HEREDITYYYYYYY
2015 July 17
c/o: Aaron, Darcie, Diana, Geeta, Kristin, Rou-Jia
Introduction
Our “teachable unit”: Heredity module
• Embedded within Introductory Biology course
• Prerequisites: None (high school level biology)
• Student population: First-year students, both majors or
non-majors
Rou-Jia
Introduction
Our “teachable unit”: Heredity module
• Embedded within Introductory Biology course
• Prerequisites: None (high school level biology)
• Student population: First-year students, both majors or
non-majors
Our “teachable tidbit”: Sex-linked traits
Rou-Jia
Introduction
Our “teachable unit”: Heredity module
Goals
Our “teachable tidbit”: Sex-linked traits
Objectives
Rou-Jia
Introduction
Our “teachable unit”: Heredity module
Goals
1) Understand how genes and chromosomes relate to traits
2) Appreciate how traits are passed on from parents to
offspring
3) Comprehend the inheritance of genetic disorders
Our “teachable tidbit”: Sex-linked traits
Objectives
Rou-Jia
Introduction
Our “teachable unit”: Heredity module
Goals
1) Understand how genes and chromosomes relate to traits
2) Appreciate how traits are passed on from parents to
offspring
3) Comprehend the inheritance of genetic disorders
Our “teachable tidbit”: Sex-linked traits
Objectives
1) Be able to diagram a single-trait sex-linked cross and
predict genotypic/phenotypic percentages.
2) Determine if a genetic disorder is sex-linked by analyzing
a pedigree.
3) Distinguish between dominant versus recessive genetic
disorders.
Rou-Jia
Prior knowledge
From the previous class:
Concepts/definitions students should be familiar with:
•
•
•
•
•
heterozygous vs homozygous
recessive vs dominant
genotype vs phenotype
carrier
autosomal single-trait crosses
• Punnett squares
Aaron
Sex-linked traits
What is a sex-linked trait?!?
Aaron
Sex-linked traits
What is a sex-linked trait?!?
Definition: A trait whose gene is located on a sex chromosome
(almost always the X-chromosome).
Aaron
Sex-linked traits
What is a sex-linked trait?!?
Definition: A trait whose gene is located on a sex chromosome
(almost always the X-chromosome).
Why is this important/why should we care?
Aaron
Sex-linked traits
What is a sex-linked trait?!?
Definition: A trait whose gene is located on a sex chromosome
(almost always the X-chromosome).
Why is this important/why should we care?
Common sex-linked diseases:
• Colorblindness
• Hemophilia
• Duchenne muscular dystrophy
Implications for genetic counseling
Aaron
Clicker Question!
Which of the following genotypes is representative of an
affected female for hemophilia, an X-linked recessive disorder?
A.
B.
C.
D.
E.
AA
Xa Y
aa
Xa Xa
XAXa
Aaron
Clicker Question!
Which of the following genotypes is representative of an
affected female for hemophilia, an X-linked recessive disorder?
A.
B.
C.
D.
E.
AA
Xa Y
aa
XaXa
XAXa
Aaron
Clicker Question round 2
Which of the following genotypes is representative of a carrier
for hemophilia, an X-linked recessive disorder?
A.
B.
C.
D.
E.
AA
Xa Y
aa
Xa Xa
XAXa
Aaron
Clicker Question round 2
Which of the following genotypes is representative of a carrier
for hemophilia, an X-linked recessive disorder?
A.
B.
C.
D.
E.
AA
Xa Y
aa
Xa Xa
XAXa
Aaron
Clicker Question round 2
Which of the following genotypes is representative of a carrier
for hemophilia, an X-linked recessive disorder?
A.
B.
C.
D.
E.
AA
Xa Y
aa
Xa Xa
XAXa
Do you think males can be carriers for sex-linked disorders?
Why?
Aaron
Pedigrees!
What is a pedigree?
A visual representation of family history for a trait.
Standard notation for analyzing/constructing a pedigree:
Diana
Pedigrees!
What is a pedigree?
A visual representation of family history for a trait.
Standard notation for analyzing/constructing a pedigree:
Diana
Pedigrees!
What is a pedigree?
A visual representation of family history for a trait.
