Genetics Homework 8 Already Graded A+
Gamete Formation during Meiosis
1. False Statement: - Statement: "Parental gametes can be formed only if there is no crossing over during meiosis." - Interpretation: This is false because crossing over can affect allele combinations, but parental
gametes ...
Genetics Homework 8 Already Graded A+
Gamete Formation during Meiosis
1. False Statement:
- Statement: "Parental gametes can be formed only if there is no crossing over during meiosis."
- Interpretation: This is false because crossing over can affect allele combinations, but parental
gametes (those with the original combinations of alleles) can still be formed even if crossing over occurs,
due to recombination and independent assortment.
2. Expected F2 Phenotypic Ratio with Complete Linkage:
- Genotype: a + b + / ab (selfed heterozygote)
- Expected Phenotypic Ratio: ✔️ 3:1.
- Explanation: In the case of complete linkage for two genes, only parental combinations will appear,
leading to a dominant to recessive phenotypic ratio.
3. Effect of Genetic Linkage on Gamete Production:
- Statement: "Genetic linkage leads to the production of a significantly greater than expected number
of gametes containing chromosomes with parental combinations of alleles."
- Interpretation: ✔️ True. Genetic linkage reduces the recombination frequency between linked
genes, thus increasing parental allele combinations.
Penetrance and Mutation Analysis
4. Penetrance of PRSS1 Mutation (Arg122His):
- Given Information: Penetrance is 86%.
- Interpretation: Individuals with this genotype have an 86% chance of exhibiting the associated
phenotype (e.g., pancreatitis).
5. Penetrance of PRSS1 Mutation (Ala16Val):
- Data: 120 individuals with the mutation, 48 did not display evidence of pancreatitis.
, - Penetrance Calculation:
- Penetrance = (Total individuals - individuals without phenotype) / Total individuals = (120 - 48) / 120
= 60%.
- Conclusion: ✔️ 60% penetrance for the Ala16Val mutation.
6. Probability of Offspring with Hereditary Pancreatitis:
- Parents: Heterozygous for Ala16Val and homozygous for normal cationic trypsinogen.
- Probability Calculation:
- Genotype options for offspring: 50% heterozygous (Ala16Val) and 50% homozygous for normal.
- Given 60% penetrance, the expected probability of offspring having pancreatitis = 0.5 0.6 = 0.3 or
30%.
- Conclusion: ✔️ 30% probability of offspring having hereditary pancreatitis.
Types of Mutations and DNA Repair
7. Types of Mutations Enabled by the Redundant Genetic Code:
- Type of Mutation: ✔️ Silent mutations.
- Explanation: Silent mutations do not alter the amino acid sequence due to the redundancy of the
genetic code.
8. DNA Sequence Change Due to DNA Polymerase Mistakes:
- Explanation: ✔️ 1. Creates mismatched base pairs that may be corrected by the mismatch repair
pathway.
9. Thymine Dimer Repair:
- Cause: Induced by UV exposure.
- Repair Mechanisms: ✔️ Repaired by nucleotide excision repair (NER) and photoreactive repair.
10. Deaminated Cytosine:
- Resulting Base: Uracil.
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