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Introduction to Genetics: The Work of Gregor Mendel
Biology Unit 6 / Chapter 11 Powerpoint #1
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Vocabulary Allele Cross pollination Gene Genetics Hybrid
Self pollination Trait True breeding
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Gregor Mendel was born in 1822 in the Czech Republic
Studied Science and Mathematics at the University of Vienna Spent the next 14 years teaching high school and working at a monastery in the garden
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Mendel noticed that the SAME type of plant could have VARIATIONS, or differences, these are the variations he noticed: Seed Shape Seed Color Seed Coat Color Round Yellow Gray Wrinkled Green White Pod Shape Pod Color Flower Position Plant Height Smooth Green Axial Tall Constricted Yellow Terminal Short
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After Mendel noticed these variations he decided to do an experiment of his own.
Mendel wanted to breed the pea plants together in different combinations to see what the offspring (seedlings) would look like. used experimental method used quantitative analysis collected data & counted them excellent example of scientific method
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Terminology Genetics: study of heredity (how traits pass from one generation to the next) True-breeding: if allowed to self-pollinate, produce offspring identical to self Self-pollination: pollen from one flower fertilizes egg cells in same flower Cross-pollination: pollen from one flower fertilizes egg cells in a different flower
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Mendel’s work Bred pea plants P F1 F2
Pollen transferred from white flower to stigma of purple flower Bred pea plants cross-pollinate true breeding parents (P) P = parental raised seed & then observed traits (F1) F = filial allowed offspring to self-pollinate & observed next generation (F2) P anthers removed all purple flowers result F1 P = parents F = filial generation self-pollinate F2
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Techniques of Mendel Describe how Mendel prevented self-pollination and controlled cross-pollination in pea plants: He cut off the male parts (anthers) of one flower, then dusted the stigma with pollen from a second flower. Why did he want to do this? He wanted plants with specific traits to breed with one another.
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Looking closer at Mendel’s work
true-breeding purple-flower peas true-breeding white-flower peas X P Where did the white flowers go? 100% F1 generation (hybrids) purple-flower peas White flowers came back! In a typical breeding experiment, Mendel would cross-pollinate (hybridize) two contrasting, true-breeding pea varieties. The true-breeding parents are the P generation and their hybrid offspring are the F1 generation. Mendel would then allow the F1 hybrids to self-pollinate to produce an F2 generation. self-pollinate F2 generation 3:1 75% purple-flower peas 25% white-flower peas
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What did Mendel’s findings mean?
Traits come in alternative versions purple vs. white flower color alleles different alleles vary in the sequence of nucleotides at the specific locus of a gene some difference in sequence of A, T, C, G purple-flower allele & white-flower allele are two DNA variations at flower-color locus different versions of gene at same location on homologous chromosomes
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Traits are inherited as discrete units
For each characteristic, an organism inherits 2 alleles, 1 from each parent diploid organism inherits 2 sets of chromosomes, 1 from each parent homologous chromosomes like having 2 editions of encyclopedia Encyclopedia Britannica Encyclopedia Americana What are the advantages of being diploid?
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What did Mendel’s findings mean?
Some traits mask others purple & white flower colors are separate traits that do not blend purple x white ≠ light purple purple masked white dominant allele functional protein masks other alleles recessive allele allele makes a malfunctioning protein masked by the dominant allele I’ll speak for both of us! wild type allele producing functional protein mutant allele producing malfunctioning protein homologous chromosomes
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Principle of Dominance
Principle of dominance: dominant trait is always seen when dominant allele is present; recessive trait is only seen when no dominant allele is present
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Mendel’s Observations
Parents Long stems short stems Red flowers white flowers Green pods yellow pods Round seeds wrinkled seeds Yellow seeds green seeds First Generation All long All red All green All round All yellow Second Generation 787 long: 277 short 705 red: 224 white 428 green: 152 yellow 5474 round: 1850 wrinkled 6022 yellow: 2001 green 1. In the first generation of each experiment, how do the characteristics of the offspring compare to the parents’ characteristics? 2. How do the characteristics of the second generation compare to the characteristics of the first generation? 3. How do we know the recessive allele did not disappear?
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