Q: Which formula would you use to calculate the expected number of offspring with a specific phenotype in a dihybrid cross with independent assortment?

$$\text{Expected} = \text{Total offspring} \times \text{Phenotypic ratio}$$

Question 1

In a cross between true-breeding red fish with short fins and true-breeding white fish with long fins, all F1 offspring are red with long fins. What does this suggest about the inheritance of these traits?

Accepted Answer

Red color and long fins are both dominant traits.

Question 2

Given the following F2 phenotypic ratio from a dihybrid cross: 9 red fish with long fins, 3 red fish with short fins, 3 white fish with long fins, and 1 white fish with short fins, which equation represents the expected ratio for independent assortment?

Accepted Answer

$$9:3:3:1$$

Question 3

A pedigree shows a trait that appears in every generation and affects both males and females equally. Which mode of inheritance is most likely?

Accepted Answer

Autosomal dominant

Question 4

If a woman with PKU (autosomal recessive) marries a man with alkaptonuria (also autosomal recessive), what is the probability that their child will be phenotypically normal for both conditions?

Accepted Answer

$$0.25$$

Question 5

In a test cross between a heterozygous curly wing fly (cur/+) and a normal wing fly (+/+), what proportion of the offspring would you expect to have curly wings if the mutation is dominant?

Accepted Answer

$$0.5$$

Question 6

A pedigree shows that only males are affected and the trait skips generations. Which inheritance pattern is most consistent with this observation?

Accepted Answer

X-linked recessive

Question 7

If the recombination frequency between the wing and antennae genes in Drosophila is calculated as $$\frac{69+71}{1000}$$, what is the genetic distance between these genes in centimorgans (cM)?

Accepted Answer

$$14\,	ext{cM}$$

Question 8

Which genotype would you assign to an individual with PKU, given that PKU is autosomal recessive and the dominant allele is $$P$$?

Accepted Answer

$$pp$$

Question 9

In a cross between two heterozygous fish for both color and fin length ($$RrLl 	imes RrLl$$), what is the expected proportion of offspring with the genotype $$rrll$$?

Accepted Answer

$$\frac{1}{16}$$

Question 10

A woman who is a carrier for an X-linked recessive trait ($$X^AX^a) $$marries a man who does not carry the trait ($$X^AY). $$What is the probability that their son will be affected?

Accepted Answer

$$0.5$$

Question 11

If two genes are located on the same chromosome and show a recombination frequency of less than $$50\%$$, what does this indicate?

Accepted Answer

The genes are linked and do not assort independently.

Question 12

In a pedigree, an affected female passes a trait to all her sons but none of her daughters. What is the most likely mode of inheritance?

Accepted Answer

Y-linked

Question 13

Which of the following best describes the genotype of a true-breeding organism?

Accepted Answer

Homozygous for the trait in question

Question 14

A cross between a red fish (homozygous) and a white fish (homozygous) produces only red offspring. If these F1 offspring are crossed, what proportion of the F2 generation will be white?

Accepted Answer

$$\frac{1}{4}$$

Question 15

In a metabolic pathway, a block in the conversion of phenylalanine to tyrosine leads to the accumulation of phenylalanine. Which disorder is associated with this defect?

Accepted Answer

Phenylketonuria (PKU)

Question 16

If a cross between two flies produces offspring in a 1:1 ratio of curly wings to normal wings, what is the most likely genotype of the parents?

Accepted Answer

One parent is heterozygous for curly wings, the other is homozygous normal

Question 17

Which formula would you use to calculate the expected number of offspring with a specific phenotype in a dihybrid cross with independent assortment?

Accepted Answer

$$	ext{Expected} = 	ext{Total offspring} 	imes 	ext{Phenotypic ratio}$$

Question 18

A test cross is performed between a heterozygous individual and a homozygous recessive individual. What is the expected ratio of dominant to recessive phenotypes in the offspring?

Accepted Answer

$$1:1$$

Question 19

If a pedigree shows that unaffected parents have affected children, which mode of inheritance is most likely?

Accepted Answer

Autosomal recessive

Question 20

In a cross between $$AaBb 	imes AaBb$$, what is the probability of obtaining an offspring with genotype $$AABB$$?

Accepted Answer

$$\frac{1}{16}$$

Genetics Study Guide: Mendelian Inheritance, Pedigrees, and Genetic Disorders

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