1. Mendel and the Gene Idea

2. Mendel and the Gene Idea
Mendel’s law of independent assortment:
Each allele pair segregates independently of other gene pairs during gamete formation.

3. Mendel and the Gene Idea
Rule of Multiplication:
The probability that an independent events will occur simultaneously is the product of their individual probabilities!

4. Mendel and the Gene Idea
What is the probability that a trihybrid cross between two organisms with genotypes AaBbCc and AaBbCc will produce an offspring with a genotype aabbcc?
Aa x Aa : probability of aa = 1/4
Bb x Bb : probability of bb = 1/4
Cc x Cc : probability of cc = 1/4
Therefore 1/4 x 1/4 x 1/4 = 1/64

5. Mendel and the Gene Idea
Rule of Addition:
The probability of an event that can occur in two or more independent ways is the sum of the separate probabilities of the different ways

6. Mendel and the Gene Idea
What fraction of the offspring from the following cross of garden peas, would show recessive phenotypes for at least two of the three traits? PpYyRr x Ppyyrr
ppyyRr 1/4 x 1/2 x 1/2 = 1/16
ppYyrr 1/4 x 1/2 x 1/2 = 1/16
Ppyyrr 1/2 x 1/2 x 1/2 = 2/16 (1/8)
PPyyrr 1/4 x 1/2 x 1/2 = 1/16
ppyyrr 1/4 x 1/2 x 1/2 = 1/16
6/16 or 3/8

7. Mendel and the Gene Idea
Test Cross: The breeding of an organism with an unknown genotype with a homozygous recessive.

8. Mendel and the Gene Idea

9. Mendel and the Gene Idea
Incomplete dominance:
Pattern of inheritance in which the dominate
phenotype is not fully
expressed in the heterozygote,
resulting in a phenotype
intermediate between the
homozygote dominate and
recessive characteristics.
Blends

10. Mendel and the Gene Idea
Codominance:
Inheritance characterized by full expression of both alleles in the heterozygote.
Blood type
AA (IAIA)
BB(IBIB)
AB(IAIB)
Calico cats

11. Mendel and the Gene Idea
Multiple Alleles
some genes may have multiple alleles; that is, more than just two alternative forms of a gene.
These multiple alleles occupy a single locus
Blood typing A, B, and O
IA IB and i

12. Multiple Alleles

13. Mendel and the Gene Idea
Human disorders
Recessive alleles that cause human disorders are usually defective versions of normal alleles.
Recessively inherited disorders range from nonlethal traits (albinism) to lethal diseases (cystic fibrosis)

14. Mendel and the Gene Idea
Cystic fibrosis: most common lethal genetic disease in the US among Caucasians
Frequency 1 in 2500
4% of the Caucasians are carriers
The dominate allele codes for a membrane protein that controls chloride traffic across the cell membrane. -absent in homozygous recessive
Disease symptoms result from the accumulation of thickened mucus in the lungs and pancreas.

15. Mendel and the Gene Idea
Tay-Sachs disease: Incidence is about 100x higher in central European Jews than among Mediterranean Jews
Frequency 1 in 3600
Brain cells of babies are unable to metabolize gangliosides - lipid
As lipids increase in the brain, the infant suffers seizures, blindness, and degeneration of motor skills and mental performance.
Child dies after a few years

16. Mendel and the Gene Idea
Pleiotropy:
The ability of a single gene to have multiple phenotypic effects.
There are many hereditary diseases in which a single defective gene causes complex sets of symptoms Sickle-cell Anemia

17. Mendel and the Gene Idea
Sickle-cell disease: most common in African Americans 1 in 400.
Single amino acid substitution in hemoglobin
Abnormal hemoglobin molecules tend to link together and crystallize when blood O2 is lower than normal
Causes the erythrocyte to form a sickle shape
Sickle cells clog small vessels causing pain, discomfort and fever.

18. Mendel and the Gene Idea
Sickle Cell
1 in 10 African Americans are carriers
Codominance - carriers may experience discomfort during periods of low blood Ox levels - other wise function normally
Believed to be result of malaria infestation in tropical regions

19. Mendel and the Gene Idea
Sickle cell:
The probability of inheriting the same rare harmful allele from both parents, is greater if the parents are closely related.

20. Mendel and the Gene Idea
Huntington’s disease
Lethal dominate (late acting)
a degenerative disease of the nervous system
does not show until age 35-40
irreversible to death
found at the tip of chromosome #4

21. Mendel and the Gene Idea
PKU (phenylketonuria):
recessive 1 in 15,000
patient cannot break down the amino acid phenylalanine
build up to toxic levels causes mental retardation
tx with a special diet to avoid toxic levels

22. Chi Square
X2 = Σ (O-E)2 E
The null hypothesis in this experiment is to validate the use of the prediction!
The alternate hypothesis in this experiment is to discredit the use of the prediction!

23. Chi Square
Degree of freedom: number of possible phenotypic categories minus one.

24. Chi Square Evaluate the calculated value with the chart!
If your calculated value is less than the chart value -- then you fail to reject the null!

25. Chi Square Last, evaluate your p= value
If you fail to reject your null, then this value identifies the percent chance that any difference in your results is due to random chance!