Download Variations of Inheritance Patterns

Biology
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Variations of Inheritance Patterns
Incomplete Inheritance
(Also called intermediate or partial dominance) expression of a heterozygous phenotype that is
different from either of the parents; an intermediate phenotype is usually observed
Ex. Black and White parent mice have Grey baby mice
Red flowered plant crossed with White flowered plant gives rise to Pink flowered plants
In Mendel’s experiment, all traits had clear dominant – recessive patterns. However the absence
of dominance of one member of a pair of alleles is quite common in most organisms. For example, in
crosses between red flowered snapdragons and white flowered snapdragons the F1 produces only
pink flowered intermediates. When the F1 are crossed with themselves, the F2 plants consist of ¼
red : ½ pink : ¼ white colored flowers.
Incomplete Inheritance Problems
1. In Four-o-clock plants the allele for red flower color (R) is incompletely dominant to the allele
for ivory colored flowers(r). The intermediate phenotype of four-o-clock plants is pink.
a. Determine the phenotype for each of the following genotypes
RR
= ____________
rr
= ____________
Rr
= ____________
b. Calculate the expected phenotype ratios for the F1 that could be produced by each of
the following crosses:
RR x RR
rr x rr
Rr x rr
Rr x Rr
2. In guinea pigs, the yellow coat color is produced by the homozygous genotype (YY), the white
coat color is produced by the genotype (yy). The heterozygote (Yy) produces a cream coat
color.
Calculate the expected phenotypic ratios of the F1 produce by each of the following example
crosses of incomplete dominance.
a. white x yellow
b. yellow x yellow
c. white x cream
d. cream x cream
3. In radishes the allele for long shape is partially dominant to the allele for round shape. The
heterozygote has an oval shape.
a. If a round radish is crossed with a long radish, what shape would the F1 offspring
have?
b. If the F1 offspring are crossed with themselves, what is the expected phenotypic ratio
of the F2 generation?
4. In humans there is a genetic disease which results in abnormally high levels of cholesterol in
the blood, hypercholesterolemia. The normal allele (H) is partially dominant to the allele
responsible for the disease (h). Heterozygous individuals have twice as much cholesterol as a
normal individual, while those homozygous for the abnormal allele have 5 times the normal
levels of cholesterol.
Calculate the expected phenotypic ratios of the offspring that could be produced by each of the
crosses listed below.
a. normal x normal
b. normal individual x individual with twice the level of cholesterol
c. normal individual x individual with 5 times the level of cholesterol
Multiple Alleles
For many genes there are more than two alleles found in the population. For example the
gene that determines blood type there are 3 possible alleles (A, B or O). However each
individual can only have 2 alleles for this gene (one from mom and one from dad).
Codominance – (nondominance) condition in which each member of an allelic pair is expressed in
the heterozygote; thus the heterozygote will exhibit both phenotypic expressions
Ex. ABO system of red blood cells
MN blood system
Hemoglobin
ABO Blood System
In the ABO system of red blood cell classification, genes determine the presence or absence of
certain proteins on the red blood cells (RBC). The determination of one’s blood type is simply
determining which proteins are present. There are three alleles that are involved in the ABO system.
However, an individual can only have two of them at any one time (1 from each parent) and the A and
B alleles are codominant.
Alleles
IA or A
IB or B
iO or O
Function
directs synthesis of the A protein
directs synthesis of the B protein
does not direct synthesis of a protein
Possible Genotypes
Possible Phenotypes
MN Blood System
Another system for typing blood is the MN system. In this system, there are only the M and N alleles
involved in the production of proteins. These alleles are also codominant.
Alleles
M
N
Function
directs synthesis of M protein
directs synthesis of N protein
Possible Genotypes
Possible Phenotypes
Hemoglobin
Hemoglobin is a complex protein found within red blood cells. This protein’s function is to temporarily
bond and transport oxygen throughout an animal’s body. An alternate form of the gene exists that
directs the synthesis of an “abnormal” protein that can result in a distortion in the shape of the red
blood cells into a pointed, sickle-like shape. The normal and the sickle alleles are codominant.
However, heterozygotes have an advantage over normal individuals. Heterozygotes are resistant to
malaria.
Alleles
HbA
HbS
Function
directs synthesis of normal hemoglobin
directs synthesis of abnormal hemoglobin
Possible Genotypes
Possible Phenotypes
*Rh Factor
Another system of typing blood is based upon the presence or absence of another protein termed the
Rh factor. There are two alleles in this system. The one allele directs the synthesis of the factor
(Rh+), while the other does not code for a factor (Rh-). However, in this system the + allele is
completely dominant to the – allele. This is NOT an example of codominance.
Alleles
Rh+ or +
Rh- or -
Function
directs synthesis of a factor
does not direct synthesis of a factor
Possible Genotypes
Possible Phenotypes
Multiple Alleles & Codominance Problems
1. Calculate the possible phenotypic ratio of the offspring that could be produced by each of the
following crosses.
a. AA x BB
b. AO x BB
c. OO x AB
d. AO x OO
e. AO x BO
f.
OO x OO
g. BB x OO
h. AB x BO
2. Could two individuals with Type O blood ever produce any offspring with:
a. Type A blood? ______ Explain.
b. Type B blood? ______ Explain.
c. Type AB blood? ______ Explain.
d. Type O blood? ______ Explain.
3. Could two individuals with Type A blood ever produce any offspring with:
a. Type A blood? ______ Explain.
b. Type B blood? ______ Explain.
c. Type AB blood? ______ Explain.
d. Type O blood? ______ Explain
4. Could two individuals with Type B blood ever produce any offspring with:
a. Type A blood? ______ Explain.
b. Type B blood? ______ Explain.
c. Type AB blood? ______ Explain.
d. Type O blood? ______ Explain
5. What offspring phenotypes are possible for two individuals that are Type AB?
Polygenic Inheritance
Some variety exists in traits because at least two or more genes control these traits. Depending on
the varying combination of dominant recessive alleles each individual could have a unique
combination resulting in a wide variety of phenotypes. For example, if a combination of 4 genes A, B,
C, and D control hair color then the homozygous dominant results in jet black hair (AABBCCDD) then
the homozygous recessive condition may result platinum blond phenotype. The varying arrangement
of the genes leads to all the unique possibilities of hair color. As scientists cross and study polygenic
inheritance they notice there is a consistent pattern. The chart below shows the pattern that exists
within a population for any highly variable polygenic trait.
List some examples of traits that might possibly exhibit polygenic inheritance.
The Importance of Environment
Not all phenotypes are based completely on genotypes. The environment the organism lives in
affects many traits. While some traits such as blood type may depend only on genotype, many others
are a result of both genotype (nature) and environment (nurture).
Ex.
Leaf shape and size in trees
Coloration of Siamese Cats
Affect of nutrition on height
Skull shape
List some examples of traits that might possibly be a result of both genetics and environment.