Bell Ringer
 Look at your classmates. Note how they vary in the
shape of the front hairline, the space between the two
upper front teeth, and the way in which the earlobes are
attached.
 Make a list of the different forms of these traits that you
have observed in the class or among other people you
know.
1.
Could these traits be inherited? From whom could they
be inherited?
2. How is it possible that these traits could be found in a
person and his or her biological grandparents but not in
the biological parents?
Bell Ringer
1. Could these traits be inherited? From whom could
they be inherited?
2. How is it possible that these traits could be found
in a person and his or her biological grandparents
but not in the biological parents?
Bell Ringer
1. Could these traits be inherited? From whom could
they be inherited?

Yes; from parents.
2. How is it possible that these traits could be found
in a person and his or her biological grandparents
but not in the biological parents?
Bell Ringer
1. Could these traits be inherited? From whom could
they be inherited?

Yes; from parents.
2. How is it possible that these traits could be found
in a person and his or her biological grandparents
but not in the biological parents?
 Genes are passed from generation to generation, but
are not necessarily expressed in every generation.
3. Every living thing – plant or animal, microbe or human
being – has a set of characteristics inherited from its
parents.
Gregor Mendel
 In 1865, Gregor Mendel published
studies of inheritance in pea plants.
 During sexual reproduction, male and
female gametes join to form a zygote in
the process known as fertilization.
 Genetics= the scientific study of heredity.
Heredity is… the passing on of traits
from parents to offspring.
1. Controlled by “factors.”
2. Passed from generation to generation.
3. Probability (pg. 267)
4. Traits – characteristics that are inherited.
1902 – Chromosome Theory
of Heredity
 Genes (Mendels “factors”) are located on
chromosomes. Genes are segments of
DNA. Genes are traits
 The different forms (variations) of a gene
are called Alleles.
 This is the basis for the modern science of
Genetics.
Genetic Principles
1. Alleles – gene form, Y or y, for each variation of a trait of an
organism.
2. Dominant or Recessive
D= visible, observable trait of an organism that masks a
recessive form of a trait.
R = a hidden trait of an organism that is masked by a dominant
gene.
3.
Separation, or Segregation; each allele will segregate or
separate from each other and it will ½ chance that you
receive either allele. Ex. Y or y
4.
Independent Assortment
Other Terms
 Phenotype – the way an organism looks and
behaves. Physical characteristics of an organism.
 Genotype – the gene combination of an organism;
the genetic make-up of a trait or gene.
 Homozygous – when an organisms two alleles for a
trait are the same. Homozygous recessive ex. rr;
homozygous dominant ex. RR
 Heterozygous – when an organisms two alleles for a
trait are not the same.
Genes VS Alleles
Gene
Allele
Genes VS Alleles
Gene
Plant Height
Flower Color
Tall Plant
Purple Flowers
Short Plant
White Flowers
Allele
R.C. Punnett
 In 1905, R.C. Punnett introduced
the Punnett square.
 Punnett squares can be used to
predict and compare the genetic
variations that will result from a
cross (pg. 268).
Using Punnett Squares
Yellow pea seed (Y) is DOMINANT to green (y).
Genotype:
YY
x
yy
Phenotype:
Yellow
x
green
Parents (P)
y
y
Y
Y
Using Punnett Squares
Yellow pea seed (Y) is DOMINANT to green (y).
Genotype:
YY
x
yy
Phenotype:
Yellow
x
green
Parents (P)
y
y
Y
Y
Using Punnett Squares
Yellow pea seed (Y) is DOMINANT to green (y).
Genotype:
YY
x
yy
Phenotype:
Yellow
x
green
Parents (P)
Y
y
Yy
y
Y
Using Punnett Squares
Yellow pea seed (Y) is DOMINANT to green (y).
Genotype:
YY
x
yy
Phenotype:
Yellow
x
green
Parents (P)
Y
y
Yy
y
Y
Using Punnett Squares
Yellow pea seed (Y) is DOMINANT to green (y).
