Predicting Inheritance
MENDELIAN GENETICS
Genetics Vocabulary
Gregor Mendel
 First person to
successfully predict
how traits are
transferred from one
generation to the next.
 Used pea plants to
show how genes were
passed down
 The “father of
genetics.”
Genetics Vocabulary
 Homozygous/Purebred: Two alleles for a
trait are the same Examples: RR, rr, FF, qq,
mm
 Heterozygous/Hybrid: Two alleles for a trait
are different Examples: Rr, Ff, Qq, Mm
Heterozygous or Homozygous?
 TT
 Pp
 dd
 Ff
 Tt
 FF
Heterozygous or Homozygous?
 TT- homozygous
 Pp- heterozygous
 dd- homozygous
 Ff- heterozygous
 Tt- heterozygous
 FF- homozygous
Rule of Unit Factors
 Alleles: expressions of a
gene; carried in gametes
 Each organism has two
alleles that control each of
its traits, one from father
and one from mother.
 Example: PP, Pp, pp
 Never: P, p, Ppp, PPp
Genotype versus Phenotype
 Genotype:
 Phenotype:
Individual’s genes
 Gen-
Individual’s physical
appearance
 Pheno-
 Produce
 Birth
 Origin
 Appear
Rule of Dominance
 Only one trait is
observed. The
observed trait is
called
dominant and
the trait that
disappeared is
called
recessive.
 Example: →
Rule of Dominance
 In Squidward’s family, a blue body color (B) is
dominant to green (b). Determine the
phenotype for each genotype below based on
this information.
 BB
 Bb
 bb
Rule of Dominance
 In Squidward’s family, a blue body color (B) is
dominant to green (b). Determine the
phenotype for each genotype below based on
this information.
 BB- blue
 Bb-blue
 bb- green
Law of Segregation
 Every individual has
two alleles for each
gene. Each gamete
receives one of these
alleles.
 During fertilization,
these gametes
randomly pair to
produce four
combinations of alleles.
 Example: →
Law of Independent Assortment
 Genes for different
traits are inherited
independently of
each other.
 Example: seed
shape (round or
wrinkled) and seed
color (green or
yellow)
Review
 What is the name for an individual with two




of the same alleles?
What is the name for an individual with two
different alleles?
What is the name of the trait that disappears?
The name of the trait that is observed?
How many alleles for each trait does an
organism have?
Answers to the Review
 Homozygous
 Heterozygous
 Recessive
 Dominant
 Two
Let’s put this into action!
 SpongeBob is known for his big round eyes
(R), which are dominant over an oval eye
shape (r). If he is heterozygous for his round
eye shape and marries a woman with oval eye
shape, what type of eyes might his kids have?
 Step 1: List the genotypes of the parents:
 Heterozygous round eyes: ____
 Oval eyes: ____
Step 2: Punnett Square
Heterozygous round eyes: Rr
Oval eyes: rr
Step 2: Punnett Square
Heterozygous round eyes: Rr
Oval eyes: rr
R
r
r
r
Step 2: Punnett Square
Heterozygous round eyes: Rr
Oval eyes: rr
R
r
r
Rr
rr
r
Rr
rr
Predictions & Ratios
 Based on the results of the Punnett Square,
identify the possible offspring combinations.
 % Homozygous round eyes (RR) ___________
 % Heterozygous round eyes (Rr) ___________
 % Homozygous oval eyes (rr)___________
Predictions & Ratios
 Based on the results of the Punnett Square,
identify the possible offspring combinations.
 Homozygous round eyes (RR) _0%_________
 Heterozygous round eyes (Rr) ___50%______
 Homozygous oval eyes (rr)__50%_________
Now you try one on your own.
 If two heterozygous round seed pea plants
(Rr) are crossed, what percentage of offspring
will be homozygous recessive? Use a Punnett
square to find the answer.
Independent Practice
 Who lives in a pineapple
under the sea?!?