Mendelian Genetics. Gregor Mendel (1822-1884) Responsible for the laws governing Inheritance of Traits

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Mendelian Genetics

Mendelian GeneticsGregor Mendel (1822-1884)

Responsible for the laws governing Inheritance of Traits

Gregor Johann MendelAustrian monkStudied the inheritance of traits in pea plantsDeveloped the laws of inheritanceMendels work was not recognized until the turn of the 20th century

Gregor Johann MendelBetween 1856 and 1863 Mendel cultivated and tested some 28,000 pea plantsHe found that the plants offspring retained traits of the parentsMendel was called the Father of Genetics

Site of Gregor Mendels experimental garden in the Czech Republic

Particulate InheritanceMendel stated that physical traits are inherited as particlesMendel did not know that these particles were actually genes on chromosomes.Remember genes are segments of DNA that code for a particular protein!

Genetic TerminologyTrait- 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 CrossesMonohybrid cross- cross involving a single traitExample: Flower color

Dihybrid cross- cross involving two traitsExample: flower color and plant height

Punnett SquaresUsed to help solve genetics problems

Designer GenesAlleles- 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 TerminologyGenotype- 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 FlowersGenotypes of alleles:R = red flowerr = yellow flower

All genes occur in pairs, so 2 alleles affect a characteristic

Possible combinations are:Genotypes:RRRrrrPhenotypes:REDREDYELLOW

GenotypesHomozygous genotype: gene combination involving 2 dominant or 2 recessive alleles (RR or rr); also called purebredHeterozygous genotype: gene combination of one dominant and one recessive allele (Rr); also called hybrid

Mendels Pea Plant Experiments

Why peas, Pisum sativum?Peas can be grown in a small areaProduce lots of offspringProduce pure plants when allowed to self-pollinate Can be artificially cross-pollinated

Reproduction in Flowering PlantsPollen contains sperm produced by the stamenOvary contains eggs found inside the flower

Mendels Experimental MethodsMendel hand-pollinated flowers using a paintbrushHe snipped the stamens (male parts) to prevent self-pollinationCovered each flower with a cloth bag

Generation GapP1 Generation- the parental generation in a breeding experimentF1 Generation- the first generation of offspring in a breeding experimentF2 Generation- the second generation of offspring in a breeding experiment (from breeding individuals from the F1 generation)

Following the GenerationsCross 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)

Mendels LawsLaw of Segregation- during the formation of gametes (sex cells; aka eggs or sperm), the two alleles responsible for a trait separate from each otherAlleles for a trait are then recombined at fertilization to produce the genotype of the offspring

bb bbLaw of SegregationPRACTICE1. A hybrid male yellow canary (Yy)


2. A pure female white flower (rr)

Law of Segregationrr

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?

Law of Segregation

XMale red flower (Rr)Female white flowerRrSperm 1Sperm 2rrEgg 1Egg 2Law of Segregation++++====11122122GenotypePhenotypeLaw of SegregationLaw of DominanceIn a cross of parents that are pure for different traits, only one form of the trait will appear in the next generationAll the offspring will be heterozygous and express only the dominant trait.GG x gg = all Gg

Law of Independent AssortmentAlleles for different traits are distributed to sex cells independently of one another.

This law can be illustrated using dihybrid crosses.

Mendel Rap Video!