Mendelian Inheritance Patterns to Know for General Biology II

Mendelian inheritance patterns explain how traits are passed down through generations. Key concepts include monohybrid and dihybrid crosses, dominance types, and inheritance mechanisms, all of which help us understand genetic variation in organisms.

1. Monohybrid crosses

   • Involves a single trait with two alleles (e.g., tall vs. short plants).
   • Follows Mendel's Law of Segregation, where alleles segregate during gamete formation.
   • Results in a phenotypic ratio of 3:1 in the F2 generation for dominant and recessive traits.

2. Dihybrid crosses

   • Examines two traits simultaneously (e.g., seed shape and color).
   • Demonstrates Mendel's Law of Independent Assortment, where genes for different traits segregate independently.
   • Produces a phenotypic ratio of 9:3:3:1 in the F2 generation.

3. Complete dominance

   • Occurs when one allele completely masks the effect of another allele.
   • The phenotype of the heterozygote is indistinguishable from that of the homozygous dominant.
   • Commonly observed in traits like flower color in pea plants.

4. Incomplete dominance

   • Results in a blending of traits in the heterozygote (e.g., red and white flowers producing pink flowers).
   • Neither allele is completely dominant, leading to an intermediate phenotype.
   • The phenotypic ratio in the F2 generation is typically 1:2:1.

5. Codominance

   • Both alleles in a heterozygote are fully expressed (e.g., AB blood type).
   • Results in a phenotype that shows both traits distinctly.
   • Important in understanding blood types and certain plant traits.

6. Multiple alleles

   • Refers to a gene that has more than two alleles in the population (e.g., ABO blood group).
   • Involves complex inheritance patterns and can lead to multiple phenotypes.
   • Demonstrates the concept of dominance hierarchy among alleles.

7. Sex-linked inheritance

   • Traits associated with genes located on sex chromosomes (X or Y).
   • Often results in different inheritance patterns in males and females (e.g., color blindness).
   • Males are more likely to express recessive traits linked to the X chromosome.

8. Autosomal inheritance

   • Involves genes located on non-sex chromosomes (autosomes).
   • Traits can be dominant or recessive and affect both sexes equally.
   • Patterns of inheritance can be tracked through pedigrees.

9. Test crosses

   • A method used to determine the genotype of an individual with a dominant phenotype.
   • Involves crossing the individual with a homozygous recessive individual.
   • The offspring's phenotypes reveal the unknown genotype.

10. Punnett squares

    • A tool used to predict the genotypic and phenotypic ratios of offspring from genetic crosses.
    • Helps visualize the combination of alleles from each parent.
    • Essential for understanding inheritance patterns and probabilities in genetics.