Presentation on theme: "Mendelian Patterns of Inheritance"— Presentation transcript:
1 Mendelian Patterns of Inheritance BIOLOGYMendelian Patterns of Inheritance
2 Gregor Mendel ( )Austrian monk who formulated fundamental laws of heredity in early 1860s.Studied science and mathematics at University of Vienna.Formulated the particulate theory of inheritance.Inheritance involves reshuffling of genes from generation to generation.
3 Gregor Mendel—Important Dates Experimented with peas, Pisum sativum,fromReported his findings to the Brunn Society for the Study of Natural Science in 1865Published Experiments with Plant Hybrids in 1866
4 One-Trait Inheritance Mendel performed cross-breeding experiments between true-breeding plants (homozygous).Chose varieties that differed in only one trait (monohybrid cross)Performed crossesParental generation = PFirst generation offspring = F1 (1st filial)Second generation offspring = F2
5 Law of Segregation Each individual has two factors for each trait. The factors separate when gametes form.A gamete contains only one of two factors.Fertilization = new individual with 2 factors for each trait.
6 Genotype Versus Phenotype Refers to the alleles an individual receives.PhenotypeRefers to the physical appearance of the individual.
7 Modern Genetics ViewEach trait is controlled by two alleles (alternate forms of a gene).Dominant allele (D) masks the expression of the recessive allele (d).Alleles occur on a homologous pair of chromosomes at a locus.Homozygous = identical allelesHeterozygous = different alleles
8 Punnett SquareAll possible kinds of sperm are lined up on one axis, and all possible kinds of eggs are lined up on the other axis.Every possible combination of alleles is placed within the squares.
9 TestcrossA monohybrid testcross determines if the phenotype is homozygous dominant (RR) or heterozygous (Rr).Those with one dominant gene will express the dominant phenotype whereas individuals with the recessive phenotype must be homozygous (rr)
10 Two-Traits Dihybrid Cross Mendel performed cross using true-breeding plants differing in two traits.Observed phenotypesamong F2 plants.Formulated law of independent assortment:Each factor segregates independently of the othersAll possible combinations of factors can occur.
11 Figure 14.7 Testing two hypotheses for segregation in a dihybrid cross
12 Two-Trait TestcrossA two-trait testcross is used to determine if an individual is homozygous dominant or heterozygous for either of the two traits.
13 Incomplete DominanceExhibited when the heterozygote has an intermediate phenotype between that of either homozygote.
15 Polygenic Inheritance Occurs when a trait is governed by two or more sets of alleles.Each dominant allele has a quantitative effect and these effects are additive like height
16 TerminologyPleiotropy - A gene that affects more than one characteristic of an individual.Sickle-cell (incomplete dominance)Epistasis - A gene at one locus interferes with the expression of a gene at a different locus.Human skin color (polygenic inheritance)