2. ● define non-mendelian pattern of inheritance;
● discuss the different types of non-mendelian
pattern of inheritance;
● present examples of each non-mendelian pattern
of inheritance.
3. Involves the pattern of inheritance that does not follow
Mendel’s laws. It describes the inheritance of traits
linked to a single gene on chromosomes.
Non-Mendelian Genetics
4. a. Codominance
b. Incomplete Dominance
c. Over Dominance
d. Multiple Allelism
e. Lethal Genes
f. Epistasis
Non-Mendelian
Patterns of
Inheritance
7. Sample Problem
A black chicken and a white chicken are crossed. Show
the Punnett Square. What is the probability that they
will have erminette chicks? ____%
8. Sample Problem
A black chicken and a white chicken are crossed. Show the Punnett Square.
What is the probability that they will have erminette chicks? _____%
Solution:
BB x WW
9. Sample Problem
A black chicken and a white chicken are crossed. Show the Punnett Square.
What is the probability that they will have erminette chicks? _____%
Solution:
BB x WW
W
W
B B
10. Sample Problem
A black chicken and a white chicken are crossed. Show the Punnett Square.
What is the probability that they will have erminette chicks? _____%
Solution:
BB x WW
BW BW
BW BW
W
W
B B
11. Sample Problem
A black chicken and a white chicken are crossed. Show the Punnett Square.
What is the probability that they will have erminette chicks? 100%
Solution:
BB x WW
BW BW
BW BW
W
W
B B
12. Occurs when the phenotype
of a heterozygous offspring
is somewhere in between
the phenotypes of both
homozygous parents; a
completely dominant allele
does not occur.
Incomplete
Dominance
18. Over dominance is the
interaction between genes
that are alleles and result
in the heterozygous
individuals being superior
to either of the
homozygous parents.
Over
Dominance
19. Overdominance may
also mean that the
heterozygote has a
higher fitness relative
to the counterpart
homozygotes.
Over
Dominance
20. An example of this is a
heterozygote for sickle
cell anemia.
Over
Dominance
22. Multiple alleles may exist
in a population level, and
different individuals in the
population may have
different pairs of these
alleles.
Multiple
Allelism
25. Sample Problem
In humans, there are four types of blood; type A, type B, type AB,
and type O. The alleles A and B are codominant to each other and
the O allele is recessive to both A and B alleles. So a person with
the genotype AA or AO will have A type of blood. In relation to this,
what will be the blood type of the offsprings if the parents has
genotypes AO and BO. Determine the genotypic and phenotypic
ratios of the F1 progeny.
30. If an allele makes one of
these genes nonfunctional, or
causes it to take on an
abnormal, harmful activity, it
may be impossible to get a
living organism with a
homozygous genotype.
Lethal Genes
37. It is a simple or dominant
epistasis whenever a
dominant allele conceals
the expression of both
recessive and dominant
alleles at other loci.
Dominant
Epistasis
38.
39.
40. It is a recessive epistasis
when the recessive allele
conceals the expressing.
Recessive
Epistasis
54. Epistasis is said to be
duplicate dominant
whenever there is a
dominant allele
concealing the
expression of recessive
alleles at two loci.
Duplicate
Dominant
59. The union of both
dominant alleles
strengthening the
phenotype or creating a
median variation is the
polymeric gene
interaction.
Polymeric
Gene
Interaction
For example, in the snapdragon, a cross between a homozygous red-flowered plant and homozygous white-flowered plant will produce offspring with pink flowers.
Now, let's try to cross the offspring of the red and white snapdragons. We can still use Mendel's model to predict the results of crosses for alleles that show incomplete dominance.
Cite for instance, if the homozygote parents were crossed who are both affected by sickle cell anemia they will produce F1 progeny with heterozygous genotype. Consequently, each heterozygote individual would have less physiological effects of the condition and have partial resistance to malaria as opposed to the homozygote parents who are suffering more from the deleterious effects of sickle cell anemia.
As an example, let’s consider a gene that specifies coat color in rabbits, called the C gene.The C gene in rabbits encodes an enzyme that is needed to make a type of pigment called melanin in hairs. The C gene comes in four common alleles:
A homozygous dominant C gene rabbit has either black or brown fur. While a homozygous recessive c superscript ch gene rabbit has chinchilla coloration (grayish fur). And the homozygous recessive c superscript h gene rabbit has Himalayan (color-point) patterning, with a white body and dark ears, face, feet, and tail. Lastly, a homozygous recessive c gene rabbit is albino, with a pure white coat.
A classic example of an allele that affects survival is the lethal yellow allele, a spontaneous mutation in mice that makes their coats yellow. Mice with homozygous alleles die during embryonic development. Lethal alleles can be dominant or recessive and can be expressed in homozygous or heterozygous conditions.
