LECTURE 5: Microevolution Part 3 Mendelian Genetics

Genetic Inheritance Blending vs. Particulate Hypothesis Gregor Mendel’s plant breeding experiments

What is a Trait? variation of a particular character Examples: Eye color Hair color Flower color

How do offspring inherit traits from both parents? 2 Hypothesis Blending Hypothesis Offspring inherit a blend of parents trait An intermediate trait between parents

How do offspring inherit traits from both parents? Blending hypothesis discarded! Gregor Mendel developed a particulate hypothesis of inheritance Parents pass on to their offspring separate and distinct factors

Who was Gregor Mendel? Father of Genetics Genetics: the study of heredity Bred Pea plants to study his hypothesis

What was Mendel’s experiment? Cross- fertilized true-breeding plants that had 2 distinct and contrasting traits Purple and White flowers Mendel used Pea plants to study flower color and seed shape http://www.dnaftb.org/dnaftb/1/concept/

Language of Genetics The offspring of 2 different true-breeding varieties are hybrids Parents (P generation) Hybrid Offspring (F1 generation) F1 generation self-fertilized or crossed (F2 generation)

Language of Genetics Cross where parents differ in only one trait (monohybrid cross) Cross where parents differ in two traits (dihybrid cross)

Results from Mendel’s Experiment Monohybrid cross P-Generation: purple x white F1 Generation- all purple F2 Generation- purple and white Must carry 2 factors for flower color Principle of Segregation

Mendel’s Principle of Segregation Alternate forms of a gene (allele) P / p Dominant (P) Expression masks recessive allele Recessive (p) Expression is masked by dominate allele For each character there are 2 alleles (homozygous PP,pp/heterozygous Pp) Meiosis results in the separating/segregation of these 2 alleles Phenotype Physical expression of alleles (purple/white) Genotype Allele expression PP,pp,Pp

Mendel’s Principle of Segregation PURPLE x WHITE PURPLE PURPLE, WHITE Which flower color is recessive? WHITE What would the genotype be for the recessive flower? pp homozygous recessive Which flower color is dominant? PURPLE What would the genotype be for the dominant flower? PP homozygous dominant Pp heterozygous

What is a Gene Pool? The combined alleles of all the individuals in a population Can determine frequencies of alleles and genotypes/phenotypes

How can you determine allele frequencies in a population? Find the number of dominant alleles Find the number of recessive alleles Divide each by the total number of alleles in that population

25 AA, 50 Aa, 25 aa A: 100 Frequency 100/200 = 50% a: 100

50 AA, 25 Aa, 25 aa A: 125 (125/ 200 = 63%) a: 75 (75/200 = 37%) Frequency 50/100 = 50% Aa:25 Frequency 25/100 = 25% aa:25