1. Mendelian Genetics
Chapter 10.2

2. Gregor Mendel Made the first discoveries in genetics
Studied basic traits of
Pea pod plants
Pea pods are true breeders – always produced offspring with the same trait.
Developed Mendel’s laws

3. Inheritance of traits
When Mendel crossed plants with different traits he expected them to blend.
Instead all offspring had the trait of one parent.

4. F1 and F2 Generations P – Cross green And yellow peas F1 – all yellow.
Self fertilization -
Cross F1 with F1
F2 – mostly yellow
Some green

5. Seven traits Mendel studied Seven characters For all traits he
found That one trait
was Dominant over
the Other trait.

6. Mendel’s Conclusions
Inheritance – factors are passed on from generation to generation
These factors are called genes
Allele – Different forms of a gene

7. Mendel’s Conclusions
2) The Principle of Dominance: Some alleles are dominant and some are recessive
Dominant covers recessive
Recessive only shows if there is no Dominant allele

8. Mendel’s Conclusions 3) There are two alleles for each gene
Genotype - the two alleles (Yy)
Phenotype – the observable trait (yellow)
Dominant alleles are written as a Capital letter (Y)
Recessive alleles are written as a lower case letter (y)

9. Genotypes and phenotypes
Homozygous Dominant (YY) – shows dominant trait (yellow)
Homozygous Recessive (yy) –shows recessive trait (green)
Heterozygous (Yy) – shows dominant trait (yellow)

10. Mendel’s conclusions
4) Law of segregation – the two alleles for each character separate during meiosis

11. Monohybrid cross Hybrid = heterozygote (Yy)
Monohybrid cross – cross between two individuals that have different alleles for one gene.
Example: Yy X Yy

12. Punnett squares
Predict the possible offspring of a cross between two known genotypes.

13. Punnett Square rules A. Divide the parent genotype in half (meiosis)
B. Put the genotype of each HAPLOID cell along top and left edge of square
C. Combine sperm and egg in each box of square
D. Capital Letters first, same letters go together

14. Monohybrid cross Example
2 parents - heterozygous genotypes Purple flower is the dominant trait X

15. Genotype of each haploid
DAD
MOM

18. B= dominant (purple)
b= recessive (white)
Phenotype
3:1 ratio

19. Punnett Square practice.
Use R = red and r = white flowers 1)Homozygous dominant mom and heterozygous dad 2)Heterozygous mom and homozygous recessive dad 3) True breeding red mom and white dad

20. Can you cross more than one allele in a punnett square?
Dihybrid cross - Cross two organisms that differ in two traits.

21. Dihybrid cross
R- round
r – wrinkled
Y – Yellow
y- green

22. Law of independent assortment
There is a random assortment of alleles that occurs during gamete formation.
4 possible combinations of gametes
Genotype – YyRr
Gametes:
YR, Yr, yR, yr

23. 4 different
phenotypes
Phenotypic ratio
9:3:3:1
9 different
genotypes

24. Practice Dihybrid Cross
S – short tail
s – long tail
B – Brown
b – white
Cross SsBb X SsBb