ch 5 gene interaction Flashcards
haplosufficiency
one copy of the normal gene is able to confer a normal phenotype (dominance)
haploinsufficiency
one copy of the normal gene is unable to confer the normal phenotype (recessive)
mutations of haplosufficient genes are
recessive
mutations of haploinsufficient genes are
dominant
complete dominance
alleles which, when combined in the heterozygote show a phenotype indistinguishable from one of the homozygotes
incomplete dominance
alleles which, when combined in the heterozygote show a phenotypic intermediate between the homozygotes
ex. snapdragons: red and white parents make pink progeny
codominance
alleles which, when combined in the heterozygote show phenotypic characteristics of both homozygotes
ex. blood groups: A, B, and AB
antigen/antibody
ex. blood type A = antigen A on blood cells, anti-B antibodies
blood type AB has antigen A and B, no antibodies
blood type O has no antigens, Anti-A and anti-B antibodies
sickle cell anemia
tropical disease caused by a mutation in the gene coding for hemoglobin
HBa/HBa - no anemia
HBs/HBs - anemic, sickle cell shaped
lethal alleles
an allele whose expression results in the death of the individual expressing it (may be recessive or dominant)
pleiotropic mutation
a mutation that affects several different phenotypic characteristics
ex. Ay in mice affects both coat color and survival
penetrance
the percentage of individuals who develop the phenotype associated with their genotype
(all have the same genotype)
100% penetrant at birth
genotype represents phenotype
ex. cystic fibrosis
expressivity
the extent to which a given phenotype is expressed in an individual
(all have the same genotype, degree to which they express phenotype is different)
biosynthetic pathways
series of steps
complete medium
has everything it needs to grow
prototroph
an organism that will survive on minimal medium
- wild type
auxotroph
an organism that will not survive on minimal medium, but whose growth depends on supplementation of medium with a specific substance
biosynthetic pathways pair-wise feeding rule
downstream mutants feed upstream mutants
complementation test
a test for determining whether two mutations are in different genes (they complement) or the same gene (they fail to complement)
- cross the two recessive mutants together, phenotype of progeny will differ if the mutants represent two alleles of one gene or mutation in two different genes
if the mutations are alleles on the same gene:
the two mutation fail to complement, therefore they represent two alleles of the same gene
P: a-1/a-1 B+/B+ x a-2/a-2 B+/B+
F1: a-1/a-2 B+/B+
results in an auxotroph
if mutations are in different genes
the two mutations complement one another, therefore they are in different genes
P: a-1/a-1 B+/B+ x A+/A+ b-1/b-1
F1: A+/a-1 B+/b-1
results in a prototroph
rules for a complementation test
- can only be done with recessive mutations
- two different genes? progeny will be wild type = complementation
- two alleles of the same gene? progeny will be mutant = no complementation
heterokaryon
a cell composed of different nuclear types (multiple nuclei) in a common cytoplasm (result of fusing two haploid cells)
4 types of gene interactions
- complementary gene action
- epistasis
- suppression
- redundancy
complementary gene action ratio
9:7
complementary gene action
harebells example
production of blue pigment is controlled by genes w1+ and w2+
last step gives blue pigment, therefore all other intermediates are white
recessive epitasis ratio
9:3:4
epistasis
the phenotype of a mutant allele at one gene overrides the phenotype of a mutant allele at another gene, such that the double mutant has the same phenotype as the first mutant
blue and magenta flower example
intermediates have different phenotypes
dominant epistasis ratio
12:3:1
suppression ratio
13:3
suppression
a mutation in one gene can cancel the effect of a mutation in a second gene, resulting in a wild type phenotype
genetic redundancy ratio
15:1
genetic redundancy
two independent genes that produce the same phenotypic effect when present individually or when present together
3 types of haploid gene interactions
epistasis
suppression
redundancy
