Genetics and Key Science Skills Flashcards
Genome
All of the genetic material in an individual or cell
Allele
A variation of a gene at a particular gene locus
Gene
The hereditary unit, which is a section of DNA occupying a specific location on a chromosome. It determines a characteristic of an organism by directing the formation of a protein.
Genotype
The allele combination of an individual
Phenotype
The physical, behavioural or physiological characteristics of an organism which are a result of the combination of the genotype and environment.
Homozygous
Having identical alleles at the same gene locus on homologous chromosomes. Sometimes referred to as ‘purebred’.
Heterozygous
Having different alleles at the same gene locus on homologous chromosomes. Sometimes referred to as ‘hybrid’.
Carrier
An individual that has inherited a copy of a recessive allele for a particular trait, but does not display the trait due to the presence of a dominant allele.
Dominant (allele)
An allele that is expressed in the heterozygous genotype
Recessive (allele)
An allele that is only expressed when the genotype is homozygous for that allele
Punnett Square
A table that shows the possible genotypes of offspring given the genotypes of the two parents
F1 generation
The offspring of the parent generation
F2 generation
The offspring of the F1 generation
Monohybrid Cross
Determination of the possible genotypes and phenotypes of offspring at a particular gene locus
Dihybrid Cross
Determination of the possible genotypes and phenotypes of offspring at two gene loci
Co-dominance
Two alleles from the genotype are both fully expressed in the phenotype of a heterozygote
Polygenic
The observed phenotype is the result of contributions from two or more genes, and does not follow Mendelian genetics
Multifactorial
The observed phenotype is the result of contributions from one or more genes plus environmental factors.
Sex-linked trait
A trait that occurs as a result of a gene on a sex chromosome. This may be on the X-chromosome (X-linked) or the Y-chromosome (Y-linked)
Test cross
A cross performed between an individual showing a dominant phenotype with a homozygous recessive individual, to determine the genotype of the individual with the dominant phenotype
Pedigree
A chart showing the relationship between family members and whether they show an inherited trait
Gene linkage
When two genes are located on the same chromosome. This will result in ‘parental’ combinations of alleles which are inherited more often than ‘recombinant’ combinations
Phenotype ratio of a monohybrid cross when both parents are heterozygous
3:1
Phenotype ratio of a monohybrid test cross if the individual with the dominant trait is heterozygous
1:1
Phenotype ratio of a dihybrid cross where both parents are double heterozygotes
9:3:3:1
Phenotype ratio of a dihybrid test cross if the parent with dominant phenotypes is a double heterozygote (no gene linkage)
1:1:1:1
Phenotype ratio of a dihybrid test cross where the parent with dominant phenotypes is a double heterozygote and there is gene linkage (assume crossing over occurs)
many:many:few:few
Evidence for a recessive inheritance pattern
An affected individual has two unaffected parents, for example….
Evidence for a dominant inheritance pattern (definitely)
Two affected parents have an unaffected child, for example….
Evidence that shows a dominant inheritance pattern is likely (but not definitive)
All affected individuals have an affected parent
Evidence that shows a recessive trait is X-linked
An affected mother passes the trait onto all sons
Evidence that a dominant trait is X-linked
An affected father passes the trait onto all daughters
Evidence that a recessive trait is autosomal
An affected mother has an unaffected son
Evidence that a dominant trait is autosomal
An affected father has an unaffected daughter
