Heredity
Subject: General Science
Sample Practice Questions
Question 1: What is the genotype ratio in the F2 generation when tall (Tt) plants are self-pollinated?
- 1:2:1 (TT:Tt:tt)
- 3:1 (Tall:Short)
- 1:1 (TT:tt)
- All Tt
Explanation: When F1 tall plants (Tt) are self-pollinated, the F2 generation shows a genotype ratio of 1:2:1 (TT:Tt:tt). The phenotype ratio is 3:1 (tall:short).
Question 2: How many pairs of chromosomes do humans have?
- 22 pairs
- 23 pairs
- 46 pairs
- 24 pairs
Explanation: Humans have 23 pairs of chromosomes (46 total). 22 pairs are autosomes (non-sex chromosomes) and 1 pair are sex chromosomes.
Question 3: What is the probability of having a boy child in humans?
- 25%
- 50%
- 75%
- 100%
Explanation: There is a 50% probability of having a boy child and 50% probability of having a girl child. This is because the father contributes either an X or Y chromosome with equal probability.
Question 4: What happens during gamete formation according to Mendel's Law of Segregation?
- The two alleles for a trait separate
- The alleles blend together
- Both alleles go to the same gamete
- Only dominant alleles are passed on
Explanation: According to the Law of Segregation, the two alleles for a trait separate during gamete formation. Each gamete receives only one allele from each pair.
Question 5: What are the two versions of a gene called?
- Chromosomes
- Alleles
- Proteins
- Traits
Explanation: The two versions of a gene are called alleles. For example, T and t are alleles for the height gene in pea plants. These can be identical or different.
Question 6: What is the term for the genetic makeup of an organism?
- Phenotype
- Genotype
- Trait
- Variation
Explanation: Genotype is the genetic makeup of an organism. It refers to the combination of alleles present for a particular trait.
Question 7: What is the result when a homozygous tall plant (TT) is crossed with a homozygous short plant (tt)?
- All plants are short
- All plants are tall
- 75% tall, 25% short
- 50% tall, 50% short
Explanation: When TT (homozygous tall) is crossed with tt (homozygous short), all F1 progeny are Tt (heterozygous tall). Tallness is dominant, so all plants appear tall.
Question 8: What are the sex chromosomes in human females?
- XY
- XX
- X
- YO
Explanation: Human females have two X chromosomes (XX). They have a perfect pair of sex chromosomes.
Question 9: What is the genotype of a person with blood group O?
- AA
- AO
- OO
- AB
Explanation: Blood group O has the genotype OO. Blood group A can be AA or AO, blood group B can be BB or BO, and blood group AB has genotype AB.
Question 10: In a cross between a heterozygous tall plant (Tt) and a short plant (tt), what is the probability of getting a tall plant?
- 100%
- 75%
- 50%
- 25%
Explanation: When Tt is crossed with tt, the possible offspring are Tt (tall) and tt (short) in a 1:1 ratio. Therefore, the probability of getting a tall plant is 50%.