Test 1 Genetics

Two linked genes, (A) and (B), are separated by 18 m.u. A man with genotype Aa Bb marries a woman who is aa bb. The man's father was AA BB. What is the probability that their first child will be Aa bb?

0.09

The pedigree below shows the segregation of an autosomal recessive trait. What is the probability that the child of III-1 and III-2 will be affected? Assume that individuals from outside the families are homozygous normal.

1/36

June has two brothers with Becker muscular dystrophy (BMD), an X-linked recessive condition that allows affected males to survive into adulthood. Her parents are phenotypically normal. She marries Sheldon, who also has BMD. June and Sheldon have a daughter. What is the probability that this daughter will have BMD?

1/4

In maize (corn), assume that the genes A and B are linked and 30 map units apart. If a plant of Ab/aB is selfed, what proportion of the progeny would be expected to be of ab/ab genotype?

2.25

In rabbits, an allelic series helps to determine coat color: C (full color), cch (chinchilla; gray color), ch (Himalayan; white with black extremities), and c (albino; all white). The C allele is dominant to all others, cch is dominant to ch and c, ch is dominant to c, and c isrecessive to all the other alleles. This dominance hierarchy can be summarized as C > cch > ch > c. Indicate the phenotypic ratios expected of rabbits with the cross Ccch × Cch .

3 full color : 1 chinchilla

If the recombination frequency between genes (A) and (B) is 5.3%, what is the distance between the genes in map units on the linkage map?

5.3 m.u.

A testcross is carried out with the parent AB/ab. The genes A and B are completely linked. What are the expected genotypes of the progeny?

AB/ab, ab/ab

Which description of a Y-linked trait in humans is CORRECT?

All the sons of an affected father will be affected with the trait.

Which statement is INCORRECT concerning an X-linked recessive trait in humans?

An affected woman almost always has an affected mother.

A mother with blood type A has a child with blood type AB. Give all possible blood types for the father of this child.

B, AB

Hair color is determined in Labrador retrievers by alleles at the B and E loci. A dominant allele B encodes black pigment, whereas a recessive allele b encodes brown pigment. Alleles at a second locus affect the deposition of the pigment in the shaft of the hair; dominant allele E allows dark pigment (black or brown) to be deposited, whereas recessive allele e prevents the deposition of dark pigment, causing the hair to be yellow. A black female Labrador retriever was mated with a yellow male. Half of the puppies were black, and half were yellow. If the genotype of the black female parent was Bb Ee, then what was the genotype of the other parent?

BB ee

Explain what the following data say about the genetic and environmental influence on each characteristic. How did you interpret these data? (MZ = monozygotic twins and DZ = dizygotic twins.)

Handedness is strongly affected by environmental factors with little or no genetic basis, while manic depression is significantly affected by genetic factors.

If the pedigree below is for an autosomal recessive characteristic, which individuals are definitely heterozygous?

I-1, I-2, II-4, II-5, III-1

Which of the following statements about SNPs are CORRECT? (Select all that apply.)

SNPs are positions where individuals differ in DNA sequence at a single nucleotide. SNPs may be associated with specific traits.

Achondroplasia is a common cause of dwarfism in humans. All individuals with achondroplasia are thought to be heterozygous at the locus that controls this trait. When two individuals with achondroplasia mate, the offspring occur in a ratio of 2achondroplasia : 1 normal. What is the MOST likely explanation for these observations? (Question 48)

The allele that causes achondroplasia is a recessive lethal allele.

If monozygotic and dizygotic twins have the same concordance value for a trait, which of the following is TRUE?

The trait is entirely due to environmental factors.

You are studying two linked genes in lizards. You have two females, and you know that both are the same genotype, heterozygous for both genes (A/a and B/b). You testcross each female to a male that is fully homozygous recessive for both genes (a/a and b/b) and get the following progeny with the following phenotypes: Female 1 Female 2 AB - 37 AB - 5 ab - 33 ab - 4 Ab - 4 Ab - 35 aB - 6 aB - 36 How can you explain the drastic difference between these two crosses?

