G E N E T I C SG E N E T I C SA Study of Heredity and InheritanceA Study of Heredity and Inheritance

Early Concepts in GeneticsEarly Concepts in GeneticsMedieval Age 1600sMedieval Age 1600s

The Blending HypothesisThe Blending Hypothesis

Traits from parentsTraits from parents passed to passed to their offspring thru sexual their offspring thru sexual union.union.

These traits blended in their These traits blended in their offspring producing offspring producing intermediate forms of the intermediate forms of the parents.parents.

Aristotle, 384-322 B.C.Aristotle, 384-322 B.C.and his Pangenic Theoryand his Pangenic Theory

PangenesPangenes in blood in blood contained memories of each contained memories of each structure in the body.structure in the body.•Blood carried these pangenes Blood carried these pangenes in the blood towards the in the blood towards the reproductive organs.reproductive organs.• Hence, terms such as blood Hence, terms such as blood relative, bloodline and blood relative, bloodline and blood kin are still used today.kin are still used today.

The Prevailing 18The Prevailing 18thth Century Century

•A chip of an old block •Any 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 workRediscovery of Mendel's work

It was not until the early It was not until the early 20th century that the that the importance of his ideas was realized. In importance of his ideas was realized. In 1900, , his work was rediscovered by his work was rediscovered by Hugo de Vries, , Carl Correns, and , and Erich von Tschermak. .

His results were quickly replicated, and His results were quickly replicated, and genetic linkage quickly worked out. 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 DesignsMendelian Experimental Designs Mendel cross pollinated two Mendel cross pollinated two

pure breeding plants with pure breeding plants with contrasting expressions for contrasting expressions for the same character. For ex., the same character. For ex., yellow and green seed coat yellow and green seed coat color.color.

The parents were referred to The parents were referred to as the first parental (Pas the first parental (P11) ) generation. The offspring generation. The offspring produced from the cross is produced from the cross is referred as the first filial (Freferred as the first filial (F11) ) generation.generation.

Only one character was Only one character was expressed in all offspring. expressed in all offspring. Mendel concluded that a Mendel concluded that a trait was being masked or trait was being masked or dominated by another.dominated by another.

This trait that was This trait that was expressed, he called asexpressed, he called as dominantdominant and the trait that was not expressed as recessive.recessive.

For seed coat color, yellow is dominant to green.

Mendelian Experimental DesignsMendelian Experimental Designs Mendel allowed the FMendel allowed the F1 1

plants (now Pplants (now P22) to self ) to self

pollinate. He counted the pollinate. He counted the number of offspring (Fnumber of offspring (F22) )

that expressed each of the that expressed each of the two contrasting traits for all two contrasting traits for all seven characters studied.seven characters studied.

The ratio of the plants with The ratio of the plants with dominant traits to the plants dominant traits to the plants with recessive traits is with recessive traits is almost 3:1.almost 3:1.

Mendel hypothesized that each Mendel hypothesized that each trait is controlled by a pair of trait is controlled by a pair of unit determiners. unit determiners.

In 1903, W. Sutton called In 1903, W. Sutton called these factors as these factors as genes.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 Mendel concluded that factors do not blenddo not blend

Mendelian Principles of InheritanceMendelian Principles of Inheritance

First parental (PFirst parental (P11) generation) generation GG GG x x gggg

GametesGametes G G G G g gg g

First filial (FFirst filial (F11) generation ) generation GGg g GGg g GGg g GGg g GenotypeGenotype Gg Gg Gg Gg Gg Gg Gg Gg Phenotype Phenotype all yellow seededall yellow seeded

• Yellow and green are the physical color and are called phenotypes.phenotypes. GG and gg are GG and gg are genotypesgenotypes, which describes the genes of the individual. Also G and g are called , which describes the genes of the individual. Also G and g are called allelesalleles or different forms of the gene for seed color. 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 InheritanceMendelian Principles of Inheritance

Second parental (PSecond parental (P22) generation ) generation GGg g x x GGgg

Gametes Gametes G G g g G G g g

Second filial (FSecond filial (F22) generation ) generation GGGG GGg g GGg ggg gg Genotype Genotype GG Gg Gg gg GG Gg Gg gg PhenotypePhenotype yellow yellowyellow yellow yellow green yellow green Genotypic ratioGenotypic ratio 1GG : 2 Gg : 1 gg 1GG : 2 Gg : 1 gg Phenotypic ratioPhenotypic ratio 3 yellow : 1 green3 yellow : 1 green

When only one character is considered for inheritance, this is called When only one character is considered for inheritance, this is called monohybrid crosses.monohybrid crosses.

Probability and GeneticsProbability and Genetics

Probability is very useful in Probability is very useful in biology. Geneticists use biology. Geneticists use probability in determining probability in determining phenotypic and genotypic phenotypic and genotypic ratio of offspring in ratio of offspring in breeding experiments. breeding experiments.

A A Punnet squarePunnet square is used to is used to grid and organize genetic grid and organize genetic informations.informations.

MaleMale

FemaleFemale GG gg

GG GGGG GGgg

gg GGgg

gggg

Mendel's Laws of Heredity Mendel's Laws of Heredity 1) The Law of Segregation:1) The Law of Segregation: Each inherited trait is defined by a Each inherited trait is defined by a

gene pair. Parental genes are randomly separated to the sex gene pair. Parental genes are randomly separated to the sex cells so that sex cells contain only one gene of the pair. cells so that sex cells contain only one gene of the pair. Offspring therefore inherit one genetic allele from each parent Offspring therefore inherit one genetic allele from each parent when sex cells unite in fertilization.when sex cells unite in fertilization.

2) The Law of Independent Assortment:2) The Law of Independent Assortment: Genes for different Genes for different traits are sorted separately from one another so that the traits are sorted separately from one another so that the inheritance of one trait is not dependent on the inheritance of inheritance of one trait is not dependent on the inheritance of another.another.

3) The Law of Dominance:3) The Law of Dominance: An organism with alternate forms An organism with alternate forms of a gene will express the form that is dominant.of a gene will express the form that is dominant.

Self - CheckSelf - Check

Widow’s peak (S) is dominant over straight hairline (s). If the Widow’s peak (S) is dominant over straight hairline (s). If the mother is heterozygous for the gene pair and the father has mother is heterozygous for the gene pair and the father has straight hairline.straight hairline.

1.1. What is the genotype of the mother? Father?What is the genotype of the mother? Father?

2.2. What are the kinds of gametes produced by the mother? What are the kinds of gametes produced by the mother? Father?Father?

3.3. Perform a Punnet Square.Perform a Punnet Square.

4.4. Give the genotypic ratio of the cross.Give the genotypic ratio of the cross.

5.5. Give the phenotypic ratio of the cross.Give the phenotypic ratio of the cross.

Assignment/HomeworkAssignment/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?