1. Mendelian Genetics Ch. 6

2. What is Genetics?
The study of the inheritance of traits and variation in organisms.
Trait: characteristics that are inherited (eye color, height, leaf shape, etc.)

3. GREGOR MENDEL Mendel is known as the “Father of Genetics.”
He was an Austrian monk & studied pea plants in the monastery garden.

4. Mendel’s Experiments:
Mendel worked with pure breeding (self-pollinating) pea plants
He controlled breeding between plants
He studied 7 different traits of pea plants: pea shape, pea color, pod shape, pod color, plant height, flower color, and flower position
First experiments were monohybrid crosses (cross one trait at a time)

5. Mendel’s Experiments:
P Generation
Tall
Short
True-breeding

6. Mendel’s Experiments:
F1 Generation
Tall
Tall
100% tall

7. Mendel’s Experiments:
F2 Generation
Tall
Tall
Tall
Short
Ratio = 3 talls to 1 Short

8. Mendel’s Experiments:
Mendel observed the same results every time he crossed two different forms of a trait.
P Generation
F1 Generation
F2 Generation
Short
Tall
Tall
Tall
Tall
Tall
Short
Tall

9. Mendel’s Conclusions:
1. Biological inheritance is determined by factors (or GENES) that are passed from one generation to the next.

10. 2. Law of Segregation:
Organisms inherit 2 copies of each gene (one from each parent)
When gametes (egg & sperm) are formed the pair of genes responsible for each trait separate.

11. 3. “Principle of Dominance” – some alleles are dominant and some are recessive. The dominant trait prevents the expression of the recessive trait.

12. An allele is a different form of the same gene
Each parent donates one allele for every gene.
Homozygous: two alleles are the same (GG or gg)
Heterozygous: two alleles are different (Gg)

13. Alleles can be represented using letters.
dominant allele: expressed when at least one copy is present; capital letter (GG or Gg)
recessive allele: expressed only when two copies are present; lowercase letter (gg)

14. All of an organism’s genetic material is called the genome.
Genotype: genetic makeup (Bb vs. bb)
Phenotype: physical traits (brown eyes vs. blue eyes)

15. Probability The likelihood that an event will occur
Probability is used to predict outcomes of genetic crosses
Ex: flipping a coin What is the probability that it will land on heads?

16. Punnett squares are used to predict genetic crosses.
The Punnett square is a grid system for predicting all possible genotypes resulting from a cross.
Axes = gametes of parents
Boxes = genotypes of offspring

17. Monohybrid crosses examine the inheritance of only one specific trait.
Examples:
Cross a homozygous dominant with a homozygous recessive:

18. Cross one heterozygous with another heterozygous

19. Cross a heterozygous with a homozygous recessive

20. Terms to Know!! Gene Allele Dominant Recessive Homozygous Heterozygous
Genotype
Phenotype