1. Mendelian Genetics
7/30/2018
Mendel’s Laws

2. Mendelian Genetics
7/30/2018
Law of Dominance
An organism with different forms (alleles) of a gene will express the form that is dominant.
Heterozygous (hybrid) individuals express only the dominant trait.
RR (round) x rr (wrinkled) yields all Rr (round seeds)

3. What happens when the F1’s are crossed?
Mendel’s Law of Dominance
Monohybrid cross –Breeding experiment that tracks the inheritance of ONE trait
What happens when the F1’s are crossed?

4. For each monohybrid cross
Mendel cross-fertilized true-breeding plants that were different in just one character
—in this case, flower color.
He then allowed the hybrids (the F1 generation) to self-fertilize.

5. Mendelian Genetics
7/30/2018
Law of Dominance

6. Mendel’s Law of Segregation
Mendelian Genetics
7/30/2018
Mendel’s Law of Segregation
Each inherited trait is controlled by a gene pair (2 alleles).
Parental genes are randomly separated to the sex cells (gametes) so that sex cells contain only one allele of the gene pair.
offspring inherit one genetic allele from each parent when sex cells unite in fertilization.

7. Applying the Law of Segregation
Mendelian Genetics
7/30/2018
Applying the Law of Segregation

8. Mendel’s Law of Independent Assortment
Mendelian Genetics
7/30/2018
Mendel’s Law of Independent Assortment
Mendel’s “Law of Independent Assortment”
a. Each pair of alleles separates Independently during gamete formation
b. Formula: 2n (n = # of heterozygotes)
A breeding experiment that tracks the inheritance of two traits.

9. Cross 2 HYBRID pea plants All possible gamete combinations
Mendelian Genetics
7/30/2018
Dihybrid Cross
2 Traits: Seed shape & Seed color
Alleles: R - round r - wrinkled Y - yellow y - green
Cross 2 HYBRID pea plants
RrYy x RrYy
RY, Ry, rY, ry
RY, Ry, rY, ry
All possible gamete combinations

10. Mendelian Genetics
7/30/2018
Dihybrid Cross RY Ry rY ry RY Ry rY ry

11. Dihybrid Cross 9:3:3:1 phenotypic ratio RY Ry rY ry Round/Yellow: 9
Mendelian Genetics
7/30/2018
Dihybrid Cross RY Ry rY ry
Round/Yellow: 9
Round/green: 3
wrinkled/Yellow: 3
wrinkled/green: 1
9:3:3:1 phenotypic ratio
RRYY
RRYy
RrYY
RrYy
RRYy
RRyy
RrYy
Rryy
RrYY
RrYy
rrYY
rrYy
RrYy
Rryy
rrYy
rryy

12. Dihybrid Cross Phenotype:
Mendelian Genetics
7/30/2018
Dihybrid Cross
Phenotype:
Round/Yellow: 9/16 Round/green: 3/16 wrinkled/Yellow:3/16 wrinkled/green:1/16
9:3:3:1

13. Mendel’s Law of Indpependent Assortment

14. Remember: 2n (n = # of heterozygotes) 1. RrYy 2. AaBbCCDd
Mendelian Genetics
7/30/2018
Question: How many different gametes will be produced for the following allele arrangements?
Remember: 2n (n = # of heterozygotes)
1. RrYy
2. AaBbCCDd
3. MmNnOoPPQQRrssTtQq

15. Answer: 1. RrYy: 2n = 22 = 4 gamete possibilities RY Ry rY ry
Mendelian Genetics
7/30/2018
Answer:
1. RrYy: 2n = 22 = 4 gamete possibilities
RY Ry rY ry
2. AaBbCCDd: 2n = 23 = 8 gamete possibilities
ABCD ABCd AbCD AbCd
aBCD aBCd abCD abCD
MmNnOoPPQQRrssTtQq: 2n = 26 = 64 gametes

16. Mendelian Genetics
7/30/2018
Test Cross
A mating between an individual of unknown genotype and a homozygous recessive individual.
Example: bbH__ x bbhh
BB = brown eyes
Bb = brown eyes
bb = blue eyes
HH = curly hair
Hh = curly hair
hh = straight hair bH
b___ bh bh

17. Test Cross PossibLe results: bbHh H bH b__ bH b__ bh bbHh bbhh or h bh
Mendelian Genetics
7/30/2018
Test Cross
PossibLe results:
bbHh H bH
b__ bH
b__ bh
bbHh
bbhh or h bh
bbHh
bbHh bh

18. Summary of Mendel’s laws
Mendelian Genetics
7/30/2018
Summary of Mendel’s laws
LAW
PARENT CROSS
OFFSPRING
DOMINANCE
TT x tt tall x short
100% Tt tall
SEGREGATION
Tt x Tt tall x tall
75% tall 25% short
INDEPENDENT ASSORTMENT
RrGg x RrGg round & green x round & green
9/16 round seeds & green pods 3/16 round seeds & yellow pods 3/16 wrinkled seeds & green pods 1/16 wrinkled seeds & yellow pods