1. Patterns of Inheritance
Chapter 12
Patterns of Inheritance

2. BACK IN THE DAY…. Theories on Inheritance Bloodlines
Heridity occurs within species
Traits are transmitted directly from parents to offspring

3. Josef Kolreuter Hybridizations
First generation looked like neither parents
Second generation was variable

4. T.A. Knight Worked with yellow and green peas
Observed all F1 generation were yellow, but F2 generation varied between green and yellow

5. Mendel Worked with pea plants Round vs wrinkled Yellow vs green seed
White vs purple flower
Green vs yellow pod
Inflated vs constricted pod
Terminal vs axial flower
Tall vs short height

6. Mendel’s experimental design
Allowed plants to self cross for many generations to ensure purity
Crossed pollen of plants true breeding for specific characteristics
Permitted hybrid offspring to self fertilize for several generations

7. Monohybrid Crosses

8. Always showed similar results
F1 generation exhibited only one of the two traits without blending….what theory did this disprove?
F2 generation exhibits both traits in a 3:1 ratio
Actually a 1:2:1 ratio…why?
Genotype vs Phenotype

9. What was Mendel able to understand based on his observations?
1. Plants did not follow blended inheritance, traits were discrete characteristics
2. For each pair of alternatives for a trait the one that was not shown in the F1 generation was still present, but it was latent
3. Pairs of alternative traits were segregated among the offspring
4. Mendelian Ratio ALWAYS seen

10. Mendel’s Model
1. Parents transmit discrete information to offspring not direct physiological traits now called genes
2. Each individual receives two genes that encode each trait. ( where are the genes found?)
3. Not all genes are identical- alternative forms called alleles
Homozygous
Heterozygous
4. Two alleles remain discrete
5. The presence of an allele does not ensure that the trait it encodes will be expressed.

11. Principle of Segregation
Two alleles for a gene segregate during gamete formation and are rejoined at random, one from each parent during fertilization

12. Punnett Squares

13. Dominant Traits in Humans
Middigital hair
Brachydactyly
Huntington Disease
PTC sensitivity
Polydactyly
Hypercholesterolemia

14. Recessive Traits Albinism Red-green color blindness Cystic fibrosis
Duchenne muscular dystrophy
Hemophilia
Sickle cell anemia

15. Pedigree

16. Independent Assortment
Alleles of each gene assort independantly
What does this mean?
Pea color does not necessarily connected to plant height
Demonstrated in Dihybrid Crosses

17. Dihybrid Cross You are looking at 4 different traits
F1 generation only shows 2 of the 4 traits…Why?
F2 generation 9:3:3:1 ratio

19. Probability Rule of addition
Probability of tow mutually exclusive events
This OR that
= Probability of event 1 + probability of even 2
Suppose a high school consists of 25% juniors, 15% seniors, and the remaining 60% is students of other grades. The relative frequency of students who are either juniors and seniors is 40%. We can add the relative frequencies of juniors and seniors because no student can be both junior and senior.
P(J or S) = which equals 0.40

20. Probability Rule of Multiplication
Probability of This AND that occuring
=Probability of Event A * probability of Event B
Suppose we have two dice. A is the event that 4 shows on the first die, and B is the event that 4 shows on the second die. If both dice are rolled at once, what is the probability that two 4s occur?
P(A) = 1/6 P(B) = 1/6 P(A and B) = P(A) . P(B) = 1/6 . 1/6 = 1/36

21. Rules can be applied to Dyhibrid cross
Example
Look at F1 generation
What are the odds of Wrinkled Seeds?
What are the odds of Green Seeds?
Multiply them together to get the odds of wrinkled green seeds.

22. Test Cross
If you do not know what genotype an organism has you can cross it with an individual who is homozygous recessive for the trait to find out.

23. Breaking the Rules Instances when Medel’s Laws may not be followed.
Polygenic Inheritance
Pleiotropy
Multiple alleles
Dominance is not always complete
Environmental Factors
Gene Interaction

24. Polygenic Inheritance
More than one gene affecting a single trait
Example Height or skin color

25. Pleiotropy A single gene affects more than one trait
Example Cystic Fibrosis, albinism
Mouse Study- Yellow Mice Die

26. Multiple Alleles for One Gene
More than one allele controlling the phenotype
Example ABO blood types

27. Incomplete Dominance
Incomplete dominance is when the heterozygote is intermediate in appearance between the two homozygote.

28. Codominance
When the heterozygote shows some piece of the phenotype of both homozygotes
Ex. ABO blood types fur color in some animals

29. ABO Blood Types

30. Genes can be affected by the environment
Example Temperature effects on Siamese Cats
Temp above 33 degrees no pigment
Temp Below 33 degrees pigment

31. Epistasis
An interaction between genes in which one gene is altered by another gene
Example Labrador Retrievers
Black is dominant to chocolate B or b Yellow is recessive epistatic (when present, it blocks the expression of the black and chocolate alleles) E or e