2.15-2.18 : gene expression and inheritance

amniocentesis

sampling the amniotic fluid to determine the sex of the foetus or any abnormalities that may be present during development

carrier

a person or other organism that has inherited a recessive allele for a genetic trait or mutation but does not usually display that trait or show symptoms of the disease, they can pass the allele onto their offspring, who may then express the genetic trait

chorionic villus sampling

sampling the placenta to test for any genetic disease that may be present in the developing foetus

codominant

when both alleles for a gene in a heterozygous organisms equally contribute to the phenotype

cystic fibrosis (CF)

an autosomal recessive genetic disorder which causes the production of excess thick mucus

directional selection

a type of selection that favours one extreme phenotype and selects against all other phenotype

disruptive selection

a type of selection where multiple extreme phenotypes are advantageous for different reasons and the average phenotype is selected against, this leads to speciation and changes in the population

dominant trait

a trail which is present if an individual has at least one copy of the allele

founder effect

a type of genetic drift in which a few individuals of a species are geographically isolated from the population and form a new colony, this results in smaller gene pools and an increased frequency of rare alleles

genetic drift

a gradual change in allele frequencies in a population over time due to chance

genotype

the genetic makeup of an organism

hardy weinberg principle

a principle that states that the frequency of alleles in a population will not change over time unless evolutionary factors are present, it can be used to calculate the frequencies of the other two genotypes when given the frequency of one genotype

heterozygote

an organism which has two different versions of the same gene

homozygote

an organism which has two of the same versions of a gene

incomplete dominance

a type of inheritance where a dominant allele does not completely mask the recessive allele and so the trait produced is a combination of both alleles

gene mutation

a change to at least one nucleotide base in DNA or the arrangement of bases, gene mutations can occur spontaneously during DNA replication and may be beneficial, damaging, or neutral

phenotype

the observable physical characteristics of an organism which is based on both the genotype and enviromental influence

population bottlenecks

a significant reduction in population size which reduces the genetic diversity of a population

pre- implantation genetic diagnosis (PGD)

a method used to diagnose disease before implantation of the embryo into the uterus

prenatal testing

testing performed before childbirth to determine the overall health of the developing foetus

recessive trait

a trait which is only present when an individual has two copies of the allele and can be masked by a dominant allele

red green colour blindness

a perception defect that is caused by a mutation on the x chromosome

selective pressures

factors which lead to selection and survival of the fittest which drives evolutionary genetic changes over time

stabilising selection

a type of selection which selects against extreme phenotype and produces a population with average phenotype

x chromosome

a sex chromosome, two of which are normally present in female cells (designated XX) and only one in male cells (designated XY)