Transcript Who was Gregor Mendel?

Who was Gregor
Mendel?
(And why was his work
so important?)
Gregor
Mendel
Gregor Mendel
was a monk who
lived in the
1800s
Mendel’s Mind Wandered…
Mendel wondered how the same
species of plants could have different
characteristics
Characteristic is a trait that makes
the plant (and you) look a certain way
Mendel began to think…
Mendel wondered about the Characteristics
that appeared with each generation
He wondered if they were “heritable
features” – “Heritable” means they are
inherited (passed down) from parents
to children
Some traits appeared more often with the
same parent plants
Mendel wondered why…
Pea Plants
Mendel performed an experiment and chose pea
plants to use
He chose pea plants because he could identify
seven pairs of contrasting traits found among
typical garden peas:
Seed color (yellow or green)
Seed shape (smooth or wrinkled)
Pod color (yellow or green)
Pod shape (inflated or pinched)
Flower color (purple or white)
Flower position (middle or end)
Stem height (tall or short)
Either or….
One or the other…
Easy to see AND collect data!
Watching the plants grow…
For two years, Mendel
grew different
varieties of peas to
make sure that their
offspring were always
the same
This meant that the
plants he used were
purebred
Purebred means an
organism always
produces the same
traits in its offspring
Think about purebred dogs…
When you purchase a purebred dog, you receive
a record of their family tree so you know who
their parents and grandparents and great
grandparents were!
Proof that the dog is purebred.
Patience is a virtue
After recording his observations over a couple
of years, Mendel decided to breed different
varieties together to make hybrids
Hybrid means it’s a “mix” - a “cross” - of
different traits
(Think… Hybrid cars!)
He made these hybrids by cross-pollinating
plants with different characteristics
Cross-pollinating means “mating” (crossing) two
different plants of the same species
White flower x Purple flower
Smooth pea x Wrinkled pea
Cross-pollinating (making hybrids)
Mendel brushed the
pollen off yellow pea
plants and put it on
green pea plants
He did the same for
plants with each of the
seven pairs of traits
He then grew
generation after
generation of hybrids
and tracked the
appearance of the
different traits
His Findings…
Crossing Hybrids gives a
3 to 1 ratio of traits in
offspring!
Crossing Characteristics
Mendel crossed many different traits and
carefully recorded the traits of the
offspring
He determined that each parent supplies one
“unit” or “factor” for each different
trait…
Somehow…
Some traits seemed
to disappear in the
first generation but
reappear later…
Recessive and Dominant
The traits that disappeared in the first
generation of hybrids he called “Recessive.”
He called those that always
appear, “Dominant.”
In later generations the
recessive traits reappeared
in a predictable pattern.
For example, later generations of plants had
one green pea for every three yellow peas.
The same ratio appeared for all seven
pairs of traits.
Pea Soup Anyone?
Mendel grew an estimated 28,000 pea plants
over eight years.
He recorded the traits of parent generations
(P) as well as the traits of the first
generation (F1)
(F1) is the “First Filial” generation: the first
offspring to be born
Can you guess what the second generation
was listed as? _____________
What Mendel Discovered
Mendel discovered that
traits are inherited
And it occurs in a
consistent pattern
Mendel used math to figure
out what was going on in
the cell and how the
“factors” (traits) would be
passed on.
See????? Math IS
useful!!!!
The “Father of Genetics”
He published his results, observations and
conclusions
These are now known as Mendel’s Laws
Mendel's laws of heredity work with other
organisms as well
They form the basis of modern genetics
Even though Mendel knew nothing about genes
and DNA, we call him the
“Father of Genetics”
Now called “Genetics”
Mendel used the terms
“unit”, “factor” and
“element” to describe
how traits are inherited
(passed) from parents
to offspring
Today, we call these “units”
GENES (DNA)
Genes are found on our
chromosomes (in the
nucleus of our cells) and
are made up of DNA
(which is made of
nucleotides!)
