Q: Which formula would you use to calculate the probability of two independent events both occurring, such as getting heads on two coin tosses?

Product rule: $$P(A \text{ and } B) = P(A) \times P(B)$$

Q: Which equation would you use to calculate the probability of either of two mutually exclusive events occurring, such as rolling a 2 or a 4 on a die?

Sum rule: $$P(A \text{ or } B) = P(A) + P(B)$$

Question 1

In a dihybrid cross between two heterozygous individuals (AaBb x AaBb), what is the expected phenotypic ratio among the F2 progeny, and which probability rule explains this outcome?

Accepted Answer

The ratio is 9:3:3:1, explained by the product rule since the traits assort independently.

Question 2

A geneticist crosses a plant with genotype Aa to a homozygous recessive plant (aa). What is the expected genotypic ratio among the progeny, and what type of cross is this?

Accepted Answer

The ratio is 1:1 (Aa:aa), and this is a testcross.

Question 3

If a trait is controlled by a single gene with two alleles, and the heterozygote shows an intermediate phenotype, which type of allele interaction is present?

Accepted Answer

Incomplete dominance

Question 4

A pedigree shows a disease affecting both males and females in every generation. What is the most likely mode of inheritance?

Accepted Answer

Autosomal dominant

Question 5

Which formula would you use to calculate the probability of two independent events both occurring, such as getting heads on two coin tosses?

Accepted Answer

Product rule: $$P(A 	ext{ and } B) = P(A) 	imes P(B)$$

Question 6

A cross between two heterozygous mice (Mm x Mm) results in a 2:1 ratio of viable to non-viable offspring. What is the most likely explanation?

Accepted Answer

A recessive lethal allele is present; homozygous recessive (mm) individuals do not survive.

Question 7

Which event during meiosis is responsible for the transition from diploid ($$2n) to $$haploid ($$n) $$cells?

Accepted Answer

Separation of homologous chromosomes during Anaphase I

Question 8

A human with the genotype XXY is phenotypically male. What is the most likely cause of this chromosomal complement?

Accepted Answer

Nondisjunction during meiosis resulting in an extra X chromosome

Question 9

Which mechanism compensates for the difference in X-linked gene dosage between XX females and XY males in humans?

Accepted Answer

X-inactivation (formation of Barr bodies)

Question 10

A plant breeder observes a 9:7 ratio in the F2 generation of a cross. Which genetic interaction is most likely responsible?

Accepted Answer

Gene redundancy (two genes with overlapping function)

Question 11

Which process increases genetic diversity by exchanging genetic material between homologous chromosomes during meiosis?

Accepted Answer

Crossing over

Question 12

A child inherits blood type AB from parents with genotypes IAIB and ii. What type of allele interaction is demonstrated?

Accepted Answer

Co-dominance

Question 13

Which equation would you use to calculate the probability of either of two mutually exclusive events occurring, such as rolling a 2 or a 4 on a die?

Accepted Answer

Sum rule: $$P(A 	ext{ or } B) = P(A) + P(B)$$

Question 14

A genetic disease is observed only in males and is passed from father to son. What is the most likely mode of inheritance?

Accepted Answer

Y-linked

Question 15

Which of the following best describes the packaging of DNA before mitosis and meiosis?

Accepted Answer

DNA is condensed into visible chromosomes

Question 16

A trait is influenced by multiple genes and shows a continuous range of phenotypes, such as human height. What is this type of trait called?

Accepted Answer

Quantitative (polygenic) trait

Question 17

Which phase of mitosis is characterized by the alignment of chromosomes at the cell's equator?

Accepted Answer

Metaphase

Question 18

A geneticist observes that a mutation in one gene can mask the effect of another gene. What is this interaction called?

Accepted Answer

Epistasis

Question 19

Which of the following is a real-world example of environmental influence on phenotype?

Accepted Answer

Siamese cat fur color, which darkens in cooler body regions

Question 20

A pedigree shows a trait skipping generations and affecting both sexes equally. What is the most likely mode of inheritance?

Accepted Answer

Autosomal recessive

Genetics Exam 1 Study Guide: Mendelian Inheritance, Extensions, Chromosomal Theory, and Sex Chromosomes

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