Lecture 2 Section 2
Exceptions to Mendelian Genetics
Today
1. Administrative issues
2. Mopping up concepts and terminology
3. Problems solving
4. Comments about Key Term set 3 reading assignment
If only 70% of individuals with a dominant mutant allele
show the dominant trait, the trait is said to be ____.
1.
2.
3.
4.
70% epistatic
70% expressive
70% penetrant
70% dominant
95%
2%
1
2%
2
1%
10
3
4
Countdown
How does genotype affect phenotype?
Gene
Gene Product
Cell Morphology/Physiology
Many genes and the
environment act together to
determine cellular/… phenotype
Tissue Morphology/Physiology
Organ Morphology/Physiology
Organismal Morphology/Physiology/Behavior
Community, population, …
A pure-breeding purple plant is crossed to
a pure-breeding colorless plant and all the
F1 are all purple. An F1 plant is allowed to
self-fertilize and produces 160 F2 with the
following distribution: 100 purple, 45 blue
and 15 colorless. Are these results
consistent with model 3? Support your
answer by performing a chi-square
analysis.
colorless
C
What is the expected
distribution of progeny
phenotypes if you crossed
AaCcBB x AaCcBB?
40%
1.
2.
3.
4.
9 purple; 4 blue; 3 colorless.
9 blue; 4 purple; 3 colorless
9 purple; 4 colorless; 3 blue
12 blue, 4 colorless
38%
19%
2%
1
2
3
10
4Countdown
A pure-breeding purple plant is crossed to
a pure-breeding colorless plant and all the
F1 are all purple. An F1 plant is allowed to
self-fertilize and produces 160 F2 with the
following distribution: 100 purple, 45 blue
and 15 colorless. Are these results
consistent with the model? Support your
answer by performing a chi-square
analysis.
Pure-breeding brown-eyed flies (bw- bw- ) are crossed to purebreeding scarlet-eyed flies (st- st- ). All the F1 have wild type
eyes. The F1 are allowed to interbreed to produce an F2. What
is the expected distribution of fly eye color in the F2?
You have two new recessive mutant lines of flies: both are purebreeding and both have brighter than wild-type eyes. The genes
responsible for the mutant phenotypes are unknown.
You know that eye color is controlled by many genes and that
different alleles of one gene can lead to different eye colors.
You cross the two mutant lines and all the progeny have wild type
eyes. This tells you ______.
You have two new recessive mutant lines of flies: both are purebreeding and both have brighter than wild-type eyes. The genes
responsible for the mutant phenotypes are unknown.
You cross the two mutant lines and all the progeny have wild
type eyes. This tells you ______.
1. That the two lines carry mutations
in the same gene.
2. That the two lines carry different
alleles of white gene.
3. That the two lines carry mutations
in different genes.
4. That the two lines carry different
alleles of the scarlet gene.
61%
25%
10%
4%
1
2
10
3
4Countdown
You have two new recessive mutant lines of flies: both are purebreeding and both have brighter than wild-type eyes. The genes
responsible for the mutant phenotypes are unknown.
You know that eye color is controlled by many genes and that
different alleles of one gene can lead to different eye colors.
You cross the two mutant lines and all the progeny have wild type
eyes. This tells you that the mutations are in different genes.
Genetic Complementation; Complementation analysis.
You cross one bright-eyed mutant female line to males from two
different fly lines. Line 1 is pure-breeding for loss of white
function (w-Y). Line 2 is pure-breeding for loss of scarlet
function (st-st-). The cross to line 1 gives all wild type progeny.
The cross to line 2 gives all bright-eyed mutant progeny. This
tells you that ____
You cross one bright-eyed mutant female line to males from two
different fly lines. Line 1 is pure-breeding for loss of white function (wY). Line 2 is pure-breeding for loss of scarlet function (st-st-). The
cross to line 1 gives all wild type progeny. The cross to line 2 gives all
bright-eyed mutant progeny. This tells you that ____
1. That the mutant line mutation is
recessive to w-.
2. That the the mutant line carries a
birght eye allele of the white gene.
3. That the mutant line carries a
mutation in a gene other than
white or scarlet.
4. That the mutant line carries a
mutant allele of the scarlet gene.
33%
22%
22%
23%
10
1
2
3
4Countdown
Pure-breeding brown-eyed flies (bw- bw- ) are crossed to purebreeding scarlet-eyed flies (st- st- ). All the F1 have wild type
eyes. The F1 are allowed to interbreed to produce an F2. What
is the expected distribution of fly eye color in the F2?
A white-eyed female is crossed to a wild type male and
all the progeny are wild type. If you allow the F1 to
interbreed, how many eye-color phenotypes do you
expect among the F2?
3) Examine the pedigrees to the right, which shows the inheritance of an X-linked, recessive trait. Assume that
individuals that “marry in” from outside the family are not carriers.
a) (10 Points) Write the genotype of each individual listed below (I-1 and I-2 are given).
I-1__X+Y____
II-3_________
III-4_________
I-2__X-X-____
II-4________
IV-2_________
II-1_________
III-2_________
V-2_________
b) (10 Points) What is the term used to describe a trait that displays this type of inheritance pattern (you were already
given that it’s X-linked recessive, so it’s more than that)?
For each pedigree, consider whether or not it COULD BE
consistent with X-linked recessive inheritance. Indicate why
or why not. Assume 100% penetrance but nothing else.