"Chap 11 Outline Introduction to Genetics"
Chap 11 Outline: Introduction to Genetics 11-1 The work of Gregor Mendel Key concepts: What is the principle of dominance? What happens during segregation? -Every living thing has a set of characteristics that it inherits from its parents. -Genetics: The study of heredity. Gregor Mendel’s Peas: -Gregor Mendel work with the pea plant laid the foundations for modern genetics -Fertilization: The joining of male and female reproductive cells. -Most pea plants were self-pollinating and produced offspring that were identical to the parent. -True-breeding: Organisms that produce offspring identical to the parent if they were allowed to self-pollinate. -Mendel wanted to produce pea plants by cross-pollination not self-pollination. Genes and Dominance: -Mendel studied seven traits in pea plants. Each trait had two contrasting and distinct characteristics. -Mendel crossed plants that had contrasting characteristics and called this generation the parental or P generation. The offspring were called the first filial or F1 generation. -Hybrid: Offspring that are produced from crosses between parents with different traits. -All of the offspring from Mendel’s crosses only had the characteristic of one the parents. -Mendel drew two conclusions from this first set of experiments. 1) Biological inheritance is determined by factors that are passed from parent to offspring. 2) Principle of dominance: Some alleles are dominant and others are recessive. When present the dominant allele is expressed. -Today we call Mendel’s factors genes. Genes come in different forms that are called alleles. Generally the dominant allele masks or hides the recessive form. Segregation: -Mendel allowed the F1 generation to self-pollinate to produce a second filial or F2 generation to see if the second trait had disappeared or was just masked. -The recessive trait reappeared in the F2 generation in 1 out of 4 of the offspring. -Mendel concluded that each form a trait was separated or segregated in the the production of gametes or sex cells. -Principle of Segregation: F1 individuals produce two types of gametes: One that has the dominant form of a gene and one that has the recessive form of a gene. 11-2 Probability and the Punnett Square: Key concepts: How do geneticists use the principles of probability? How do geneticists use punnett squares? Genetics and Probability: -Probability: The likelihood that a particular event is going to occur. -The principles of probabilities can be used to predict the outcome of genetic crosses Punnett Squares: -The gene combinations that might result from a genetic cross can be determined by drawing a punnett square. -Punnett squares can be used to predict and compare the genetic variations that will result from a cross. -Homozygous: Organisms that have two identical alleles for a particular trait. -Heterozygous: Organisms that have two different alleles for a particular trait. -Genotype: Genetic make up of an organism. -Phenotype: Physical characteristics of an organism. Expression of the genotype. 11-3 Exploring Mendelian Genetics: Key concepts: What is the principle of independent assortment? What inheritance patterns exist besides simple dominance? Independent Assortment: -Mendel wanted to know if different traits segregated independently of one another into gametes. -Mendel crossed round yellow pea plants(RRYY) with green wrinkled pea plants(rryy). 1) All of the F1 offspring were round and yellow pea plants. 2) F1 generation was then allowed to self-pollinate. 3) In the F2 generation Mendel found that both parent phenotypes showed up as well as different combinations of parent phenotypes. -Principle of independent assortment: States that genes of different traits can segregate independently of one another during gamete formation. Summary of Mendel’s Principles: -Principle of Dominance: Of the dominant allele is present it will be expressed -Principle of Segregation: Alleles separate/segregate into gametes randomly. -Principle of Independent Assortment: Alleles of different traits segregate independently of one another during gamete formation. Beyond Dominant and Recessive Alleles: -Some alleles are neither dominant nor recessive, and many traits are controlled by multiple alleles or multiple genes. -Incomplete dominance: Occurs when one allele is not completely dominant over another. -Codominance: Occurs when both alleles are expressed and contribute to the phenotype. -Multiple alleles: Occurs when a gene has more than two alleles for a gene. -Polygenic Traits: Traits that are controlled by two or more genes. Applying Mendel’s Principles: -Mendel’s principles apply to all living things and can be used to study the inheritance of genetic traits and the probabilities of certain traits appearing in offspring of any organism. Genetics and the Environment: -The characteristics of any living thing are not solely determined by the genes that it inherits. -Phenotype = Genotype + Environment 11-5 Linkage and Gene Maps: Key Concepts: What structures actually assort independently? Gene Linkage: -Thomas Morgan noticed that certain traits were always observed together in fruit flies. -From this he concluded that chromosomes are actually groups of linked genes. -Mendel’s principle of independent assortment still holds true, but chromosomes assort independently of one another not individual genes. -Using linked genes geneticists can make gene maps which show the relative location of genes on a chromosome.