Pedigree/Product Rule/ChiSquare Test/Weird Genetics

Pedigree Analysis

commonly used tool to determine inheritance patterns of human diseases

Recessive pattern

2 normal heterozygous individuals= 25% of offspring affected. 2 affected individuals will produce 100% affected offspring

Dominant

Affected individual will have inheritated the gene from at least 1 affected parent

Inheritance patterns in pedigrees

1. Autosomal recessive

2. Autosomal dominant

3. X-linked recessive

4. X-linked dominant

Autosomal recessive

Affected offspring will have two unaffected parents, two affected individuals have 100% affected children, trait occurs w/same frequency in both sexes, two unaffected heterozygotes= 25% affected children

Autosomal Dominant features

Affected offspring has 1 or both affected parents (can be altered by reduced penetrance) Affected individual w/ only one affected parent is expected to produce 50% affected offspring, two affected heterozygotes=25% unaffected offspring, trait occurs w/same frequence in both sexes

X-linked recessive

males more likely to exhibit the trait, mothers of affected males often have brothers or fathers who are affected, daughters of affected males will produce 50% affected sons

X-linked dominant

Doesn’t skip generations, males more likely to be affected, affected mothers 50% chance of passing the trait to daughters

Product rule

“and” order given, multiply the probabilities together

Binomial Expansion Equation

represents all of the possibilites for a given set of unordered events, n=total # of events, x= # of events in one category, p=individual probability of x q=individual probability of the other category

Chi square test

Used to see if observed data fits the expected data, if p-value is <0.05 the observed+expected data differ, O=observed data E=expected data

Simple mendelian inheritance

Single gene w/2 different alleles, alleles display a simple dom/rec relationship

Incomplete Penetrance

Dominant allele doesn’t influence the outcome of a trait in a heterozygote individual, in some cases, individuals carry the cominant allel but do not exhibit the trait

Expressivity

Degree to which a trait is expressed ex. polydactyly (high expression or low expression)

Environmental Effects on Gene expression

impact phenotype, temperature sensitive alleles

Wild-type allele

standard, most frequently occurring version of a gene found in a natural population of organisms

Genetic polymorphism

the presence of two or more variant forms of a specific DNA sequence or trait in a population, where the least common allele occurs at a frequency of at least 1%

Norm of reaction

the pattern or range of phenotypic expressions that a single genotype can produce across a continuous or discrete range of environments

Incomplete dominance

The heterozygote exhibits a phenotype that is intermediate between the corresponding homozygotes ex. pink phenotype after cross of red and white flowers

Codominance

Many genes have multiple alleles, ex ABO blood typing, Alleles I^A I^B are codominant

Type A genotype

I^AI^A or I^Ai

Type B genotype

I^BI^B or I^Bi

Type O blood type

ii

Type AB blood type

I^AI^B

X-linked genes

Certain traits are governed by genes on the sex chromosomes, a pedigree for x-linked diseases show that it is mosly males that are affected w/ their mothers as carriers

Lethal Alleles

Potential to cause the death of an organism, may produce ratios that seemingly deviate from Mendelian ratios (2/3 or 1/3)

Pleiotropy

genes have multiple effects, multiple effects of a single gene on the phenotype is pleiotropy ex. cystic fibrosis effects multiple organ groups

Gene interactions

two or more genes influence outcome of a single trait, ex epistasis

Epistasis

one gene masks phenotypic effects of alleles of another gene, ex. yellow labs ee gene masks the allel at 1st locus

Complementation

production of offspring with a wild type phenotype from parents that both display the same/similar recessive phenotype

Double recessive epistasis

9:7 two genes in recessive copies that produce mutant phenotype

Molecular mechanism for double recessive epistasis