INCOMPLETE DOMINANCE
the heterozygote has a third phenotype that is intermediate between those of two homozygote parent (r1r1 red flowers x r2r2 white flowers
This is an example of when a heterozygous offspring does not share the phenotype of either parent
CODOMINANCE
2 different alleles are expressed together in the phenotype
Explain codominance in blood type
A person’s ABO blood type is determined by the I gene: which has three possible ales ; IA, IB AND ii. The I gene encodes an enzyme that inserts either an A OR a B. the allele i is recessive so ii has neither A or B and thus has type O blood.
IA, iA = A blood type
IB, iB = B blood type
However, IB IA = AB blood type ( both alleles are dominant, both are expressed)
The difference between a recessive and dominant allele.
RECESSIVE: Encodes for a nonfunctional protein
DOMINANT: code for a functional protein
Why are some conditions hard to trace in families
one gene may influence the phenotype in many ways; conversely multiple genes may contribute to one phono type
PLEIOTROPY
one gene has multiple effects on the phenotype.
It arises when one protein is important in different biochemical pathways or affects more than one body part or process.
EPISTASIS
A type of interaction ( protein ), which occurs when one one gene’s product affects the expression of another gene
What conditions interfere with the predictability of mendelian genetics
1.Incomplete dominance 2 Codominance 3 Pleiotropy 4. Protein interactions 5. Epistasis
. How do incomplete dominance and codominance increase the number of phenotypes?
Incomplete dominance and codominance produce phenotypes that are intermediate between or combinations of those produced by homozygous dominant or homozygous recessive individuals.
In incomplete dominance the hetereozygote has a third phenotype that is an intermediate.
In codominance two different alleles are are expressed together as they are both dominant; in blood type gene I there a three possible alleles resulting in 6 genotype and 4 phenotype
What is the difference between recombinant and parental chromatids, and how do they arise?
Recombinant chromatids are non- sister chromatids, that have a mixture of maternal and paternal alleles instead of alleles from just a single parent. In contrast, parental chromatids carry the same combinations of alleles that were inherited from the parents. Crossing over has not altered them.
What is pleiotropy?
Pleiotropy occurs when a gene produces multiple phenotypic expressions. Pleiotropy results when the protein encoded by a gene enters several different biochemical pathways or affects more than one body part or process.
How can the same phenotype stem from many different genotypes
Each gene encodes one protein, but many different proteins may interact in a single metabolic pathway. A mutation in a gene encoding any of these proteins may produce a flawed metabolic pathway. In this way, different genotypes can produce the same phenotype (failure of the metabolic pathway to operate properly).
How can epistasis decrease the number of phenotypes observed in a population?
In epistasis, one gene affects the expression of another. The gene interaction may cause some phenotypes to appear to be missing from a population.
