Mendelian Classical Genetics
Mendel used observations of
patterns to establish his
understanding of genetics
Terminology
How Mendel’s Observations Relate to
a Chromosome
Words that mean aa or AA
• Homozygous
• True breeding
• What do dominant and recessive mean?
Wild-type
• Each type of geneticist has their own
“notation”
• Drosophila geneticists
– Wild-type vs. mutant
Does wild type always mean more common?
Fruit flies are cool…
• How can one gene cause such a dramatic
change?
• Hox genes: Eukaryotic genes that control a
series of downstream genes.
– What bacterial genes are these analogous to?
Mendel’s 3 Laws
Law of Segregation
Law of Independent Assortment
Law of Dominance
How are all 3 laws displayed here!
Let’s practice a dihybrid cross
• Aliens:
– Skin color: Dominant, purple; Recessive, green
– # of eyes: Dominant, 1; Recessive, 3
1) Test cross of a parent that is heterozygous for
both genes
2) Test cross of a parent that is homozygous for
both genes
3) Cross between two heterozygous parents
Mendel’s Law of Dominance doesn’t
always apply…be able to define and
give an example of:
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Incomplete dominance
Co-dominance
Multiple Alleles
Epistasis
Pleiotropy
Recessive lethal
Polygenic
Sex-linked
Incomplete Dominance
• How does the
phenotypic ratio
change?
Co-Dominance
Multiple Alleles…Blood Type
• Dominant Alleles: IA and IB
• Recessive allele: i
• Allows for Blood Types A, B, O, AB
– What genotypes allow for the above phenotypes?
An aside…blood donation
What is rH?
Why doesn’t rH incompatibility happen until later
pregnancy (use your knowledge of the immune system to
explain!)
Epistasis
• How do the
results deviate
from a normal
cross between
two
heterozygotes?
Pleiotropy
Recessive Lethal
• How would this affect the phenotypic ratios expected
from a mating between 2 heterozygous individuals?
• Why is CF considered recessive lethal?
• Will it always be considered recessive lethal?
Tay Sachs
Is the mutation an insertion or a
deletion?
• Technique:
– Exon analysis
– What is needed
To be able to
compare the exons
of affected and
normal
individuals?
Why is it important
to be able to
diagnose a carrier?
Polygenic
• Most visible
genes: eye
color (7), skin
color (3)
Sex-linked
• More common in
males
• On X chromosome
• Muscular dystrophy,
Hemophelia,
colorblindness
• DO not confuse with
LINKAGE!
Colorblindness
• Rods
• Cones
Pedigrees
• Show genetic
traits over
many
generations
– What is this
inheritance
pattern?
– What would
an
inheritance
pattern for
autosomal
dominant
look like?
Autosomal
recessive?
What is next?
• Review the problems related to what we
discussed today. (Due Wednesday 4/3)
• Chi-square (Monday)
– How can chi-square be used to analyze the results of a
genetic cross?
• Linked genes (Monday and Tuesday)
– Recognize when genes are linked.
– Use linkage and recombination frequency to calculate
map distance.
– Practice mapping eukaryotic genes and bacterial
plasmids