Genetics and Molecular Biology Flashcards

Flashcards for Genetics and Molecular Biology lecture review.

Mendel's experiments with peas

Peas had different traits (alleles) for certain phenotypes.

Mendel's theory

Offspring gets one allele from one parent and one allele from the other parent.

Key in Mendel's experiments

Test-crosses reveal heterozygous individuals.

Advantage Mendel had by using peas

Traits (phenotypes) investigated were dominant or recessive.

Advantage Mendel had by using peas

Genes were not linked (close together on the same chromosome).

Advantage Mendel had by using peas

Phenotypes were defined by a single allele.

Conventional symbols used in pedigrees

Males, females, sex unspecified, unaffected, diseased, multiple progeny, mating line, generation, sibship line, deceased, consanguineous mating, line of descent, individual number within generation.

Key assumptions when analyzing pedigrees: Rare in population

One can assume that people who marry into the family do not carry the mutation.

An unaffected individual cannot have any alleles of a dominant trait.

A single allele of a dominant trait causes an individual to be affected.

Individuals marrying into the family are assumed to have no disease alleles.

The trait is rare in the population.

An unaffected individual can be a carrier (have one allele) of a recessive trait.

Two alleles of a recessive trait are required for an individual to be affected.

When a trait is X-linked

A single recessive allele is sufficient for a male to be affected.

X-linked genes transmissions

A father transmits his allele of X-linked genes to his daughters, but not his sons. A mother transmits an allele of X-linked genes to both her daughters and her sons.

Examples for an autosomal dominant trait: Huntington’s disease

Affects both sexes; every affected person has an affected parent; approximately 1/2 of the progeny is affected.

Examples for an autosomal recessive trait: Albinism

Affects both sexes; most affected persons have unaffected parents; approximately 1/4 of the progeny of heterozygotes are affected; parents of affected individuals are often close relatives.

Special case for calculating likelihoods: Likelihood is 2/3

Two out of three combinations are heterozygous (= carriers).

Monohybrid crosses: The principle of incomplete dominance

The offspring doesn’t look like either parental strain but a mixture of both.

Important aspect of flower color as an example for incomplete dominance

We can directly infer the genotype from the phenotype.

Important aspect of lentil seed structure as an example of co-dominance

We can directly infer the genotype from the phenotype.

Incomplete dominance and codominance – cases in which the phenotype of heterozygotes is

Different than that of either type of homozygote.

Incomplete dominance describes alleles where the

Heterozygote has a phenotype in between that of either homozygote.

Codominance describes alleles where the

Heterozygotes for codominant alleles have the phenotypes associated with both homozygotes

Wild-type alleles

Alleles with a frequency of greater than 1% in the population.

Mutant alleles

Rare alleles with a frequency of less than 1% in the population.

Monomorphic gene

A gene with only one common, wild-type allele.

Polymorphic gene

A gene with many wild-type alleles.

Alleles are not inherently dominant or recessive, it is always

Related to a second allele that it is compared to.

Dominance series of multiple alleles

Although each individual has only two alleles of a gene, many alleles of the gene may exist in the population.

Mechanism of alleles of dihybrid crosses that generate a new phenotype – they have additive interactions

Encode enzymes that change pigmentation.

Alleles are not necessarily always dominant -

It is always relative to the allele that you compare it to.

Incomplete Dominance

Phenotype in between the parental phenotypes for heterozygous.

Co-Dominance

Phenotype of heterozygous individual shows both features of the parents.

Additive interactions

Genes work in the same pathway which can change the phenotype but 9:3:3:1 ratio still holds true.

Pleiotropy

A gene may affect more than one phenotype.

Epistasis

An allele of one gene hides the effects of different alleles at a second gene.

Epistatic gene

Gene that is doing the masking.

Gene B

Required for depositing Eumelanin.

Locus heterogeneity

Mutation in any one of two or more genes results in the same mutant phenotype.

Complementation test

Method of discovering whether two mutations are in the same gene or in separate genes.

Penetrance

The fraction of individuals with a particular genotype who display the genotype’s characteristic phenotype.

Expressivity

The degree to which an affected individual displays the phenotype associated with that individual’s genotype.