Mendel and the Gene Idea

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

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

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

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

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

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

Mendel and the Gene Idea

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

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

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

Multiple Alleles

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)

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.

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

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

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.

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

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.

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

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

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!

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

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!

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!