DYHYBRID CROSS
Write the genotypes for parents who are heterozygous for both widows peak and being tall
WwTt x WwTt
Now determine the alleles that each parent can donate in combination in their gametes
FOIL: First, outer, inner, last
EXECPTIONS
* Incomplete Dominance: Neither allele is completely dominant, resulting in a blending of traits (e.g., red + white flowers = pink flowers).
* Codominance: Both alleles are expressed equally (e.g., AB blood type).
* Multiple Alleles: Some traits have more than two allele options (e.g., blood type).
* Polygenic Inheritance: Traits controlled by multiple genes (e.g., human skin color).
INCOMPLETE DOMINANCE
* Definition: Incomplete dominance occurs when neither allele is completely dominant over the other. As a result, the heterozygous phenotype is a blend or intermediate between the two parental traits.
* Example: Flower Color in Snapdragons:
* Red flowers (RR) crossed with White flowers (rr) produce offspring with Pink flowers (Rr).
* This results in a blending of the traits, which is characteristic of incomplete dominance.
* Genotypic Notation:
* RR = Red flowers
* rr = White flowers
* Rr = Pink flowers (heterozygous, intermediate phenotype)
Codominance
* Definition: Both alleles contribute equally and visibly to the phenotype.
* Example: AB Blood Type
* IA and IB are co-dominant.
* Genotype: IAIB = AB blood type.
Multiple alleles
* Some traits are controlled by more than two alleles.
* Example: Human Blood Type
* The ABO blood group system involves three alleles: IA, IB, and i.
* IA and IB are dominant, while i is recessive.
* Possible blood types:
* IAIA = Type A
* IAi = Type A
* IBIB = Type B
* IBi = Type B
* IAIB = Type AB (co-dominant)
* ii = Type O (recessive)
Polygenetic traits
* Traits that are controlled by more than one gene.
* These traits exhibit a range of phenotypes and are influenced by environmental factors.
* Example: Human Skin Color
* Skin color is determined by the interaction of multiple genes, each contributing to the final phenotype.
* The more dominant alleles, the darker the skin.