In-depth summary for content covered in the Inheritance topic of A-level AQA Biology, including content covering genes and alleles, punnet squares, monohybrid and dihybrid inheritance, codominance, epistasis and more.
This will still be applicable to other exam boards, but take caution when look...
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 F 1 generation
for shorthand
The notation for this is shown on the right Figure 2 – reproduced from [1]
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