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Chapters 14 & 15: Mendel and the gene Idea; The Chromosomal Basis of…
Chapters 14 & 15: Mendel and the gene Idea; The Chromosomal Basis of Inheritance
Foundations of genetics
Law of Segregation
Alleles separate during gamete formation
Each gamete receives 1 allele per gene
Mendel's experiments
Identified heritable factors (genes)
Studied inheritance through breeding pea plants
Established rules of inheritance ↓
Law of Independent Assortment
Genes for different traits assort independently
Applies to genes on different chromosomes or far apart on the same chromosome
Genes and Alleles
Gene = heritable unit of information
Allele = different version of a gene
Dominant vs Recessive alleles
Genotype (genetic makeup) vs Phenotype (observable trait)
Patterns of Inheritance
Complete dominance
Incomplete dominance
Codominance
Pleiotropy = 1 gene effects many traits
Epistasis = 1 gene affects expression of another gene
Polygenic inheritance = many genes effects 1 trait (i.e. height)
Chromosomal Basis of Inheritance
Sex-Linked Inheritance
Genes on X (or occasionally Y) chromosomes
X-linked recessive traits more common in males (i.e. color blindness)
Linked Genes
Do not independently assort
Recombination occurs through crossing over
More distance between genes → more recombination
Basis for genetic maps
Located near each other on the same chromosome
Thomas Hunt Morgan's experiments with fruit flies
Discovered sex-linked genes
Linked specific genes to specific chromosomes
Chromosomal Abnormalities
Nondisjunction
Failure of chromosomes to separate
Leads to aneuploidy
Trisomy
Monosomy
Structural changes
Duplication
Inversion
Deletion
Translocation