What are Genes, Anyway?
Genes are the basic “unit” of heredity
They are a sequence of DNA that causes a
certain characteristic to appear in an
organism
Genetics is the science of genes, traits and
heredity
Genetics is the
study of how traits
are inherited
(through genes)
from one generation
to another
The Punnett Square
Mendel found out that
every trait is
controlled by two
“elements” (genes)
One from one parent and one
from the other parent
Now, the “Punnett Square”
is used to show how
different traits are
passed from one
generation to the next
This is called Probability
The chance that a given
event will occur
Predictable Ratios
Mendel repeated his experiments over and over
and the F2 generation always had a 3:1 ratio
of yellow to green or round to wrinkly
Mendel then crossed plants that differed in
more than one trait: round, yellow peas
with wrinkled, green one, or tall, violetflowered plants with short, white-flowered
ones
These traits appeared in predictable ratios, too
Dominant & Recessive
Mendel determined that, in order to show-up,
a Dominant trait needs only one trait
“unit” from one of the parents
A dominant trait can “cover up” (mask) a
recessive trait
Dominant is stronger, more powerful
The Recessive trait needs two “units”, from
both parents, in order to show up in the
next generation
Recessive is “weak”, possessing little
power/influence
Mendel’s Laws of Inheritance
Mendel came up with these important
conclusions known as Mendel’s Laws:
The Law of Dominance states that some unit
characters can mask the expression of
others.
The Law of Segregation states that each
unit character separates into a different sex
cell.
The Law of Independent Assortment states
that genes segregate (separate) according to
chance.
The Vocabulary of Genetics
The genetic make-up of an organism is called
its “genotype”
It is the type of genes found in the cell
The appearance of the organism that is
determined by its genotype is called its
“phenotype”
It is how the organism looks (appears) on
the outside
Homologous Pairs
When making a new organism, one gene
from the mother matches up with a
“similar” gene from the father
These genes are called “homologous” pairs
Homologous means similar (in length, size,
genetic make up, etc…)
The homologous “genes” are found on
chromosomes – so, if homologous genes
pair up, they create homologous
chromosomes!
Genes Vs. Alleles
A gene is a section of DNA which codes for a
certain characteristic, such as height.
Genes, however, can have variations and this is
where alleles come in…
Height can be either tall or short
Alleles are different versions of a gene.
For example, a tall allele or a short allele.
They are the different sequences of DNA that
determine a single characteristic (height).
They occur in pairs (one from one parent, one
from the other) and can be classified as recessive
or dominant.
More Vocab!
Homozygous means that the two alleles
(genes) for an organism are exactly the same
(TT or tt).
Also known as Purebred…
Heterozygous means that the two alleles for
an organism are different (Tt).
Also known as Hybrid…
Heredity
Heredity is the passing of traits from one
generation to another”.
Inherited traits are passed (genetically),
from the parent generation to the
offspring
How do Geneticists figure it out?
Geneticists use letters to represent alleles.
The same letter is used to indicate both
alleles.
A capital letter = a Dominant trait
A lowercase letter = a Recessive trait
Examples:
Flower color: P= purple, p= white
Seed color: Y= yellow, y = green
Seed shape: W = wrinkled, w = round
In humans….
Widow's peak: W = widow's peak, w = continuous
hairline
Freckles: F = freckles, f = no freckles
Earlobes: E = unattached, e = attached
Thumbs: H = hitch-hiker, h = non-hitch-hiker
Cleft chin: C = cleft chin, c = no cleft chin
Hair on Fingers: F = hair, f = no hair
Spock Fingers: S = spock yes, s = spock no
Handedness: R = right handed, r = left handed
Genes & Mutations
Each gene carries a separate piece of
information
DNA codes for all genes
Changes in the sequence of the DNA molecule
(and therefore the gene) are called mutations
A mutation may change the manner in which a
trait is expressed by an organism.
So, a mutation in the genotype, changes
the phenotype
Remember that not all mutations are bad!