Lecture 4- Mutations, Epistasis and Pleiotropy

Question 1

Epistasis

Answer 1

• interactions between different genes
• when few genes influence one trait
• leads to an alteration of mendelian ratios
• typically the homozygous expression of an allele on locus 1 “overrides” the alleles at a 2nd locus
• We say locus 1 is “epistatic” to locus 2

Question 2

Wild type allele

Answer 2

-Most commonly found allele in a population
- Responsible for the “wild type” phenotype (wt)
-Is typically given the abbreviation with the Upper case letter
Ex. In peas, yellow color was the wild type allele, so it was denoted as G
- The mutant is usually denoted with the lower case letter
Ex. In peas, green color was the mutant allele/less common, so it was denoted as g

Question 3

null mutation

Answer 3

• A type of mutation in which all gene function has been lost
• This allows us to determine what that gene does not code for/is required for
• Also allows us to determine exactly what is needed for a gene to code properly/work?

Question 4

Complete dominance

Answer 4

• When one allele completely dominates over the other
• The other allele (the recessive one) is considered to be a null mutation is the case when the dominant allele is present
• This is basically what Mendel saw and what gives Mendelian ratios

Question 5

Incomplete dominance

Answer 5

• When the two alleles for a trait are both expressed, leading to an intermediate phenotype of the parent’s phenotypes, if the parents are both homozygous for different alleles
• If offspring inherits a copy of each different allele, it will show a new, intermediate phenotype different from if it had been homozygous for either allele.

Question 6

Co-dominance

Answer 6

• When two alleles of a gene can produce distinct, detectable gene products in heterozygous codominance
• An example is MN blood groups with A, B, and AB
• If you have an A, you will produce an A antigen on your red blood cells, if you have a B, you will produce a B antigen, and if you have both A and B, you will produce both antigens. There is also the O allele which doesn’t code for any antigen. The fact that O is also present makes blood types also an example of multiple alleles

Question 7

Pleiotropy

Answer 7

• When one gene controls multiple traits

Question 8

Complementation analysis

Answer 8

• Allow us to determine if two mutants are defective on the same gene to screen for mutant phenotypes
• Works by taking two mutants with the same phenotype and crossing them with one another to see if the mutations that lead to that phenotype are on the same gene or different genes
• If the cross results in the offspring showing the wild type phenotype, then we can conclude that the mutations are on different genes since there is a wild type allele that dominates over the mutant
• If the cross results in offspring that show the mutant phenotype, we can conclude that the mutation was on the same gene since the phenotype indicates there isn’t a wild type allele to dominate over either mutant allele
• If mutants are in same gene, the mutants “fail to complement”
• If mutants are on DIFFERENT genes, the mutants “complement”
• If still confusing, look at notes, or better, lecture slides, there is a really good diagram

Question 9

Hemizygous

Answer 9

• When you only have one copy of an allele so you can’t be homozygous or heterozygous
• This typically occurs in males with x-chromosome linked traits