Presentation on theme: "Patterns of Inheritance"— Presentation transcript:
1 Patterns of Inheritance Chapter 12Patterns of Inheritance
2 BACK IN THE DAY…. Theories on Inheritance Bloodlines Heridity occurs within speciesTraits are transmitted directly from parents to offspring
3 Josef Kolreuter Hybridizations First generation looked like neither parentsSecond 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 flowerGreen vs yellow podInflated vs constricted podTerminal vs axial flowerTall vs short height
6 Mendel’s experimental design Allowed plants to self cross for many generations to ensure purityCrossed pollen of plants true breeding for specific characteristicsPermitted hybrid offspring to self fertilize for several generations
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 ratioActually 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 characteristics2. For each pair of alternatives for a trait the one that was not shown in the F1 generation was still present, but it was latent3. Pairs of alternative traits were segregated among the offspring4. Mendelian Ratio ALWAYS seen
10 Mendel’s Model1. Parents transmit discrete information to offspring not direct physiological traits now called genes2. Each individual receives two genes that encode each trait. ( where are the genes found?)3. Not all genes are identical- alternative forms called allelesHomozygousHeterozygous4. Two alleles remain discrete5. 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
19 Probability Rule of addition Probability of tow mutually exclusive eventsThis OR that= Probability of event 1 + probability of even 2Suppose 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 BSuppose 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 ExampleLook at F1 generationWhat 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 CrossIf 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 InheritancePleiotropyMultiple allelesDominance is not always completeEnvironmental FactorsGene Interaction
24 Polygenic Inheritance More than one gene affecting a single traitExample Height or skin color
25 Pleiotropy A single gene affects more than one trait Example Cystic Fibrosis, albinismMouse Study- Yellow Mice Die
26 Multiple Alleles for One Gene More than one allele controlling the phenotypeExample ABO blood types
27 Incomplete DominanceIncomplete dominance is when the heterozygote is intermediate in appearance between the two homozygote.
28 CodominanceWhen the heterozygote shows some piece of the phenotype of both homozygotesEx. ABO blood types fur color in some animals
30 Genes can be affected by the environment Example Temperature effects on Siamese CatsTemp above 33 degrees no pigmentTemp Below 33 degrees pigment
31 EpistasisAn interaction between genes in which one gene is altered by another geneExample Labrador RetrieversBlack 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