Presentation on theme: "Introduction to Genetics. Who was Gregor Mendel? He was known as the “FATHER OF GENETICS” He discovered how traits were inherited GENETICS – study of."— Presentation transcript:
Introduction to Genetics
Who was Gregor Mendel? He was known as the “FATHER OF GENETICS” He discovered how traits were inherited GENETICS – study of heredity HEREDITY – the passing of traits from parents to offspring
Mendel’s Peas Mendel did his study on pea plants Pea plants have many traits (tall/short, purple flowers/white flowers) Pea plants can be self-fertilized or cross-fertilized
Mendel’s Peas He studied seven traits.
Types of Plants True-Breeding - these plants always create plants that look like themselves when crossed. AKA: Purebred Tall=Tall x Tall or Short =Short x Short Hybrids – offspring from crosses of two true-breeding plants (with different traits) Hybrid=Tall x Short
Mendel’s Experiments He experimentally crosses different varieties to develop hybrids. He then crossed the hybrids and analyzed the results. P F1F1 F2F2
Genes and Alleles Mendel discovered that each trait is controlled by two factors (alleles) Genes* – factors that determines traits So…. Alleles are two forms of the same gene ex. B vs b *FYI--Danish botanist Wilhelm Johannsen coined the word "gene“ in 1909.
Explaining the Cross When a parent makes sperm or eggs, their genes (2 factors) separate ( LAW OF SEGREGATION) The GAMETES (egg or sperm) contain one allele for each trait. (let T be tall and t be short) T T t t T
Dominance Some traits were dominant over others. PRINCIPLE OF DOMINANCE Tall x Short = all tall offspring (hybrids) Tall is the dominant trait Short is recessive trait (hidden) or Tall allele is dominant to the Short allele
Mendel's -First Law In a cross of parents that are pure for contrasting traits, only one form of the trait will appear in the next generation. Offspring that are hybrid for a trait will have only the dominant trait in the phenotype. “One trait will “hide” the other trait.” The Principle of Dominance
Mendel's Second Law During the formation of gametes (eggs or sperm), the two alleles responsible for a trait separate from each other. Alleles for a trait are then "recombined" at fertilization, producing the genotype for the traits of the offspring. The Law of Segregation
PHENOTYPE - what it looks like, the organisms physical description. (tall or short) GENOTYPE - the genes an organism has, represented by letters, (TT, Tt, tt) Mendel studied the appearance of his peas but did not know about genes.
Check for understanding 1. A one-eyed purple people eater is crossed with a two eyed purple people eater. All of their offspring have two eyes. Which trait is dominant? 2. If you use the letter E for this gene. What is the genotype of the offspring? Are these offspring the F1 or F2 generation? 4. If you crossed the offspring with each other? How many ofthe new offspring would you expect to have two eyes?
Mendel's Third Law Ma-Ma-Ma-Ma-Mendel's Third Law The Law of Independent Assortment Alleles for different traits are distributed to sex cells (& offspring) independently of one another. The Law of Independent Assortment
Vocabulary for this section Mendel, dominant, recessive, trait, gene, genetics, heredity, allele, heterozygous, homozygous, hybrid, true breeding/pure breeding, test cross, P1, G1, F1, (remember the 1’s are subscripts), Punnett square, phenotype, genotype (know ratios for phenotype/genotype), classic Mendelian ratio, gamete, zygote, law of independent assortment, law of segregation This material is covered in ch. 6 – specifically 6.3, 6.4 and 6.5