topic 7 biology: genetics, populations, evolution and ecosystems

define genotype

all of the alleles that an organism carries on it chromosomes

define a dominant allele

an allele that will always be expressed in the phenotype

define multiple alleles

more than two alleles for a single gene

define autosomal linkage

when genes that are located on the same autosomal chromosome (not the X or Y sex chromosome) are likely to be inherited together

define phenotype

an individual's observable traits

define homozygous

a pair of homologous chromosomes carrying the same alleles for a single gene

define heterozygous

a pair of homologous chromosomes carrying two different alleles for a single gene

define a recessive allele

an allele only expressed if no dominant allele is present

define codominance

a type of inheritance in which two alleles are expressed, creating a blend of the two characteristics/phenotypes

define sex-linkage

a trait which is coded for by a gene on a sex chromosome

define epistasis

the interaction between two non-linked genes which causes one gene to mask the expression of the other phenotype

define monohybrid

genetic inheritance cross for a characteristic determined by one gene

define dihybrid

genetic inheritance cross for a characteristic determined by two genes

what is chi squared used for

It can be used to determine whether there is a significant difference between the frequency you expect and the frequency you observe

gene 1
allele A: dominant and inhibits the enzyme needed to make green or yellow fruit
allele a: recessive and enzyme functions normally to make green or yellow fruit
gene 2
allele B: dominant and enzyme functions normally to make yellow fruit
allele b: recessive and enzyme is non-functional so cannot make yellow fruit
what fruit colour would you expect Aabb and aaBB to have?

Aabb: white
aaBB: yellow

define gene

small section of dna which codes for a polypeptide

what is the ratio in a dihybrid cross, if two heterozygous parents for both genes are crossed (without autosomal linkage or crossing over in meiosis)

9:3:3:1

what happens during crossing over in meiosis

results in new combinations of alleles in the gametes

what is the importance of crossing over in autosomal linkage

autosomal linkage is only possible if crossing over occurs during meiosis to make new combinations of gametes

define gene pool

all of the alleles of all the genes within a population at one time

define population

all the individuals of one species in one area at one time

define allele frequency

the proportion of an allele within the gene pool

what are the assumptions for the hardy weinberg principle