G E N E T I C S A Study of Heredity and Inheritance

Early Concepts in Genetics Medieval Age 1600s The Blending Hypothesis The Blending Hypothesis Traits from parents passed to their offspring thru sexual union. Traits from parents passed to their offspring thru sexual union. These traits blended in their offspring producing intermediate forms of the parents. These traits blended in their offspring producing intermediate forms of the parents. Aristotle, B.C. and his Pangenic Theory Pangenes Pangenes in blood contained memories of each structure in the body. BloodBlood carried these pangenes in the blood towards the reproductive organs. Hence, terms such as blood relative, bloodline and blood kin are still used today.

The Prevailing 18th Century A chip of an old blockAny traits can be passed

Modern Genetics begun in 1860s when an Austrian monk and scientist, Johann Gregor Mendel worked with a species of garden pea plants. He had studied biology, mathematics and physics that enabled him to interpret his observations. In his paper "Versuche über Pflanzenhybriden" ("Experiments in Plant Hybridization"), presented in 1865 to the Brunn Natural History Society, Gregor Mendel traced the inheritance patterns of certain traits in pea plants and showed that they could be described mathematically. However, his works were not fully recognized until 50 years later.

Rediscovery of Mendel's work It was not until the early 20th century that the importance of his ideas was realized. In 1900, his work was rediscovered by Hugo de Vries, Carl Correns, and Erich von Tschermak. It was not until the early 20th century that the importance of his ideas was realized. In 1900, his work was rediscovered by Hugo de Vries, Carl Correns, and Erich von Tschermak.20th century1900Hugo de Vries Carl CorrensErich von Tschermak20th century1900Hugo de Vries Carl CorrensErich von Tschermak His results were quickly replicated, and genetic linkage quickly worked out. His results were quickly replicated, and genetic linkage quickly worked out.

Kingdom:Plantae Division:Magnoliophyta Class:Magnoliopsida Order:Fabales Family:Fabaceae Subfamily:Faboideae Tribe:Vicieae Genus:Pisum Species:P. sativum Mendel used the garden pea plants for several reasons: 1.The plants have several characters, each with two distinct forms. 2.The garden pea plants reproduce at a fast rate. This gave him the results in just about 90 days. 3.They are a hardy plants; they do not need much caring or cultivating. 4.The plants are also structurally adapted for self pollination. Hence, pure breds are possible. 5.At the same time, cross-pollination is manually possible. Control and variation in results can be obtained.

Mendelian Experimental Designs Mendel cross pollinated two pure breeding plants with contrasting expressions for the same character. For ex., yellow and green seed coat color. The parents were referred to as the first parental (P1) generation. The offspring produced from the cross is referred as the first filial (F1) generation. Only one character was expressed in all offspring. Mendel concluded that a trait was being masked or dominated by another. This trait that was expressed, he called as dominant and the trait that was not expressed as recessive. For seed coat color, yellow is dominant to green.

Mendelian Experimental Designs Mendel allowed the F 1 plants (now P 2 ) to self pollinate. He counted the number of offspring (F 2 ) that expressed each of the two contrasting traits for all seven characters studied. Mendel allowed the F 1 plants (now P 2 ) to self pollinate. He counted the number of offspring (F 2 ) that expressed each of the two contrasting traits for all seven characters studied. The ratio of the plants with dominant traits to the plants with recessive traits is almost 3:1. The ratio of the plants with dominant traits to the plants with recessive traits is almost 3:1. Mendel hypothesized that each trait is controlled by a pair of unit determiners. In 1903, W. Sutton called these factors as genes. He knew each species must have two factors for a trait that remain separate and distinct during gametogenesis. As a result, some trait will disappear and reappear in succeeding generations. Mendel concluded that factors do not blend

Mendelian Principles of Inheritance First parental (P1) generation GG x x gg Gametes G G g g First filial (F1) generation Gg G Gg g g Genotype Gg Gg Gg Gg Phenotypeall yellow seeded Yellow and green are the physical color and are called p pp phenotypes. GG and gg are genotypes, which describes the genes of the individual. Also G and g are called alleles or different forms of the gene for seed color. Gene pairs are also said to be homozygous if they are made up of the same alleles, GG or gg (pure breds). If they have dissimilar alleles, then it is called heterozygous.

Mendelian Principles of Inheritance Second parental (P2) generation Gg x Gg Gametes G g G g Second filial (F2) generation GG Gg Gg gg Genotype GG Gg Gg gg Phenotypeyellow yellow yellow green Genotypic ratio 1GG : 2 Gg : 1 gg Phenotypic ratio3 yellow : 1 green When only one character is considered for inheritance, this is called monohybrid crosses.

Probability and Genetics Probability is very useful in biology. Geneticists use probability in determining phenotypic and genotypic ratio of offspring in breeding experiments. A Punnet square is used to grid and organize genetic informations. Male MaleFemale G g G GG GG Gg Gg g gg gg

Mendel's Laws of Heredity 1) The Law of Segregation: Each inherited trait is defined by a gene pair. Parental genes are randomly separated to the sex cells so that sex cells contain only one gene of the pair. Offspring therefore inherit one genetic allele from each parent when sex cells unite in fertilization. 2) The Law of Independent Assortment: Genes for different traits are sorted separately from one another so that the inheritance of one trait is not dependent on the inheritance of another. 3) The Law of Dominance: An organism with alternate forms of a gene will express the form that is dominant.

Self - Check Widow’s peak (S) is dominant over straight hairline (s). If the mother is heterozygous for the gene pair and the father has straight hairline. Widow’s peak (S) is dominant over straight hairline (s). If the mother is heterozygous for the gene pair and the father has straight hairline. 1. What is the genotype of the mother? Father? 2. What are the kinds of gametes produced by the mother? Father? 3. Perform a Punnet Square. 4. Give the genotypic ratio of the cross. 5. Give the phenotypic ratio of the cross.

Assignment/Homework What are Non-Mendelian Crosses? What are Non-Mendelian Crosses? What are multiple allelic traits? What are multiple allelic traits? What are polygenes or multiple genes? What are polygenes or multiple genes? What is Incomplete Dominance? What is Incomplete Dominance? What is Codominance? Penetrance? Heritability? What is Codominance? Penetrance? Heritability? What is Pedigree-making in family trait studies? What is Pedigree-making in family trait studies?