Genetics-And-Evolution-Principles-Of-Inheritance-And-Variation-4
Incomplete Dominance:
Incomplete dominance is when neither allele completely masks the other in a heterozygous condition.
The heterozygous phenotype is an intermediate blend of the two homozygous phenotypes.
Example: Snapdragons with red (RR) and white (WW) flowers produce pink (RW) flowers in the F1 generation.
No dominant or recessive alleles in incomplete dominance.
Genotypic and phenotypic ratios are the same.
Co-dominance:
Co-dominance is when both alleles in a heterozygous individual are fully expressed.
The phenotype simultaneously shows both traits without blending.
Example: In the ABO blood group system, IAIB individuals have both A and B antigens.
No dominant or recessive alleles in co-dominance.
Genotypic and phenotypic ratios often reflect each other.
Mirabilis jalapa (Four O’Clock Flower):
Wide genetic variability in flower colors, including red, pink, yellow, white, and bicolor combinations.
Multiple alleles control flower color, leading to incomplete dominance or co-dominance.
A model for studying complex genetic traits and inheritance.
Snapdragons (Antirrhinum majus):
Known for flower color variation, including red, pink, white, and yellow.
Follow Mendelian inheritance patterns, demonstrating incomplete dominance and co-dominance.
Used in genetic research and educational settings.
Exhibit genetic diversity beyond flower color.
Genetically Controlled Sex Determination:
Two common mechanisms: XX-XY system and ZZ-ZW system.
XX-XY system: Males have one X and one Y chromosome, while females have two X chromosomes (e.g., humans).
ZZ-ZW system: Males have two of the same sex chromosomes (ZZ), while females have two different sex chromosomes (ZW) (e.g., birds).
Other complex systems exist in various species.
Understanding these mechanisms is crucial for studying sex-related traits in genetics.
