GENETICS EXAM 3 KEY CONCEPTS AND
PRACTICE QUESTIONS
◉ Lethal Alleles.
Answer: Some allele combinations cause death; often null mutations.
◉ Lethal Ratio Patterns.
Answer: Expected 1:2:1, observed 2:1; one genotype dies.
◉ Agouti Mouse Example.
Answer: Aᵞ allele → yellow fur in heterozygotes; AᵞAᵞ = lethal.
◉ Delayed-Onset Lethal Alleles.
Answer: Express disease after reproductive age, avoiding
elimination by natural selection.
◉ Example of Delayed-Onset Lethal Alleles.
Answer: Huntington's disease (dominant lethal) → symptoms
appear in 30s-40s.
◉ Wild type.
Answer: Common allele.
,◉ Mutant.
Answer: DNA change alters phenotype.
◉ Intermediate phenotype.
Answer: Pink flowers.
◉ Haplosufficient.
Answer: 1 copy is enough for wild-type dominance.
◉ Haploinsufficient.
Answer: 1 copy not enough; leads to dominant mutant.
◉ Lethal allele.
Answer: Causes death; AᵞAᵞ mice (2:1 ratio).
◉ Delayed lethal.
Answer: Expressed after reproduction; Huntington's disease.
◉ Purpose of Mitosis.
Answer: Cell division producing two genetically identical diploid
daughter cells from one parental cell.
, ◉ Occurs in.
Answer: Somatic cells (non-reproductive body cells).
◉ Ensures.
Answer: Growth & development, Tissue repair, Replacement of
old/damaged cells.
◉ Key principle.
Answer: Genomic integrity — daughter cells get identical DNA.
◉ Interphase.
Answer: Cell growth, DNA replication.
◉ M Phase.
Answer: Mitosis + Cytokinesis.
◉ G₁ Phase.
Answer: Cell grows, performs normal functions, synthesizes
proteins; Some cells enter G₀ (non-dividing state).
◉ S Phase.
PRACTICE QUESTIONS
◉ Lethal Alleles.
Answer: Some allele combinations cause death; often null mutations.
◉ Lethal Ratio Patterns.
Answer: Expected 1:2:1, observed 2:1; one genotype dies.
◉ Agouti Mouse Example.
Answer: Aᵞ allele → yellow fur in heterozygotes; AᵞAᵞ = lethal.
◉ Delayed-Onset Lethal Alleles.
Answer: Express disease after reproductive age, avoiding
elimination by natural selection.
◉ Example of Delayed-Onset Lethal Alleles.
Answer: Huntington's disease (dominant lethal) → symptoms
appear in 30s-40s.
◉ Wild type.
Answer: Common allele.
,◉ Mutant.
Answer: DNA change alters phenotype.
◉ Intermediate phenotype.
Answer: Pink flowers.
◉ Haplosufficient.
Answer: 1 copy is enough for wild-type dominance.
◉ Haploinsufficient.
Answer: 1 copy not enough; leads to dominant mutant.
◉ Lethal allele.
Answer: Causes death; AᵞAᵞ mice (2:1 ratio).
◉ Delayed lethal.
Answer: Expressed after reproduction; Huntington's disease.
◉ Purpose of Mitosis.
Answer: Cell division producing two genetically identical diploid
daughter cells from one parental cell.
, ◉ Occurs in.
Answer: Somatic cells (non-reproductive body cells).
◉ Ensures.
Answer: Growth & development, Tissue repair, Replacement of
old/damaged cells.
◉ Key principle.
Answer: Genomic integrity — daughter cells get identical DNA.
◉ Interphase.
Answer: Cell growth, DNA replication.
◉ M Phase.
Answer: Mitosis + Cytokinesis.
◉ G₁ Phase.
Answer: Cell grows, performs normal functions, synthesizes
proteins; Some cells enter G₀ (non-dividing state).
◉ S Phase.
