1. Mendelian genetics

2. Mendel and His Beloved Peas
Mendel and His Beloved Peas
Garden peas are:
Self-pollinating
Easy to experimentally cross-pollinate
Clear traits—pure purple, pure white, etc.

3. Trait: any single feature of an organism Traits That Mendel Studied
ALLELES
ALLELES

4. Gregor Mendel: Hereditary Genetics
Three Principles:
Principle of Dominance
Some alleles are dominant, others are recessive
Principle of Segregation
Alleles are separate from one another; each gamete only carries a single copy of each gene
Principle of Independent Assortment
Genes for different traits segregate independently of one another during the formation of gametes (sperm/egg)
Video clip: Alleles & Genes

5. What Mendel Noticed:  Whoa! P Generation (“Parent”)
F1 Generation (“First Filial”) (Kids)
“Short” trait disappears…
Whoa!
F2 Generation (“Second Filial”) (Grandkids)
…then reappears!

6. Did You Catch That?
Where did that short plant (trait) come from?

7. Recessive Traits “Hide” Behind Dominant Traits
Recessive Traits “Hide” Behind Dominant Traits
Sexual organisms have two of each trait (homologous pairs)
One of each pair is passed on to offspring by each parent.
(p265)

8. Recessive Traits “Hide” Behind Dominant Traits
Recessive Traits “Hide” Behind Dominant Traits
Different forms of the same trait are called alleles
PLANT HEIGHT
What TRAIT is being studied in this experiment?
“Tall”
… and …
What are the TWO ALLELES (forms) of the trait being studied?
“Short”

9. 
Mendel proposed that “Factors” segregate (separate) from pairs to be passed on to offspring, one from each parent! (p )
(Sound familiar?)

10. Homologous chromosomes split up in Anaphase II so that only one allele of each trait gets passed on in your gametes!

11. The pair of alleles you have (for any trait) is called your GENOTYPE
The pair of alleles you have (for any trait) is called your GENOTYPE
Example Trait: Nose Shape
(Let us pretend that round nose is dominant to pointy nose)
(usually, letters are used to represent alleles, upper case for dominant)
Alleles: ___ (dominant), ___ (recessive)
Genotypes: ____, ____, ____ N n NN Nn nn
“Homozygous Dominant” (Purebred)
“Homozygous Dominant”
(Purebred)
“Heterozygous” (hybrid or carrier)

12. Another Example: What’s the TRAIT? What are the ALLELES?
Which is dominant? PP pp Pp

13. Remember: Only one of each allele is passed on from each parent!Pp Pp
What is Mom’s genotype?
What is Dad’s genotype?
GERM CELL 
Heterozygous
Ova
(either)
Heterozygous Pp
GERM CELL
Sperm
(either) 

14. Let’s Look At the Offspring Probabilities
Ova
(either)
What if this egg meets this sperm?
What if this egg meets this sperm?
What if this egg meets this sperm?
Sperm
(either)
What if this egg meets this sperm?
What if this egg meets this sperm?

15. This Is Called A Punnett Square
Punnett squares allow us to predict probabilities about offspring

16. What percentages does this Punnett square predict?
How many Purple? ______
75% (3/4)
How many White? ______
25%
25%
25% (1/4)
How many homozygous dominant? ___
25% (1/4)
How many heterozygous? ______
25%
25%
50% (2/4)
How many homozygous recessive? ___
25% (1/4)

17. What is the probability that this couple will have a baby with the “a” disease?
Healthy allelle = A
Disease allele = a
25% (1/4)

18. What is the probability that this couple will have a baby who is a CARRIER for the “a” disease?
Healthy allelle = A
Disease allele = a
50% (2/4)
A CARRIER is a heterozygote (he or she can “pass on” the trait but does not exhibit it) 

19. 
Your Turn! (For disease “A”): What if a homozygous dominant man marries a carrier woman? AA Aa
Offspring Genotype:
- HD (AA) = ___%
- Het (Aa)= ___%
- HR (aa)= ___%
____ X ____
Dad
Mom 50 A a 50 A AA Aa
Offspring Phenotype:
- Healthy* = ___%
- Disease = ___%
- *(Healthy) Carrier = _____%
100 A AA Aa 50

20. 
One More Time! (For disease “A”): What if a carrier man marries a woman with the disease? Aa aa
____ X ____
Offspring Genotype:
- HD (AA) = ___%
- Het (Aa)= ___%
- HR (aa)= ___%
Dad
Mom a a 50 50 A Aa Aa
Offspring Phenotype:
- Healthy* = ___%
- Disease = ___%
- *(Healthy) Carrier = _____% 50 50 a aa aa 50