Download VariationsOfInheritancePatterns Notes 2016

Biology
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Variations of Inheritance Patterns
Intermediate Inheritance
(Also called incomplete 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.
Intermediate 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
c. Could two plants with ivory flowers ever produce any offspring with red flowers?
Explain.
d. Could two plants with red flowers ever produce any offspring with ivory flowers?
Explain.
e. Could two plants with ivory flowers ever produce any offspring with pink flowers?
Explain.
f.
What plants would you cross to produce pink flowers? Explain.
g. Could two plants with pink flowers produce offspring with red flowers? Explain.
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 horses coat color is exhibited as intermediate inheritance. The allele for chestnut coat color
(C) is partially dominant to the allele for cream coat color (c). The intermediate coat color is
palomino.
a. If you had a mixed heard of cream and palomino horses, how would you produce the
chestnut coloration?
b. If you had a mixed heard of cream and chestnut horses, how would you produce the
palomino coloration?
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
IB
i
Function
directs synthesis of the A protein
directs synthesis of the B protein
does not direct synthesis of a protein
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?
6. An example of codominance is found in chickens. When white (b) chickens are crossed with black
(B) chickens, the result is not a grey chicken, but a chicken with both black and white feathers.
a. genotype phenotype
BB =
Bb =
bb =
b. If a black and white chicken is crossed with a white chicken, predict the genotypic and
phenotypic ratios.
c. If black and white chickens are crossed, predict the genotypic and phenotypic ratios.
d. If you want to produce all black and white chickens, what parent phenotypes should be
crossed?
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.
Sex-Linked Inheritance
In female mammals, the two X chromosomes are the same length and the alleles are typically
present in pairs. Their expression depends on the combination of alleles present and their dominance
relationship to one another. Genes located on the X chromosome are referred as X- linked genes.
However, in the male there are few corresponding genes on the Y chromosome. Thus, in a male, the
genes on the X chromosome will be expressed regardless of whether they are dominant or recessive.
Because these genes are located on the X chromosome and not on the Y, a somewhat different
pattern of inheritance is observed in the X-linked traits.
Sex-Linked Gene – a gene located on one of the sex chromosomes (X or Y chromosomes); most
sex-linked gene disorders are due to recessive alleles on the X chromosome and are seen
mostly in men since they have only one copy of the gene
Ex.
Colorblindness
Hemophilia A
White-eyes in fruit flies
Yellow body in fruit flies
Color blindness is an X-linked recessive trait.
XB = normal vision
Xb = colorblindness
List all the possible genotypes and the corresponding phenotype for males and females.
Genotypes
Phenotypes
Females
Males
Hemophilia A is the inability to clot ones blood. It is caused by the presence of the sex-linked
recessive allele (Xh). The presence of the normal dominant allele (XH) allows one to synthesize the
necessary clotting factor.
List all the possible genotypes and the corresponding phenotype for males and females.
Genotypes
Phenotypes
Females
Males
Sex-Linked Problems
1. Predict the male and female phenotypic ratios for the following crosses:
a. XBY x XBXb
b. XbY x XBXB
c. XbY x XBXb
d. Can a normal male have a colorblind father? _______
A normal mother?______ Explain.
e. Can a color blind male have a normal father?________
A normal mother? ______ Explain.
f.
The only member of Arlene’s family who is colorblind is her brother. What is the
brother’s genotype? ________ The father’s genotype? _______ The mother’s
genotype? ______
What is Arlene’s genotype is she later has a colorblind son? ______
2. Predict the male and female phenotypic ratios for the following crosses:
a. XHY x XHXh
b. XhY x XHXH
c. XhY x XHXh
d. Under what circumstances could two normal clotting individuals have a child with
hemophilia?
3. In fruit flies, the white-eye coloration is inherited as a sex-linked recessive allele (Xr). The wild
(red eyes) coloration is produced by the presence of the dominant allele (XR)
a. What are the five possible genotypes and their corresponding phenotypes?
b. Determine the expected genotypes and phenotypes of the F1 produced by crossing a
wild male and a white female.
c. Cross the F1 with itself to produce the F2. What is the expected phenotypic ratio for this
generation? (See 3b)
d. Determine the expected genotypes and phenotypes of the F1 produced by crossing a
white male with a purebred wild female.
e.
Cross the F1 with itself to produce the F2. What is the expected phenotypic ratio for this
generation? (See 3d)
4. In fruit flies the yellow body color is dependent on the sex-linked recessive allele (Xy). The
corresponding wild body color allele (XY) is dominant.
a. Determine the expected genotypes and phenotypes of the F1 produced by crossing a
wild male with a yellow female.
b. Cross the F1 with itself to produce the F2. What is the expected phenotypic ratio for
this generation? (See 4a)
c. Determine the expected genotypes and phenotypes of the F1 produced by crossing a
yellow male with a purebred wild female.
d. Cross the F1 with itself to produce the F2. What is the expected phenotypic ratio for
this generation? (See 4c)
e. Determine the expected genotypes and phenotypes of the F1 produced by crossing a
white-eyed male with a yellow-bodied female. (Assume the flies are purebred.)
f.
Cross the F1 with itself to produce the F2. What is the expected phenotypic ratio for
this generation? (See 4e)