Introduction to Genetics The Work of Gregor Mendel.

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Introduction Introduction to Genetics to Genetics The Work of Gregor Mendel The Work of Gregor Mendel

Transcript of Introduction to Genetics The Work of Gregor Mendel.

Page 1: Introduction to Genetics The Work of Gregor Mendel.

Introduction Introduction to Geneticsto GeneticsThe Work of Gregor MendelThe Work of Gregor Mendel

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Genetics• Scientific study of heredity

• Gregor Mendel–Born in 1822 in Czech Republic

–Worked in monastery garden while teaching H.S. (math & science)

–Worked w/ true-breeding pea plants• If allowed to self-pollinate, produce offspring identical to themselves

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Genes and Dominance

• Mendel studied 7 traits–Specific characteristic that varies

from one individual to another– color, height

–Each trait had two contrasting characters – greed seeds vs. yellow

–Crossed true-breeding plants of each type to opposing character

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• True-breeding yellow seed X True-breeding green seed

• Original pair of plants = P (parental) generation

• Offspring = F1 (first filial)

• Offspring of crosses between parents w/ different traits = hybrids

Genes and Dominance

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• What did the F1 hybrids look like? Did they look like a blend of both parents? No!

• All F1 offspring only showed the character of one parent.

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Mendel’s Two Conclusions

• 1. Biological inheritance is determined by factors that are passed on from one generation to the next–Genes – chemical factors that determine traits

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• Each trait that Mendel studied was controlled by one gene that occurred in two contrasting forms–Ex: Gene for Plant Height = One form for tall one for short

• Alleles – different forms of a gene

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• 2. Principle of Dominance – some alleles are dominant and others are recessive–If there is a dominant present, that form is shown

–If there are two recessive present, the recessive is shown

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Segregation• Did the recessive alleles disappear,

or were they still present ?–To find the answer, he allowed F1

generation plants to self-pollinate to create an F2 generation

• What happened? –Traits reappeared. ¼ of the F2

plants showed the recessive allele

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Segregation, cont’d

• Law of Segregation–Two alleles separate from each other so that each gamete carries only a single copy of each gene

–Ex: Fig. 11-5

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Introduction Introduction to Geneticsto Genetics

Genetics and Genetics and ProbabilityProbability

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Genetics and Probability

• Probability–The likelihood that a particular event

will occur• Ex: tossing a quarter

–Heads = 1 in 2

–Tails = 1 in 2

–3 tails in a row ½ x ½ x ½ = 1/8

–Principles can be used to predict outcome of genetic crosses

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Genetic Vocabulary

• Character– Detectable

inheritable feature of an organism

• Trait– Variant of inheritable

character

= allele / alleles

• Dominant– Capital letter (SS)

• Recessive– Lower case (ss)

• Two alleles for each character– Mom and dad

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Genetic Vocabulary

• Genotype–The genetic makeup of an organism

–Written in letter format

–PP, pp, Pp

• Phenotype

–The physical traits of an organism

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Genetic Vocabulary

• Homozygous–Having two

identical alleles for a given trait• PP

• ss

• Heterozygous–Having two

different alleles for a given trait• Pp

• Ss

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Basic Crosses

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Recessive/Dominant

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