1. Mendelian Genetics

2. The Pea Plant
Peas reproduce sexually (they produce two different gametes - male and female)
Pollination= transfer of male pollen to pistil
Fertilization= uniting of male and female gametes
POLLEN + OVULE  SEED
Self-pollination= flower pollinates itself; male and female gametes come from same plant
Cross-pollination= male and female gametes come from different plants

3. Gregor Mendel 1850’s Austrian monk and gardner
“Father of Genetics” (study of heredity)
Heredity= passing on of traits from parent to offspring
Traits= characteristics that are inherited
Mendel’s garden

4. Mendel’s Experimental Methods
Mendel hand-pollinated flowers using a paintbrush
He could snip the stamens to prevent self-pollination
Covered each flower with a cloth bag
He traced traits through the several generations

5. Mendel’s Studies
He first studied one trait at a time (the first trait he studied was the height of pea plants)
Monohybrid cross= mating between parents that only differ by ONE trait
(Other traits he studied: flower position, flower color, seed color, pod color, seed shape, pod shape)

6. Mendel’s Studies

7. Mendel’s Studies
Mendel tested 6 more traits. In every cross, one trait disappeared in F1, then reappeared in a ration of ¼ in the F2 plants.
*Remember- a good science experiment must give reproducible results!
P1 (Parent) Generation: X
Cross-pollinate
F1 (filial) Generation:
Hybrids= offspring of parents with different forms of the same trait
Self-pollinate
F2 Generation:

8. Mendel’s Laws
From his pea plant experiments, Mendel came up with rules or “laws” about how traits are passed down from parent to offspring:
Rule of Heritable Factors:
EACH ORGANISM HAS 2 COPIES OF A GENE THAT CONTROLS EACH TRAIT; ONE COPY CAME FROM THE MALE PARENTS AND ONE COPY CAME FROM THE FEMALE PARENT
Each chromosome has genes (a gene is a piece of DNA that controls a trait- ex. height)

9. Mendel’s Laws
There can be different forms of the same gene; these different forms are called alleles.
ex. For the height gene, the alleles are tall and short
The offspring can inherit any combination of alleles from the parents
ex. Tall + tall, short + short, tall + short, or short + tall

10. Mendel’s Laws Example: height T = tall t = short A plant can be:
2. Rule of Dominance
ALLELES CAN BE DOMINANT OR RECESSIVE; THE DOMINANT ALLELE, IF PRESENT, COMPLETELY MASKS THE RECESSIVE ALLELE
Dominant Trait- remained in the F1 generation (ex. tall)
Recessive Trait- disappearned in F1 (ex. short)
So we say that tall is dominant to short.
When writing alleles, follow these rules:
Use the same letter for different forms of the same gene.
Use uppercase letter for dominant allele.
Use lowercase letter for recessive allele.
Always write dominant allele first.
Example: height
T = tall t = short
A plant can be:
TT tall
Tt tall
tt short

11. Punnett Square
Used to help solve genetics problems

12. Mendel’s Laws 3. Law of Segregation
THE TWO ALLELES THAT CONTROL EACH TRAIT WILL SEPARATE DURING GAMETE FORMATION TT X tt
Result: Tt (all tall)
Then Tt Tt X
Result: TT, Tt (tall) and tt (short)

13. Mendel’s Laws 4. Law of Independent Assortment
TRAITS ON DIFFERENT CHROMOSOMES ARE INHERITED INDEPENDENTLY OF ONE ANOTHER
This can be seen in dihybrid crosses. For example,
Round Yellow seeded hybrid crossed with a Round, Yellow seeded hybrid
(RrYy x RrYy)

14. Other Important Information:
Phenotype = written description of appearance/behavior
Examples: tall and short
BUT, two organisms can look the same but have different gene (or allele) combinations*:
Genotype = 2-letter gene combination
Examples: TT, Tt, tt
*Note: TT and Tt are both genotypes for the same phenotype, tall

15. Other Important Information:
There are 3 different types of genotypes:
homozygous dominant (TT)
homozygous recessive (tt)
heterozygous (Tt)
Homo- means same
Hetero- means different
FYI: homozygous is the same as PUREBRED
heterozygous is the same as HYBRID

16. JUST A LITTLE PRACTICE Description Genotype or Phenotype?
Homo- or Heterozygous?
Red Hair GG mm
White eyes
Short toe Dd

17. Steps to Solving Genetics Problems- When solving genetics problems, ask yourself the following:
What’s dominant?
What letter do I use? What are my possible combinations?
What am I crossing? (What are parents’ genotypes?)
How do I set up my punnett square?
What is the answer to the problem I’m trying to solve?

18. Example
Tall pea plants are dominant to short plants. A farmer crossed a homozygous tall plant with a short plant. How many of the offspring will be tall plants?

19. Steps to Solving Genetics Problems
Identify the dominant trait. (ex. Tall is dominant to short.)
Use the first letter of the dominant trait to represent each possible combination of alleles in the problem. (TT= tall, Tt= tall, tt= short)
Identify the parents’ genotypes, and write out what the cross would be. (Homozygous tall crossed with short is TT x tt.)
Set up your punnett square. Put one parent’s alleles on one side, and the other parent’s on the other side.
Solve your punnett square.
Answer the question. T T Tt Tt t
100% will be tall plants. t Tt Tt