Download Mendel

Who was this Mendel and what the heck is
he doing in a monastery?
• born in 1822
• trained himself to be a
naturalist early in life
• worked as a substitute
science teacher
• failed the qualifying exams to be
a regular high school teacher!
• joined a monastery in Brunn,
Austria
• sent to Vienna U. to study
science and math
MendelWeb
Mendel’s
first
published
work:
"Versuche über Pflanzen-Hybriden“
or Experiments in Plant Hybridization
was a landmark in clarity and insight!
Trained as a mathematician
and a biologist, he figured
out the laws of inheritance…
mathematically!!
The work of Gregor Mendel
• worked with pea plants…
…he called
them his
children!
Why pea plants???
There was a long-standing tradition of breeding pea
plants at the monastery where Mendel lived and worked
Science Humor
So…they were readily available and they come in lots
of varieties!
…there were plants with different flower colors, seed
color, flower position etc..
Mendel’ Pea Plants
Mendel based his laws on his studies of
garden pea plants. Mendel was able to
observe differences in multiple traits
over many generations because pea
plants reproduce rapidly, and have many
visible traits such as:
Seed Color
Plant Height
Green Yellow
Tall
Short
Pod color
Green
Yellow
Seed Shape
Pod Shape
Wrinkled Round
Smooth Pinched
‘Brother Greg... We grow tired of peas again!!!’
And best of all…
Pea plants flowers can
reproduce by themselves
This allowed Mendel to see if
strains were true breeding and to
produce hybrids
How Mendel made hybrids…
He’d then tie little
bags around the
flowers to prevent
contact with stray
pollen.
Mendel’s Experiments
Mendel noticed that some plants always produced offspring
that had a form of a trait exactly like the parent plant. He
called these plants “purebred” plants. For instance, purebred
short plants always produced short offspring and purebred tall
plants always produced tall offspring.
X
Purebred Short Parents
Short Offspring
X
Purebred Tall Parents
Tall Offspring
Mendel’s First Experiment
Mendel crossed purebred plants with opposite forms of a trait.
He called these plants the parental generation , or P generation.
For instance, purebred tall plants were crossed with purebred
short plants.
X
Parent Tall
P generation
Parent Short
P generation
Offspring Tall
F1 generation
Mendel observed that all of the offspring grew to be tall
plants. None resembled the short short parent. He called this
generation of offspring the first filial , or F1 generation, (The
word filial means “son” in Latin.)
Mendel’s Second Experiment
Mendel then crossed two of the offspring tall plants produced
from his first experiment.
Parent Plants
Offspring
X
Tall
F1 generation
3⁄4 Tall & 1⁄4 Short
F2 generation
Mendel called this second generation of plants the second
filial, F2, generation. To his surprise, Mendel observed that
this generation had a mix of tall and short plants. This
occurred even though none of the F1 parents were short.
The results of Mendel’s monohybrid
crosses led him to propose…
1. All organisms contain two “units of heredity”
for each trait (alleles).
Genes- a segment of DNA that carries hereditary
instructions and is passed from parent to offspring
Alleles- multiple forms of the same gene
Heredity- the passing of traits from parent to
offspring.
2. Dominant and recessive alleles…
…and organisms can have any combination of the
two alleles (2 dominants, 2 recessives or a
mixture 1 dominant and 1 recessive).
Dominant trait- the trait observed when at least one
dominant allele for a characteristic is inherited
Recessive trait- a trait that is apparent only when
two recessive alleles for the same characteristic
are inherited
Purebred - all of the offspring will have the same
trait as the parent when self-pollinated
Hybrid- an organism has two different alleles for a
trait
3. The Law of Segregation – during gamete
formation, alleles separate randomly into
separate gametes.
A bit of genetic jargon…
phenotype vs. genotype
What the
organism
looks like –
its
What alleles
Physical
the organism
makeup
has - its
genetic makeup
More jargon…
homozygous vs. heterozygous
P
2 of the
same alleles:
RR or rr
2 different
alleles:
Rr
p
A Punnett
square
A Punnett square…
Gametes from
one parent
r
R
Gametes from
other parent
R
RR
round
r
Rr
round
Rr
round
rr
wrinkled
Ratio: 3:1 or ¾ round, ¼ wrinkled
These slides are a
combination of two power
point presentations on
Gregor Mendel
Original presentations can be found at:
wsscience.wikispaces.com/file/view/Genet
ics+Gregor+Mendel.ppt
p5cdn4static.sharpschool.com/UserFiles/
Servers/Server.../Mendel.pptx