Gregor Mendel “The Father of Genetics” GENETICS INTRODUCTION
Introductory Vocabulary Genetics is the study of heredity Heredity - is the passing of traits from the parents to their offspring Trait- is the characteristic that is passed from the parent to the offspring (eye color) Characteristic (phenotype)- will describe the trait. (blue eyes) Alleles: factors that determine the phenotype of a trait. (B or b)
Phenotype vs. Genotype Genotype - is the arrangement of alleles that determines a trait. (WW) Phenotype is the specific physical characteristic of a trait. (e.g. Widow’s Peak) GenotypePhenotype WWWidow’s Peak WwWidow’s Peak wwNormal (Rounded) Hairline Where “W” = Dominant allele, and “w” = recessive allele
About Gregor Mendel Mendel was an Austrian Monk Gardner for the monastery. Studied the growth of peas and their offspring. Recorded physical characteristics (Phenotypes) of the offspring. Controlled his experiment by examining only one variable at a time.
One Lucky Monk Mendel’s Choice to study pea plants was divine intervention at work! 1.Pea Plants undergo sexual reproduction. 2.Pea plants have both sexual parts on the same flower (stamen and pistils) 3.Pea Plants grow fast with a quick generational time. 4.Pea Plants reproduce many offspring. 5.Traits studied all were controlled by one gene (i.e. Mendelian Traits), so only had 2 outcomes.
Mendel’s Laws Mendel’s Studies helped him achieve 3 important conclusions: 1. Parents donate only 1 copy (allele) of each gene in their gametes (sex cells). (=Law of Segregation) 2. Traits (genes) are inherited as discrete, solitary units. (=Law of Independent Assortment) 3. Organisms inherit two copies of each gene, one from each parent.
Mendel’s Laws 1.Law of Segregation : 2 alleles for each trait must separate when gametes are formed (=Anaphase II). parents randomly pass only 1 allele for each trait to each offspring. 2 organisms can look alike (TT or Tt) but have different underlying gene combinations. Tt
Law of Segregation Mendel’s 1 st Experiment: Law of Segregation Alleles: S = Smooth s = wrinkled Cross Parents: SS x ss F1 = 1 st offspring (All Ss) Cross F1: Ss x Ss F2 = 75% Smooth, 25% wrinkled Wrinkled phenotype appears again in the second generation.
Mendel’s Laws 2. Law Independent Assortment: Genes for different traits (e.g. seed shape and seed color) are inherited independently of each other. Organisms don’t inherit traits as packages. Genes are sorted randomly when gametes are formed. Occurs during Synapsis. of Prophase I RrYy Ex. A pea plant, RrYy (Round Yellow) produces 4 gametes RY, Ry, rY, ry = 4 different combinations
Mendel: Law of Independent Assortment YELLOW SEEDS yellow podsYELLOW SEEDS yellow pods Outcome: 9 = GREEN PODS, YELLOW SEEDS (G_Y_) 3 = GREEN PODS, green seeds (G_ yy) 3 = yellow pods, YELLOW SEEDS (gg, Y_) 1 = yellow pods, green seeds (gg, yy) Parental Cross: GGYY x ggyy: Outcome 100% Green Pods Yellow Seeds (GgYy)
Punnett Squares One factor cross: Tt x Tt (Parent 1) x (Parent 2)
Punnett Squares One factor cross: Tt x Tt (Parent 1) x (Parent 2) Parent 1 Parent 2
Punnett Squares One factor cross: Tt x Tt (Parent 1) x (Parent 2) T t T t Tt
Punnett Squares One factor cross: Tt x Tt (Parent 1) x (Parent 2) T t T t T t t t
Punnett Squares One factor cross: Tt x Tt (Parent 1) x (Parent 2) T t T t T t t t T t
Punnett Squares One factor cross: Tt x Tt (Parent 1) x (Parent 2) T t T t T t t t T t T
Punnett Squares Genotypic ratio = TT:Tt:tt = 1 : 2 : 1 T t T t T t t t T t T
Punnett Squares Phenotypic ratio = 3 talls : 1 short Genotypic ratio = 1 TT, 2 Tt, 1 tt T t T t T t t t T t T tall short Phenotypic ratio = 3 : 1 Genotypic ratio = 1:2:1