Topic 7

locus/loci

the specific, fixed position on a chromosome where a particular gene or genetic marker is located.

alleles

versions of a gene that exist at a given locus. Can be dominant or recessive, influencing the trait expressed in an organism.

homozygous

having two identical alleles for a specific gene.

heterozygous

having two different alleles at a given locus.

what makes a mutant allele faulty

it makes a protein that does not function properly (loss of function)

genotype

the genetic makeup of an individual, including the alleles for a specific gene.

phenotype

the observable physical or physiological traits of an organism, determined by its genotype and environmental influences.

which phrase best describes sister chromatids

two chromosomes having an identical DNA sequence

which phrase best describes two homologous chromosomes

two chromosomes having the same genes in the same order but with potentially different alleles

which of the following is a result of nondisjunction

a change in the normal ploidy of a cell

which is correct about a crossing over event in meiosis

it involves 2 out of 4 chromatids of a tetrad

the frequency of progeny phenotypes in a test cross

equals the frequency of the tested gametes

Law of Segregation

• First Mendelian Law

• alleles of a gene separate independently from each other during transmission from parent to offspring (meiosis)

• 3:1 distribution

Law of Independent Assortment

• second Mendelian Law

• alleles of 2 or more genes (loci) segregate independently during transmission from parent to offspring

• In the F2 generation 2 new recombinant phenotypes appear

• 9:3:3:1

Test Cross

A genetic cross between a homozygous recessive individual and an individual with an unknown genotype, used to determine the genotype of the latter by analyzing the phenotypes of the offspring.

incomplete dominance

• one allele for a specific trait is not completely expressed over its paired allele in F1 hybrids

• results in a third phenotype with a combination of the phenotypes of both alleles

Codominance

• cross between organisms with 2 different phenotypes that produces offspring with a third, different phenotype

• both of the parental traits appear together

• coat colours in cattle, dogs, horses

Pleiotrophy

determination of more than one characteristic by a single gene. This phenomenon occurs when one gene influences multiple, seemingly unrelated phenotypic traits.

Epistasis

A genetic interaction where one gene suppresses or enhances the expression of another gene. This can affect multiple traits and lead to variations in phenotypes.

polygenic inheritance

• the determination of a characteristic by multiple genes, where each gene contributes to the phenotype in a cumulative manner.

• phenotypes fall in a bell curve

gene linkage

the tendency of genes located close to each other on a chromosome to be inherited together, affecting the assortment of traits.

Recombination frequency (RF)

• the percentage of offspring exhibiting a recombinant phenotype compared to the total number of offspring. It reflects the likelihood of crossover events between genes during meiosis.

in what situation would you have a lower RF and tighter gene linkage

2 genes located close together, reducing the chances of crossing over

gene linkage mapping

a method used to determine the distance between genes on a chromosome based on recombination frequencies. (1% recombination = 1centiMorgans)

s*x linkage

the association of genes on sex chromosomes, leading to inheritance patterns that differ between males and females.