1. Chapter 12
Mendel & Heredity

2. Section 12.1
Genetics – study of heredity; how traits are passed from parents to offspring
Gregor Mendel “Father of Genetics”
History of
Lived in a monastery in Austria in 1842
In 1851, moved to the University of Vienna where he studied science and mathematics
Returned to monastery, taught, & kept a garden (most famous for studies on peas)

3. Initial Observation
Mendel crossed (mated) purple flowered peas plants with white flowered pea plants.
All the offspring had purple flowers.
Two of these first offspring were crossed, and some of their offspring had purple flowers, but a few had white flowers!

4. II. Features of Pea Plants
Vocabulary
Characters – physical features that are inherited
Flower color in peas is a character
Trait – one of several possible forms of a character
The flower colors of purple or white are traits
Hybrid – offspring of a cross between parents with different traits
If a purple flowered peas crosses with a white flowered pea, its offspring would be a hybrid

5. Pea Plant Characters – Mendel observed 7 characters (do not need to write down)
Height of plant’s stem (tall or short)
Position of flower on stem (mid-stem or end of stem)
Pod Color (green or yellow)
Pod Appearance (smooth or bumpy)
Seed Texture (round or wrinkled)
Seed Color (green or yellow)
Flower Color (purple or white)

6. Pollination – Mendel manually took pollen from an anther (male) & transferred it to the stigma (female).
Self-Pollination: a flower will pollinate itself or another flower on the same plant
Cross Pollination: a flower will pollinate a flower on a different plant
***Mendel uses both forms of pollination in is experiments.

7. III. Mendel’s Experiment
Mendel first used true-breeding plants.
True-Breeding – a plant that is pure for a trait; when self-pollinated, its offspring will always have that same trait
A true-breeding purple flowered plant will always produce purple flowered plants!
Mendel formed 14 strains that were true-breeding.
These true-breeding plants were labeled the P1 generation since they were the original parents.

8. Two P1 generation plants of contrasting traits were cross-pollinated
Two P1 generation plants of contrasting traits were cross-pollinated. Their offspring were labeled the F1 generation.
An F1 generation plant was allowed to self-pollinate. Its offspring were labeled the F2 generation.

9. An Example of Mendel’s Results
P1 = True-Breeding Purple X True-Breeding White
F1 = 100% were Purple Flowers
F2 = 75% Purple flowers & 25% White flowers
* = 3 Purple : 1 White Ratio

10. **Mendel crossed all 14 traits and always received
a 3:1 ratio in the F2 generation

11. Calculating Ratios Probability – chance something will happen
Probability = # of times an event happens
# of times it could of happened
Ex: In an F2 generation, Mendel recorded 705 purple flowered plants and 234 white flowered plants.
Purple: happened 705 times out of 939; 705/939 = 75.1 %
White: happened 234 times out of 939; 234/939 = 24.9%

12. Section 12.2 Explaining Mendel’s Experiments
Alternate Versions of Genes = alleles
For each character, there are 2 possible traits
Each trait is controlled by a specific gene
Purple flowers is controlled by one gene for flower color & white flowers is controlled by a different gene for flower color
The purple gene is called the purple allele

13. Dominant & Recessive Alleles
Dominant Allele – the allele whose trait is always expressed
Recessive Allele – not expressed when a dominant allele is present.
P = purple allele
p = white allele
2 Dominant alleles (PP) = purple flowers
1 Dominant 1 Recessive (Pp) = purple flowers
2 Recessive alleles (pp) = white flowers

14. We receive one allele for each character from each parent.
So 2 alleles are needed to determine our traits

15. Mendel’s Laws Law of Segregation
A pair of alleles are segregated (separated) during meiosis.
This means one allele on one chromosome will be separated from the other allele on the other homologous chromosome during meiosis to make gametes.

16. Law of Segregation

17. Law of Independent Assortment
Alleles are separated randomly and independently into gametes

18. Section 12.3
Vocabulary
Genotype – all the alleles/genes inherited; an individual’s genetic information
Example –Pp is the genotype for a purple flowered plant
Phenotype – the physical expression of one’s genotype
Example – the color purple is the phenotype of a plant with a genotype of Pp.

19. Homozygous – genotype with 2 identical alleles
Example: PP = homozygous dominant
pp = homozygous recessive
Heterozygous – genotype with 2 different alleles
Example: Pp = heterozygous

20. Punnett Squares – model/tool that predicts the outcomes of a genetic cross
Monohybrid Cross – cross between individuals involving one trait (just flower color)
Example: In pea plants, purple is dominant over white flowers. Determine the probabilities of possible outcomes for a cross between a homozygous dominant plant and a homozygous recessive plant.

21. Types of Dominance
Incomplete Dominance – an allele does not completely dominate another; phenotype will be a blend.
Ex: In snapdragons, the red allele (R) does not completely dominate the white allele. A heterozygote (Rr) will have pink flowers.

22. Codominance – both alleles for a trait are fully expressed (spots, AB blood type in humans)
A heterozygous plant
(Rr) would display a
phenotype of spots 

23. Multiple Alleles – a trait has 3 or more possible alleles (an individual still has only 2 alleles for the trait).
Ex: Blood type in humans. There are alleles a person can inherit: the A allele, B allele, and O allele.
Type A = AA or AO
Type B = BB or BO
Type AB = AB (codominance)
Type O = OO