1. Genetics
The study of heredity

2. Gregor Mendel Mendel was an Austrian monk.
Mendel formulated two fundamental laws of heredity in the early 1860's.
He had studied science and mathematics (including statistics) at the University of Vienna.
Mendel’s knowledge of statistics later proved valuable in his research on Heredity – the transmission of characteristics from Parent to Offspring.
Mendel's work was unrecognized until 1900.

4. Genetics Vocabulary
Monohybrid cross - cross involving a single pair of genes, one trait
P – “parents”
F1 – “kids”
F2 – “grandkids”

5. Law of Segregation: Each organism contains two factors for each trait; factors segregate in the formation of gametes. When two gametes combine during fertilization, the offspring have two factors controlling a specific trait.
Law of Independent Assortment: states that factors for different characteristics are distributed to gametes independently.

7. Genetics Vocabulary
Gene - the unit of heredity; a section of DNA sequence encoding a single protein
Alleles - two genes that occupy the same position on homologous chromosomes and cover the same trait
Locus - a fixed location on a strand of DNA where a gene or one of its alleles is located
Trait: observed
expression of the gene
(Physical manifestation
of information)

8. F1 Crosses In the first generation of each experiment, how do the
Seed Shape
Seed Color
Seed Coat
Color
Pod
Shape
Pod Color
Flower Position
Plant Height
Round
Yellow
Gray
Smooth
Green
Axial
Tall
Wrinkled
Green
White
Constricted
Yellow
Terminal
Short
Round
Yellow
Gray
Smooth
Green
Axial
Tall
In the first generation of each experiment, how do the
characteristics of the offspring compare to the parents’
characteristics?

9. Genetics Vocabulary
Dominant - the trait that appears in the heterozygous condition.
Dominant allele  capital letter Height ex: T = tall
Recessive - the trait that is masked in the heterozygous condition.
Recessive allele  lowercase letter
Height ex: t = short

10. Mendel’s 3rd Law Principle of Dominance
2. Some alleles are…
DOMINANT
recessive

11. Genetics Vocabulary
Homozygous - having identical genes (one from each parent) for a particular characteristic.
Heterozygous - having two different genes for a particular characteristic.

12. Genotype & Phenotype Genotype Phenotype Genetic makeup Can’t see
Height ex: TT, Tt, or tt (letter code)
Physical characteristic/appearance
Can see
Depends on genotype
Height ex: tall or short
Question: Can two organisms have the same phenotype but have different genotypes? Explain.

13. Traits exist because of 2 alleles
Every trait has 2 _______ that determines its phenotype.
AA or Aa or aa
AA = Homozygous Dominant
Aa = Heterozygous
aa = ___________ __________
It is because of this, that the recessive trait can disappear in the F1 generation.

14. Genetics Vocabulary
Punnett squares - used to aid in predicting the probability that certain traits will be inherited by offspring
Probability - is the likelihood that a specific event will occur or is the likely outcome a given event will occur from random chance

15. Monohybrid Crosses 1. Determine the dominant and recessive trait
Will be stated in the problem
ie. Black is dominant to white in bunnies

16. 2. Assign letters for the trait
Dominant trait gets the capital letter
Recessive traits gets the lower case letter
B = black
b = white

17. 3. Determine genotype for parents
White male = bb
Heterozygous black female = Bb

18. 4. Put parents on the square
Bb x bb
B b b

19. Punnett square holds offspring genotypes
B b b
Genotype = letter code
5. Determine genotype of offspring Bb bb

20. 6. Determine genotype ratio
Count offspring in the Punnett square genotype ratio =
2Bb:2bb

21. Phenotype = what they look like
Count offspring in the Punnett square phenotype ratio =
2 black:2 white
*If ratio doesn’t add up to total number of boxes in the punnett square you’ve made a mistake
7. Determine phenotype ratio

22. Practice Problems
A pure-breed white flower crosses with a pure-breed purple flower. Purple is dominant to white.
Show the punnett square
What is the genotype of the F1 generation
What is the phenotype of the F1 generation

23. Genotype = Pp
Phenotype = Purple

24. More practice
A homozygous black rat is crossed with a heterozygous black rat.
B = black b = brown
Show the punnett square
What are the genotypes of F1?
What are the genotype ratio of F1?

25. Genotypes = BB and Bb
Genotype Ratio = 2BB:2Bb

26. More practice
If you had a black rat how could you tell it’s genotype was homozygous or heterozygous?

27. Use a test cross: cross with a pure breed (homozygous) recessive and look at the F1 generation

28. Possible Answer Formats
% - chance out of total possible
1 out of 4 = 25%
Fraction
1 out of 4 = 1/4
Ratio – ratio adds up to total possible
1 out of 4 = 1:3