Genetics Mendelian Genetics Genetic Engineering

Gregor Mendel Used pea plants to experiment on genetic traits Pea plants can self-pollinate, producing purebred offspring. The offspring had the same characteristics as the parent Mendel cross-pollinated pea plants, fertilizing the egg and sperm from different plants, to produce hybrids.

Dominance Trait – a specific characteristic, such as seed color or plant height, that varies from one individual to another. Gene – the chemical factors that determine traits. Alleles – the different forms of a gene. –Example: Gene = hair color, Allele = brown hair

Dominance Mendel discovered the principle of dominance – some alleles are dominant and others are recessive. Dominant – only one allele of the trait is required for the trait to appear. Recessive – both alleles of the trait are required for the trait to appear.

Dominance

Segregation The separation of alleles during meiosis during the formation of the gametes. When the parent plant produces gametes, the two alleles segregate from each other so that each gamete carries only a single copy of each gene. Therefore, each plant produces two types of gametes.

Segregation P = parental generation F1 = 1 st filial generation F2 = 2 nd filial generation

Segregation

Probability The likelihood that a particular event will occur. Used to predict the outcomes of genetic crosses. Punnett Squares – used to determine the probability that a trait will occur.

Punnett Square

Homozygous – organisms that have two identical alleles for the same trait –Ex. BB or bb Heterozygous – organisms that have two different alleles for the same trait –Ex. Bb Phenotype – the physical characteristics represented by the alleles –Purple coloring Genotype – the genetic makeup –BB

Punnett Squares Which alleles are homozygous? –XX Which alleles are heterozygous? –XY What is the genotype? –XX and XY What is the phenotype? –Male and female

Punnett Squares What is the percentage of the genotype? –XX = 2/4 = 50% –XY = 2/4 = 50% What is the percentage of the phenotype? –Female = 2/4 = 50% –Male = 2/4 = 50%

Punnett Square What is the percentage of genotype and phenotype for a heterozygous brown-eyed male and a heterozygous brown-eyed female? B = brown, b = blue Genotype = 25% BB, 50% Bb, 25% bb Phenotype = 75% brown, 25% blue

Law of Independent Assortment Genes from different traits can segregate independently during the formation of gametes. Independent assortment helps account for the many genetic variations observed in plants, animals, and other organisms.

Law of Independent Assortment

Summary of Mendel’s Principles The inheritance of biological characteristics is determined by individual units called genes. Genes are passed from parents to offspring. In cases in which two or more forms of the genes for a single trait exist, some forms of the gene may be dominant and others many be recessive.

Summary of Mendel’s principles In most sexually reproducing organisms, each adult has two copies of each gene, one from each parent. These genes are segregated from each other when gametes are formed. The alleles fro different genes usually segregated independently of one another.

Exceptions Incomplete dominance – the heterozygous phenotype is expressed somewhere in between the two homozygous phenotypes.

Exceptions Codominance – both alleles contribute to the phenotype

Exceptions Multiple Alleles – Genes having more than two alleles

Exceptions Polygenic traits – traits controlled by two or more genes

Exceptions Pleiotropy – one gene that affects many traits

Sex – linked inheritance Traits that are located on the sex chromosomes are sex – linked. Most traits are found on the X chromosome because it is much larger. Muscular dystrophy, hemophilia, colorblindness, and melanoma are diseases linked to the sex chromosomes

Sex-linked characteristics What are the genotypic and phenotypic ratios for a normal male and a carrier female of hemophilia? What are the genotypic and phenotypic ratios for a colorblind male and a carrier female of colorblindness? What are the genotypic and phenotypic ratios for a normal male and a bald female?

Genetic Engineering Humans have always genetically altered the offspring of plants and animals. Selective breeding: breeding only organisms with desired characteristics. –Hybridization: crossing dissimilar organisms to gain the best characteristics –Inbreeding: breeding to similar organisms to keep particular characteristics Breeding can increase genetic variation by introducing mutations.

Genetic Engineering Cell transformation: a cell takes in DNA from outside the cell, which becomes a component of the cell’s DNA Transgenic organisms: cells of an organism contain the genetic components of a different organism Cloning: a member of a population of genetically identical cells produced from a single cell