Extensions to Mendel's Rules I - Lecture 6 Flashcards
(24 cards)
Dominance
The heterozygote possessed the same phenotype as one of the homozygotes
Incomplete Dominance
Phenotype of heterozygote is intermediate (falls within the range) between the phenotypes of the two homozygotes
1:2:1 phenotypic and genotypic ratio for simple crosses
Codominance
Phenotype of heterozygote includes phenotype of both homozygotes
Ex. MN blood type
Penetrance
Percentage of individuals having a specific genotype that express the expected phenotype
Expressivity
The degree to which a character is expressed
Lethal Allele
Causes death at an early stage in development - often before birth
Some genotypes may not appear among the progeny
2:1 ratio
Multiple alleles
More than two alleles present within a group of organisms
Inheritance may be same, but variety of possible genotypes and phenotypes.
Ex. is feather pattern of mallard ducks, ABO blood group
Gene interaction that produces novel phenotypes
Gene interaction takes place when genes at multiple loci determine a single phenotype. Frequently, genes exhibit ind assort. but do not act independently in their phenotypic expression.
Epistasis
The masking of the expression of one gene by another gene at a different locus
Epistatic gene
Does the masking
Hypostatic gene
Is masked
Recessive Epistasis
Homozygous recessive genotype masks the effects of the hypostatic gene
Ex. Coat color in labrador
Dominant Epistasis
Homozygous dominant or heterozygous genotypes mask the effects of the hypostatic gene
-only a single copy of an allele is required to inhibit the expression of the allele at a different locus
Ex. Two loci for fruit color in summer squash
Duplicate Recessive Epistasis
Presence of either of two homozygous recessive genotypes will mask hypostatic gene
-two recessive alleles at either of two loci are capable of suppressing a phenotype
Complementation Test
Determining whether mutations are at the same locus or at different loci
Parents that are homozygous for different mutations are crossed.
Complementation has occurred if an individual possessing two mutant alleles has a wild-type phenotype and is an indicator that the mutations are nonallelic genes.
Incomplete Penetrance
The genotype does not always produce the expected phenotype
If an F1 eggplant is used in a testcross, what proportion of the progeny from this cross will be all white?
1/2
How do complete dominance, incomplete dominance and codominance differ?
With complete dominance, the heterozygote expresses the same phenotype as that of one of the homozygotes. Incomplete, hetero has a phenotype that is intermediate. Codominance the hetero has pheno that is both of homo.
How does incomplete dominance differ from incomplete penetrance?
In incomplete dominance, the hetero is intermediate to homo; in incomplete penetrance, some individuals do not express the expected phenotype
A cross between two green corn plants yields 2/3 progeny that are green and 1/3 progeny that are white. What is the genotype of the green progeny?
Ww
How many genotypes are present at a locus with five alleles?
15
How does gene interaction differ from dominance between alleles?
Gene interaction is interaction between genes at different loci. Dominance is interaction between alleles at a single locus.
A number of all white cats are crossed and they produce the following types of progeny: 12/16 all white, 3/16 black and 1/16 grey.
What is the genotype of the black progeny?
A_bb
Brindle (tiger-striped appearance) is a recessive trait in dogs. What types of crosses would you carry out to determine if genes are at the same locus?
Cross a homo bulldog for brindle with a homo chihuahua homo brindle. If the two brindle genes are allelic, all of the offspring will be brindle. bb x bb = all bb
If, on other hand, it is due to recessive genes at different loci, then none of the offspring will be brindle.
a+a+bb x aab+b+ = a+ab+b
