Mendelian Genetics
Mendel’s Laws of Inheritance:
Law of Segregation: During formation, the two alleles separate, and each gamete receives only one allele for each gene
Law of Independent Assortment: Alleles for different traits segregate independently during gamete formation
Law of Dominance: In a heterozygous genotype, one allele may conceal the presence of another allele for the same trait
Q: Why did Mendel choose to experiment with peas?
Q: What is the importance of true-breeding varieties?
Generations:
P (Parental generation): True-breeding individuals with homozygous traits
F1 (First filial generation): Offspring from the cross of the P generation, showing heterozygous genotypes
F2 (Second filial generation): Offspring from F1 self-pollination, exhibiting a phenotypic ratio of 3:1
Q: What are heritable factors now known as?
Dominant trait: Masks the effect of a recessive trait
Recessive trait: Hidden in the presence of a dominant trait
Alleles: Alternative versions of a gene
Locus: The specific position of a gene on a chromosome
Q: Define phenotype
Q: Define genotype
Q: When might the Law of Independent Assortment be observed?
Q: What is the phenotypic ratio of a heterozygous dihybrid cross?
Patterns of Allelic Interaction:
Complete Dominance: Dominant allele masks the recessive allele
Codominance: Both alleles are equally expressed (e.g. AB blood type)
Incomplete Dominance: Heterozygotes show an intermediate phenotype (e.g. pink flowers)
Extension of Mendelian Genetics:
Pleiotropy: A single gene affects multiple traits (e.g. cystic fibrosis & sickle-cell disease)
Epistasis: Interaction between genes alters phenotypes (e.g. coat color in dogs)
Polygenic Inheritance: 2 or more genes affect a single trait (e.g. human skin color)