Secondary 3 Biology Genetics Inheritance Quiz

Answer Key - Secondary 3 Biology Quiz: Genetics Inheritance

Section A: Multiple Choice

1. B (A gene is a segment of DNA located on a chromosome).
2. C (Cross: Rr x rr $\rightarrow$ 50% Rr, 50% rr. White is recessive).
3. C (A-T and C-G are the complementary pairs).
4. C (Heterozygous means two different alleles).
5. A (DNA $\rightarrow$ mRNA via transcription $\rightarrow$ Protein via translation).

Section B: Structured Response

6. Gene: A segment of DNA on a chromosome that codes for a specific polypeptide/protein. [2]
7. Nucleotide Structure: Consists of a phosphate group, a pentose sugar (deoxyribose), and a nitrogenous base (A, T, C, or G). [3]
8. Phenotype vs Genotype: Genotype is the genetic makeup/alleles of an organism (e.g., Bb); phenotype is the observable physical characteristic (e.g., Brown eyes). [2]
9. X-linked Disorders: Males have only one X chromosome. If they inherit the recessive allele, there is no second X chromosome with a dominant allele to mask it, so the disorder is expressed. [3]
10. DNA Ligase: An enzyme that joins two pieces of DNA together by forming phosphodiester bonds (acts as "molecular glue"). [2]
11. Pea Plant Cross: (a) Punnett Square: T x T / T x t / t x T / t x t. [2] (b) Genotypic Ratio: 1 TT : 2 Tt : 1 tt. [1]
12. Mutation to Protein: A change in the DNA base sequence $\rightarrow$ changes the mRNA codon $\rightarrow$ changes the amino acid sequence in the polypeptide $\rightarrow$ alters the folding/shape of the protein, affecting its function. [3]
13. Double Helix/Replication: Complementary base pairing (A-T, C-G) ensures that each strand serves as a template. When split, the exact same sequence can be reconstructed on both sides. [3]
14. Transgenic Organism: An organism that contains genetic material from a different species (foreign DNA), whereas natural organisms only contain DNA from their own species/ancestors. [2]
15. Bacterial Plasmid: Plasmids are small, circular DNA molecules that can replicate independently and are easily taken up by bacteria (transformation), ensuring the gene is stably maintained and expressed. [3]

Section C: Extended Response

16. Transcription vs Translation:
    • Transcription: Occurs in nucleus; DNA $\rightarrow$ mRNA; involves RNA polymerase. [2]
    • Translation: Occurs at ribosome (cytoplasm); mRNA $\rightarrow$ polypeptide; involves tRNA and ribosomes. [2]
17. Cystic Fibrosis: (a) Both parents are heterozygous (Cc). [2] (b) Both parents are carriers; they possess one dominant healthy allele and one recessive disease allele. Each parent passed the recessive allele to the child, resulting in a homozygous recessive (cc) genotype. [3]
18. Recombinant Plasmid Steps:
    1. Isolate the target human gene using restriction enzymes. [1]
    2. Cut the bacterial plasmid with the same restriction enzyme to create compatible sticky ends. [1]
    3. Mix the gene and plasmid; DNA ligase joins them. [1]
    4. Insert the recombinant plasmid into a bacterium via transformation. [1]
    5. Grow bacteria in a fermenter to produce the protein. [1]
19. Ethical Consideration: (Accept any well-reasoned point) e.g., "Designer babies" (altering traits for non-medical reasons) may lead to social inequality or unforeseen biological consequences/mutations in future generations. [4]
20. DNA Sequence to Function: The sequence of bases determines the sequence of codons $\rightarrow$ determines the sequence of amino acids $\rightarrow$ determines the 3D folding/shape of the protein $\

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# Answer Key - Secondary 3 Biology Quiz: Genetics Inheritance

### Section A: Multiple Choice
1. **B** (A gene is a segment of DNA located on a chromosome).
2. **C** (Cross: Rr x rr $\rightarrow$ 50% Rr, 50% rr. White is recessive).
3. **C** (A-T and C-G are the complementary pairs).
4. **C** (Heterozygous means two different alleles).
5. **A** (DNA $\rightarrow$ mRNA via transcription $\rightarrow$ Protein via translation).

### Section B: Structured Response
6. **Gene:** A segment of DNA on a chromosome that codes for a specific polypeptide/protein. [2]
7. **Nucleotide Structure:** Consists of a phosphate group, a pentose sugar (deoxyribose), and a nitrogenous base (A, T, C, or G). [3]
8. **Phenotype vs Genotype:** Genotype is the genetic makeup/alleles of an organism (e.g., Bb); phenotype is the observable physical characteristic (e.g., Brown eyes). [2]
9. **X-linked Disorders:** Males have only one X chromosome. If they inherit the recessive allele, there is no second X chromosome with a dominant allele to mask it, so the disorder is expressed. [3]
10. **DNA Ligase:** An enzyme that joins two pieces of DNA together by forming phosphodiester bonds (acts as "molecular glue"). [2]
11. **Pea Plant Cross:**
    (a) Punnett Square: T x T / T x t / t x T / t x t. [2]
    (b) Genotypic Ratio: 1 TT : 2 Tt : 1 tt. [1]
12. **Mutation to Protein:** A change in the DNA base sequence $\rightarrow$ changes the mRNA codon $\rightarrow$ changes the amino acid sequence in the polypeptide $\rightarrow$ alters the folding/shape of the protein, affecting its function. [3]
13. **Double Helix/Replication:** Complementary base pairing (A-T, C-G) ensures that each strand serves as a template. When split, the exact same sequence can be reconstructed on both sides. [3]
14. **Transgenic Organism:** An organism that contains genetic material from a different species (foreign DNA), whereas natural organisms only contain DNA from their own species/ancestors. [2]
15. **Bacterial Plasmid:** Plasmids are small, circular DNA molecules that can replicate independently and are easily taken up by bacteria (transformation), ensuring the gene is stably maintained and expressed. [3]

### Section C: Extended Response
16. **Transcription vs Translation:**
    - Transcription: Occurs in nucleus; DNA $\rightarrow$ mRNA; involves RNA polymerase. [2]
    - Translation: Occurs at ribosome (cytoplasm); mRNA $\rightarrow$ polypeptide; involves tRNA and ribosomes. [2]
17. **Cystic Fibrosis:**
    (a) Both parents are heterozygous (Cc). [2]
    (b) Both parents are carriers; they possess one dominant healthy allele and one recessive disease allele. Each parent passed the recessive allele to the child, resulting in a homozygous recessive (cc) genotype. [3]
18. **Recombinant Plasmid Steps:**
    1. Isolate the target human gene using restriction enzymes. [1]
    2. Cut the bacterial plasmid with the same restriction enzyme to create compatible sticky ends. [1]
    3. Mix the gene and plasmid; DNA ligase joins them. [1]
    4. Insert the recombinant plasmid into a bacterium via transformation. [1]
    5. Grow bacteria in a fermenter to produce the protein. [1]
19. **Ethical Consideration:** (Accept any well-reasoned point) e.g., "Designer babies" (altering traits for non-medical reasons) may lead to social inequality or unforeseen biological consequences/mutations in future generations. [4]
20. **DNA Sequence to Function:** The sequence of bases determines the sequence of codons $\rightarrow$ determines the sequence of amino acids $\rightarrow$ determines the 3D folding/shape of the protein $\rightarrow$ the specific shape determines how the protein interacts with other molecules, which defines its biological function. [4]