Genotype
Genetic constitution of an organism
The alleles an organism possesses
Phenotype
Expression of genotype and its interaction with environment
What are the types of allele?
Dominant
Recessive
Codominant
What are alleles?
Different versions of genes
Occupy same locus but different base sequence
Homozygous
2 copies of same allele
Heterozygous
Different alleles
Dominant alleles
Always expressed in phenotype
Expressed in both homozygous and heterozygous individuals
Recessive alleles
Only expressed in phenotype if no dominant allele is present
Only expressed in homozygous individuals
Codominance
When both alleles in a heterozygous genotype are fully expressed / observed in phenotype
Codominance notation
Capital letter represents gene, superscript represents alleles
Eg Iᴬ, Iᴮ, Iᴼ
Test cross
Determines genotype of an individual showing dominant phenotype
Crossed with homozygous recessive
If all offspring show dominant phenotype unknown genotype is homozygous dominant
If offspring are 50% dominant and 50% recessive unknown genotype is heterozygous
Linkage
Refers to genes inherited together because they are on same chromosome
Sex linkage
Women have 2 copies of X chromosome whereas men have 1 X and 1 Y
Sex linked genes are on X chromosome
Males more likely to express recessive sex linked traits
Autosomal linkage
Occurs on autosomes (any chromosome that isn’t a sex chromosome)
2 or more genes on same chromosome don’t assort independently during meiosis
Genes are linked and stay together in original parental combination