Standard notation for analyzing/constructing a pedigree:
Female
Male
Diana
Pedigrees!
What is a pedigree?
A visual representation of family history for a trait.
Standard notation for analyzing/constructing a pedigree:
Mating Line
Female
Male
Descent Line
Diana
Pedigrees!
What is a pedigree?
A visual representation of family history for a trait.
Standard notation for analyzing/constructing a pedigree:
Mating Line
Generation designation:
I, II, III, IV…
Female
Male
I.1
I.2
Individual designation:
1, 2, 3, 4…
Descent Line
II.1
II.2
Diana
Pedigrees!
What is a pedigree?
A visual representation of family history for a trait.
Standard notation for analyzing/constructing a pedigree:
Mating Line
Generation designation:
I, II, III, IV…
Female
Male
I.1
I.2
Individual designation:
1, 2, 3, 4…
Descent Line
Trait
Present
Trait
Absent
II.1
II.2
Phenotype designation
Diana
Pedigree activity
Assume the pedigree below displays information about a
recessive, X-linked disorder. Work with a partner to fill in the
phenotypes for generation I individuals and genotypes and
phenotypes for generation II individuals.
X aX a
XAY
XA XA
X aY
Working together in pairs, fill out the provided worksheet
Kristin
Pedigrees!
What is a pedigree?
A visual representation of family history for a trait.
Standard notation for analyzing/constructing a pedigree:
Mating Line
Generation designation:
I, II, III, IV…
Female
Male
I.1
I.2
Individual designation:
1, 2, 3, 4…
Descent Line
Trait
Present
Trait
Absent
II.1
II.2
Phenotype designation
Kristin
Pedigree activity
Assume the pedigree below displays information about a
recessive, X-linked disorder. Work with a partner to fill in the
phenotypes for generation I individuals and genotypes and
phenotypes for generation II individuals.
X aX a
XAY
XA XA
X aY
Working together in pairs, fill out the provided worksheet
Kristin
Pedigree activity
Assume the pedigree below displays information about a
recessive, X-linked disorder. Work with a partner to fill in the
phenotypes for generation I individuals and genotypes and
phenotypes for generation II individuals.
X aX a
X AX a
XAY
XA XA
X aY
X aY
X AX a
Working together in pairs, fill out the provided worksheet
Kristin
What about Generation III?
If II.2 and II.3 have children:
1) Is it possible for them to show the trait?
2) If so, can both boys and/or girls show the trait?
Xa Xa
X AX a
XAY
XA XA
X aY
X aY
X AX a
Kristin
Mating activity for Generation III!
Instructions
You have each received a pair of cards representing alleles for
the proud parents-to-be from Generation II. Now:
1)
2)
3)
4)
5)
6)
7)
Find a partner with the opposite color cards.
Hold your cards behind your back, one in each hand.
Have your partner randomly select one of your hands.
Place your selected card on the table.
Repeat 3-4 with your partner’s cards.
Now define your offspring’s genotype.
ONE OF YOU report your offspring by clicking the
appropriate choice.
Geeta
Mating activity for Generation III!
Click in the resulting genotype of your offspring!
A.
B.
C.
D.
Xa Xa
XAXa
Xa Y
XAY
Xa Xa
X AX a
XAY
XA XA
X aY
X aY
X AX a
Geeta
Main takeways from today
• You should be able to define what a sex-linked trait is and
understand their heredity.
• You should be able to analyze a pedigree and predict the
phenotypes and genotypes of the offspring.
Darcie
Summative Assessments
Darcie
1) Colorblindness is an X-linked recessive trait. If a father who is XRY has
children with an XrXr mother, what is the probability (percentage)
that a daughter born to the couple would be colorblind?
a. 0%
b. 25%
c. 50%
d. 75%
e. 100%
Darcie
1) Analyze the following pedigree for the pattern of inheritance, and answer the following
questions. Assume that individuals II-1 and II-4 do not have the detrimental allele.
Is this a dominant or recessive trait? Additionally, circle the couple that best supports your reasoning and
explain.
Is this a sex-linked trait? Why or why not?
What is the genotype of individual I-1? Explain your reasoning.
Darcie