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
a. Drosophila developmental biology
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 wings is attached to the second thoracic segment.
④ The third thoracic segment has a haltere, a reduced and modified wing.
⑤ The halteres help maintain 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 Morgan discovered it in 1910 through natural occurrence.
② Type 1. w1 mutant allele
○ First mutant allele discovered.
○ Obtained through natural occurrence.
○ The protein produced by this gene is membrane-bound and involved in synthesizing pigment precursors.
○ It is located at the 3C2 position of the polytene chromosome.
③ Type 2. w118 mutant allele
○ Obtained through natural occurrence.
○ The protein produced by this gene is membrane-bound and involved in synthesizing pigment precursors.
○ More commonly used than w1 allele.
○ It is located at the 3C2 position of the polytene 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.
○ It is located at the 16A1-2 position of the polytene chromosome.
③ A normal gene is duplicated, resulting in the bar-eye phenotype.
○ A normal male has approximately 740 ommatidia, while a normal female has about 780.
○ In the bar-eye mutation, males have about 90 ommatidia, and homozygous females have about 70.
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 occurrence.
○ Located on the second chromosome: It is located at the 49D2-E1 position of the polytene 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 occurrence.
○ Located on the second chromosome.
○ Inherited in a recessive manner.
○ Encodes an enzyme that converts the red pigment precursor into other intermediate products.
○ Newly emerged pupae appear brown, but they gradually darken with age.
⑷ Antennapedia Ebony Mutant (Antp e, antennapedia ebony)
Figure 4. Antennapedia Ebony Mutant
① Double mutant.
② Component 1. Antennapedia gene
○ First discovered by Abbot using X-ray.
○ Later discovered by Green through natural occurrence (commonly used).
○ Located on the third chromosome: It is located at the 85B1-2 position of the polytene chromosome.
○ Inherited in a dominant manner.
○ Homeotic genes, which are crucial for animal development, are normally expressed in the thorax to determine structures such as legs.
○ Homeosis or homeotic transformation occurs.
③ Component 2. Ebony body gene
○ Discovered by Wallace in 1923 through natural occurrence.
○ Located on the third chromosome: It is located at the 93D2-6 position of the polytene chromosome.
○ Inherited in a recessive 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 occurrence.
② Located on the second chromosome: It is located at the 22F4-23B2 position of the polytene 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 occurrence.
② Located on the second chromosome: It is located at 41B-C on the polytene chromosome.
③ Inherited in a recessive 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