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LH. Biology
Heredity
Benchmark 1
Explain how characteristics of living things are
passed on from generation to generation.
Being Able to Curl up both sides of the
Tongue is under the control of a dominant
allele at one gene locus.
Homozygous Dominant
rr
Homozygous recessive
RR
Rr
Heterozygous
Inheritance for Tongue Rolling
and Non-tongue Rolling
Susan’s mom is a tongue roller. Her father is a
non-tongue roller. Susan has three older
brothers and one younger sister. Her three
brothers are all tongue rollers. Her sister is
a non-roller. What are the genotypes of each
member of Susan’s family?
R = allele for ability to roll the tongue
r = allele for non-roller
What are Susan’s Family
Tongue Rolling Genotypes?
Dad = rr (non-roller, recessive trait expressed)
Sister = rr (non-roller, recessive expressed)
Mom = Rr (heterozygous, mom had to donate
the “r” allele to Susan’s sister and since mom is
a roller she must have the “R” allele)
Susan and her brothers = Rr (heterozygous, each
child inherits an “r” allele from dad and because
they can roll they each inherited an “R” allele
from mom)
Mark marries Susan. . .
Mark’s mom is a non-roller and his dad is a
roller. Mark’s two brothers are rollers.
What is Mark’s genotype for ability to
roll the tongue? Rr
Mark and Susan are planning a family. What is
the probability that Susan will deliver a
roller, a non-roller?
Punnett Square
Mark
S
u
s
a
n
R
r
R
Roller
R R
Roller
R r
r
Roller
R r
Non
r Roller
r
Genotypic Ratio 1:2:1
Phenotypic Ratio 3:1
After fourteen years of marriage...
…are all happy ROLLERS !!!
Mark
Jessica
Susan
Ashley
Baby
Peas Don’t Go
Gregor Mendel
Father of Heredity
Baby
Peas Don’t Go
Look, the
Structure
of DNA!
Watson
Crick
DNA Model
1953
rr
Rr
If Mary and Peter
are both Rollers, what
are the chances for
Anne to be roller,
a non-roller ?
rr
Rr
Key Concepts
Traits
Dominant
Recessive
Genetic material
gene pair
gene combination
gene sorting
Real-world contexts
Common contexts
Inheritance of a human genetic
disease/disorder, such as sickle cell anemia
A family tree focused on certain traits
Examining animal or plant pedigrees.
Sickle Cell Anemia
http://www.bio.miami.edu/dana/250/25002_4print.html
A particular species of bird can be brown or white.
The white color is a recessive trait,
while the brown color is a dominant trait.
When two brown birds mate,
is it possible for them to have white offspring?
a. no because both parents have
only genes for being brown
b. yes, because offspring color
does not depend on the genes of the parents
c. yes, because both parents
have and pass on the gene for being white
d. no, because the parents can only
pass on the dominant gene to their offspring.
a. no because both parents have only genes for being brown
Incorrect: You don’t know for sure if both parents
have two genes for being brown (BB).
They could have a Brown gene and
a white gene (Bb) and still have the
phenotype (what they look like) of white color
Return to the question
b. yes, because offspring color
does not depend on the genes
of the parents
Incorrect: The color does
depend on their genes. This is
an inherited trait.
Return to the question
c. yes, because both parents have and pass on
the gene for being white
Correct: You don’t know for sure if both parents
have two genes for being brown (BB).
They could have a Brown gene and
a white gene (Bb) and still have the
phenotype (what they look like) of white color
Return to the question
d. no, because the parents can
only pass on the dominant
gene to their offspring.
Incorrect: They have an equal
chance of passing on the
dominant and recessive gene
if the contain both. The term
dominant means that when
an individual has two different
genes for a trait the dominant
is the one that shows up in
the phenotype (appearance)
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