Genetics Chapter 11

Genetics Genetics is the study of heredity Every living thing- plant or animal, microbe or human being- has a set of characteristics inherited from its parent or parents.

Gregor Mendel “Father” of genetics Austrian monk, mid-1800s Researched pea plant inheritance Easy to grow, fast reproduction Studied plant height, pea shape/color, pod color, etc.

Pea Plant Fertilization Self-pollination Male gametes (pollen) fertilize egg of same flower Produces pure-bred offspring, meaning that all characteristics are received from a single parent or plant True-breeding: produce offspring identical to parent when self-pollinated

Pea Plant Fertilization Cross-pollination Pollen from one plant fertilizes egg of another plant Mendel had to prevent self-pollination in order to cross-pollinate. He did this by cutting away the pollen-bearing male parts and dusting pollen from another plant into eggs of the flower. Offspring have two parents

Mendel’s Experiments P = Parent generation F1 = First filial generation Filius = Latin for “sons” and “daughter” F2 = Second filial generation (F1 X F1) P Pure Green X Pure Yellow F1 All Green F2 3 Green:1 Yellow

Mendel’s Conclusions Law of Dominance – one allele (form of a gene) is dominant, one is recessive Recessive trait was hidden in F1 generation Green = dominant Yellow = recessive

Mendel’s Conclusions Law of Segregation: alleles for a gene separate (segregate) when gametes (sex cells) form (meiosis I) Each F1 plant produces two types of gametes, in the Mendel’s pea pod case one allele for tallness and one for shortness

Punnett Squares First must determine possible gametes Heterozygous tall plant = Tt Half of gametes will get ‘T’, other half will get ‘t’ Homozygous tall plant = TT All gametes will get ‘T’

Punnett Squares Monohybrid cross Gametes go on the top and side Tt X Tt Monohybrid cross Cross involving one trait Gametes go on the top and side Combine gametes to find possible offspring

Punnett Squares Genotype (genetic make-up) ratio 1TT: 2Tt: 1tt Tt X Tt Genotype (genetic make-up) ratio 1TT: 2Tt: 1tt Phenotype (physical characteristics) ratio 3 tall: 1 short

Probability Punnett squares are used to predict the probability of certain traits in offspring of genetic crosses Tt X Tt ½ chance of getting ‘t’ from mom, ½ chance of getting ‘t’ from dad ½ X ½ = ¼ tt in offspring

Dihybrid Cross Mendel looked at the inheritance patterns of two traits Seed shape and seed color Found that the traits were inherited independently of each other Law of Independent Assortment Genes on separate chromosomes are inherited at random