Gaokao Exam Biology: Genetics and Evolution 1 — Questions and Answers
Question 1: In a monohybrid cross between two heterozygous parents (Aa × Aa), what is the expected phenotypic ratio in the offspring?
- 1:1
- 1:2:1
- 3:1 (Correct answer)
- 2:1
Correct answer: 3:1
A Punnett square for Aa × Aa yields AA, Aa, Aa, aa — a 3:1 dominant-to-recessive phenotypic ratio.
Question 2: Which molecule carries the genetic instructions from the nucleus to the ribosome during protein synthesis?
- tRNA
- rRNA
- mRNA (Correct answer)
- DNA
Correct answer: mRNA
Messenger RNA (mRNA) transcribes the DNA code in the nucleus and carries it to ribosomes for translation.
Question 3: Darwin's theory of natural selection is best described as:
- Organisms acquire traits by use or disuse during their lifetime
- Individuals with favorable traits survive and reproduce more successfully (Correct answer)
- Evolution occurs through random genetic mutations only
- All members of a species evolve simultaneously
Correct answer: Individuals with favorable traits survive and reproduce more successfully
Natural selection states that heritable traits increasing survival and reproduction become more common over generations.
Question 4: A sex-linked recessive trait is carried on the X chromosome. If the mother is a carrier (X^A X^a) and the father is unaffected (X^A Y), what percentage of their sons will be affected?
- 0%
- 25%
- 50% (Correct answer)
- 100%
Correct answer: 50%
Sons receive either X^A (unaffected) or X^a (affected) from the mother with equal probability, so 50% of sons are affected.
Question 5: Which term describes a mutation that changes a single nucleotide base in the DNA sequence?
- Frameshift mutation
- Chromosomal deletion
- Point mutation (Correct answer)
- Translocation
Correct answer: Point mutation
A point mutation involves the substitution, insertion, or deletion of a single nucleotide in the DNA sequence.
Question 6: Which structure within the cell contains most of an organism's genetic material?
- Mitochondria
- Ribosome
- Nucleus (Correct answer)
- Cell membrane
Correct answer: Nucleus
The nucleus houses the cell's chromosomal DNA, which carries the majority of the organism's genetic information.
Gaokao Exam Biology: Genetics and Evolution 1
In a monohybrid cross between two heterozygous parents (Aa × Aa), what is the expected phenotypic ratio in the offspring?