Unit 5 AP Biology: Classified Questions with Answers and Explanations
Unit 5 of AP Biology covers Heredity and Genetics, a fundamental topic for understanding how traits are passed from one generation to another. This guide provides classified questions along with detailed answers and explanations to help you prepare effectively.
Key Topics in Unit 5:
- Mendelian Genetics and Laws of Inheritance
- Non-Mendelian Genetics (Incomplete Dominance, Codominance, Multiple Alleles, and Epistasis)
- Chromosomal Inheritance and Genetic Disorders
- Probability and Statistics in Genetics
- Biotechnology and Genetic Engineering
Classified Questions and Answers
1. Mendelian Genetics
Question: In a cross between two heterozygous (Bb) organisms, what is the expected genotypic ratio of the offspring?
Answer: The genotypic ratio is 1:2:1 (1 BB: 2 Bb: 1 bb).
Explanation: A Punnett square shows the possible combinations:
| B | b | |
|---|---|---|
| B | BB | Bb |
| b | Bb | bb |
The expected genotypic ratio is 1 BB : 2 Bb : 1 bb, while the phenotypic ratio depends on whether B is dominant over b.
2. Non-Mendelian Genetics
Question: A red flower (RR) is crossed with a white flower (WW), producing all pink flowers (RW). What type of inheritance is this?
Answer: Incomplete Dominance
Explanation: In incomplete dominance, neither allele is completely dominant. The heterozygous (RW) individuals exhibit a blended phenotype.
3. Chromosomal Inheritance
Question: A male inherits a sex-linked disorder from which parent?
Answer: The mother
Explanation: Sex-linked disorders are often found on the X chromosome. Males (XY) inherit their X chromosome from their mother and Y from their father. If the mother carries a defective allele on her X chromosome, the son has no second X to compensate, resulting in the disorder.
4. Probability in Genetics
Question: If two carriers of a recessive genetic disorder (Aa) have children, what is the probability that their child will inherit the disorder?
Answer: 25%
Explanation: Using a Punnett square:
| A | a | |
| A | AA | Aa |
| a | Aa | aa |
Only aa individuals (25%) inherit the disorder since it is recessive.
5. Biotechnology in Genetics
Question: What is the purpose of gel electrophoresis in genetic studies?
Answer: To separate DNA fragments by size
Explanation: Gel electrophoresis uses an electric current to sort DNA fragments based on length. This technique is crucial for DNA fingerprinting, paternity tests, and genetic research.
Unit 5 AP biology
Classified Questions with Answers and Explanations
Question 1: Mendelian Genetics
Q: A heterozygous pea plant (Tt) is crossed with another heterozygous pea plant (Tt). What is the probability of producing an offspring with a recessive phenotype?
A: The probability is 25%.
Explanation:
Using a Punnett square, we can determine the possible genotypes of the offspring:
- Parental genotypes: Tt × Tt
- Possible gametes: T or t from each parent
- Offspring genotypes: TT, Tt, Tt, tt
The recessive phenotype (short plants) occurs only when the genotype is tt , which happens in 1 out of 4 (25%) cases.
Question 2: DNA Replication
Q: During DNA replication, what enzyme is responsible for adding complementary nucleotides to the growing DNA strand?
A: DNA polymerase
Explanation:
DNA polymerase plays a crucial role in DNA replication by synthesizing new strands of DNA. It adds complementary nucleotides (A-T and C-G) to the template strand, ensuring accurate copying of genetic information. Additionally, DNA polymerase has proofreading capabilities to correct errors during replication.
Question 3: Genetic Mutations
Q: A point mutation occurs in a gene sequence, changing a single nucleotide. If the resulting codon still codes for the same amino acid, what type of mutation is this?
A: Silent mutation
Explanation:
A silent mutation occurs when a nucleotide substitution does not alter the amino acid sequence of the protein. This is due to the redundancy of the genetic code, where multiple codons can code for the same amino acid. For example, both GGU and GGC code for glycine.
Question 4: Evolutionary Processes
Q: In a population of beetles, green coloration (G) is dominant over brown (g). If 64% of the population exhibits green coloration, what percentage of the population is heterozygous (Gg)?
A: 48%
Explanation:
Using the Hardy-Weinberg equation:
p² + 2pq + q² = 1
Where:
- p² = frequency of homozygous dominant individuals (GG)
- 2pq = frequency of heterozygous individuals (Gg)
- q² = frequency of homozygous recessive individuals (gg)
Given that 64% exhibit green coloration (dominant phenotype), this includes both GG and Gg individuals. Therefore, q² (brown beetles) = 1 – 0.64 = 0.36. Solving for q gives √0.36 = 0.6. Then, p = 1 – q = 0.4. Finally, 2pq = 2(0.4)(0.6) = 0.48 or 48%.
Question 5: Gene Expression
Q: What is the role of RNA polymerase in transcription?
A: RNA polymerase synthesizes mRNA by reading the DNA template strand and assembling complementary RNA nucleotides.
Explanation:
During transcription, RNA polymerase binds to the promoter region of a gene and unwinds the DNA double helix. It then adds RNA nucleotides to form a complementary RNA strand (mRNA). This mRNA serves as a template for protein synthesis during translation.
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