Pre AP Biology -GEN 5.1 Inheritance Patterns- MCQ Exam Style Questions -New Syllabus

Pre AP Biology -GEN 5.1 Inheritance Patterns- MCQ Exam Style Questions – New Syllabus 2025-2026

Pre AP Biology -GEN 5.1 Inheritance Patterns- MCQ Exam Style Questions – Pre AP Biology – per latest Pre AP Biology Syllabus.

Pre AP Biology – MCQ Exam Style Questions- All Topics

Question

Which of these environmental factors is particularly important for reptiles, and why?

a. humidity, because it determines their body temperature
b. humidity, because it determines their food quality
c. temperature, because it determines their sex
d. temperature, because it determines their nesting sites

▶️ Answer/Explanation

Detailed solution

The correct option is c. temperature, because it determines their sex.
In many reptile species, such as crocodiles and turtles, the sex of the offspring is not determined by chromosomes.
Instead, it is determined by the incubation temperature of the eggs during a critical period of development.
This biological phenomenon is known as Temperature-dependent Sex Determination (TSD).
Higher or lower temperatures can result in a clutch being entirely male or entirely female.
Environmental temperature changes can therefore significantly impact the population sex ratios.
Other options are incorrect as humidity does not regulate internal body temperature in reptiles.

Question

Perky ears in a certain mammal are coded by a dominant allele; the recessive allele codes for droopy ears. In males of these mammals, the gene encoding ear shape is transcribed only from the chromosome received from the female parent. This is because the gene from the male parent is silenced by methylation. What will be the result of a cross of a droopy-eared female and a homozygous, perky-eared male?

a. Daughters’ ears will be perky and sons’ ears will be droopy.
b. All offspring will have perky ears.
c. Sons will have one perky ear and one droopy ear.
d. There will be equal numbers of perky-eared and droopy-eared sons and daughters.

▶️ Answer/Explanation

Detailed solution

Let $P$ be the dominant perky allele and $p$ be the recessive droopy allele.
The female parent is droopy-eared, so her genotype must be $pp$.
The male parent is homozygous perky-eared, so his genotype is $PP$.
All offspring (sons and daughters) will inherit the genotype $Pp$ ($P$ from father, $p$ from mother).
In daughters, genomic imprinting is not mentioned as sex-specific, so $P$ is dominant over $p$, resulting in perky ears.
In sons, the paternal allele ($P$) is silenced by methylation, meaning only the maternal allele ($p$) is expressed.
Since sons only express the maternal $p$ allele, they will have droopy ears.
Therefore, the correct result is option a.

Question

Context: Most fruit flies have red eyes; some have white eyes. The gene affecting color is on the X chromosome. Red allele ($X^R$) is dominant to white allele ($X^r$).

Experiment 1: Red female ($X^R X^R$) x White male. Result: 100% Red eyes.
Experiment 2: Offspring from Exp 1 mated. Result: Females 100% Red; Males 50% Red, 50% White.
Experiment 3: Female offspring from Exp 1 x White male. Result: 50% Red, 50% White (both sexes).
Experiment 4: White female from Exp 3 x Red male. Result: Females 100% Red; Males 100% White.

Q. To produce only white-eyed offspring, one would mate fruit flies with which of the following sets of genotypes?

A. $X^r X^r$ and $X^r Y$

B. $X^R X^r$ and $X^r Y$

C. $X^r X^r$ and $X^R Y$

D. $X^R X^r$ and $X^R Y$

Q. Which of the four Experiments contained male offspring with one copy of the white-eye allele?

A. 2 and 4 only

B. 3 and 4 only

C. 1, 2, and 3 only

D. 2, 3, and 4 only

Q. The total ratio of red-eyed offspring to white-eyed offspring produced in Experiment 2 was

A. 1:0

B. 1:1

C. 2:1

D. 3:1

▶️ Answer/Explanation

A. Answer: A
To get 100% white-eyed offspring, every child must receive the recessive allele ($X^r$) and no dominant alleles ($X^R$).
The father must be white-eyed ($X^r Y$) to pass the allele to daughters (and Y to sons).
The mother must be homozygous recessive ($X^r X^r$) to pass the white allele to all offspring.
Therefore, the cross is $X^r X^r \times X^r Y$.

A. Answer: D
Males have one X chromosome, so a male with a white-eye allele has the genotype $X^r Y$ (white eyes).
Experiment 1 produced 100% red-eyed males ($X^R Y$).
Experiment 2 produced 50% white-eyed males ($X^r Y$).
Experiment 3 produced 50% white-eyed males ($X^r Y$).
Experiment 4 produced 100% white-eyed males ($X^r Y$).
Thus, the correct experiments are 2, 3, and 4.

A. Answer: D
Experiment 2 is a cross between offspring of Exp 1: $X^R X^r$ (female) $\times$ $X^R Y$ (male).
The possible genotypes are: $X^R X^R$ (Red Female), $X^R X^r$ (Red Female), $X^R Y$ (Red Male), and $X^r Y$ (White Male).
Counting the phenotypes: 3 offspring are Red-eyed and 1 offspring is White-eyed.
Therefore, the ratio of Red:White is 3:1.

Pre AP Biology -GEN 5.1 Inheritance Patterns- MCQ Exam Style Questions -New Syllabus