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Introduction to Genetics

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1 Introduction to Genetics

2 Who was Gregor Mendel? “FATHER OF GENETICS” He was known as the
He discovered how traits were inherited GENETICS – study of heredity HEREDITY – the passing of traits from parents to offspring Click on picture for a 15 min video at Youtube on Mendel and intro. to genetics GOOD

3 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

4 He studied seven traits.
Mendel’s Peas He studied seven traits.

5 Mendel's Procedures

6 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

7 Mendel’s Experiments P He experimentally crosses different varieties to develop hybrids. He then crossed the hybrids and analyzed the results. F1 F2

8 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.

9 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

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

11 The Principle of Dominance
Mendel's -First Law The Principle of Dominance 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.”

12 Mendel's Second Law The Law of Segregation
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.


14 Mendel studied the appearance of his peas
but did not know about genes. PHENOTYPE   - what it looks like, the organisms physical description. (tall or short) GENOTYPE  -  the genes an organism has, represented by letters, (TT, Tt, tt)

15 Are these offspring the F1 or F2 generation?
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?


17 The Law of Independent Assortment
Mendel's Third Law The Law of Independent Assortment 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.

18 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

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