Chapter 3 Flashcards
1) When an F1 hybrid does not resemble either pure breeding parents
2) Intermediate phenotype where both parental alleles contribute to the phenotype
3) 1:2:1 phenotypic ratio exactly reflects the genotype can ratio
4) recessive may not be expressing a viable protein (snap dragons)
Incomplete dominance
1) Both traits show up equally in the heterozygotes phenotype in the F1 cross (spotted dotted lentils) 2)1:2:1 in the F2 generation 3) blood group alleles (a and b sugars)
Codominant
Novel phenotype determined by 2 or more genes, or from interactions between genes and the environment (green lentils) 9:3:3:1
Multifactorial
A given gene may have more than two alleles.
Sugar adding enzyme in blood
Multiple alleles
Alleles are listed in order from most to least dominant
Dominance series
Chance alterations of the genetic material that are spontaneous in nature
Mutations
Percentage of the total number of gene copies
Allele frequency
The most common alleles of each gene In a population, or if present, at a frequency of greater than 1%, often designated +
Wild type
Rare allele
Mutant allele
A gene with only one common wild type allele,
Agouti,
More than 99% frequency
Monomorphic
Some genes have more than one common allele,
ABO blood type system
Polymorphic
High frequency alleles of a polymorphic gene,
ABO blood type system
Common variants
When a single gene determines a # of distinct and seemingly unrelated characteristics,
Mutations can influence multiple biochemical processes
Plieotropy
An allele that negatively affects the survival of a Homozygote, 1:2 phenotypic ratio indicates a missing genotype
Recessive lethal alleles
Extension: Incomplete dominance or codominance,
On crossing F1, Phenotypes are 1:2:1,
Unlike either Homozygote
Extension to complete dominance
Extension: multiple alleles
Multiplicity of Phenotypes
Series of 3:1 ratios
Extension to two alleles
Extension: recessive lethal alleles
2:1 instead of 3:1
Heterozygotes survive but may have visible Phenotypes
Extension to all alleles are equally viable
Extension: Plieotropy,
One gene affects Several traits, affected several ways depending on dominance relationships, Different ratios
Extension to one gene determines one trait
Two genes working in tandem To produce purple sweet pea flowers, a dominant allele of each gene (producing white flowers) must be present (in opposite parents) to produce that color
9:7 in the F2; A-B- is the only purple phenotype
Complementary gene action
A gene interaction in which the effects of an allele at one gene hide the effects of alleles at another gene. Can be either dominant or recessive.
Epistasis
Homozygous for a recessive allele of the second gene is required to hide the effects of another gene to cause a masking phenomenon
9:3:4 in Chocolate labs
Recessive Epistasis
Dark color in dog coats
Eumelanin
Light color of dog coats
Pheomelanin
Epistasis when the dominant allele of one gene hides the effects of another gene
Chickens
Dominant Epistasis
15:1
Specify nearly identical proteins that perform the same function
Redundant gene action
One dominant allele of each of 2 genes is Necessary to produce phenotype
9:7
Sweet pea flowers
Complementarity
Homozygous recessive of one gene masks both alleles of another
9:3:4
Labrador retriever coat color
Recessive Epistasis
Dominant allele of one gene masks the effects of both alleles of another gene 12:3:1
Summer squash color
Dominant Epistasis 1
Dominant allele of one gene hides effects of dominant allele of other gene
13:3
Chicken feathers
Dominant Epistasis 2
Only one dominant allele of either of 2 genes is necessary to produce a phenotype
15:1
Maize leaves
Redundancy
A mutation at any one of a number of genes can give rise to the same phenotype, deafness
Heterogeneous trait
When what appears to be an identical recessive phenotype arises in two separate breeding lines. Are mutations in the same gene responsible for the phenotype in both lines? If offspring receiving the two mutations (one from each parent) expresses the wild type complementation has occurred
Complementation test
Dominant allele which also acts as a recessive lethal in mice
Agouti
OAC, case of complementation, aaBB x AAbb
Ocular cutaneous albanism
How members of a population with a particular genotype show the expected phenotype, %, occourance
Penetrance
Degree or intensity with which a particular genotype is expressed in a phenotype, can be variable (retinoblastoma) or unvarying (like peas) seriousness of disease
Expressivity
Alter the Phenotypes produced by the alleles of other genes, subtle, T mutation in mice
Modifier genes
Environment acting on phenotype, temperature sensitive enzyme
Siamese variant
Temp sensitive shibire gene in fruit flies, lethal only under certain conditions
Conditional lethal
Conditions under which an organism remains viable
Permissive conditions
Conditions that are lethal
Restrictive conditions
A change in phenotype similar to that of mutant genes, not heritable, thalidomide, pku
Phenocopy
Discrete trait like pea plant height
Discontinuous trait
Continuous phenotypic variation, skin color, height in humans, polygenic
Continuous trait
Population in which individuals differ in alleles of many genes
Outbred population
Homozygotes may survive beyond birth but die before passing on a disease allele (Tay Sachs)
Delayed lethality
Homozygote may pass on recessive lethal alleles (cancer)
Late-onset diseases
All ____________ early lethal mutant alleles must be new mutations.
Dominant, they have never been passed on.
Plieotropy, recessive lethality, different dominance relations. Hb alpha (wild type) and Hb beta genes. 400 mutants Hb beta s causes sickle-cell.
Sickle-cell anemia
Hb beta a and Hb beta s show dominance recessive (shape), codominance (shape at high altitudes), and incomplete dominance (concentration of cells), and dominance recessive (susceptiblity to malaria).
relationships in sickle cell-anemia
The allele that does the masking is ___________ to the gene that is being masked (the hypostatic gene).
Epistatic
Gene _____ determine black and chocolate coat color in labs.
B alleles
Recessive allele __ of __ gene is Epistatic to ___ and determines yellow coat color In labs.
e, E, B
9:3:4 ratio in the ____ indicates __________ Epistasis.
F2, recessive
_______ ________ in humans causes rare Bombay blood type.
Recessive Epistasis
H, H__
Gene for substance _____ is epistatic to the ABO gene. All type A, type AB, type B, and type O are ____.
