Genetics: Epistasis and Labrador Traits

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Questions and Answers

What ratio represents the Duplicate Recessive interaction in modified dihybrid Mendelian ratios?

15:1

9:7 (correct)

12:3:1

9:3:4

Which modified dihybrid ratio indicates that a dominant trait at one locus masks the expression of the second locus?

9:6:1

9:3:4

12:3:1 (correct)

15:1

What does the ratio of 15:1 signify in the context of modified dihybrid Mendelian ratios?

Dominant and Recessive interaction

Single Dominant interaction

Single Recessive interaction

Duplicate Dominant interaction (correct)

In the context of modified dihybrid ratios, what does a result of 9:6:1 represent?

Two dominant, one dominant, none dominant Signup and view all the answers

Which modified dihybrid Mendelian ratio shows a situation where a recessive trait at one locus masks the second locus effect?

9:3:4 Signup and view all the answers

Which environmental factors can influence plant growth?

Soil type Signup and view all the answers

What effect does temperature have on the phenotype of evening primrose?

White flowers at 18°C Signup and view all the answers

How does temperature affect pigment production in Siamese cats?

Cooler areas enhance enzyme activity for pigment production Signup and view all the answers

What determines the sex of some reptiles like crocodiles and turtles?

The temperature during incubation Signup and view all the answers

In plants at higher altitudes, what general phenotype is observed?

Stunted or smaller growth Signup and view all the answers

Which of the following is NOT an environmental factor that can affect organisms?

Genetic mutations Signup and view all the answers

What are the roles of epistatic and hypostatic alleles in gene interaction?

Epistatic alleles mask the effect of hypostatic alleles. Signup and view all the answers

Which of the following statements about epistasis is correct?

Epistasis can be classified as recessive or dominant. Signup and view all the answers

What general characteristic is observed in animals whose sex is influenced by incubation temperature?

Temperature-dependent sex determination Signup and view all the answers

In the context of Labrador Retrievers, what determines their fur color?

A combination of B and E alleles. Signup and view all the answers

What kind of fur pattern is associated with temperature-sensitive pigment production in species like Himalayan rabbits?

Darker fur only on cooler areas Signup and view all the answers

What will be the fur color of a Labrador Retriever with the genotype bb and at least one dominant E allele?

Brown fur. Signup and view all the answers

How can one identify whether an epistatic interaction is recessive or dominant?

Through dihybrid crosses involving both allelic pairs. Signup and view all the answers

What happens if a Labrador Retriever receives two recessive alleles of gene B?

The fur will be brown regardless of gene E. Signup and view all the answers

Why do dihybrid crosses remain important for solving epistatic problems?

They allow for easier observation of multiple alleles at play. Signup and view all the answers

Which of the following best defines a polygenic trait?

A trait influenced by multiple genes. Signup and view all the answers

What combined effects may influence vegetation patterns on mountainsides?

Cooler temperatures and greater water availability Signup and view all the answers

Which statement about predator effects on phenotypes is correct?

The presence of predators may result in permanent changes in prey phenotypes. Signup and view all the answers

In sandaggers wrasse, what role does the male play in sex determination?

Juvenile fish develop into females in the presence of the male. Signup and view all the answers

What happens to neurospora if it cannot synthesize leucine?

It will be unable to synthesize proteins. Signup and view all the answers

What characteristic is common to auxotrophs in microorganisms?

They carry mutations that hinder the synthesis of nutrients. Signup and view all the answers

What is a potential consequence of the presence of a male sandaggers wrasse in a group?

The dominant female may change sex to male if the male dies. Signup and view all the answers

Which of the following is not a factor influencing vegetation on mountainsides?

Uplifted terrain Signup and view all the answers

Why does the presence of leucine in the growth medium benefit neurospora?

It allows neurospora to bypass the effects of its enzyme mutation. Signup and view all the answers

What is the primary condition described that prevents the metabolism of phenylalanine?

Phenylketonuria Signup and view all the answers

What phenomenon occurs in plants that grow in low light conditions?

Longer stems and lack of pigmentation Signup and view all the answers

Which soil pH results in pink flowers for hydrangeas?

Acid soil Signup and view all the answers

What is a consequence of taking thalidomide during pregnancy?

Improper limb development Signup and view all the answers

What condition prevents the metabolism of galactose?

Galactosemia Signup and view all the answers

How can the phenotype associated with metabolic disorders be potentially improved?

By drastically reducing or eliminating the involved molecule Signup and view all the answers

What effect do many plants experience when grown with insufficient sunlight?

