Lecture 18 Flashcards
Non Mendelian inheritance (when Mendel doesn’t work)
Alleles of some genes can exhibit different degrees of dominance and “recessiveness” in relation to each other
Mendels pea cross invoking purple and white alleles the purple allele showed complete dominance over white alleles
But for some genes neither allele is completely dominant. Such that heterozygous F1 monohybrids have a phenotype intermediate between the 2 phenotypes of homozygous parents
This is incomplete dominance
Effects of the recessive allele can be detected to some extent in heterozygotes
Incomplete dominance in snap dragons
Red crossed with white makes pink
What is dominance
Alleles encode for proteins and enzymes that affect phenotypes
Alleles can encode for a functions or less functioning or non functioning version. This will produce recessive or non recessive traits
Is AB blood type a
Good or bad recipient
And
Good or bad donor
Universal recipient
Bad donor
Is O blood type a
Good or bad recipient
And
Good or bad donor
Universal donor
Bad recipient
Epistasis
In some types of inheritance the activity of one gene influences the activity of another gene
In epistasis, alleles of one gene can mask the expression of the alleles of another gene
-with the result that some expected phenotypes won’t appear among the offspring
Epistasis is an interaction between 2 or more genes to control a single phenotype
Epistasis in Labradors
B encodes for black fur. So BB dogs or Bb dogs will be black
bb produces less so it’ll be chocolate
HOWEVER it doesn’t matter if melanin doesn’t get there
A second gene E determines in pigment produced by gene B will actually be deposited in the hairs
E will allow pigment deposition to occur in hairs. So dogs will be either black or chocolate depending on Ellen’s present for B gene
If dogs are ee they will haven’t almost no melanin pigment no matter what alleles are present for B gene
Fur will be yellow
E gene is epistatic to B gene
Epistatic dihybrid cross Labradors
Regular heterozygous cross
BbEe x BbEe
Every ee will be yellow
Every BB with at least one E will be black
Every Bb with at least one E will be chocolate
Ration
9 black: 3 chocolate: 4 yellow
Polygenetic inheritance
Traits subject to polygenetic Inheritance exhibit continuous variation over a range of phenotypic expression
Lack of clearly defined phenotypic variants
Tend to have normal continuous variation (bell curve)
Gene loci act in an idditive fashion, each adding or subtracting a small amount from phenotype
Identical phenotypes may be displayed by a great variety of genotypes
Examples of polygenetic inheritance
Height. Weight. Skin color
Pleiotropy
Single genes affecting more than one character of an organism
Pleiotropy and Mendel
Mendel noted flower colour gene in peas also affected seed coat colour, axial leaf coloration as well as color of flower petals
Underlying mechanism of Pleiotropy
The Pleiotropic gene codes for a product that is used in more than one cell type or the product of the gene has a signaling function on various target cells (ie. the gene that codes for insulin receptor protein on cell membranes)
In humans what is a deleterious allele
In just one gene can cause widespread problems throughout the body
Pleiotropy example
Sickle cell disease
Recessive deleterious allele for sickle cell anemias affects structure of human hemoglobin
If u have it ur red blood cells are sickle shaped.
Can causes blockages in small blood vessels in different areas of the body
Sickles cells are destroyed prematurely by the spleen. Resulting in anemia (u lack enough healthy red blood cells to carry enough oxygen to body tissues)
