Presentation on theme: "Mendelian Patterns of Inheritance BIOLOGY. Gregor Mendel (1822-1884) Austrian monk who formulated fundamental laws of heredity in early 1860s. –Studied."— Presentation transcript:
Mendelian Patterns of Inheritance BIOLOGY
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.
Gregor Mendel Important Dates Experimented with peas, Pisum sativum, from Reported his findings to the Brunn Society for the Study of Natural Science in 1865 Published Experiments with Plant Hybrids in 1866
One-Trait Inheritance Mendel performed cross-breeding experiments between true-breeding plants (homozygous). –Chose varieties that differed in only one trait (monohybrid cross) –Performed crosses Parental generation = P First generation offspring = F 1 (1 st filial) Second generation offspring = F 2
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.
Genotype Versus Phenotype Genotype –Refers to the alleles an individual receives. Phenotype –Refers to the physical appearance of the individual.
Modern Genetics View Each 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 alleles –Heterozygous = different alleles
Punnett Square All 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.
Testcross A 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)
Two-Traits Dihybrid Cross Mendel performed cross using true-breeding plants differing in two traits. –Observed phenotypes among F 2 plants. –Formulated law of independent assortment: Each factor segregates independently of the others All possible combinations of factors can occur.
Figure 14.7 Testing two hypotheses for segregation in a dihybrid cross
Two-Trait Testcross A two-trait testcross is used to determine if an individual is homozygous dominant or heterozygous for either of the two traits.
Incomplete Dominance Exhibited when the heterozygote has an intermediate phenotype between that of either homozygote.
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
Terminology Pleiotropy - 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)