Mendel and the Gene Idea Mendel and the

Mendel and the Gene Idea

Mendel and the Gene Idea 4 Mendel’s law of independent assortment: – Each allele pair segregates independently of other gene pairs during gamete formation.

Mendel and the Gene Idea 4 Rule of Multiplication: – The probability that an independent events will occur simultaneously is the product of their individual probabilities!

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

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

Mendel and the Gene Idea 4 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 4 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 4 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 4 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 4 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 4 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 4 Tay-Sachs disease: Incidence is about 100 x 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 4 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 4 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 O 2 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 4 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 4 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 4 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 4 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 4 X 2 = Σ (O-E)2 4 E 4 The null hypothesis in this experiment is to validate the use of the prediction! 4 The alternate hypothesis in this experiment is to discredit the use of the prediction!

Chi Square 4 Degree of freedom: number of possible phenotypic categories minus one.

Chi Square 4 Evaluate the calculated value with the chart! 4 If your calculated value is less than the chart value -- then you fail to reject the null!

Chi Square 4 Last, evaluate your p= value 4 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!