encodes β-alanyl dopamine synthetase enzyme, promoting synthesis of β-alanyl dopamine from dopamine and β-alanine with the help of ATP and MgCl2.
⑸ Curly Wing Mutant (Cy, curly)
Figure. 5. Curly Wing Mutant]
① Discovered by Ward in 1923 through natural variation.
② Located on the second chromosome: Position 22F4-23B2 on the third chromosome.
③ Inherited in a dominant manner.
④ Homozygous mutants die during late embryo or early larval stages.
⑹ Apterous Mutant (ap, apterous)
Figure. 6. Apterous Mutant]
① Discovered by Wallace in 1914 through natural variation.
② Located on the second chromosome: Position 41B-C on the third chromosome.
③ Inherited in a dominant manner.
3. Drosophila Salivary Gland Chromosomes
Figure. 7. Sketch of Calvin B. Bridge’s Salivary Gland Chromosomes
⑴ Salivary gland chromosomes are clustered together in chromocenters.
⑵ This clustering facilitates the production of glue required for pupation.
⑶ Salivary gland chromosomes have a polytene structure with 1024 strands.
⑷ Salivary glands undergo degeneration during metamorphosis.
Input : 2020.06.28 01:20