INTRODUCTION TO GENETICS Chapter 10

Genetics Genetics: the study of heredity Heredity: the passing of characteristics from parents → offspring Characteristics = height, eye color, hair texture, etc. Trait: type of characteristic i.e.: tall, blue, curly, etc.

Genes and Alleles Gene: a section of DNA that codes for a particular characteristic i.e.: hair color gene, eye color gene Alleles: different forms of a gene that codes for a particular trait i.e.: brown hair allele, blue eye allele

Types of Alleles 2 Types: Dominant: will always be displayed Represented by capital letter i.e.: “T”, “R”, etc. Recessive: will only be displayed if dominant allele is absent Represented by lower-case letter i.e. “t”, “r”, etc.

Genotype & Phenotype Offspring inherit 1 allele from each parent’s homologous chromosome Genotype: combination of parent’s alleles; genetic makeup Example: Mom’s allele → “T” (dominant) Dad’s allele → “t” (recessive) Offspring’s genotype = “Tt” Phenotype: physical appearance; determined by genotype

Genotype Combinations Homozygous: same allele from each parent is inherited (“True-Breed”) i.e.: “TT”, “tt” Heterozygous: different allele from each parent is inherited (“Hybrid”) i.e.: “Tt” Will usually only show dominant trait

Probability Probability: the likelihood that an event will occur i.e.: coin flip = ½ or 50% Determined by: Probability = # times expected to occur total # trials Past outcomes do not affect future ones Used to predict the outcome of genetic crosses

Punnett Squares Punnett Square: use probability to predict traits of offspring Based on genotypes of parents Parents lined up on top & left Letters inside represent allele combinations of offspring D A D MOMMOM 100% offspring have genotype Tt 100% offspring are tall