Inheritance & Genes

Learning Objectives To understand how traits are passed from parents to offspring. To know the difference between dominant and recessive genes. To be able to construct and interpret Punnett squares. To determine the expected ratio of phenotypes in a genetic cross.

Key Words Alleles - Alternative form of a gene Genes – the units of inheritance. Genetics - Scientific study of heredity and hereditary variations Genotype - Genetic makeup of an organism Heredity - Transmission of characteristics from parents to offspring Heterozygous - Having tow different alleles for a given gene Homozygous - Having two identical alleles for a given gene Pedigree - Family tree representing the occurrence of heritable traits in parents and offspring across a number of generations Phenotype - The expressed traits of an organism; outward appearance Punnett square - Diagram used in the study of inheritance to show the results of random fertilization.

Genes are the units of Inheritance

Dominant/Recessive Inheritance Homozygous parents CROSSCHART BOTH parents are PURE-BREEDING (CAN ONLY PASS ON ONE TYPE OF ALLELE for that TRAIT.

Dominan/Recessive Inheritance Heterozygous parents CROSSCHART Both parents have a copy of TWO DIFFERENT ALLELES that can be passed on for that TRAIT.

Punnett Squares Ff = “carrier” of cystic fibrosis

Pedigree Analysis