Genotype:
YY
x
yy
Phenotype:
Yellow
x
green
Parents (P)
Y
y
Yy
y
Yy
Y
Using Punnett Squares
Yellow pea seed (Y) is DOMINANT to green (y).
Genotype:
YY
x
yy
Phenotype:
Yellow
x
green
Parents (P)
Y
y
Yy
y
Yy
Y
Using Punnett Squares
Yellow pea seed (Y) is DOMINANT to green (y).
Genotype:
YY
x
yy
Phenotype:
Yellow
x
green
Parents (P)
Y
Y
y
Yy
Yy
y
Yy
Using Punnett Squares
Yellow pea seed (Y) is DOMINANT to green (y).
Genotype:
YY
x
yy
Phenotype:
Yellow
x
green
Parents (P)
Y
Y
y
Yy
Yy
y
Yy
Using Punnett Squares
Yellow pea seed (Y) is DOMINANT to green (y).
Genotype:
YY
x
yy
Phenotype:
Yellow
x
green
Parents (P)
Y
Y
y
Yy
Yy
y
Yy
Yy
Using Punnett Squares
Yellow pea seed (Y) is DOMINANT to green (y).
Genotype:
YY
x
yy
Phenotype:
Yellow
x
green
Parents (P)
Y
Y
y
Yy
Yy
y
Yy
Yy
All (100%) offspring in F1 Generation are Yellow hybrids.
Monohybrid Cross
Yy
x
Yy
Yellow
x
Yellow
F1 Generation
Y
y
Monohybrid Cross
Genotype:
Yy
Phenotype: Yellow
F1 Generation
Y
y
Y
x
Yy
x
Yellow
y
Monohybrid Cross
Genotype:
Yy
Phenotype: Yellow
F1 Generation
Y
y
Y
x
Yy
x
Yellow
y
Monohybrid Cross
Genotype:
Yy
Phenotype: Yellow
F1 Generation
Y
Y
YY
y
x
Yy
x
Yellow
y
Monohybrid Cross
Genotype:
Yy
Phenotype: Yellow
F1 Generation
Y
Y
YY
y
x
Yy
x
Yellow
y
Monohybrid Cross
Genotype:
Yy
Phenotype: Yellow
F1 Generation
Y
Y
YY
y
Yy
x
Yy
x
Yellow
y
Monohybrid Cross
Genotype:
Yy
Phenotype: Yellow
F1 Generation
Y
Y
YY
y
Yy
x
Yy
x
Yellow
y
Monohybrid Cross
Genotype:
Yy
Phenotype: Yellow
x
Yy
x
Yellow
F1 Generation
Y
y
Y
YY
Yy
y
Yy
Monohybrid Cross
Genotype:
Yy
Phenotype: Yellow
x
Yy
x
Yellow
F1 Generation
Y
y
Y
YY
Yy
y
Yy
Monohybrid Cross
Genotype:
Yy
Phenotype: Yellow
x
Yy
x
Yellow
F1 Generation
Y
y
Y
YY
Yy
y
Yy
yy
Monohybrid Cross
Genotype:
Yy
x
Yy
Phenotype:
Yellow
x
Yellow
F1 Generation
Y
y
Y
YY
Yy
y
Yy
yy
Phenotypic Ratio:
75% (3/4) offspring are Yellow; Ratio is 3:4 (Yellow : total)
25% (1/4) offspring are green; Ratio is 1:4 (green : total)
Dihybrid Cross
 Round pea seed (R) is dominant to
wrinkled pea seed (r).
 FOIL: YyRr

YR, Yr, yR, yr
 (These are the possible genotypic
combinations)
Dihybrid Cross
Round pea seed (R) is dominant to
wrinkled pea seed (r).
