Lab. 9 Deviation of Mendel`s first law “Monohybrid” part 2

Lab. 9
Deviation of Mendel’s first
law “Monohybrid” part 2
Main topics:


Deviation of Mutation
a. ABO type
b. Fur color of rabbits
Deviation of Sex
a. Sex limited
b. Sex influence
c. Sex linkage
Deviation from Mendel’s law
Sometimes during the crosses the ratio obtained does not obey Mendelian’s law.
Deviation from Mendel’s
1. Dominance:
law I:
a. Co-dominance
b. Incomplete dominance
2. Lethal alleles
c. Dominance lethal alleles
d. Recessive lethal alleles
3. Mutation:
a. Multiple alleles
4. Sex :
a. Sex- limited
b. Sex- influences
c. Sex- linkage
Principles of Genetics
1
3. Multiple alleles:
In Mendel's studies, he proposed that there are two alleles for every gene, the dominant
of the two having its phenotype expressed in a heterozygote. However, a gene can
have more than two allelic forms segregating within a population.
These genes are referred to as having multiple alleles. This does not mean that the
gene in a particular individual possesses more than two alleles. An individual can only
have a maximum of two of the alleles, one maternal and one paternal, no matter how
many alleles exists in the population.
Examples:

ABO blood types are an example of multiple alleles.

Fur color in rabbits is determined by one gene with four different possible alleles.
1. ABO blood types
For the ABO gene, the three alleles are the I A, IB and i alleles. We
typically call these alleles "A," "B," and "O," but of course our rules for
assigning symbols to alleles demand that all three be represented by
some version of the same symbol. In this case, that common symbol
is the letter "I," which stands for “Isoagglutinogen."
By now, the concept of dominance should be familiar to you. Of course, things get a bit
more complicated when there are three alleles instead of just two. As the symbols
above should suggest, the i allele (the "O" allele) is recessive to both the IA and IB
alleles (the "A" and "B" alleles). The IA and IB show Co-Dominance. This means that in
an individual who is heterozygous for these two alleles, the phenotypes of both alleles
are completely expressed, thus producing blood type AB.
Principles of Genetics
2
Thus we have the following:
Genotype
Phenotype
ii
Type O
IAIA or IAi
Type A
IBIB or IBi
Type B
IAIB
Type AB
ABO blood group antigens present on red blood cells and IgM
antibodies present in the serum:
Principles of Genetics
3
Genetic Analysis of Blood group:
P:
Gp:
F1:
2. Fur color in rabbits is determined by one gene with four different
possible alleles.
Fur color in rabbits is determined by a
single gene loci for which there are four
alleles.
Four phenotypes are possible:
Black, Chinchilla (gray color caused by
white hairs with black tips), Himalayan
(white with black patches on extremities of
rabbit), and white.
The black allele (C) is dominant over all
other alleles, Chinchilla (Cch) is dominant
over Himalayan (Ch), and white or
Albino (c) is recessive to all others.
Figure: Fur color in rabbits
Principles of Genetics
4
Ex. Fur color in rabbits.
What is the genotype and the Phenotype of the parents and
offspring in hybrids following:
 Wild x wild --------------- ¾ wild : ¼ Himalayan
Genetic Analysis:
P:
Gp:
F1:
 Wild x Himalayan ----------- ½ wild : ¼ Himalayan : ¼
Albino
Genetic Analysis:
P:
Gp:
F1:
 Gender & inheritance:
For most inherited traits, the gender of the bearer of the
genes is immaterial. Characteristics like free earlobes, fur
color, etc., generally operate the same in males as they do
in females. But there are exceptions. These fall into three
primary categories.
Sex limited traits
There are many examples where the action of a gene is influenced by the sex of the
individual. This is known as sex-limited inheritance (also known as sex-controlled
inheritance) and, in Butterflies, typically affects color, wing shape, markings and
behavior. The resulting sexual dimorphism results from the action of sex-limited
genes which, although present in both sexes, only have an effect in one sex. We have
two examples in the British Isles - the valesina form of the female Silver-washed
Principles of Genetics
5
Fritillary and the helices form of the female Clouded Yellow, where the named form is
only expressed in the female. In both cases, the allele controlling the form is dominant
(which has been proven through captive rearing and examining the ratios of offspring)
rather than recessive (which is what we might expect given the ratios we see in the wild,
which we'll come back to).
Now let's consider a couple of pairings. The figure below shows a pairing of a normal
male (that doesn't carry the valesina allele) with a valesina female. In this example,
we're considering both the sex chromosomes (X and Y), as well as the allele for wing
color (represented using the letter V). Since the male is XXvv, the only combination of
alleles in the gametes is Xv (as shown). We can see that we get equal numbers of
normal and valesina females in the offspring.
Figure: Sex limited
Principles of Genetics
6
Sex influenced traits
Sex
influenced
traits
are
also
autosomal,
meaning that their genes are not carried on the sex
chromosomes. Again, what makes these traits
unusual
is
the
way
they
are
expressed
phenotypically. In this case, the difference is in the
ways the two genders express the genes.
Figure: Sex influenced
One classic example of a sex influenced trait is
Pattern Baldness in humans (sometimes called
“male pattern baldness,” though the condition isn’t
restricted to males). This gene has two alleles,
“bald” and “non-bald.” The behaviors of the
products of these genes are highly influenced by
the hormones in the individual, particularly by the
hormone testosterone. In the presence of high levels of testosterone, the baldness allele
has a very powerful influence. In the presence of low levels of testosterone, this allele is
quite ineffectual. All humans have testosterone, but males have much higher levels of
this hormone than females do. The result is that in males, the baldness allele behaves
like a dominant allele, while in females it behaves like a recessive allele. As in all cases,
dominance only matters in the heterozygote, so this means that heterozygous males will
experience hair loss and heterozygous females will not. Even homozygous females may
experience no more than a thinning of their hair, but many develop bald spots or have
receding hairlines.
Ex. Baldness in human
Genetics P: HH x hh
Analysis:
(♀ hair, ♂ baldness) x (♀ baldness, ♂ hair)
F1: Hh (♀ hair less, ♂ baldness)
F2: HH : 2 Hh: hh
Principles of Genetics
7
Sex Linked Traits:
Sex Linked Traits are traits whose loci are literally on the sex chromosomes, so their
transmission from generation to generation is affected by the sex chromosome
complement of the individual. In any species with non-homologous sex chromosomes,
these traits can be significant.
The first demonstration of sex linkage was the white eye gene in Drosophila, the fruit fly
which has become so important to the study of classical genetics. Normal fruit fly eye
color is a dull brick red. Mutations in this gene cause the eyes to be white. The white
allele is recessive, but it was quickly determined that the inheritance pattern for this
gene was different from those of other genes being studied. In some kinds of mating,
reciprocal crosses produced different results, something which had never been
observed to happen with other genes. Not only that, but in some kinds of mating, the
results for the male offspring would be different from the results for the female offspring.
For instance, if a white-eyed female was mated to a red-eyed male, all of the female
offspring would be red eyed, but all of the male offspring would be white eyed.
It turned out that this particular eye color gene was literally located on the X
chromosome. Since females have two X chromosomes and males have only one,
genetic effects in the two genders are different. And since females contribute an X to
each offspring, male or female, and males contribute X chromosomes only to female
offspring, naturally transmission patterns were different in different kinds of mating.
“Linkage” refers to the physical connection that exists between genes whose loci are on
the same chromosome. Genes on the X chromosome are all linked to each other-thus
they are X-linked.
Principles of Genetics
8
Figure: sex linked in Drosophila melanogaster.
Ex. Sex linked in Drosophila melanogaster (♀ wild, ♂ white)
Genetics
P:
Analysis:
F1:
F2:
Ex. Sex linked in Drosophila melanogaster (♀ white, ♂ wild)
P:
F1:
F2:
Principles of Genetics
9
Gender Human
Roach
Butterfly
Chicken
Male XY
XO
XX
XX
Female XX
XX
XY
XO
References:
http://biotech.gsu.edu/houghton/2107/lecture11.html
Yazer M, Olsson M, Palcic M; Olsson; Palcic (2006). "The cis-AB blood group phenotype: fundamental lessons in glycobiology". Transfus Med
Rev 20 (3): 207–17.doi:10.1016/j.tmrv.2006.03.002. PMID 16787828.
Muramatsu M, Gonzalez HD, Cacciola R, Aikawa A, Yaqoob MM, Puliatti C (2014)."ABO incompatible renal transplants: Good or bad?". WORLD
JOURNAL OF TRANSPLANTATION 4 (1): 18–29. doi:10.5500/wjt.v4.i1.18. PMID 11532188.
http://staff.jccc.net/pdecell/bio205/webct/medelproblems.html
http://lhs.dcsdschools.org/UserFiles/Servers/Server_3858408/File/Shaw/sex-linked%20traits.pdf
http://www.okstate.edu/artsci/zoology/ravdb/files/4.pdf
Principles of Genetics
10
Exercise 9
1. Choose the right answer from the following:

