Epistasia em labradores - Aula 12 - Módulo 2: Genética

Summary

This lesson explores epistasis in genetics using Labradors as an example. The instructor explains how gene interactions influence coat color in Labradors—gold, brown, and black—through the action or inhibition of specific enzymes. The concept of recessive epistasis is highlighted, where a gene can prevent the expression of another gene, resulting in color variations. The video also offers a detailed explanation of how to calculate phenotypic ratios in genetic crosses. Additionally, the instructor promotes a comprehensive genetics course with exercises for deeper learning, providing a link and discount for interested students.

Takeaways

• 🐶 Labrador retrievers' coat colors are influenced by epistasis, where specific genes can suppress the expression of others.
• 🟡 Golden Labradors (also known as albino) can only produce golden offspring.
• 🐾 Brown Labradors can produce brown or golden offspring.
• ⚫ Black Labradors can produce black, brown, or golden offspring due to epistatic interactions.
• 🧬 Epistasis occurs when one gene can block the manifestation of another, leading to different phenotypes.
• 🎨 The precursor to color in Labradors is colorless and is influenced by the action of enzymes.
• 🟤 If enzyme 'E' is present, it allows for the brown pigment to form, depositing melanin in the dog's fur.
• ⚫ If both enzyme 'E' and enzyme 'B' are present, the dog will have black fur due to increased melanin deposition.
• ⛔ If enzyme 'E' is not present (recessive ee), no pigment can form, resulting in a golden (albino) Labrador, regardless of other genes.
• 📊 The proportion of Labrador offspring with different colors follows Mendelian inheritance ratios, with specific probabilities for black, brown, and golden fur.

Q & A

What is epistasis?

Epistasis is a genetic phenomenon where one gene can inhibit or mask the expression of another gene. In the case of Labrador coat colors, certain genes control whether pigment is produced, and other genes control the type of pigment.

What coat colors can Labradors have based on genetic combinations?

Labradors can be black, brown (chocolate), or golden (yellow/albino). The black coat requires a dominant gene for black pigmentation (B), the brown coat requires recessive alleles (bb), and the golden coat occurs when a recessive gene (ee) inhibits the production of pigment altogether.

How does the epistatic gene influence Labrador coat colors?

The 'E' gene is epistatic, meaning it controls whether or not color is expressed. If a Labrador has the recessive 'ee' combination, it will be golden, regardless of the genes controlling black or brown pigment.

Why do some Labradors with the 'ee' genotype appear golden?

In Labradors with the 'ee' genotype, the recessive 'ee' combination inhibits the production of pigment, meaning neither black nor brown pigment is deposited, resulting in a golden (albino) coat.

What happens if a Labrador has the 'Ee' or 'EE' genotype?

If a Labrador has the 'Ee' or 'EE' genotype, the epistatic effect is not present, and color can be expressed based on the other gene (B for black or bb for brown).

What is the role of the 'B' gene in Labrador coat colors?

The 'B' gene determines the pigment color. 'B' (dominant) leads to black pigmentation, while 'bb' (recessive) leads to brown (chocolate) pigmentation. However, this only occurs if the 'E' gene allows pigmentation to be expressed.

What does it mean when the instructor refers to epistasis as recessive?

Recessive epistasis refers to the fact that the recessive 'ee' genotype inhibits the expression of both black and brown pigments, resulting in a golden Labrador. The epistatic gene must be recessive (ee) to block color expression.

What is the genetic combination needed for a black Labrador?

For a black Labrador, the dog must have at least one dominant 'E' gene (either 'Ee' or 'EE') to allow pigmentation and at least one dominant 'B' gene (either 'BB' or 'Bb') to produce black pigment.

What genetic combination results in a brown (chocolate) Labrador?

A brown (chocolate) Labrador has the genotype 'Ee' or 'EE' to allow pigmentation and the genotype 'bb' to produce brown pigment.

What are the phenotypic ratios mentioned for Labrador coat colors in a dihybrid cross?

The phenotypic ratios for Labrador coat colors in a dihybrid cross involving epistasis are 9 black: 3 brown: 4 golden. This reflects the proportions of offspring expressing each coat color based on their genetic combinations.