Mendelian Inheritance Flashcards

Mendel's Laws of Inheritance

  • Gregor Mendel's experiments with pea plants led to the discovery of basic inheritance principles.
  • Mendel tracked characters with distinct alternative forms (e.g., seed color: green or yellow).
  • Self-fertilization: female gamete fertilized by male gamete from same plant.
  • Cross-fertilization: involves the union of female and male gametes from different individuals

Mendel's Three Important Ideas

  • Dominant and Recessive Traits: Dominant traits mask recessive traits.
  • Genes and Alleles: Each individual has two genes for a character; genes have variant forms called alleles.
  • Segregation of Alleles: Alleles segregate during gamete formation, with each gamete carrying only one allele.

Mendel's Law of Segregation

  • Two alleles of a gene separate during gamete formation, ensuring each gamete carries only one allele.

Mendel's Law of Independent Assortment

  • Alleles of different genes assort independently during gamete formation.

Genotype and Phenotype

  • Genotype: Genetic composition (e.g., TT, tt, Tt).
  • Phenotype: Physical or behavioral characteristics resulting from gene expression (e.g., tall, dwarf).
  • Homozygous: two identical alleles of a gene (TT & tt).
  • Heterozygous: two different alleles of a gene (Tt).

Punnett Square

  • Used to predict offspring genotypes and phenotypes from a genetic cross.

Testcrosses

  • Used to determine if an individual with a dominant phenotype is homozygous or heterozygous by crossing with a recessive homozygote.

Two-Factor Cross (Dihybrid Cross)

  • Examines the inheritance of two different characters.
  • Possible inheritance patterns:
    • Linked genes: Variants inherited together.
    • Independent genes: Variants randomly distributed.

Chromosome Theory of Inheritance

  1. Chromosomes contain DNA and genes.
  2. Chromosomes are replicated and passed on through generations.
  3. Diploid cells have two sets of chromosomes in homologous pairs.
  4. During meiosis, one member of each chromosome pair segregates into daughter nuclei independently.
  5. Gametes are haploid and combine during fertilization to form a diploid offspring.

Chromosomes and Segregation

  • Mendel’s Law of Segregation is explained by homologous chromosome pairing and segregation during meiosis.
  • The gene's locus is its physical location on a chromosome.

Chromosomes and Independent Assortment

  • Random alignment of chromosome pairs leads to independent assortment of genes on different chromosomes.

Sex Chromosomes and X-linked Inheritance Patterns

  • Sex chromosomes determine sex in many species (e.g., X-Y system in mammals).
  • X-linked genes are located on the X chromosome and exhibit unique inheritance patterns.

Variations in Inheritance Patterns

  • Incomplete dominance
  • Codominance: Both alleles are expressed in the phenotype.
  • Multiple alleles: More than two alleles exist for a gene in a population (e.g., ABO blood groups).

Gene Interaction

  • A single trait is controlled by two or more genes.
  • Epistasis: One gene alters the phenotypic expression of another gene.
  • Pleiotropy: One gene has multiple phenotypic effects.

Role of Environment on Phenotype

  • The environment influences phenotype; genotype provides the plan, while the environment provides resources.
  • Norm of reaction: The range of phenotypic variation due to environmental effects.

Types of Traits

  • Discrete: Clearly defined variants (e.g., flower color).
  • Quantitative: Continuous variation (e.g., height), often polygenic and influenced by the environment.