Possible
Combinations
YR
Yr
yR
yr
YR
Yr
yR
yr
Dihybrid Cross
Round pea seed (R) is dominant to
wrinkled pea seed (r).
Possible
Combinations
YR
Yr
yR
yr
YR
YYRR
YYRr
YyRR
YyRr
Yr
YYRr
YYrr
YyRr
Yyrr
yR
YyRR
YyRr
yyRR
yyRr
yr
YyRr
Yyrr
yyRr
yyrr
Possible
Combos
YR
Yr
yR
yr
YR
YYRR
Yellow, Round
YYRr
Yellow, Round
YyRR
Yellow, Round
YyRr
Yellow, Round
Yr
YYRr
Yellow, Round
Yyrr
Yellow, wrinkled
YyRr
Yellow, Round
Yyrr
Yellow, wrinkled
yR
YyRR
Yellow, Round
YyRr
Yellow, Round
yyRR
green, Round
yyRr
green, Round
yr
YyRr
Yellow, Round
Yyrr
Yellow, wrinkled
yyRr
green, Round
Yyrr
green, wrinkled
What is the probability that the plant will produce:
Yellow, Round Peas:
Yellow, Wrinkled Peas:
Green, Round Peas:
Green, Wrinkled Peas:
Possible
Combos
YR
Yr
yR
yr
YR
YYRR
Yellow, Round
YYRr
Yellow, Round
YyRR
Yellow, Round
YyRr
Yellow, Round
Yr
YYRr
Yellow, Round
Yyrr
Yellow, wrinkled
YyRr
Yellow, Round
Yyrr
Yellow, wrinkled
yR
YyRR
Yellow, Round
YyRr
Yellow, Round
yyRR
green, Round
yyRr
green, Round
yr
YyRr
Yellow, Round
Yyrr
Yellow, wrinkled
yyRr
green, Round
Yyrr
green, wrinkled
What is the probability that the plant will produce:
Yellow, Round Peas:
9/16
Yellow, Wrinkled Peas: 3/16
Green, Round Peas:
3/16
Green, Wrinkled Peas:
1/16
To find the probability that
two different events will
happen at the same time,
multiply the probabilities
of each event happening
separately.
To find the probability that two different events will
happen at the same time, multiply the probabilities of each
event happening separately.
Probability of offspring having YELLOW pea
seeds:
¾
Probability of offspring having ROUND pea
seeds:
¾
Probability of offspring having BOTH YELLOW
AND ROUND PEAS:
¾ X ¾ = 9/16
Trihybrid Cross
 Tall Stem (T) is dominant to short stem (t).
 The probability of producing tall stems in a
monohybrid cross is:
 What is the probability that the offspring in a
trihybrid cross will be Yellow, Round, and Tall?
Trihybrid Cross
 Tall Stem (T) is dominant to short stem (t).
 The probability of producing tall stems in a
monohybrid cross is:
¾
 What is the probability that the offspring in a
trihybrid cross will be Yellow, Round, and Tall?
¾ X ¾ X ¾ = 27/64
 Incomplete dominance (also called partial dominance)
occurs when the phenotype of the heterozygous genotype
is distinct from and often intermediate to the phenotypes of
the homozygous genotypes. For example, the snapdragon
flower color is either homozygous for red or white.
Example: Red flowers
(RR) crosses with white
flowers (WW) shows
incomplete dominance
for pink flowers (RW)
Ex. Of Incomplete
Dominance
 Codominance – when both alleles contribute to the
phenotype.
Example – black feathers
codominant with white feathers
in chickens, both white and
black feathers are present
separately. Also blood types
and a cholesterol enzyme in
humans.
What is the difference?
Other Terms
 Multiple alleles-genes that have more than 2
alleles
 This means that there are more than 2 possible
alleles in a population
 Example: rabbit fur colors
 Polygenic traits – traits controlled by more
than 2 genes
 Example: human skin color is controlled by more
than 4 different genes
Blood types
Height and Multiple alleles