SMATH #14
-Cans project widely
known as Tokyo
underground flood
tunnels is the
networks of tunnels
6.4 kilometers (four
miles) long built
deep under the
ground in the Tokyo
suburbs. All this
infrastructure is
dedicated to prevent
flooding when Tokyo
metropolitan area
rivers are overfilling
during the rain
seasons or in case
of typhoons.
Introduction to
Genetics Notes
CH 11
Go to
Section:
Introductory Vocabulary
Slide # 2
1. Character: inheritable feature of an organism
a. Example of characters in pea plants: Plant
height, flower color, seed color, seed shape
2. Trait: variation in an inheritable feature
Character
Traits
Height
Tall
or
Short
Flower Color
Purple
or
White
Seed Color
Yellow
or
Green
Seed Shape
Round
or
Wrinkled
Slide # 3
Introductory Vocabulary
3. Heredity: transfer of traits from
parent to offspring
a. Inherited traits: traits received
from parents
b. Acquired traits: traits done to
an organism that alter the
appearance of the organism
4. Genetics: study of heredity
5. Pure breeding: producing same
traits each generation
6. Hybrid: offspring from mating 2
different purebreds
Character: Stem height
Traits: Tall or dwarf
Slide # 4
Gregor Mendel:
The Father of Genetics
1. Gregor Mendel: 1822-1884
Austrian monk
a.Did genetics (breeding)
experiments on garden pea
plants.
b.1866: Published paper on
experiments
Gregor
Mendel
The Monastery Garden:
Eight Years of Pea Experiments
Gregor J. Mendel, O.S.A., experimental
garden (35x7 meters) in the grounds of
the Augustinian Monastery in Old
Brno. Its appearance before 1922.
Courtesy of Villanova University
Archives.
The Monastery Garden with the
greenhouse which Gregor J.
Mendel, O.S.A., had built in 1870.
Its appearance before 1902.
Courtesy of Villanova University
Archives.
Slide # 5
Why Mendel Chose
Pea Plants
1. Mendel chose pea plants for
several reasons
a. Grow quickly; grow many
generations in short time
b. Produce many offspring
c. Have distinct traits
• Tall or dwarf
• Yellow or green seeds
d. Could strictly control
pollination
Cut stamens (holds pollen)
off of one flower
Brushed pollen from a 2nd flower onto
carpel (holds eggs) of 1st flower
Carpel
develops into
a pea pod.
Experiments with Pea Plants
The distinct “either or“ traits.
Seed shape
(Smooth or wrinkled)
Slide # 6
Mendel’s Experiment
Purple Flowers X White Flowers
1. Began with pure breeding parents.
2. All traits were the same in BOTH
plants EXCEPT the trait being crossed.
3. All F1 generation flowers (first
generation) had purple flowers – it
appeared as though white trait was lost!
4. Allowed 2 F1’s to self pollinate.
In F2 generation, Mendel counted 705
purple flowered plants and 224 white
flowered plants. (3 purple:1 white ratio)
5. The white flower trait was not lost; it was masked by the purple
flower trait!
Question: What were the
offspring of this P cross
between a white and a purple
flowering pea plant?
•The F1 generation plants
all had purple flowers.
Question: What happens
when the F1 generation of pea
plants are allowed to selffertilize?
•The white trait reappeared!
Question: What was the ratio
for purple to white flowering
plants in the F2 generation?
•3 purple :1 white
Slide # 7
Mendel Found a Similar Pattern in Other Traits
Seed
Shape
Seed
Color
Seed Coat
Color
Pod
Shape
Pod
Color
Green
Round
Yellow
Gray
Smooth
Wrinkled
Green
White
Constricted
Round
Yellow
Gray
Smooth
Flower
Position
Axial
Plant
Height
Tall
P
Yellow
Terminal
Short
F1
Green
Axial
Only one trait showed up in F1’s;
& both traits appeared in F2’s at a 3:1 ratio.
