GeneticsGenetics
Gregor MendelGregor Mendel
“Father of Genetics”1866- published findings on plant breeding and inheritance
(During American Civil War)Not discovered until early 1900s
“Father of Genetics”1866- published findings on plant breeding and inheritance
(During American Civil War)Not discovered until early 1900s
Keys to SuccessKeys to SuccessUsed “True-Breeding” pea plants (“purebreds”)Always produce offspring with only one form of a trait
Studied only 1 characteristic at a time
Analyzed data mathematically
Used “True-Breeding” pea plants (“purebreds”)Always produce offspring with only one form of a trait
Studied only 1 characteristic at a time
Analyzed data mathematically
Pea Plant ReproductionPea Plant Reproduction
1. Self-pollination Pollen fertilizes egg cells on
same flower 1 parent
2. Cross-pollination Pollen from flower of one plant
fertilizes egg cells on another plant
2 parents
1. Self-pollination Pollen fertilizes egg cells on
same flower 1 parent
2. Cross-pollination Pollen from flower of one plant
fertilizes egg cells on another plant
2 parents
Mendel controlled breeding by cross-pollinating
To prevent self-pollination, Mendel removed male parts from a flower and dusted the flower with pollen from a different pea plant
Mendel controlled breeding by cross-pollinating
To prevent self-pollination, Mendel removed male parts from a flower and dusted the flower with pollen from a different pea plant
Genetics:The science of heredity
Heredity:The biological inheritance of traits from parent to offspring
Genetics:The science of heredity
Heredity:The biological inheritance of traits from parent to offspring
Genetics used for:Genetics used for:
1.Preventing & treating diseases
2.Developing tougher plants to increase food production
1.Preventing & treating diseases
2.Developing tougher plants to increase food production
GenerationsGenerations1. P generation: parent generation
“true - breeding”
2. F1 generation First generation of offspring
3. F2 generation Second generation produced
when f1 generations are crossed
1. P generation: parent generation “true - breeding”
2. F1 generation First generation of offspring
3. F2 generation Second generation produced
when f1 generations are crossed
AlleleThe different forms of a gene2, 3, or even 12 possible alleles per gene
AlleleThe different forms of a gene2, 3, or even 12 possible alleles per gene
Dominant
Form of the gene that is expressed
Capital letter: T
Dominant
Form of the gene that is expressed
Capital letter: T
Recessive
Form of a gene (allele) that is only expressed in homozygous state
Lowercase letter: t
Recessive
Form of a gene (allele) that is only expressed in homozygous state
Lowercase letter: t
Homozygous
2 identical alleles for the same trait
Homozygous dominant: TTHomozygous recessive: tt
Homozygous
2 identical alleles for the same trait
Homozygous dominant: TTHomozygous recessive: tt
Heterozygous
2 different alleles for the same trait
Tt : dominant trait will be expressed
Also called a “hybrid”
Heterozygous
2 different alleles for the same trait
Tt : dominant trait will be expressed
Also called a “hybrid”
Genotype
Genetic make-up of an organism
The “letters”Tt or TT or ttAa or AA or aa
Genotype
Genetic make-up of an organism
The “letters”Tt or TT or ttAa or AA or aa
Phenotype
Physical expression of a trait
Ex: Tall or Short
Phenotype
Physical expression of a trait
Ex: Tall or Short
Examples:
TT = genotypeTall = phenotype
tt = genotypeShort = phenotype
Examples:
TT = genotypeTall = phenotype
tt = genotypeShort = phenotype
Law of segregationLaw of segregation
The two alleles for each trait separate during meiosis
So, for each gene, an organism receives one allele from each parent - during fertilization
The two alleles for each trait separate during meiosis
So, for each gene, an organism receives one allele from each parent - during fertilization
Part 2Part 2
Seed ColorSeed Color P generation cross: (“true -
breeding”)Yellow peas x Green peas
F1 generation:All yellow
F2 generation:6022 yellow : 2001 green3 yellow : 1 green
P generation cross: (“true - breeding”)Yellow peas x Green peas
F1 generation:All yellow
F2 generation:6022 yellow : 2001 green3 yellow : 1 green
Monohybrid crossMonohybrid cross
Use a Punnett square to cross 2 hybrids:
Yy x Yy What are the possible
genotypes?
What is the genotypic ratio?
What is the phenotypic ratio?
Use a Punnett square to cross 2 hybrids:
Yy x Yy What are the possible
genotypes?
What is the genotypic ratio?
What is the phenotypic ratio?
Law of Independent Assortment
Law of Independent Assortment
Genes on separate chromosomes sort independently during meiosis
Alleles for seed shape separate independently from seed color alleles
So, seed shape is not connected to seed color
Genes on separate chromosomes sort independently during meiosis
Alleles for seed shape separate independently from seed color alleles
So, seed shape is not connected to seed color
Dihybrid crossDihybrid cross
A Special type of two - factor cross
YyRr x YyRr (heterozygous for both traits)
You will always find the same phenotypic ratio. What is this ratio?
A Special type of two - factor cross
YyRr x YyRr (heterozygous for both traits)
You will always find the same phenotypic ratio. What is this ratio?