Transcript Heredity It is all about Life

Gregor Mendel
Monk and Scientist
Father of Genetics
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In 1843, at the age of 21, Gregor
Mendel entered the monastery .
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Born in what is now known as the
Czech Republic.
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Researched heredity, experiments
often involved garden pea plants.
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Heredity - The transmission of
characteristics from parent to
offspring.
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Known as the “Father of Genetics”.
Genetics Is the branch of biology that focuses
on heredity.
 The study of the structure and function
of chromosomes & genes.
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A gene is a segment of DNA on a
chromosome that controls a particular
hereditary trait. Genes occur in pairs.
 Each of two or more alternative forms
of a gene is called an allele.
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Mendel’s Peas
He chose garden pea plants because:
 Can be grown in a small area
 Produce lots of offspring
 In peas many traits appear in two forms (i.e. tall
or short, round or wrinkled, yellow or green.)
 The flower is the reproductive organ and the
male and female are both in the same flower.
Thus able to self pollinate.
Mendel’s Peas
Mendel’s Pea plant
experiment
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Used pea plants to study traits such as: height,
flower position, pod color, seed texture, seed
color, flower color.
Grew plants that were “true-breed” (pure) for
each trait.
– True breed will always give the same trait generation
after generation if self pollinated.
 Self pollination - The transfer of pollen from one
flower to the same or other flowers on the same
plant.
Mendel’s Pea plant
experiment
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Then cross pollinated pairs of plants that
were true breeding for contrasting traits.
Called the P generation.
– Example: cross green pod plant w/ yellow
pod plant.
Mendel’s Pea plant
experiment
Allowed offspring to mature. Called the
F1 generation.
 Recorded the number of each type of
offspring produced.
 Allowed flowers from F1 generation to
self pollinate and collected the seeds.
 These seeds grew into what is called
the F2 generation.

Mendel’s Experiments
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He experimentally
crosses different
strains to develop
hybrids.
He then crossed
the hybrids and
analyzed the
results.
Description of traits

Genotype – genetic makeup, or set of
alleles that an organism has.
– Represented by the letters! (TT, Tt, tt)

Phenotype – organism’s appearance.
– Visual! What it looks like.
Dominant Traits RULE
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Strong Hereditary traits cover weak
traits.
– Trait – genetically determined variant of a
characteristic. (color, height)
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Mendal called stronger traits
– Dominant - masks or dominates other
traits.
– capital letters (T)
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Mendal called weaker traits
– Recessive – trait that does not appear
when dominant trait is present.
– lower case letters (t)
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Heterozygous – two alleles in a gene
are different. (Tt)
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Homozygous – two alleles in a gene
are the same (TT, tt)
Punnett square – a
diagram used to aid
in predicting the
probability of
inherited traits in
offspring.
Mendel’s Results
Mendel crossed purebred tall plants with
purebred short plants and the first generation
plants were all tall.
When these tall offspring were crossed the
result was a ratio of 3 tall to 1 short.
Mendel's traits included:
a. Seed shape --- Round (R) or Wrinkled (r)
b. Seed Color ---- Yellow (Y) or Green (y)
c. Pod Shape --- Smooth (S) or wrinkled (s)
d. Pod Color --- Green (G) or Yellow (g)
e. Seed Coat Color --- Gray (G) or White (g)
f. Flower position --- Axial (A) or Terminal (a)
g. Plant Height --- Tall (T) or Short (t)
h. Flower color --- Purple (P) or white (p)
Mendel’s Observations
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Law of segregation – in the formation of
gametes, only one copy of each allele will
be given to each sex cell.
A woman has the genotype Bb.
the big B for Brown eyes,
 the little b for blue eyes.
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Only one of them will wind up in each
egg cell.
Mendel’s Observations
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Law of independent assortment – each
chromosome is selected independently of
each other during formation of gametes.
A woman’s trait for brown eyes won't
determine her hair color, because
these traits assort into gametes
independently.