Genetics Chapter 12

12-1: Origins of Hereditary Science

Mendel’s Experiments Genetics – The study of how characteristics are transmitted from parents to offspring Heredity – The passing on of genetic characteristics from one generation to another

Mendel’s Experiments Gregor Mendel (an Austrian monk) used cross-pollination techniques in which pollen is transferred between flowers of two different plants.

Mendel’s Experiments Reasons Mendel used pea plants Require little care Produce many offspring Mature quickly (8-10 weeks)

Mendel’s Experiments P (parental) generation – Organisms that are true-bred for specific traits F1 generation – Offspring of the P generation F2 generation – Offspring of the F1 generation F = Filial (pertainting to a son or daughter)

Mendel’s Experiments Self-pollination – A plant with both male and female reproductive organs that fertilizes itself Cross-pollination – Pollen from one plant is carried to the flower of another plant

Mendel’s Experiments Three Steps of Mendel’s Experiments

Mendel’s Experiments Gene – A section of DNA that carries the information on how to make one protein

Mendel’s Experiments Allele – An alternative form of a gene One allele for each trait is passed from each parent to the offspring.

Mendel’s Experiments Dominant trait – An allele that is fully expressed whenever the allele is present in an individual The trait that masks the other Recessive trait – An allele that is expressed only when there is no dominant allele present in an individual The trait that is masked

12-2: Genetic Crosses

Monohybrid Cross Monohybrid cross – A cross in which one characteristic is tracked Punnett square – used to predict the outcome of genetic crosses

Monohybrid Cross Genotype – the genetic makeup of an organism (use letters) Phenotype – the appearance of an organism (physical appearance)

Monohybrid Cross Homozygous – having identical alleles Heterozygous – having different alleles

Monohybrid Cross Trait – Plant height Phenotype Genotype T – tall t – short Genotype TT – homozygous dominant (pure bred) Tt – heterozygous (hybrid) tt – homozygous recessive (pure bred)

Monohybrid Cross Probability – the likelihood that a specific event will occur Probability = number of one kind of possible outcome total number of all possible outcomes A probability may be expressed as a decimal, a percentage, or a fraction

Mendel’s Characteristics

Monohybrid Cross Ratios and percentages TT x tt = 100% heterozygous TT x TT = 100% homozygous dominant tt x tt = 100% homozygous recessive Tt x tt 50% heterozygous 50% homozygous recessive

Monohybrid Cross Ratios and percentages Tt x Tt = Genotypic ratio – 1:2:1 ratio 25% homozygous dominant 50% heterozygous 25% homozygous recessive Tt x Tt = Phenotypic ratio – 3:1 75% tall 25% short

Dihybrid Cross Dihybrid cross – A breeding experiment that tracks the inheritance of two traits Example Traits: Seed shape & Seed color Alleles: R – round r – wrinkled Y – yellow y – green

Dihybrid Cross RrYy x RrYy Use the FOIL method for each parent to set-up the Punnett square RrYy x RrYy RY Ry rY ry RY Ry rY ry

Dihybrid Cross RY Ry rY ry RY Ry rY ry

Dihybrid Cross RY Ry rY ry Round/Yellow: 9 Round/green: 3 Mendelian Genetics 4/23/2017 Dihybrid Cross RY Ry rY ry Round/Yellow: 9 Round/green: 3 wrinkled/Yellow: 3 wrinkled/green: 1 9:3:3:1 phenotypic ratio RRYY RRYy RrYY RrYy RRyy Rryy rrYY rrYy rryy 24 24

Why eye color changes in people is unknown The trait for eye color actually has three alleles: AaBbCc This chart is used to illustrate the variety of eye colors

Other Monohybrid Crosses Incomplete dominance – a form of intermediate inheritance in which one allele for a specific trait is not completely dominant over the other allele This results in a combined phenotype.

Other Monohybrid Crosses Codominance – Two alleles are expressed (multiple alleles) in heterozygous individuals Two alleles that are both dominant Example: blood types Key A = IA B = IB O = I A and B are dominant over O

Other Monohybrid Crosses Genotypes Phenotypes Type A = IAIA or IAi AA or AO Type B = IBIB or IBi BB or BO Type AB = IAIB AB Type O = ii OO

Other Monohybrid Crosses Sex-Linked traits – Traits (genes) located on sex chromosomes X – Female sex chromosome Y – Male sex chromosome Many sex-linked traits carried on X chromosome

Pedigree Pedigree – A diagram of family relationships that uses symbols to represent people and lines to represent genetic relationships