Transcript Mendel and His Pea Plants PowerPoint

Genetics
Mendel And His Peas
Genetics – the scientific study of
heredity
Gregor Mendel – 1800s
His monastery garden pea plant
experiments laid the foundations of the
science of genetics.
Summary of the pea plant
experiments:
1) Mendel developed pure-bred (truebreeding) plants by allowing plants to selfpollinate. (always produce identical
offspring)
In order to discuss what’s next we must look at the
structure of a pea plant flower
(a) stigma – traps pollen
(b) anther – makes pollen
e) stamen = anther + filament
(f) carpel (or pistil) =
stigma, and style
(c ) ovary – eggs and seeds g) sepal (bud leaf)
form here
(d) filament – lifts anther
2) Mendel crossed-pollinated pure bred plants and
then crossed their offspring. (anther cut off one
plant to eliminate its pollen, and then dusted
pollen from another plant.)
3) After numerous
experiments,
Mendel analyzed
data and drew
conclusions
about
inheritance.
WHAT EXACTLY DID MENDEL DO?
First, Mendel crossed a pure-bred (true
breeding) TALL plant with a pure-bred
SHORT plant.
about 6 feet tall
under two feet
Result: The offspring were all TALL.
Second, Mendel crossed two of the TALL
offspring.
Result:
¾ of the offspring were TALL
¼ of the offspring were SHORT
(This same result happed
for other characteristics
such as seed shape,
seed color, position
of flowers etc.
--pg 264) Seven
pea plant traits
studied by Mendel
WHY DID THIS HAPPEN?
Mendel found that some
genes for specific traits
are dominant over other
genes.
Contrasting genes for a
particular trait are called
alleles, so they are dominant
alleles.
The genes that are not expressed because
dominant alleles are present, are said to be
recessive alleles.
Using Punnett Squares to
explain Mendel’s results:
They were
developed by
Actual pollen grains
Try this:
What if Mendel crossed an
F1offspring
(heterozygous) with a
pure-bred tall
(homozygous) plant.
X
What would be the phenotypic & genotypic ratios?
Monohybrid & Dihybrid Crosses
“The principle of dominance” – some alleles
are dominant and some are recessive.
Dominant allele blocked the expression of
recessives. (Mendel called alleles or genes
“factors”)
“The principle of segregation” – alleles
separate during the formation of gametes.
“The principle of independent
assortment”- genes for different traits can
segregate independently during the
formation of gametes.
(where one allele goes does not affect
where the other goes.)
He was a mathematician and
statistician – he was better
able to analyze his data.
He worked with large
numbers of plants etc..
He luckily chose plant traits to
observe, in which the alleles for
those traits were on separate
chromosomes, or at least not
close together.