GENETICS AND HEREDITY Genes found on chromosomes in the nucleus of a cell, code for the inherited characteristics we call traits The passing of traits from parents to offspring is known as heredity The scientific study of heredity is called genetics Lacking today’s technology the first studies of genetics were based on physical appearance and mathematics

GREGOR MENDEL Mendel was an Austrian monk who loved gardening and mathematics He designed simple experiments with pea plants to determine how heritable traits were transferred from one generation to the next

MENDEL’S PEA TRAITS

MENDEL’S CONCLUSIONS Each trait is controlled by two genes that they receive from their parents Some genes are dominant over others (shown in capital letters) Genes that are masked by dominant genes are called recessive genes (shown in lower case letters) The combination of these two genes determines the traits offspring will exhibit How often these traits will appear is predictable

TERMINOLOGY GENOTYPE  - PHENOTYPE  - PUREBRED (homozygous)  - HYBRID (heterozygous)  -

REGINALD PUNNETT Dominant genes are - Recessive genes are - Based on the work of Mendel, he developed the “Punnett Square” as a method of predicting the results of a genetic cross (breeding) Dominant genes are - Recessive genes are -

CROSS #1 t t T - - T - - PHENOTYPE BOX Tall purebred pea plant (TT) x Short purebred pea plant (tt) Tall (T)  dominant Short (t)  recessive GENOTYPE BOX t t T - - RESULT: - T - -

Tall hybrid pea plant (Tt) x Tall (T)  dominant Short (t)  recessive CROSS #2 PHENOTYPE BOX Tall hybrid pea plant (Tt) x Tall (T)  dominant Short (t)  recessive GENOTYPE BOX T t RESULT: - T - - t - -

Principles of Genetics -