The two alleles are in the coupling configuration in female 1 but in the repulsion configuration in female 2.

Pedigrees showing a hypothetical human trait show the following characteristics: -If a phenotypically normal woman with an affected father has children with an unaffected man, half of the sons and none of the daughters are affected. -Affected females always have an affected father and an affected maternal grandfather. -The trait is never passed from father to son. What is the MOST likely mode of inheritance for this disorder?

X-linked recessive

Could the characteristics followed in the pedigree be caused by an X-linked recessive allele? (number 62)

Yes, all individuals fit the X-linked recessive inheritance pattern.

Is it possible for two different genes located on the same chromosome to assort independently?

Yes, if the genes are far enough apart on the same chromosome, a crossover will occur between them in just about every meiotic event.

Leber hereditary optic neuropathy (LHON) is a human disease that exhibits cytoplasmic inheritance. It is characterized by rapid loss of vision in both eyes, resulting from the death of cells in the optic nerve. A teenager loses vision in both eyes and is later diagnosed with LHON. How did this individual MOST likely inherit the mutant DNA responsible for this condition?

a mitochondrial gene from the mother

Suppose that the "fabulous" phenotype is controlled by two genes, A and B, as shown in the following diagram. One copy of allele A produces enough enzyme 1 to convert "plain" to "smashing." Allele a produces no enzyme 1. One copy of allele B produces enough enzyme 2 to convert "smashing" to "fabulous." Allele b produces no enzyme 2. The A and B genes are both autosomal and assort independently. What will be the phenotype(s) of the F1 offspring of a true-breeding "fabulous" father and a true-breeding "plain" mother (aa bb)?

all "fabulous"

What is the MOST likely mode of inheritance in the pedigree below? (number 64)

autosomal dominant

Pedigrees showing a hypothetical human trait show the following characteristics: -Males and females are equally affected. -Two unaffected parents can have an affected child. -In families in which the parents are unaffected but the children are affected, one-fourth of the children are affected. What is the MOST likely mode of inheritance for this disorder?

autosomal recessive

A testcross is performed on an individual to examine three linked genes. The most frequent phenotypes of the progeny were Abc and aBC, and the least frequent phenotypes were abc and ABC. What was the genotype of the heterozygous individual that is testcrossed with the correct order of the three genes?

bAc/BaC

Recombination occurs through:

crossing over and independent assortment.

Heterozygous genetic screening is used mainly to:

detect adult members of a particular population who may be heterozygous carriers for recessive disorders.

In addition to determining genotypes, two- and three-factor testcrosses can be used to:

map gene loci.

Linked genes always exhibit:

recombination frequencies of less than 50%.

The presence of a beard on some goats is determined by an autosomal gene that is dominant in males and recessive in females. Heterozygous males are bearded, while heterozygous females are beardless. What type of inheritance is exhibited by this trait?

sex-influenced

In corn, small pollen (sp) is recessive to normal pollen (sp + ) and banded necrotic tissue, called zebra necrotic (zn), is recessive to normal tissue (zn + ). The genes that produce these phenotypes are closely linked on chromosome 10. If no crossing over occurs between these two loci, give the types of progeny expected from the following cross: sp+ zn+/sp zn x sp+ zn+/sp zn

sp+ zn+ /sp+ zn+ ; sp+ zn+ /sp zn; sp zn/sp zn

The himalayan allele in rabbits produces dark fur at the extremities of the body—on the nose, ears, and feet. The dark pigment develops, however, only when a rabbit is reared at a temperature of 25°C or lower; if a Himalayan rabbit is reared at 30°C, no dark patches develop. What does this exemplify?

temperature-sensitive allele

Two parents are phenotypically normal, but one of their four biological children has a typical autosomal recessive trait. The other three children are phenotypically normal. It is very likely that:

the parents are both heterozygous for the trait.