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Biology-Genetics
Characteristics of living things:
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movement
produce waste
responds to stimulus
cellular structure
reproduction
growth
repair

Levels of Biological organisation:
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Atoms
Molecules
Macro-molecules such as proteins
Organelles
Cells
Tissue
Organs
Organ system
Organism

Mendel’s Experiments, Observations, and Laws:
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Gregor Mendel = the father of genetics (1822-1884)
Austrian monk
Studied patterns of pea plants in his garden
Pea plants turned out to be ideal to study:
-They have simple characteristics (only 2 traits per characteristics)
-Can self-fertilize them to keep same traits or cross fertilize to combine traits
-They grow and mature quickly
He realized: In order for a characteristic to be inherited, the same “thing” must be passed
on from parent to offspring
Those “things” which he called “factors” must be inside pollen/egg cells and combine
when gametes/sex cells unite (fertilization)
Found that some plants “breed true” for some characteristics  breed true= when selffertilized, the offspring are always the same as the parent
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Result: all offspring were tall!!!
He called these first generation plants First Filial or F1 tall pure-bred x short pure-bred =
100% tall F1 offspring

Law of Segregation:
Every organism has two factors for a certain trait
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One letter = one factor
TT=Pure-bred tall plant

tt= pure-bred short plant

Since one of the factors are passed on, we make a punnet square to easily illustrate the
composition of traits in the offspring
T

T

t

Tt

Tt

t

Tt

Tt

We know that the tall gene is DOMINANT because when plants contain this gene, they
express it, which is why all offspring were tall
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This is because a recessive gene will
only be exhibited by an organism who contains two copies of the gene
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(gene=factor)
F2 Generation:
 Mendel then self-fertilized the plant obtain from the pure-bred tall and short
plants
 He discovered something interesting: The tall factor had reappeared!
 Remember; offspring from F1 gen
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This punnet square shows that ¾ of the offspring were tall, only one was
pure-bred, the two others were hybrids and only one of the four offspring
was small
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Therefore, the short factor had to be present in the F1 generation (as
illustrated in the above punnet squares) but they were not expressed!!! Only the
tall factor was!

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Mendel concluded: each individual possesses two factors/traits for each
characteristic
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Hair colour is a characteristic
and brown is a factor/trait
Law of dominance: When two factors for the same characteristic are present, one
will be shown (Dominant) and the other will be masked (recessive)
Law of segregation: each individual only contributes one of their factors for each
characteristic to the offspring
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Mendel also concluded that there was NO RELATIONSHIP between
characteristics
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Therefore, each factor is passed on independently from other
characteristics (Law of Independent Assortment) Later, this was discovered to
only prove true for pea-plants, since Asian or African-American people can not
be born with natural blonde hair
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Usually; First letter for
dominant trait in caps (eg: T for tall because it is dominant) and for recessive; the first letter of
the dominant trait in lower case (eg: t for short)
Vocabulary:
Characteristic: general categories of description: height, gender, seed shape, etc
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Genotype: symbolic description of the way factors are expressed
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Ex: tall, short, etc

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