MOLGEN4500 ---[4: Extensions Of Mendelian Genes]

Why can multiple alleles only be studied in

populations?

Because multiple allelism involves three or more alleles of the same gene, no single diploid organism can have all the alleles in a multiple allele system.

A homozygote for a recessive lethal allele will not survive (T/F)

True

If the gene product is essential for survival, having two mutant alleles means the organism will not produce the gene product at all.

Epistasis

describes the phenomenon in which the expression of one gene pair masks or modifies the expression of a second gene pair, leading to discontinuous variation.

Look over the pedigree you constructed in Part A.

Based on the inheritance pattern, which mode of inheritance must be the cause of galactosemia?

sex-linked recessive

sex-linked dominant

autosomal dominant

autosomal recessive

Autosomal recessive

Because neither Jane nor John has the same condition as their daughter, and there is no evidence of sex-linkage, galactosemia must be an autosomal recessive trait.

If Jane and John want to have another child, they plan to see a genetic counselor to find out when it would be best to test for galactosemia.  A newborn with galactosemia must be put on a lactose- and galactose-free diet as soon as possible after birth. Even on this diet, affected individuals may still suffer from learning disabilities, ovarian failure (in young women), early-onset cataracts, and early death.

Which of the following tests would be most useful for Jane and John to

have?

carrier screening of Jane and John (to identify whether either or both of them carry the allele for galactosemia)

fetal chromosome analysis (examining fetal chromosomes for abnormalities as early as 11 weeks into the pregnancy)

newborn screening (either assaying for the GALT enzyme or measuring excess galactose in the newborn's blood)

no testing

newborn screening (either assaying for the GALT enzyme or measuring excess galactose in the newborn's blood) because this can put the baby immediately into a diet (lactose free/galactose free)

A. already know that leah is carrier so its useless

B. Looks at kayottype but galactosemia is caused by a single gene not the entire chromosome

Determine the proportion of offspring phenotypes that would result when two merle dogs mate, if one dog is true-breeding for the long-coat trait and the other dog is true-breeding for the short-coat trait.

1. double merle with short coat:

2. double merle with long coat:

3. merle with short coat:

4. merle with long coat:

5. solid with short coat:

6. solid with long coat:

Determine the proportion of offspring phenotypes that would result when two merle dogs mate, if both dogs are heterozygous (Ll) for the gene that regulates coat length.

1. double merle with short coat:

2. double merle with long coat:

3. merle with short coat:

4. merle with long coat:

5. solid with short coat:

6. solid with long coat:

Interestingly, double merles are subject to a variety of health problems, including hearing loss and vision deficiencies. Therefore, it is not recommended that breeders breed for the double merle phenotype.

If you were in the business of breeding dogs, which of the following crosses would you avoid in an effort to not produce double merle

puppies?

solid x solid

double merle x solid

merle x solid

merle x merle

merle x merle

A mutation that causes a yellowing of leaves in snapdragon plants was discovered in the early 1900s. Plants with this condition, termed aurea, have less chlorophyll than green plants.

Crosses between various combinations of green and aurea plants yielded the following results.

green x green = all green

aurea x aurea = 2/3 aurea, 1/3 green

green x aurea = 1/2 green, 1/2 aurea

If the green allele is designated as G, and the aurea allele is designated as G^A, Assign genotypes to the phenotypes listed. (green and aurea)

How can the unusual results from the crosses be explained?

Green

GG

Aurea

GG^A

The aurea allele behaves as a recessive lethal allele.

A mutation that causes a yellowing of leaves in snapdragon plants was discovered in the early 1900s. Plants with this condition, termed aurea, have less chlorophyll than green plants.

Crosses between various combinations of green and aurea plants yielded the following results.

green x green = all green

aurea x aurea = 2/3 aurea, 1/3 green

green x aurea = 1/2 green, 1/2 aurea

With respect to snapdragon color, what can be said of the Gand G^Aalleles?

The G^A is dominant to the G allele.

Epistasis is the interaction between genes such that one gene influences or interferes with the expression of another gene, leading to a specific phenotype.  Epistatic genes can be dominant or recessive.  Use your knowledge of epistasis to determine the genotypes of offspring in the following crosses.

In freshwater snails, pigment color is influenced by two genes. If two heterozygous pigmented freshwater snails were crossed and offspring were produced in a ratio of 9 pigmented snails to 7 albino snails, what are the genotypes of the offspring? IS THIS dominant or recessive epistasis?

In sheep, coat color is influenced by two genes. Gene A influences pigment production, while gene B produces black or brown pigment.

If two heterozygous white sheep were crossed and offspring were produced in a ratio of 12 white sheep to 3 black sheep to 1 brown sheep, what are the genotypes of the offspring? IS THIS dominant or recessive epistasis?

In labrador retrievers, pigment color is influenced by two genes. Gene A determines the type of pigment produced and gene B affects whether the pigment gets deposited in the hair shaft.  

If two heterozygous black labrador retrievers were crossed and offspring were produced in a ratio of 9 black dogs to 3 brown dogs to 4 yellow dogs, what are the genotypes of the offspring? IS THIS recessive or dominant epistasis?

What would be the expected frequency of agouti brown offspring in the

litter?

Note