Chapter 5 Beyond Mendal Law Flashcards
Pleiotrophy
where one gene controls several functions or has more than one effect.
Ex. Missing enzyme porphyria accumulates it effects urine, digestive system, muscles, and nervous tissue
Royal family effected with porphyria
The varied illnesses and quirks appeared to be different unrelated disorders
Penetrance?
all or none expression of a single gene .
A genotype is incompletely penetrant if some individuals do not express the phenotype
Ex polydactyly
Variably expressivity
When one genotype produces a range of phenotype.
One gene can affect one individual much more severely than another individual
Ex. Polydactyly
Explain multiple alleles
An individual carries two alleles for each autosomal gene
However, gene can have multiple alleles
Different allele combinations can produce variations in the phenotype
Ex. ABO blood typing
Incomplete dominance?
The heterozygous phenotype is between those of the two homozygotes
Ex. Familial hypercholesterolemia (FH)
A heterozygous has approximately half the normal number of receptors in the liver for LDL cholesterol
A homozygous for the mutant allele totally lacks the receptor and so their serum cholesterol level is very high
Epistasis
The phenomenon where one gene affects the expression of a second gene
Ex albinism
They have the pigment for color but the gene for albinism blocks color from showing
Labs yellow lab is the lab without color because the the e e gene that blocks the brown or black color
Lethal Alleles
A double dose of a dominant allele may be lethal and causes death before the individual can reproduce
Have to be heterozygous
Ex. plum eyes in fruit flies and achondroplasia dwarfism
Genetic Heterogeneity
Different genes can produce identical phenotypes Genes may encode enzymes that catalyze the same biochemical pathway, or different proteins that are part of the pathway
More than one gene creates the same outcome phenotype
If you are heterozygous for two different genes that cause the same phenotype you will not have the disorder ex blindness
Phenocopy
A trait that appears inherited but is caused by the environment
May have symptoms that resemble an inherited trait or occur within families
Examples exposure to teratogens (harmful things)
Thalidomide cause limb defects similar to inherited phocomelia –> attached arms
PKU autosomal recessive
Affected mother not following diet will pass elevated levels of phenylalanine to fetus
Mitochondrion (genetic)
mitochondrial genes are transferred by the mother to all of her offspring.
No crossing over little DNA repair
High exposures to free radicals, mutation rates are greater. Mitochondrial genes encode proteins that participate in protein synthesis and energy production
DNA = 37 genes
Mitochondrial disorders
Mitochondrial myopathies – Weak and flaccid muscles
- MERRF (myoclonic epilepsy with ragged red fibers) - Leber optical atrophy – Impaired vision
Ooplasmic transfer technique can enable woman to avoid transmitting a mitochondrial disorder
Heteroplasmy
The condition where the mtDNA sequence is not the same in all copies of the genome
- Thus, a mitochondrion will have different alleles for
the same gene At each cell division, the mitochondria are distributed at random into daughter cells
If an oocyte is heteroplasmic, differing number of copies of a mutant mtDNA may be transmitted
- The phenotype reflects the proportion of
mitochondria bearing the mutation
Codominance
The heterozygous phenotype results from the expression of both alleles
ex:Alleles IA and IB are codominant, and both are completely dominant to i
ABO gene encodes a cell surface glycoprotein
IA produces antigen A
IB produces antigens B
io produces no antigen
Blood typing
assume heterozygous when you can’t determine a person blood typing alleles
Porphyria
Diseases that result from deficiencies of any of several enzymes required to make heme
In each disease an intermediate biochemical builds up
May be excreted in urine or accumulate in tissues causing symptoms are
These symptoms including reddish teeth and photosensitivity may have inspired the vampire and werewolf legends
