1. LECTURE 5: Microevolution Part 3 Mendelian Genetics

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

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

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

6. 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

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

8. 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

9. 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)

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

11. 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

12. 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

13. 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

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

15. 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

16. 25 AA, 50 Aa, 25 aa
A: 100
Frequency 100/200 = 50%
a: 100

17. 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