A child is born with the blood type B. The mother of the child is blood type
O. Which of the following statements is most correct?
(A) The father must be type B
(B) The father could be type A
(C) The father passed along a recessive allele
(D) The mother could have passed along a type B allele
(E) The mother could have passed along a dominant allele

Hemophilia is a sex-linked recessive trait.
A male hemophiliac and
phenotypically normal female have a girl that is a hemophiliac. All of the
following statements are correct EXCEPT:
(A) The daughter inherited a recessive gene from each parent.
(B) The daughter inherited a dominant allele from her mother.
(C) The mother is a carrier of hemophilia
(D) The genotype of the mother is X H X h
(E) The genotype of the father is X h Y

Suppose a newborn baby was accidentally mixed up in the hospital. In an
effort to determine the parents of the baby, the blood types of the baby and
two sets of parents were determined. Baby 1 had type O Mrs. Brown had type
B Mr. Brown had type AB. Mrs. Smith had type B Mr. Smith had type B.
a. Draw Punnett squares for each couple (you may need to do more than 1
square/couple).
b. To which parents does baby #1 belong? Why? Hint you may want to refer to your Punnett
squares.
Principles of Genetics
11

A man heterozygous for blood type B marries a woman heterozygous for
blood type A. What is the chance that their first offspring will have type O?

Hemophilia in humans is inherited as an X linked recessive trait. A woman
whose father is hemophilia marries a man with normal clotting ability. What is
the probability that her first child will have hemophilia? Assume that the
woman's mother is homozygous dominant.

Red/Green color blindness is a sex linked traits. If a man with normal color
vision marries a colorblind woman, will all of the offspring be colorblind? If
not, who won't be colorblind (sons or daughter)?
Principles of Genetics
12

What is the probability of child will be bald if his father is homozygous and
balding, and his mother is homozygous and not balding?

A male homozygous for clubfoot reproduces with a normal homozygous
female. What are the genotypes and phenotypes of their children if
testosterone alters the phenotypic expression of the trait in the
heterozygous expression?
1. Let F represent normal feet
2. Let f represent clubfoot.

Two heterozygous individuals get married and have lots of children. The
father suffers with a painful condition called gout. What are the parent’s
genotypes? What are the genotypes and phenotypes of the children?

Let G represent no gout, and g represent gout.
Principles of Genetics
13