THE WORK OF THE WORK OF GREGOR MENDELGREGOR MENDEL

Background information . . .Background information . . .

►HEREDITY = the transmission of HEREDITY = the transmission of characteristics from one generation to characteristics from one generation to the nextthe next

►GENETICS = the science which deals GENETICS = the science which deals with the study of hereditywith the study of heredity

GREGOR MENDEL (1822-GREGOR MENDEL (1822-1884)1884)

►Austrian MonkAustrian Monk

►Student of both biology and mathematicsStudent of both biology and mathematics

►Considered to be the “Father of Genetics”Considered to be the “Father of Genetics”

►His conclusions have formed the His conclusions have formed the foundation for much of what we foundation for much of what we understand about heredity todayunderstand about heredity today

Biologists liked Mendel’s Biologists liked Mendel’s Research Methods . . . Research Methods . . .

►Sound experimental designSound experimental design►Simple but powerful experimentsSimple but powerful experiments►Hundreds of repetitionsHundreds of repetitions►Meticulous record keepingMeticulous record keeping►Quantitative as well as qualitative Quantitative as well as qualitative

observationsobservations►Mathematical manipulation of Mathematical manipulation of

numerical data (underlying patterns)numerical data (underlying patterns)

THE PEA PLANT . . .THE PEA PLANT . . .

►Much of Mendel’s success was due to Much of Mendel’s success was due to his choice of the pea plant for his choice of the pea plant for experimentsexperiments

►He used the common pea plant He used the common pea plant (Pisum (Pisum sativum)sativum)

Why was the common pea plant Why was the common pea plant so suitable for genetic so suitable for genetic

experiments?experiments?An excellent choice for 4 main reasons:An excellent choice for 4 main reasons:

►Commercially available throughout Commercially available throughout EuropeEurope

►Easy to grow & matured quicklyEasy to grow & matured quickly►Has several characteristics that express Has several characteristics that express

themselves as pairs of contrasting traitsthemselves as pairs of contrasting traits► Is a self-pollinating plant (allows one to Is a self-pollinating plant (allows one to

control which individuals are crossed)control which individuals are crossed)

Mendel examined 7 different Mendel examined 7 different traits:traits:

Mendel’s First Experiment – A Mendel’s First Experiment – A Monohybrid CrossMonohybrid Cross

►Mendel took purebred plants and designated Mendel took purebred plants and designated them as the parent generation or “P them as the parent generation or “P generation”generation”

►He crossed a pure breeding tall pea plant He crossed a pure breeding tall pea plant with a pure breeding short pea plantwith a pure breeding short pea plant

► The offspring from this cross were the first The offspring from this cross were the first filial generation, or the Ffilial generation, or the F11 generation generation

►Mendel called the F1 generation HYBRID Mendel called the F1 generation HYBRID plants to indicate they were the result of a plants to indicate they were the result of a cross between two different purebred plantscross between two different purebred plants

► This is called a MONOHYBRID cross because This is called a MONOHYBRID cross because only one trait, plant height was involvedonly one trait, plant height was involved

►Pure breeding tall X pure breeding Pure breeding tall X pure breeding shortshort

►RESULTS - FRESULTS - F11 Generation = All TALL Generation = All TALL

►Conclusion: The trait for tallness is Conclusion: The trait for tallness is DOMINANT to the trait for shortnessDOMINANT to the trait for shortness

►This led Mendel to formulate The This led Mendel to formulate The Principle of Dominance . . .Principle of Dominance . . .

PRINCIPLE OF DOMINANCEPRINCIPLE OF DOMINANCE

►When individuals with When individuals with contrasting traits are contrasting traits are crossed (dominant and crossed (dominant and recessive), the offspring recessive), the offspring will express only the will express only the dominant traitdominant trait

Mendel’s Second Mendel’s Second Experiment . . .Experiment . . .

►Allowed the FAllowed the F11 generation to self- generation to self-pollinatepollinate

►Results: Results:

FF22 generation was ¾ Tall and ¼ short generation was ¾ Tall and ¼ short

►3:1 ratio3:1 ratio►Conclusions: The FConclusions: The F11 generation plants generation plants

were hybrids (contain both traits – were hybrids (contain both traits – tallness and the trait for shortness)tallness and the trait for shortness)

Mendel’s Hypothesis:Mendel’s Hypothesis:

►Each trait is determined by pairs of Each trait is determined by pairs of discrete physical units or factors (we discrete physical units or factors (we now call genes)now call genes)

►Pairs of genes separate from each other Pairs of genes separate from each other during gamete formation (Principle of during gamete formation (Principle of Segregation)Segregation)

►Which member of a pair of genes Which member of a pair of genes becomes included in a gamete is becomes included in a gamete is determined by chancedetermined by chance

Continued . . . Continued . . .

►There may be 2 or more alternative There may be 2 or more alternative forms of a gene (alternative forms of a forms of a gene (alternative forms of a gene are called alleles, 1 allele may be gene are called alleles, 1 allele may be dominant to another allele)dominant to another allele)

►True breeding organisms have 2 of the True breeding organisms have 2 of the same allele (homozygous) while hybrid same allele (homozygous) while hybrid have 2 different alleles (heterozygous)have 2 different alleles (heterozygous)