1. Patterns of Inheritance

2. Inheritance Hypotheses
Blending Hypothesis – parental contributions combined
Particulate Hypothesis – parents pass along discrete heritable units

3. Some Important Vocabulary
Allele= an alternative form of a gene (one member of a pair) that is located at a specific position on a specific chromosome.
Homozygous = two identical alleles (Ex. tt, TT)
Heterozygous = two different alleles (Ex. Tt)
Genotype
The two genes that an organism inherits for a certain trait (Example Tt, TT, or tt)
Phenotype
Physical characteristics (example: tall and short)

4. Analyzing Patterns
Genetic Cross – controlled experiment to determine the inheritance of a trait
P – parental generation
F1 – first generation
F2 – second generation P F1 F2

5. Homologous chromosomes
Review Meiosis
Of your father’s 46 chromosomes how many do you receive?
Of your mother’s 46 chromosomes how many do you receive?
So for each allele you share __(#) copy from mom and ___(#) copy from dad.
If this is one of your chromosomes what two possible alleles would you have at this locus to pass on to your offspring? Y y
Homologous chromosomes

6. General Patterns of Inheritance
Alternative versions of genes cause variation
Offspring inherit one copy from each parent
Dominant alleles are expressed in phenotype
Recessive alleles are expressed in phenotype in the absences of dominate alleles
Alleles for genes separate during meiosis
Gametes fuse randomly

7. Mendel’s Laws Father of modern genetics Researched pea plants
Developed ideas of dominance and trait segregation
Allelic Interactions
Pleiotropy
Epistasis
Environment
Polygenics

8. Mendel's Law of Segregation
Each allele separates from the other so that the offspring get only one allele from each parent for a given trait.
Let’s cross a heterozygous tall plant (Tt) with a short plant (tt).
Each plant will give only one of its’ two genes to the offspring or F1 generation. T t
Plant 1 (tall)
Plant 2 (short)
Possible zygotes after meiosis X

9. Law of Segregation and Punnett Squares
Plant 1 (tall)
Plant 2 (short)
Possible zygotes after meiosis X
Plant 2
Plant 1 Tt TT tt Tt T t t T

10. Developed ideas of dominance and trait segregation
Allelic Interactions
Complete dominance
Incomplete dominance
Co-dominance
Pleiotropy
Epistasis
Environment
Polygenics

11. Allelic Interactions
Complete dominance: dominant allele fully expressed
Incomplete dominance: neither allele fully expressed
Co-dominance: both alleles fully expressed

12. Allelic Interactions: Complete Dominance
The dominant allele is the only one seen in the phenotype
Dominant vs. Recessive Gene
Dominant Gene: A gene that always expresses itself. It is symbolized by a CAPITAL letter
Recessive Gene: a gene that expresses itself only when a dominant form of the gene is NOT present. It is symbolized by a lower case letter
Monohybrid cross is looking at 1 gene
Dihybrid cross is looking at 2 genes
Monohybrid Cross X

13. Allelic Interactions: Complete Dominance
Practice Problem:
Let's say that in seals, the gene for the length of the whiskers has two alleles.  The dominant allele (W) codes long whiskers & the recessive allele (w) codes for short whiskers.
a)  What percentage of offspring would be expected to have short whiskers from the cross of two long-whiskered seals, one that is homozygous dominant and one that is heterozygous?
b) If one parent seal is homozygous long-whiskered and the other is short-whiskered, what percent of offspring would have short whiskers?
c) Is this a mono- or dihybrid cross?

14. Complete Dominance Dihybrid Cross
What are the possible gametes from each of these pea plants?
YyRr
YyRr X
Use FOIL if you want! == YR, yR, Yr, yr
Y=yellow
y=green
R=round
r=wrinkly

15. Allelic Interactions: Incomplete Dominance
Neither allele fully expressed, they are mixed
The phenotype of the heterozygote will be intermediate between the phenotypes of the two homozygotes
Example:
RR = Red snapdragon flower
Rr = pink snapdragon flower
rr = white snapdragon flower

16. Allelic Interactions: Incomplete Dominance
Practice Problem: Cross a red snapdragon with a pink snapdragon flower. What will the genotype and phenotype % be for the offspring.

17. Co-Dominance
If two alleles have a co dominant relationship, in the heterozygote both alleles will be completely expressed.
Example: blood type

18. Example: Blood Types

19. Co-Dominance
What would happen if you crossed a man with AB blood type with a women with O blood type? (a) Give the genotypes and phenotypes for the offspring. (b) How many of the offspring would have AO? _____% (c) How many of the offspring would have BO? _____% (d) How many of the offspring would have AB? _____% (e) How many of the offspring would have O? _____%

20. Sex Linked (X-Linked) Traits
The genes that are located on the chromosomes are called sex-linked traits
Many traits that are carried on the X chromosome do not have a corresponding spot on the Y chromosome. This causes for some unique possibilities for the offspring.
Ex. Color blindness in humans, fruit fly eye color, hemophilia.

21. Analyzing Patterns
Pedigree – illustration of relationships among family members over multiple generations

22. Inheritance and Genetic Disorders
Hereditary disorders
Autosomal or sex-linked
Recessive or dominant
Genetic disorders are often polygenic and influenced by environment

23. Autosomal Recessive Disorders
Carriers – heterozygotes that have one allele but not the disorder
Examples – Cystic Fibrosis, Tay Sachs

24. Autosomal Dominant Disorders
Disorders that are expressed with only one copy of the allele
Example – polydactyly
Example – Huntington’s

25. Sex-linked Recessive Disorders
Disorders that are on the sex chromosome
Example – Hemophilia

26. Sex-linked Dominant Disorders

27. Pleiotropy Condition where a single gene influences multiple traits
Example: Marfan’s Syndrome

28. Polygenics Traits that are determined by many genes
Examples – eye color, skin color, height, etc.

29. Environment Phenotype = Genotype + Environment
Epigenetics – study of changes in phenotype due to mechanisms other than changes in DNA sequence
Epigenetics