sex cells Flashcards
(27 cards)
Who was Gregor Mendel, and why is he significant?
An Austrian monk (1822–1884) known as the “father of genetics.” He pioneered inheritance studies using pea plants, establishing foundational principles like dominance, segregation, and independent assortment. His work was initially ignored but later became the basis of modern genetics.
Name four reasons Mendel chose pea plants for his experiments.
- Controlled pollination: Could self- or cross-pollinate manually.
- True-breeding lines: Homozygous plants produced consistent offspring.
- Clear traits: Seven distinct characteristics (e.g., seed shape, flower color).
- Short generation time: Allowed tracking of traits across multiple generations.
What does “P,” “F₁,” and “F₂” mean in Mendelian experiments?
- P: Parental generation (purebred plants).
- F₁: First filial generation (offspring of P).
- F₂: Second filial generation (offspring of F₁ self-pollination)
Explain the Principle of Dominance with an example
A dominant allele masks the recessive allele in heterozygotes.
- Example: In pea plants, T (tall) is dominant over t (short). A Tt plant is tall.
What is the Principle of Segregation?
During gamete formation, allele pairs separate so each gamete carries only one allele for each gene.
- Example: A Tt plant produces 50% T and 50% t gametes.
Describe the Principle of Independent Assortment and its limitation.
Genes for different traits segregate independently during gamete formation.
- Limitation: Only applies to genes on different chromosomes (linked genes violate this).
- Example: Seed shape (round/wrinkled) and flower color (purple/white) are inherited independently.
What is the phenotypic ratio of a monohybrid cross (e.g., Tt × Tt)?
3:1 (e.g., 3 tall : 1 short plants)
What is the genotypic ratio of a monohybrid cross?
1:2:1 (e.g., 1 TT : 2 Tt : 1 tt)
Define homozygous and heterozygous
- Homozygous: Two identical alleles (TT or tt).
- Heterozygous: Two different allelesk (Tt).
Contrast genotype and phenotype
- Genotype: Genetic makeup
- Phenotype: Observable trait
What is a Punnett square, and how is it used?
A grid predicting possible offspring genotypes/phenotypes by combining parental gametes.
Incomplete Dominance vs. Codominance
- Incomplete: Blended phenotype (e.g., pink flowers from red + white parents).
- Codominance: Both alleles expressed (e.g., AB blood type with A and B antigens).
Explain multiple alleles using the ABO blood system
Three alleles (IA, IB, i) determine blood type:
- IAIA or IAi = Type A
- IBIB or IBi = Type B
- IAIB = Type AB (codominant)
- ii = Type O
What are polygenic traits? Provide examples.
Traits controlled by multiple genes.
- Examples: Human skin color (melanin genes), height, eye color.
Compare Meiosis I and Meiosis II
- Meiosis I: Separates homologous chromosomes → 2 haploid cells.
- Meiosis II: Separates sister chromatids → 4 haploid gametes
Contrast spermatogenesis and oogenesis
- Spermatogenesis:
- 4 functional sperm
- Equal cytoplasm division
- Continuous from puberty - Oogenesis:
- 1 egg + 3 polar bodies
- Unequal division (egg retains cytoplasm)
- Begins pre-birth, resumes at puberty
What happens during Prophase I of meiosis?
Homologous chromosomes pair (synapsis).
- Crossing-over occurs, increasing genetic diversity.
Mitosis: purpose and outcome
- Purpose: Growth, repair, asexual reproduction.
- Outcome: 2 diploid, genetically identical daughter cells.
Meiosis: purpose and outcome.
- Purpose: Gamete formation for sexual reproduction.
- Outcome: 4 haploid, genetically unique gametes.
Key difference in genetic variation between mitosis and meiosis.
- Mitosis: No variation (clones).
- Meiosis: High variation (crossing-over, independent assortment).
Why is Type O blood considered a “universal donor”?
No A/B antigens → won’t trigger immune reactions in recipients.
Define hemophilia and its inheritance pattern.
A recessive X-linked disorder impairing blood clotting. Males (XY) are more likely to inherit it.
True/False: Mitosis produces haploid cells.
False. Mitosis produces diploid cells; meiosis produces haploid cells.
What is the source of genetic variation in meiosis?
- Crossing-over (Prophase I).
- Independent assortment (Metaphase I/II).
- Random fertilization.
