1. Genetics Gregor Mendel
Genotypes: Homozygous and Heterozygous, Dominant, Recessive
Phenotypes: Traits you see
Law of Heredity
- law of segregation
- law of independent assortment
Probability: punnett squares
Pedigree charts: genes are sex-linked or autosomal
Polygenetic traits, incomplete dominance, codominance, multiple alleles.

2. Gregor Mendel: Father of Genetics
Found the following using Pea plant
- Inheritance: passing of traits
- Heredity: transmission of traits from parents to offspring
Used pea plants for his experiments. WHY??
- Either the flower is either purple or white, no intermediate
colors such as pink
- You can control pollination. (able to control the mating)
- small, easily grown, matures quickly, produces many offspring

3. Mendel’s Experiments
He did the experiment by both self-pollinating (pollen is not transferred to another plant, the plant uses its pollen) and cross-pollinating (cross-fertilization: transferring pollen from one plant to the other)
His experiment
1. He crossed a purple flower with a purple flower producing
plants with purple flowers and a white flower with a white flower
producing plants with only white flowers. He referred to this as
“True-breeding” (display 1 particular trait). These plants
served as his parental generation or “P” generation
EX: White X White = All White
Purple X Purple = All Purple

5. Mendel’s Experiment Con’t
2. He then crossed a white P generation flower with a purple
P generation flower. He called the offspring of the P generation
the F1 Generation. All offspring were purple
EX: White X Purple == All Purple
3. He then enabled the F1 generation to self-pollinate. This produced the F2 generation. 705 were purple and 224 flowers were white . A ratio of 3:1
EX: Purple X purple == 3 Purple, 1 White
See the following website:

7. Mendel’s Conclusions
1. He concluded that purple was the dominant color
2. He concluded that purple was masking the white color.
3. He concluded that white was recessive because it returned in the F2 generation

8. Mendel’s Hypotheses
1. For each inherited trait, an individual has 2 copies of the gene- one from the father one from the mother

10. Through the process of meiosis, parents can only contribute one allele for an inherited trait.
When two different alleles occur together, only 1 may be completely expressed. The other may not have an observable effect on the organism’s appearance.

11. Other Important Info.
Dominant: The gene (trait) that is expressed in the physical appearance. Represented by a capitol letter (T, S, H)
Recessive: the gene (trait) that is not expressed, but you still have the gene for the trait. It is masked by the dominant trait. Represented by a lower case letter. (t, s, h)
Genotype: set of alleles or genes that an individual has
Phenotype: The physical appearance of an individual. (determined by your alleles)
Alleles can be homozygous or heterozygous
-- homozygous: alleles are the same for a particular trait
ex: TT, SS, HH=== Homozygous dominant
tt, ss, hh=== Homozygous recessive
--- heterozygous: alleles are different for a particular trait
ex: Tt, Ss, Hh

12. Laws of Heredity Mendel’s findings led to the laws of heredity 2 laws
1. Law of segregation: two alleles for the same trait separate when gametes are formed. (remember when chromosomes separate during meiosis)

13. 2. Law of independent assortment: alleles of different genes (ex hair and eye color), separate independently of one another during gamete formation. One gene does not influence the inheritance of the other.

14. Studying Heredity
Punnett Square: Finding the probability that a trait will be passed from one generation to the next.
-- monohybrid: 1 trait
-- dihybrid: 2 traits
Pedigree charts: family history chart that shows how a trait has been inherited over several generations.

15. Punnett Squares Monohybrid crosses
A man homozygous dominant for blonde hair marries a women who in homozygous recessive for black hair. What is the likelihood that their children will have black hair??
b b
B Bb Bb Genotypes: 4 or 100% Heterozygous
Phenotypes: 100% Blonde
B Bb Bb
No chance of having a child with black hair

16. Punnett Squares Continued
Dihybrid crosses
-- Look at 2 traits. Two heterozygous black haired and blue eyed
people marry. Look at probability of having a child with black
hair and blue eyes. B- black, b-blonde, E-blue, e-brown
-- Genotypes Father: Bb, Ee Mother: Bb, Ee
1. find all possible genotypes: Father BE, Be, bE, be
Mother: BE, Be, bE,be

17. Dihybrid cross BE Be bE be BE BBEE BBEe BbEE BbEe
Phenotypes Genotypes
9 or 56.25% black haired and blue eyed Homo dominant
3 or 18.75% blonde haired and blue eyed Heter
1 or 6.25% blonde haired and brown eyed Homo Recessive
3 or 18.75% black haired and brown eyed Ratio: 1:2:1

18. Pedigree Charts
A family history that shows how a trait has been inherited over many generations.
Scientist can determine the following:
Autosomal or sex-linked? If a trait is autosomal, traits will appear in both sexes equally. If a trait is sex-linked, males will show the trait. A sex-linked trait is a recessive trait whose allele is located on the X chromosome. Because males only have one X chromosome, a male who carries this recessive allele on the x chromosome will show the trait. The only way a female will exhibit the trait if both of her X chromosomes carries the recessive trait.
Dominant or Recessive? If the trait is autosomal dominant, every offspring that has the trait will have a parent with the trait. If it is recessive, the individual will have 1, 2, or neither parent exhibit the trait (depending on their genotype)
Heterozygous or Homozygous? If the trait is dominant, they will have a genotype of homozygous dominant or heterozygous and their phenotype will show the trait. Two people heterozygous for a recessive trait will not show the trait but can pass it on to their children.

19. Pedigree charts Horizontal lines: indicate matings
Vertical lines: Offspring
Males Male affected Carrier
females female affected

20. Complex Heredity
There is more to the patterns of heredity than the simple dominant/recessive patterns.
Polygenic traits
Incomplete dominance
Codominance
Multiple alleles
Environmental influences

21. Polygenic traits Traits influenced by several genes
Hard to determine effects because many different combinations occur due to independent assortment and crossing-over.
Examples: eye color, height, weight, hair and skin color.

22. Incomplete Dominance
An individual displays a trait that is intermediate between the two parents.
Ex: Red flower is crossed with a White flower: Results in pink flowers
Pink flowers because they show less pigment than red but more than white.
Ex: One parent with curly hair and one parent has straight hair and their child has wavy hair.

23. Codominance Traits with two forms displayed at once.
2 dominant alleles displayed at the same time
EX: A homozygous white horse and a homozygous red horse produces a heterozygous offspring. The offspring will show both red and white hair and in equal numbers. (called a Roan horse)

24. Multiple Alleles Genes with 3 or more alleles.
ABO blood system: IA, IB, i
A and B are carbohydrates located on red blood cells
i does not have this carbohydrates
Nor A or B are dominate over each other: they are codominant
They are dominant over i
3 alleles can produce 4 genotypes: A, B, AB, O
IA IB i
IA IAIA IAIB IAi
IB IBIA IBIB IBi
i IAi IBi ii

25. Environmental Influences
EX: Hydrangea plants: color of flowers depends on the acidity of the soil
Hair Color of some animals: Artic fox; during summer months it turns reddish brown to blend in with its environment. In the winter it is white
Humans: skin color- exposure to the sun, behavior, height and weight controlled by nutrition. Identical twins are genetically the same but can be very different