chapter 4 Flashcards
What are the types of gene interactions?
More than 2 alleles per gene, dominance can be incomplete, multiple genes can affect one trait, interaction with nongenetic factors
What is the molecular basis of dominance?
When there are recessive and dominant genes and the dominant one mask the recessive
The dominant/recessive relationship depends on what?
The protein being produced
What is haplosufficency?
one copy of it is enough for normal function in heterozygotes
What is haploinsuffiency?
one copy of it is not enough for normal function
What is an example of a recessive mutant allele?
Wild-type allele (R+) produces enzyme; mutant allele (r) doesn’t. (haplosufficent)
What is an example of a dominant mutant allele?
Mutant allele (T2) produces insufficient enzyme; heterozygous individuals are mutant (haploinsufficient).
What are the loss of function mutations?
Null (amorphic) and leaky (hypomorphic)
What is a null mutation?
the complete loss of function
What is a leaky mutation?
the partial loss of gene function
What are double negative mutations?
Mutant protein spoils multimeric complex
What are the gain of function mutations?
hypermorphic and neomorphic (usually dominant)
What is hypermorphic?
increased activity in genes compared to normal
What is neomorphic?
mutations acquire novel gene activities not
found in the wild type
What are the types of dominance?
Incomplete, codominance, and multiple alleles
What is incomplete (partial) dominance?
Heterozygote shows intermediate phenotype (e.g., flower color)
What is codominance?
Both alleles fully expressed (e.g., ABO blood group)
What are multiple alleles?
Allelic series(order of dominance among alleles), like the C-gene for mammalian coat color (C > c^ch > c^h > c).
What are the alleles for ABo blood type?
I^A, I^B and i
(I^A and I^B are completely dominant over i but are codominant with each other)
The c^h allele is what?
temperature sensitive
How is blood type determined?
by an antigen-antibody reaction on a microscope slide
Blood group antigens are based on what?
sugar modifications on the H antigen
What is a recessive lethal allele?
Homozygous individuals die (e.g., yellow coat color in mice)
What are lethal alleles?
They are recessively inherited and they can cause single gene mutations to kill an organism
What are embryonic lethal allele?
They are detected by missing progeny classes.
What is delayed onset lethal alleles?
Some lethal alleles act after reproduction (e.g., Huntington’s disease)
What is complete penatrance?
If a given genotype always produces the same phenotype
What is incomplete penetrance?
when some people with a disease-causing mutation (change) in a gene develop the disease while others don’t
What is variable expressivity?
The degree to which a trait is expressed varies.
What are sex limited traits?
Only expressed in one sex (e.g., milk production in mammals).
What are sex influenced traits?
Expression varies between sexes (e.g., beards in goats).
What is nonpenetrance?
An organism that does not produce the phenotype generally associated with the genotype
What is fully penetrant?
When the genotype is always expressed in the
phenotype
What is an example of incomplete penetrance?
Polydactyly - an autosomal dominant condition in which affected individuals have more than five fingers and toes
What is gene environment interaction?
the influence of the environment on the expression of genes and on the phenotypes of organisms
What is pleiotrophy?
the alteration of multiple distinct traits by a
mutation in a single gene. ex: drosophila and sickle cell
What is gene interaction?
It refers to the collaboration of multiple genes in producing a single phenotypic trait or group of related traits.
What are anabolic pathways?
Biosynthesis of complex compounds.
What are catabolic pathways?
Degradation of complex compounds.
true or false. Signal Transduction and Developmental Pathways also involve gene interactions.
true
Who proposed the one-gene-one enzyme hypothesis?
Beadle and Tatum after studying Neurospora crassa.
Each gene controls the production of what?
a single enzyme, affecting a specific step in a metabolic pathway
What was Horowitz’s experiment about?
The genetic dissection of met− mutants in Neurospora.
What is the purpose of Horowitz experiment?
To determine steps in the methionine biosynthesis pathway and identify steps affected by mutations.
What was the results of Horowitz experiment?
To identify the specific steps blocked by mutations based on growth patterns.
Do all genes code for enzymes?
no, some produce structural, regulatory, or transport proteins.
Som genes produce what instead of proteins?
RNA
What protein needs to combine with others to function
B-globin
What is epistasis?
A type of gene interaction where one gene’s mutation can prevent the production of a phenotypic outcome, altering expected ratios in offspring.
Why can phenotypic rations deviate from mendel’s classic 9:3:3:1 ratio? (6 ways)
Because of gene interaction
What is the ratio for no interaction?
9:3:3:1
Cross between blue budgies (BByy) and yellow budgies (bbYY) leads to F1 with wild-type green feathers (BbYy).
What is the ratio for Complementary Gene Interaction?
(9:7)
when genes work in tandem to produce
a single product. crossed two pure-breeding strains of white-flowered sweet peas
What is the ratio for Duplicate Gene Action?
(15:1)
they encode the same product. A dominant allele at either locus gives rise to a wild-type phenotype
What is the ratio for Dominant Gene Interaction?
9:6:1
Plants that have one or two dominant alleles for just one of either of the genes will have round fruit and those with only recessive alleles of both genes will have long fruit
What is the ratio for Recessive Epistasis?
9:3:4
homozygosity for the recessive allele at one locus will mask the phenotypic expression of
the alleles at a second locus
What is the ratio for Dominant Epistasis?
12:3:1
a dominant allele at one locus will mask the phenotypic expression of the alleles at a second locus
What is the ratio for dominant suppression?
13:3
a dominant allele at one locus completely suppresses the phenotypic expression of the
alleles at a second locus
