Patterns of Inheritance
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Phenotype
The characteristics displayed by an organism
Genotype
The alleles an organism has
Intraspecific
Differences between individuals of the same species
Interspecific
Differences between different species
Continuous variation
Quantitative- Any feature that can be measured Can be controlled by genes and environment Non- distinct categories
Discontinuous variation
Qualitative- Any feature that can’t be measured Controlled by only genes Distinct categories
Allele
Form of a gene
Phenotypic variation - genetic factors
Polygenic: * more than one gene controls it (can be affected by the environment) Monogenic: * only 1 gene controls it (not affected by the environment)
Phenotypic variation - environmental factors
Etiolation: * plants grow abnormally long and spindly due to not enogh light Chlorosis: * plants don’t produce enough chlorophyll due to a lack of Mg or Fe
Genetic Variation
• Crossing over • Independent segregation of chromosomes • Random fertilisation
Meiosis
Gene
A sequence of nucleotide bases that codes for a protein/ polypeptide
Dominant
An allele that is always expressed when present
Recessive
An allele that is only expressed when both are recessive
Homozygous
When the 2 alleles are the same
Heterozygous
When the 2 alleles are different
Locus
Where on the chromosome the alleles are
Codominance
Both alleles are expressed and neither is recessive Example: Sickle-cell can create a carrier of the gene
Monohybrid
Dihybrid
Inheritance of 2 characteristics controlled by different genes