Genetics 2

First Law: Segregation

1. Each individual organism possesses two alleles encoding a trait (diploid)

2. Alleles seperate when gametes are formed

3. Alleles seperate in equal proportions

Second Law: Independent Assortment

1. Alleles at different loci seperate independently

Dominant

For a given trait, Phen 1 is dominant to Phen 2 if F1 heterozygotes have Phen 1

Recessive

Phen 2 is recessive to Phen 1 if the F1 homozygote has Phen 2

Penetrance

Percentage of individuals with a particular genotype that express the phenotype expected of that genotype

Epistasis

Type of gene interaction in which a gene at one locus masks or supresses the effects of a gene at a different locus

• Caused by epistasis gene

Incomplete penetrance

A case in which some individuals possess the genotype for a trait but do not express the expected phenotype

Expressivity

Degree to which a trait is expressed

Gene interaction

Interaction between genes at different loci that affect the same characteristic

Hypostatic gene

Gene that is masked or supressed by the action of a gene at a different locus

Recessive epistasis

The recessive genotype at one locus masks the phenotype at a second locus

Dominant epistasis

A single copy of an allele at one locus masks the phenotype of a second locus

Duplicate recessive epistasis

Two recessive alleles at either of two loci are capable of suppressing a phenotype

Sex influenced

Characteristic encoded by autosomal genese that are more readily epressed in one sex (eg. higher penetrance in males than females)

Sex limited

Characteristic encoded by autosomal genes and expressed in only one sex

Cytoplasmic inheritence

Inheritence of characteristics encoded by genes located in the cytoplasm (inherited by only one parent)

Genetic maternal effect

Determination of the phenotype of an offspring not by its own genotype, but by the nuclear genotype of its mother

Genomic imprinting

Differential expression of a gene that depends on the sex of the parent that transmitted the gene

Complete dominance

Same phenotype is expressed in homozygotes (AA) and heterozygotes (Aa)

Incomplete dominence

Phenotype of the heterozygote is intermediate between the phenotypes of two homozygotes

Codominance

Allelic interaction where the heterozygote simultaneously expressed traits of both homozygotes

[n(n+1)/2]

Number of gentypes possible

Lethal allele

Allele that causes death of individual organism

Compound heterozygote

An individual who carries two different alleles at a locus that results in a recessiv phenotype

Gene interaction

Interaction between genes at different loci that affect the same characteristic

Chi-squared goodness of fit test

Statistical test used to evaluate how well a set of observed calues fit the expected values

Multiplication rule

States that the probability of two or more independant events occuring together is calculated by multiplying the probabilities of each individual events

• “And”

Addition rule

States that the proba ility of any two or more exclusive events occuring is calculated by adding the probabilities of the individual events

• “Or”

You can accept the alternative hypothesis (T or F)

False; never accept alternative hypothesis becuase we dont know what it is specifically; can only accept or reject null hypothesis

Test cross

Cross between an individual with an unknown genotype and an individual with a homozygous recessive phenotype (R_ x rr)

A priori

From the earlier

A posteriori

From the later

Backcross

Cross between F₁ genotype and either of the parental genotypes

Reciprocal backcross

Cross between both parents but reversing sexes of the parents to determine if a genotype is sex-linked or autosomal

Lyon Hypothesis

One of two female X chromosomes is inactivated

• Inactive female X chromosme known as “Barr body”