Abnormally long stems and insufficient pigmentation Signup and view all the answers

What is the color outcome for hydrangeas grown in alkaline soil?

Blue flowers Signup and view all the answers

Study Notes

Epistasis vs. Hypostasis

Epistasis occurs when one gene masks the expression of another gene at a different locus.
The masking allele is called epistatic, while the masked allele is called hypostatic.
Epistasis is a type of gene interaction that involves polygenic traits.

How to Solve Epistatic Problems

Use dihybrid crosses to solve epistatic problems, similar to polygenic trait crosses.
One pair of alleles is masking the other pair.

Recessive and Dominant Epistasis

Epistasis can be recessive or dominant.
Recessive epistasis occurs when two recessive alleles at one locus mask the expression of the dominant allele at another locus.
Dominant epistasis occurs when one dominant allele at one locus masks the expression of both alleles at another locus.

Labrador Retrievers

Fur color in Labrador Retrievers is controlled by two genes.
Gene 1 (B) controls the color:
- Dominant B - black fur
- Recessive bb - brown fur
Gene 2 (E) controls the expression of the B allele:
- Dominant E - allows the B allele to express its color
- Recessive ee - blocks the expression of the B allele, resulting in a yellow coat

Modified Dihybrid Mendelian Ratios

Dihybrid crosses involving epistatic interactions result in modified phenotypic ratios.
Duplicate recessive epistasis (9:7): Recessive alleles at either locus mask the expression of the dominant phenotype at the other locus.
Single recessive epistasis (9:3:4): Recessive allele at one locus masks the effect of the second locus.
Duplicate dominant epistasis (15:1): Dominant allele at either locus results in one phenotype, while the other phenotype is homozygous recessive at both loci.
Single dominant epistasis (12:3:1): Dominant allele at one locus masks the expression of the second locus.
Dominant x Recessive epistasis (9:6:1): Two dominant alleles (one at each locus) create a phenotype, one dominant allele results in another phenotype, and no dominant alleles results in a third phenotype.

Environmental Factors Influencing Phenotypes

Environmental factors can significantly influence gene expression and phenotypic variation.
Examples of such factors include:
- Wind exposure
- Water availability
- Acidity (pH)
- Temperature
- Soil type
- Light intensity
- Predation

Temperature Effects on Phenotype

Temperature can affect gene expression through its effect on the rate of chemical reactions.
Example: Evening primroses produce red flowers at 23°C and white flowers at 18°C.

Color Pointing

Some animals, like Siamese cats and Himalayan rabbits, exhibit color pointing – darker fur on extremities.
This is due to a temperature-sensitive enzyme involved in pigment production.
The enzyme only functions at cooler temperatures, leading to darker fur on the extremities.

Sex Determination

In some species, sex is determined by incubation temperature during embryonic development.
Examples: Crocodiles, American alligators, and turtles.
High incubation temperatures may produce males, while low temperatures may produce females (or vice versa, depending on the species).

Altitude Effects on Phenotype

Plants of the same species can have a smaller or stunted phenotype at higher altitudes.
This may be due to:
- Wind exposure
- Cooler temperatures
- Water availability
- Rarified atmosphere (low oxygen)

Effects of Other Organisms on Phenotypes

Other organisms can influence the phenotype of individuals.
Predation: Predator presence or activity can cause permanent changes in prey phenotypes.
Sex Determination: The presence of other individuals within a group can determine sex in some species.

Nutritional Effects

Nutritional deficiencies can affect phenotype.
Auxotroph: In microorganisms, mutations might prevent synthesis of specific nutrients.
- Example: Bread mold, Neurospora, lacking leucine.
Nutritional deficiencies in humans can also lead to phenotypic changes.
- Example: Phenylketonuria, galactosemia, lactose intolerance.

Light Effects on Phenotype

Light intensity can affect plant growth and development.
Low light levels can cause plants to grow abnormally long stems with less pigmentation.
Light exposure (sunlight) leads to tanning in human skin.

Acidity Effects on Phenotype

Soil pH levels can affect flower color in some plants.
Example: Hydrangeas
- Acidic soil (low pH) - pink flowers.
- Alkaline soil (high pH) - blue flowers.

Chemical Effects on Phenotype

Exposure to chemicals can have a profound impact on phenotype.
Example: Thalidomide, a sedative, led to birth defects, including stunted limbs, in babies exposed to its effects in utero.

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Description

Explore the concepts of epistasis and hypostasis in genetics through this quiz. Learn how gene interactions influence traits, particularly in the case of Labrador Retrievers. Test your understanding of dominant and recessive epistasis as well as dihybrid crosses.