Extensions and Modifications of Basic Principles Flashcards
What is incomplete dominance?
-BB, Bb and bb all differ phenotypically, Bb is intermediate between homozygous phenotypes
ex: flower colour (red,
white, pink-new phenotype)
-the phenotype of the heterozygote falls between the phenotypes of the two homozygotes
What does codominance mean?
-BB, Bb and bb all differ phenotypically but Bb exhibits phenotypes of both homozygotes
ex:blood type
-alleles are equal to the phenotypes
What is the P generation for incomplete dominance?
-two true breeding gametes are crossed
-one with two dominant alleles (PP-purple)
-one with two recessive alleles (pp-white)
What is the F1generation for incomplete dominance?
-mixture of alleles occurs and two heterozygous gametes are produced
-Pp (violet)
What is the F2 generation for incomplete dominance?
-two heterozygous gametes with mixed phenotype
-one homozygous dominant
gamete
-one homozygous recessive
gamete
-1:2:1 ratio
What happens when multiple alleles exist for a gene at a particular locus?
-some genes have many alleles some common some rare (form mutants of wild type gene)
-some are associated with certain breeds or variety of plants and animals
-wild type gene is the most common type in nature
What does population mean?
Multiple alleles may exist
What does individual/diploid mean?
-only two alleles coexist in each cell
What does > and = indicate in an allelic series?
-> dominance
-= incomplete dominance or codominance
-start of series is dominant over all alleles end is the most recessive allele
What is an allelic series?
-describes the dominance hierarchy of multiple alleles
-null=nonfunctional
-Hypomorphic=partial function
What does each allele signifiy in codominance of the ABO blood phenotype?
-gene I encodes transferase enzyme
-three alleles Ia Ib i
-A and Ab = over 90% of population
-B and O are more rare as they are determined by recessive alleles
What does Ia encode and transfer?
transferase, which transfers acetyl galactosamine
-phenotype is the protein inside the gene
What does Ib encode and transfer?
-transferase which adds galactose
-galactose has red blood cells
What does i encode and transfer?
-non-functional transferase
-transfers nothing to red blood cells
What are the possible genotypes for type A blood?
-IAIA or IAi
-i allele is frequent even though it is recessive therefore it is not technically rare
What are the possible genotypes for type B blood?
IBIB or IBi
What are is possible genotypes for type O blood?
ii
What is the genotype for AB blood?
-IAIB
-red blood cells have both a & b at the surface
-contain both acetylgalactosamine and galactose
-is an example of codominance as both alleles are fully expressed in the heterozygote
What is the wildtype allele?
-a functional enzyme or other protein is produced
-refers to the normal version of that gene or the most common in the wildtype
What is the loss of function allele?
-an enzyme or other protein is no longer being produces is produced at lower levels or is nonfunctional
-sometimes losing one copy affects the genotype
-some can function on one good copy
What is haplosufficiency?
-when wildtype alleles are dominant over the loss of function
-half as much protein is synthesized yet it is sufficient to achieve the wildtype phenotype
-still phenotypically normal but only half (haplo) is sufficient
What is a gain of function mutation?
-the mutant allele produces a protein that has increased (detrimental) function
It does not matter if you have one normal copy you are still affected
-dominant alleles isn’t normal and recessive allele isn’t mutation
Ex: Huntington’s disease
What does haploinsufficient mean?
-one loss of function allele causes a phenotype (dominant allele)
-in the heterozygote half as much protein is synthesized and this is not sufficient for a normal phenotype
ex: Tailless cats (Manx)
-has normal allele (tail) one copy of no tail allele and it takes over
What is recessive lethal alleles?
-essential genes when mutated lead to a lethal phenotype (embryos die)
-only expressed in the homozygote
-individuals homozygous for a Tay Sachs allele often die before the age of 3
tsts lethal, TSts not lethal, TSTS not lethal
Ex: Manx cats are tailless
What are dominant lethal alleles?
-can be expressed in both the heterozygote and the homozygote
-has to be rare
-Huntington disease can be considered Bb lethal, BB lethal bb not lethal
-typically comes after reproduction and becomes lethal later in time
What is the severe mutant phenotype?
-recessive amorphic loss of function allele does not produce a functional polypeptide (cannot do its job)
-1/2 functioning
-1/2 not functioning
What is the mild mutant phenotype?
-recessive hypomorphic loss-of-function allele produces a partially functional polypeptide (protein is misshapen slightly)
-1/2 functioning
-1/2 not functioning
What is a dominant severe mutant phenotype?
-dominant-negative allele produces a polypeptide that interferes with the wild-type polypeptide (single copy carries phenotype)
-the negative touches the normal protein and cant perform its job
