Download Principles of Heredity

Human Genetics Lab
When Students Are the Subjects……
Loci, Genes and Alleles
• Locus = area on chromosome
where gene is located
(plural = loci)
• Gene = sequence of DNA that
codes for a protein, gives rise to
physical trait
• Alleles = alternative forms of a
gene
– Dominant allele masks other alleles
– Recessive allele is masked
Locus 1
Locus 2
Locus 3
Genotype and Phenotype
Term
Definition
Alleles carried by an individual
All diploid individuals have two
copies of each allele
homozygous = both alleles are
the same
heterozygous = two different
alleles
Phenotype Physical characteristic or
appearance of an individual
Genotype
Example
EE, Ee, ee
free or
attached
earlobe
Earlobe Attachment
Genotype
Phenotype
EE or Ee
Free
earlobe
E is dominant
over e
ee
Attached
Earlobe
Phenotype
Solving Genetics Problems
1. Convert parental phenotypes to
genotypes
--may need to use info about grandparents or
children already born to complete these
genotypes
2. Use Punnett Square to determine
genotypes of offspring
3. Convert offspring genotypes to
phenotypes
Genetics Problem 6, p. 104
George has attached ear lobes. Laura has free
earlobes, but she is heterozygous for this trait.
What are the chances of their child having free
earlobes?
Genotype for
George
Genotype for
Laura
ee
Ee
Homozygous parents can only pass
one form of an allele to their offspring.
e
e
e
e
Heterozygous parents can pass either of
two forms of an allele to their offspring.
E
e
E
e
Genetics Problem 6, p. 104
George has attached ear lobes. Laura has free
earlobes, but she is heterozygous for this trait.
What are the chances of their child having free
earlobes?
Genotype for George
Genotype for Laura
ee
Ee
e
e
E
e
Ee
ee
Ee
ee
50% free earlobes
50% attached earlobes
Genetics Problem 16, p. 105
Both Willy and Ethyl are heterozygous for earlobe
attachment and also for hitchhiker’s thumb. What are
the chances of a child with…
…attached earlobes and a hitchhiker’s thumb?
…free earlobes and no hitchhiker’s thumb?
Genotype for
Willy
Genotype for
Ethyl
EeHh
EeHh
EH Eh eH eh
EH Eh eH eh
EH
Eh
eH
eh
EEHH
EEHh
EeHH
EeHh
Eh
EEHh
EEhh
EeHh
Eehh
eH
EeHH
EeHh
eeHH
eeHh
eh
EeHh
Eehh
eeHh
eehh
EH
…attached earlobes and a hitchhiker’s thumb? eehh = 1/16
…free earlobes and no hitchhiker’s thumb?
E_H_ = 9/16
Lab Today
• Simple Inheritance (12 traits)
• The “Which Classmate Shares the Most
Traits with You?” Game: Four student
volunteers – single elimination
• “Direct Comparisons with Individuals” – four
classmates and find % of traits shared
• Complex Inheritance: Height, ABO blood
type
• Solving Genetics Problems with Punnett
squares
Simple Inheritance
Trait
Your
Your Genotype
Phenotype
Bent little finger

Not bent
or
BB or Bb
(list any ONE
genotype that fits)

bb
Determine your phenotype and potential genotype for each trait.
At a specified time, your instructor will conduct a class tally
for all traits.
Direct Comparisons with Individuals
Your Phenotype 1st
attached earlobe
widow’s peak
person
20%
2nd
person
--
--
20%
hitchhiker’s thumb
20%
--
pigmented iris
20%
--
long index finger
--
20%
% Traits Shared
60%
40%
Sex-Influenced Traits Change
Dominance Pattern by Gender
Trait
Males
Females
Short
Index
Finger
Dominant
Recessive
Long
Index
Finger
SS or Ss
ss
Recessive Dominant
ss
SS or Ss
Height Distribution of Class Members
Height
Have a partner
measure your
height in cm.
We will do a class
tally to group the
data as shown in
this table.
< 150
150-154
155-159
160-164
165-169
170-174
175-179
180-184
185-189
190-194
195-199
Male
Female
Total
Genetic Patterns for Blood Type
So far we have seen
Alternative Patterns
Complete Dominance
Codominance
Two alleles per gene
Multiple Alleles
Codominance: Neither allele masks the other
so that effects of both alleles are observed in
heterozygotes without blending
Multiple Alleles: Three or more alleles exist for
one trait
Note: A diploid individual can only carry any two
of these alleles at once.
Multiple Alleles and Codominance
ABO Blood Type in Humans
Blood Type
Allele
Type A
A
Type B
B
Type O
o
A= B > o
A and B are codominant.
A and B are completely dominant over o.
Human ABO Blood Types
•Type
•Genotype
•Antigen on RBCs
•Antibodies
•Receives
•Donates
•Freq
•A
•AA or Ao
Type A
•B
•A or O
•A or AB
•40%
•B
•BB or Bo
Type B
•A
•B or O
•B or AB
•10%
•Neither
•AB, A,
B, O
•AB
•AB
•AB
A and B
(universal)
•O
•oo
Neither
•Both
•O
(universal)
•O,AB,
A,B
(universal)
Codominance is observed for Type AB Blood since the
products of both the A and B alleles are found on the cells.
•4%
•46%
Paternity Testing before DNA Fingerprinting
Joan Barry
Charlie Chaplin
Type A Blood
Type O Blood
Possible Genotypes
AA
Ao
?
Genotype
oo
Baby
Type B Blood
Possible Genotypes
BB
X
Bo
Can Charlie Chaplin
be the father?
Worksheet
• Complete pages 99-105 from lab
manual
• Be sure your instructor checks your
completed worksheet before you leave
the lab. Partial completion will be
accepted for students who have entered
and evaluated all the necessary data
and attempted some of the genetics
problems.