BSCI222 Extensions to Inheritance

how to tell if a trait is Mendelian or not?

use Chi square analysis

= Sum of (O - E)^2/E

- do for all possible genotypes and sum them up

complete dominance

heterozygotes have same phenotype as homozygotes (Mendelian)

wildtype allele

most common allele variant in a population

- denoted as __+

non-wildtype allele

least common allele variant in a population

- denoted as __-

Incomplete dominance

heterozygotes display intermediate phenotype

1:2:1 phenotypic ratio

- example: mix of colors

Codominance

heterozygotes show both phenotypes at once

- example: colors or blood type

Pleiotropy

single gene determines multiple distinct and sometimes unrelated phenotypes; ONE GENE CODES FOR MANY THINGS

- example: albinism causes loss of pigmentation in many areas

can pleiotropy alleles be recessive or dominant?

they can be both regarding specific genes

Example: achondroplasia, allele is dominant; if two dominant alleles are inherited, makes it lethal (so recessive for lethality)

Lethal allele

allele that causes death early in development

- anyone in progeny with lethal allele are not observed in offspring ratios

More than two alleles

multiple variants of alleles are present in a population, each individual still only has 2, but there is greater selection

penetrance

the percentage if individuals having a particular genotype that express the expected phenotype

- observed/expected

expressivity

degree to which a phenotype is expressed from the same genotype (not based on heterozygous genotype like in incomplete dominance)

sex-influence traits

for same genotype, phenotype is expressed more or more fully in one sex

sex-limited traits

phenotype is expressed only in one sex, occurs despite being autosomal trait

phenotype expression affected by environment

phenotype expression or prevalence is affected by an environmental condition

conditional phenotype

plays into environmental expression: allele/genotype determines susceptibility to developing a particular phenotype

relationship/difference between gene expression and penetrance

penetrance is how many express it, expression is how much it is expressed

ways that alleles for more than one gene affect phenotypes

1. heterogenetic traits

2. polygenetic traits

3. novel phenotypes

4. epistasis

heterogenetic traits

traits for which non-wildtype phenotypes can be caused by many genes due to dominance variation at different loci

complementation test

used to determine the location of recessive, non-wildtype alleles occur at the same locus or are coded by 2 separate alleles at 2 different loci

what are the two hypotheses for complementation test?

1. alleles a and b both encode for the gene and occur on separate loci

2. alleles a and b both encode the gene but occur on the same loci

how to test hypothesis 1 of complementation test?

cross two individuals who have two recessive, non-wild type alleles and two wild type alleles at different loci and observe gamete outcomes

example: ab+/ab+ X a+b/a+b = a+ab+b gametes

how to tell if hypothesis 1 of complementation test is correct?

wildtype phenotype is produced, then alleles are complementary (occur at different loci)

how to test hypothesis 2 of complementation test?

cross two individuals who both have two different alleles for the same gene (more than 2 alleles) which occurs on the same loci

example: a/a X b/b = ab gametes

how to tell if hypothesis 2 of complementation test is correct?

nonwild type phenotype is produced

polygenetic traits

traits which phenotypes are encoded by genes at many locations, results in wide distribution of phenotypes

example- skin color, height

novel phenotypes

two genes act independently of each other and when fusion of gametes occurs it results in novel (new) phenotypes

epistasis

gene interaction where one gene masks or suppresses another gene at a different locus

epistatic gene

does the affecting in epistasis

- in labs = ee locus affects coat color

hypostatic gene

gets affected by the epistatic gene

- in labs = loci which does fur color can be controlled by another gene at a different locus

dominant epistasis ratio and number of phenotypes

12:3:1 and 3 phenotypes

Recessive epistasis ratio and number of phenotypes

9:3:4 and 3 phenotypes

recessive epistasis

homozygous recessive genotype at the epistatic gene will cause masking of hypostatic gene

dominant epistasis

dominant genotype at the epistatic gene will cause masking of hypostatic gene

duplicate dominant epistasis

dominant allele at either of the two genes will hide the other gene

duplicate recessive epistasis

homozygous recessive genotype at either gene will cause masking of the other gene

duplicate dominant epistasis ratio and number of phenotypes

15:1 and 2

duplicate recessive epistasis ratio and number of phenotypes

9:7 and 2