Download Genetic Principles

Introduction
Heredity
Gregor Mendel
The Man,
The Legend…
Father of
Genetics
Gregor Mendel
• Priest who worked in the monastery
garden
• Observed traits, or characteristics, of pea
plants. Some were short or tall, had green
or yellow seeds, etc.
• He did experiments on these pea plants
for over ten years.
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Pea Plants
• Pea plants are easy to study because their
traits come in two forms (unlike human
hair color).
• They also produce lots of offspring per
generation, so he could get lots of data.
• They usually self-pollinate, but Mendel
cross-pollinated them to chose the parents
of a generation.
Purebred
• He would cross two plants with opposite
traits, ex. One tall and one short. He
picked purebred plants, which always
produce offspring with the same trait as
the parent.
• He called the parents the parental, or P,
generation. The offspring were the first
filial generation, or F1.
Parents: 1 Tall & 1 Short
• F1 generation was all tall
• F2 generation was ¾ tall, ¼ short
• He did this for six other traits: seed shape,
seed color, seed coat color, pod shape,
pod color, and flower position. The “lost”
trait always reappeared in ¼ of the F2
generation!
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Inheritance
• Traits must come in pairs, with one from
each parent. Some can hide others.
Ex. Tall pea plant trait hides short pea
plant traits
• Today, these traits are called genes.
• The different forms of genes are alleles.
Ex. Each F1 plant got one tall allele and
one short allele.
Dominant & Recessive Traits
• Individual alleles control the inheritance of
traits.
• Some are dominant and always show up.
Others are recessive and are masked by
the dominant trait.
• The tall allele was dominant over the short
allele.
• Only plants that got 2 short alleles ended
up short.
Hybrids
• The F1 plants are hybrids b/c they have 2
different alleles for the trait
• In the F2 generation, some got 2 short
alleles and were short, some got 2 tall
alleles and were tall, and some got 1 of
each and were tall.
Genetic Symbols
• We use letters to
represent alleles. The
dominant allele is
capitalized and the
recessive is lower case.
• So a plant with_______
would be written like this
_______
– 2 Tall alleles, TT
– 1 tall, 1 short: Tt
– 2 short: tt
Father of Genetics
• He presented his work at the monastery,
but others didn’t realize its significance.
Since he wasn’t at a university, word of his
work didn’t spread. He was forgotten for
34 years….
• In 1900 his work was rediscovered and its
importance realized. Now he’s considered
the Father of Genetics.
Genetic Principles
1. Traits, or characteristics, are passed on from one
generation of organisms to the next generation.
2. The traits of an organism are controlled by genes.
3. Organisms inherit genes in pair, one gene for each
parent.
4. Some genes are dominant, whereas other genes are
recessive.
5. Dominant genes hide recessive genes when both are
inherited by an organism.
6. Some genes are neither dominant nor recessive.
These genes show incomplete dominance.
Vocabulary
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Gregor Mendel: father of genetics; studied pea plants
Genetics: scientific study of heredity, or the passing on of
traits from an organism to its offspring
Dominant trait: the stronger trait (dominates recessive
traits- always appears)
**represented by a capital letter
Ex: “T” would represent the gene, tallness
Recessive trait: the weaker trait (usually hidden by the
dominant trait- seems to disappear)
**represented by a lowercase letter
Ex: “t” would represent the gene, shortness
Genes: set of instructions for each characteristic
Alleles: two forms of a gene
Phenotype: inherited appearance (brown hair)
Genotype: inherited combination of alleles (letters)
Vocabulary Notes
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Gregor Mendel:
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Genetics:
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Dominant Trait: ___________________________________________________
Ex: _____________________________________________________________
Recessive Trait: ___________________________________________________
Ex:______________________________________________________________
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Genes____________________________________________________________
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Alleles:
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Phenotype:
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Genotype:
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