A classic example of an allele that affects survival is the lethal yellow allele, a spontaneous mutation in mice that makes their coats yellow. Mice with homozygous alleles die during embryonic development. Lethal alleles can be dominant or recessive and can be expressed in homozygous or heterozygous conditions.
Often the biochemical basis of epistasis is a gene pathway in which the expression of one gene is dependent on the function of a gene that precedes or follows it in the pathway.
Cite for example, the case of the fruit color of summer squash, the dominant W allele at W locus, suppresses the expression of any allele at the Y locus.
Cite for these particular offsprings, even if they have homozygous dominant and recessive Y allele at the other locus, their fruit color is white due to the presence of the dominant W allele. And if this particular allele is homozygous recessive, then the fruit color of the summer squash is either yellow or green depending now on the Y allele on the other locus.
The wild-type coat color, agouti (AA), is dominant to black-colored fur (aa). However, a separate gene (C) is necessary for pigment production. A mouse with a recessive c allele at this locus is unable to produce pigment and is albino regardless of the allele present at locus A.
A cross between heterozygotes for both genes (AaCc x AaCc) would generate offspring with a phenotypic ratio of 9 agouti:3 solid color:4 albino. In this case, the C gene is epistatic to the A gene.
A cross between heterozygotes for both genes (AaCc x AaCc) would generate offspring with a phenotypic ratio of 9 agouti:3 solid color:4 albino. In this case, the C gene is epistatic to the A gene.
It is a result of genes acting as suppressors or a component inhibiting the expression of other alleles.
An example of this type of epistasis is the production of Malvidin, a chemical produced by Primula which is a type of plant that has flowers. Malvidin is what makes the flower color of primula blue and the production of Malvidin is determined by the K gene where the suppression of its production is regulated by the D gene. Both of these genes are dominant characteristics. There is no expression of a dominant D allele even in the presence of dominant K allele. In other words, dominant D allele impedes the K allele.
And if we cross dominant K and D gene with their recessive counterpart, we will have 13: 3 ratio.
Duplicate epistasis is based on two loci.
This is also referred as a complementary gene action as both the genes are necessary for the accurate phenotype to be available.
The best example of duplicate recessive epistasis if found for flower colour in sweet pea.The purple colour of flower in sweet pea is governed by two dominant genes A and B. When these genes are in separate individuals as dominant allele (AAbb or aaBB) or recessive (aabb) they produce white flower.
A cross between purple flower (AABB) and white flower (aabb) strains produced purple color in F1 generation. Inter-mating of F1 plants produced purple and white flower plants in 9: 7 ratios in F2 generation instead of the normal dihybrid segregation ratio of 9:3:3:1.
That is because recessive allele a is epistatic to B/b alleles and mask the expression of these alleles. Another recessive allele b is epistatic to A/a alleles and mask their expression.
Hence, in F2, plants with AB genotypes will have purple flowers, and plants with recessive a allele, recessive b allele and double recessive genotypes produce white flowers.
A good example of duplicate dominant epistasis is the awn character in rice. Development of awn in rice is controlled by two dominant duplicate genes (A and B). The presence of any of these two alleles can produce awn. The awnless condition develops only when both genes are in homozygous recessive state (aabb).
A cross between awned and awnless strains produced awned rice plants in F1. Inter-mating of F1 plants produced awned and awnless plants in 15:1 ratio in F2 generation instead of the normal ratio of 9:3:3:1.
Again likewise on the previous type of epistasis, but the only difference is that the dominant alleles are epistatic to the expression of recessive allele at two loci. For the awn character of rice, the dominant allele A is epistatic to B/b alleles and all plants having dominant allele A will develop awn. Another dominant allele B is epistatic to A/a alleles and individuals with this allele will also develop awn character.
So rice grains with either the dominant A or B allele at one locus will develop awn and of course, those with double recessive alleles.
When on their own, each of these dominant alleles generates a physical characteristic differing from the united dominant alleles. Consequently, 3 phenotypes are created for 2 dominant alleles only.
A well-known example of polymeric gene interaction is fruit shape in summer squash. There are three types of fruit shape in this plant: disc, spherical and long. The disc shape is controlled by two dominant genes (A and B), the spherical shape is produced by either dominant allele (A or B) and long shaped fruits develop in double recessive (aabb) plants.
A cross between disc shape (AABB) and long shape (aabb) strains produced disc shape fruits in F1. Inter-mating of F1 plants produced plants with disc, spherical and long shape fruits in 9 : 6 : 1 ratio in F2.
Again, instead of the normal ratio of 9:3:3:1, it was modified in F2 progeny because plants with AB genotypes produce disc shape fruits, those genotypes with dominant A and recessive a alleles and dominant B and recessive b alleles produce spherical fruits, and plants with double recessive genotype produce long fruits.
That is why, having either of the dominant A and B allele. The phenotypic expression is the same, and for the summer squash, they are all spherical.