Go to
Section:
Tall
Slide # 9
Conclusions made by Mendel:
1. Each parent MUST contribute one gene for
each trait to the offspring.
– Evidence: F2’s had white flowers (present but
hidden in F1 generation.)
2. Each parent must have two copies of a
gene; and can have two different versions
of that gene called alleles at the same
time.
-- Evidence: F2’s had white flowers both parents
must have had at least one white allele!
 Dominant: allele that is expressed when 1
or both are present (capital letter)
 Recessive: allele that is masked by
presence of dominant allele (lower case)
a. The individual MUST have both recessive
alleles to show the recessive trait
The F1 purple
flowering plants
must have a second
hidden gene for
white flowers!
Slide # 8
Alleles
Homologous
Chromosomes
1. Alleles: alternate forms of
a gene or trait
FROM MOM
a. Parents may have two of
the same alleles or two
different alleles
b. Homozygous: having 2 FROM DAD
identical alleles
c. Heterozygous: having 2
different alleles
Every organism has two copies of
the same gene. One copy came
2. Alleles are located on
from MOM in her egg, the other gene
chromosomes
copy came from DAD in his sperm.
This plant has 2 different alleles
for the flower color character.
Homologous Chromosomes:
-are similar gene carrying chromosomes
from the opposite-sex parents .
Vocabulary Review
Match these in your head, be ready to share.
Gene
Chromosome
a. Threadlike structures
made of DNA found in
nucleus
b. Unit of inheritance
Homologous Pair c. One form of a gene
Allele
d.Two chromosomes that
carry the same genes, but
just different versions of
those genes.
Slide # 10
Mendel Solves the Genetics Puzzle
Phenotypes: Purple & White
Genotypes: PP
x
pp
1. Mendel reasoned that each
parent must have 2 possible
alleles to contribute
– Genotype: the alleles the
organism has (two letters)
Gametes: P
~ p
– Phenotype: physical
appearance of an organism
2. Mendel reasoned that the two
alleles separated when gametes
Fertilization:
Pp
(sex cells like eggs) formed.
3. Mendel also reasoned that the
alleles paired up again during
Phenotype of F1: All Purple
fertilization (joining of egg &sperm)
Genotype of F1: All Pp
To show possible outcomes of genes
the new generation will have
We use:
Gene diagrams
or
Punnett Squares
Gene Diagram – Flower color
Alleles-
P = Purple flower
p = White flower
All genes occur in pairs – so 2 alleles affect a
characteristic – possible combinations are;
genotypes
PP
Phenotypes PURPLE
Pp
PURPLE
pp
WHITE
Gene Diagram – Flower color
parent
Male
female
Pp
Pp
gamete
P
p
Offspring
genotype
PP
pp
Phenotype
Purple
White
P
p
Pp
Pp
Purple
3 purple : 1 white
Purple
Punnett Square
Another method of showing crosses
Punnett Square
1.
Determine what the alleles are. P=purple
p=white
2. Parent genotypes are determined. --Both are Pp
3. Parent’s possible gametes are determined and placed one
next to -or above each box.
Complete the Cross
Pp
purple
female
P
p
Pp Purple male
P
p
PP
Pp
Pp
pp
3 purple and 1
white offspring
3:1 chance with
these parents
Slide # 11
Why the White Flowers Reappeared in the F2’s
Genotype of F1: Pp
x
Pp
Gametes: ½ P
½P
½ p
½p
F2 Genotypes: 1 PP: 2 Pp: 1 pp
F2 Phenotypes: 3 Purple : 1 White
In Summary, Mendel’s Work Showed:
1. Each parent contributes one allele for each
trait.
2. The two alleles of each trait separate from each
other when gametes form (in meiosis) and pair up
again during fertilization.
3. Male’s (sperm) and female’s (egg) contribute
equally.
4. Acquired traits are not inherited.