Mendelian Genetics
Gregor Mendel ( ) Responsible for the laws governing Inheritance of Traits
Gregor Johann Mendel Austrian monk Studied the inheritance of traits in pea plants Developed the laws of inheritance Mendel’s work was not recognized until the turn of the 20 th century
Gregor Johann Mendel Between 1856 and 1863 Mendel cultivated and tested some 28,000 pea plants He found that the plants’ offspring retained traits of the parents Mendel was called the “Father of Genetics”
Site of Gregor Mendel’s experimental garden in the Czech Republic
Particulate Inheritance -Mendel stated that physical traits are inherited as “particles” -Mendel did not know that these “particles” were actually genes on chromosomes. -Remember genes are segments of DNA that code for a particular protein!
Genetic Terminology Trait- any characteristic that can be passed from parent to offspring Heredity- passing of traits from parent to offspring Genetics- study of heredity
Types of Genetic Crosses Monohybrid cross- cross involving a single trait Example: Flower color Dihybrid cross- cross involving two traits Example: flower color and plant height
Punnett Squares Used to help solve genetics problems
Designer “Genes” Alleles- two forms of a gene (dominant and recessive) Dominant- stronger of the two genes and expressed in a hybrid (represented by a capital letter) Recessive- shows up less often in a cross and is hidden when a dominant gene is present (represented by a lower case letter)
More Terminology Genotype- gene combination for a trait (Example: RR, Rr, or rr) Phenotype- the physical feature resulting from a genotype (Example: Red or white)
Genotype and Phenotype in Flowers Genotypes of alleles: R = red flower r = yellow flower All genes occur in pairs, so 2 alleles affect a characteristic Possible combinations are: Genotypes:RRRrrr Phenotypes:REDREDYELLOW
Genotypes Homozygous genotype: gene combination involving 2 dominant or 2 recessive alleles (RR or rr); also called purebred Heterozygous genotype: gene combination of one dominant and one recessive allele (Rr); also called hybrid
Mendel’s Pea Plant Experiments
Why peas, Pisum sativum? Peas can be grown in a small area Produce lots of offspring Produce pure plants when allowed to self- pollinate Can be artificially cross- pollinated
Reproduction in Flowering Plants Pollen contains sperm produced by the stamen Ovary contains eggs found inside the flower
Mendel’s Experimental Methods -Mendel hand-pollinated flowers using a paintbrush -He snipped the stamens (male parts) to prevent self-pollination -Covered each flower with a cloth bag
Generation “Gap” P 1 Generation- the parental generation in a breeding experiment F 1 Generation- the first generation of offspring in a breeding experiment F 2 Generation- the second generation of offspring in a breeding experiment (from breeding individuals from the F 1 generation)
Following the Generations Cross 2 pure plants TT and ss Results in all hybrids (Ts) Cross two hybrids and get 3 tall and one short (TT, Ts, and ss)
Mendel’s Laws Law of Segregation- during the formation of gametes (sex cells; aka eggs or sperm), the two alleles responsible for a trait separate from each other Alleles for a trait are then “recombined” at fertilization to produce the genotype of the offspring bb b b
Law of Segregation PRACTICE 1. A hybrid male yellow canary (Yy) Yy
2. A pure female white flower (rr) rr
If a male red flower (Rr) and a pure white flower (rr) from above got their gametes together (fertilization) what kind of combinations could be formed? X
Male red flower (Rr) Female white flower Rr Sperm 1Sperm 2 rr Egg 1Egg 2
= = = = GenotypePhenotype
Law of Dominance In a cross of parents that are pure for different traits, only one form of the trait will appear in the next generation All the offspring will be heterozygous and express only the dominant trait. GG x gg = all Gg
Law of Independent Assortment Alleles for different traits are distributed to sex cells independently of one another. This law can be illustrated using dihybrid crosses.
Mendel Rap Video!