Lecture 7 - Extenstions to Mendel's Rules, Cont. Flashcards
What is epistasis?
L7 S27
When one gene masks or influences the effect of another gene.
What are the different types of epistasis?
L7 S27-30
Recessive:
-presence of two recessive alleles in a certain gene that eliminates expression of a phenotype of another gene (Bombay phenotype in blood)
Dominant:
-requires presence of at least a single dominant allele in one gene that eliminates expression of phenotype of another gene
Duplicate recessive:
-requires presence of at least a single dominant allele in two different genes to express a certain phenotype
What is complementation?
L7 S37
When two genes at different loci have the same homozygous recessive mutant phenotype but produce the wild-type phenotype when crossed.
Ex. AAbb and aaBB both result in the same mutant characteristic but when crossed they produced AaBb which gives the wild type characteristic.
What is pleiotrophy?
L7 S43
When one gene affects the outcome of 2 or more unrelated phenotypes.
ex. Sickle cell anemia, mutated hemoglobin also results in blindness, liver failure, and MIs.
What does it mean for a trait to be sex-influenced?
L7 S50
When a trait that is located on an autosome but its expression is determined by the organisms sex.
ex. The same gene for beardedness in goats (and humans) is dominant in males but recessive in females
What does it mean for a trait to be sex-limited?
L7 S52
When a trait that is located on an autosome can only be expressed in a certain sex but not in the other, regardless of genotype.
What is genomic imprinting and the maternal effect?
L7 S53
Certain regions of the chromosomes are methylated, and therefore, inactivated. Leaving only the copy on the other chromosome that is actice
In maternal effect this occurs in certain regions of chromosomes inherited from the mother. This leaves only the genes in those regions on the chromosome from the father that are active.
ex. Igf2 (insulin-like growth factor 2)
What defines an epigenetic trait?
L7 S57
A heritable phenotype that results from alterations to a chromosome that does not change the DNA sequence
ex. DNA and histone methylation
What is anticipation and how does it relate to disease?
L7 S59
When a genetic trait becomes more strongly expressed or is expressed earlier as it is passed through generations.
Typically occurs due to expansion of unstable regions of DNA containing trinucleotide repeats.
ex. Huntington’s (CAG repeat) and Fragile X (CGG repeat)
