lecture 8 Flashcards
what are the two postulates for the basic principle of gene expression?
genes are present on homologous chromosomes, and chromosomes segregate and assort independently
is dominance and recessiveness always the rule?
no
what are mutations?
the ultimate source of alleles
how do new phenotypes arise?
the result of changes in functional activity of gene product
examples of how mutations arise
eliminating enzyme function, changing relative enzyme efficiency, changing overall enzyme function
loss-of-function mutation
causes loss of WT function
gain-of-function mutations
mutation enhances function of WT and increases the quantity of gene product
neutral mutations
no change to the phenotype of tho the evolutionary fitness of the organism
what does a loss of function mutation cause?
the gene being partilally or fully inactivated
what is complete loss of function result in in a loss of function mutation?
a null allele
are loss of function mutations usually dominant or recessive?
recessive
what are gain of function mutations often called?
activating mutations
what are loss of function mutations often called?
inactivating mutations
what do gain of function mutations usually do?
enhances activation of the gene or its products
are gain of function mutations usually dominant or recessive?
dominant
what are dominate-negative mutations?
the mutant allele acts antagonistically to the WT allele
what are dominant negative mutations also called?
antimorphic mutations
what are dominant negative mutations often implicated in?
cancer
neutral mutations
have no selective benefit or negative effect
what is an example of a neutral mutation?
a silent mutation (they can’t be seen)
what are the new gene notation rules?
there is no dominance/ recessive interaction, superscripts are used on an italic uppercase letter
incomplete or partial dominance
results in an intermediate phenotype
incomplete dominance example:
a red and a white snapdragon will produce pink offspring
tay sachs disease
human biochemical disorder from incomplete dominance: homozygous recessive results in death, heterozygous results in 1/2 enzyme activity as compared to WT homozygous individuals
codominance
two alleles of a single gene are both expressed in heterozygotes
example of codominance:
a pure red and pure white cow produce a roan cow which is red with white spots
codominance in humans
MN blood groups in humans; characterized by antigen glycoprotein which is found on the surface of red blood cells.
codominant inheritance
distinct expression of gene products of both alleles
multiple allele
three or more alleles of the same genes which result in a mode of unique inheritance
example of multiple inheritance in humans
ABO blood groups
does the i allele produce antigen?
no
essential genes
genes that are absolutely required for survival, but mutations can be tolerated if heterozygous
what would happen if someone was homozygous recessive for an essential gene?
they would not survive
what makes a gene considered essential?
when the los of its function compromises the viability or fitness of the organism
lethal alleles
are of essential genes
recessive lethal alleles
result in homozygous recessive individuals and do not survive
dominant lethal alleles
presence of one copy of allele results in death
huntingtons disease
dominant autosomal allele, onset of disease in heterozygotes are delayed until adulthood. characterized by the degeneration of nervous system, demetica, and early death
homozygous lethal alleles
some may result in a distinctive mutant phenotype
lethal alleles in mice
mutant alleles behave dominantly to normal alleles to control coat color, behaves as homozygous recessive lethal allele
