(A-level) AQA Biology Populations and Evolution Topic Summary
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AQA
In-depth summary for content covered in the Populations and Evolution topic of A-level AQA Biology, covering content on the Hardy-Weinberg principle, speciation types, selection and more.
This will still be applicable to other exam boards, but take caution when looking at key-words and the order...
• This determines the limits characteristics of an individual
• Excluding the effect of the environment – e.g. diet
Phenotype is the observable characteristics of an organism
-> therefore, influenced by both environment and genotype
Genes and Alleles:
A gene is a length of DNA / sequence of nucleotide bases
-> these code for the 1o structure of a polypeptide or functional RNA
• Genes exist in different forms, coding for variations of the same structure
• Due to different sequence of bases
• These are called alleles
The position of a gene on a strand of DNA is known as a locus
-> all of these features influence the inheritance for the offspring of an organism
• Only one allele of a gene can occur at a specific locus of a chromosome
• However, in diploid organism (2 chromosomes)
• Homologous pairs of chromosomes mean there are two alleles for the same gene
These can be of a few variations –
1. Homozygous – two of the same alleles carried; either dominant or recessive usually
2. Heterozygous – two different alleles carried
Heterozygous characteristics are usually determined by a
dominant allele
-> these express themselves over their recessive
counterpart
• Usually represented by alternating letters e.g. Bb
, Oliver Dyson
Notation for genetics:
Genetic crosses are usually represented by using standard shorthand
-> this is described by the table below
Figure 1 – reproduced from [1]
Monohybrid inheritance: (e.g. in pea pod colour)
Monohybrid describes the inheritance of a single gene
-> for example pea pod colour can be modelled
• The colour green is dominant – GG or Gg
• And yellow is recessive - gg
Each generation of inheritance is called a ‘filial’
• For example the first filial is called the F1 generation
for shorthand
• The notation for this is shown on the right Figure 2 – reproduced from [1]
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