How is comb inheritance a type of complementary gene action
similar to the 9:7 F2 dihybrid flower color
ratio
?
3.Vincent van Gogh "Irises"
The red pigment cyanidin is synthesized from a colorless precursor. Addition
of a hydroxyl group (-OH) to cyanidin results in a purple pigment. Two purple
plants were crossed to give : 94 purple, 31 red, 43 white. Assign
genotpyes to the purple plants and explain the progeny flower colors.
6. Four babies become accidently
mixed up in a maternity ward. The ABO types of babies are : A, B, O, AB. The
ABO types for the four sets of parents are :
AB X O; A X O; O X O; A X AB. Match
the baby with the biological parents.
7.
Coat color
in the
guinea pig may be controlled by at least four alleles. C (black), ck
(sepia), cd (cream), ca (albino) where C > ck
> cd > ca.
cream |
 black |
(i) For the cross P1 sepia x P2 cream,
when sepia and cream both had an albino parent, determine the phenotypic ratios.
?
(ii) For the cross P1 sepia x P2 cream,
when sepia had an albino parent and cream had two sepia parents, determine
the phenotypic ratios.
Sepia has three possible genotypes : ckck, ckcd,
ckca. Cream has two possible genotypes : cdcd, cdca.
P1 parent is : ckca since one allele must be ck (from ck_
parent) and one allele must be ca (from caca parent). P2
parents can be ckcd or ckca, so P2 can be cdcd or
cdca. ?
8. This
deaf-mutism problem
is modified from one of
Dr. Robert Huskey's pages.
The pedigree above demonstrates four generations of deaf-mutism (DM) in families of northern Ireland. The family to the right
of the dashed line shows segregation for an autosomal recessive form of DM as clearly illustrated by the mating of I-3 and I-4
who produce all affected children.
The family to the left of the dashed line is also segregating for an autosomal recessive form of DM although the parents II-1 and
II-2 must both be heterozygous for the trait.
The curiousity is that although III-8 (from the left family) and III-9 (from the right family) each have the DM trait, none of their
children show the trait of deaf-mutism!
Given the genotypes of I-1 and I-3 ?
, fill in the remaining genotypes.
9. Blue Sclera
Bone Fractures
Osteogenesis imperfecta is caused by a dominant allele COL1A1
and is 100% penetrant for brittle bones. However other aspects of the pleiotropic
phenotype such as hearing loss and blue sclera have variable expressivity.
The following was modified from OMIM and indicates
the type of complex variable phenotypes associated with genetic diseases -
and other phenotypes!
|
Osteogenesis imperfecta is characterized chiefly by
multiple bone fractures, usually resulting
from minimal trauma. Affected individuals have blue sclerae,
normal teeth, and normal or near-normal stature. Hearing loss of conductive
or mixed type occurs in about 50% of families, beginning in
the late teens and leading, gradually, to profound deafness, tinnitus,
and vertigo by the end of the fourth to fifth decade.
The disorder may exhibit considerable interfamilial
and intrafamilial variability in the number of fractures and degree
of disability. Most striking were identical twins, the offspring of
a mildly affected mother. Twin B was born small for gestational age,
had 12 fractures and was 150 cm tall (third centile) at 11 years of
age. Her twin was born appropriate for gestational age and had had
only 2 fractures at age 8 and 9 secondary to strenuous exercise; her
current height was 162 cm (fiftieth centile).
Willing et al., 1990 noticed that the more severely
affected family members had children with both mild and severe phenotypes,
while the mildly affected individual had an offspring with a mild
phenotype. This suggested to them that there might be some other,
not identified, factor segregating independently in this family that
acts to modulate the final phenotype.
|
The pedigree
follows the inheritance of COL1A1 and the resultant phenotypes for brittle
bones, blue sclera and deafness.
10. Interacting biochemical pathways
provide an apt model of the genetic mechanic. Many of the tens of thousands
of genes in a eukaryotic species participate in biochemical pathways whose
products merge and interact to craft the phenotype. In the following problem
three biochemical pathways interact. A, B, C, D, and E are completely dominant
alleles resutling in the corresponding biochemicals A
- yellow, B - red,
C - yellow,
D - white, and E -blue.
Recessive alleles a, b, c, d, and e result in the absence of colored compounds.
Imagine colors represent spots on a pelicans pouch, or what ever suits your
fancy. Pathway III normally does not influence color but if D is recessive,
white3 builds up in concentration and can be converted to yellow
by pathway IV. Caveats are: red + blue
= purple ; blue
+ yellow =
green ;
white is colorless - that is, white is white.
|
Pathway I -----> white1 ---(E)------>
blue
Pathway II ----> white2 ---(A)------>yellow---(B)-->
red
Pathway III - - - -------------------> white3 ---(D)--->
white 4
Pathway IV ------white3 of pathway III----(C)---->yellow
of pathway II.
|
Explain the following F2s derived from pure breeding
parentals.
(i) 9 purple : 3 green : 4 blue
?
(ii) 9 purple : 3 red : 3 blue : 1 white ? -->
Lab 4 exercise
(iii) 13 purple : 3 blue ? -->
Lab 4 exercise
(iv) 9 purple : 3 red : 3 green : 1 yellow ? ->
Lab 4 exercise
|
A difficult problem. But imagine how complexity spirals with gene numbers
>104, alleles>102,
and rampant interactions that oscillate with time and the environment!
How Mendel ! ......
Hearken Stern and Sherwood.
|
(i) what fraction of albino children will have vision
reduced 25% ? Concept problem 2
(ii)What fraction of childen will be albino and blind
?
Concept problem 2
12.
How might Mendel have responsed to earlier questions posed by William Blake (1759-1827) in his poem "The
Tyger".
Jenny Fowler's Answer
Additional Problems: do problems 9-13
Rembrandt " The Anatomy Lesson of Dr. Nicolaes
Tulp"
Codominance is seen in the inheritance of ABO blood group alleles.
Red blood cells have complex glycoprotein antigens on their surface that result,
in part, from the expression of specific blood group alleles. Allele IA
determines one type of antigen and allele IB determines
another type of antigen. ))
Complementary gene interaction
))
))
))
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