I achieved a high A* Grade in my final A-Level exams using these notes!!!
I believe you can achieve an A* if you can memorise these notes! Simply use blurting, a method of active recall, to write everything you remember from the notes, then identify the parts you couldn’t remember, then repeat ...
a. Alleles = different form of same gene
Gene = physical unit of heredity: sequence of DNA – codes for polypeptide
Locus: position of gene on chromosome
Allele: variant nucleotide sequence = altered phenotype
Dominant: expressed in hetero/homozygote
Recessive: only expressed in homozygote
Codominant: both alleles contribute to phenotype
Genotype: all alleles
Phenotype: characteristic – due to genotype + environment
Homozygous (dominant/recessive) same allele from both parents = pure breed
Heterozygous: different alleles from both parents
F1: 1st filial generation
b. Monohybrid: inheritance of single gene
Mendel
- pea plants: easy to grow, clear phenotype differences, large number of seeds (reliable results)
- tall vs dwarf / yellow vs green seeds / round vs wrinkled seeds
o controlled by single genes on different chromosomes (unlinked)
o discontinuous: easy to distinguish
1. law of segregation: characteristic determined by alleles (occur in pairs) & 1 allele in single gamete
Genetic diagrams
1. parents genotype & phenotype
2. gametes in circles (after meiosis)
3. fertilisation arrows / punnet square – F1 genotype & phenotype
4. ratio/percentage for phenotype
Back cross: test genotype + homozygous recessive genotype
- if homozygous dominant = 100% dominant phenotype
- if heterozygous = 50%
co-dominance IA IB – both alleles dominant = both equally expressed in phenotype
incomplete dominance = intermediate phenotype
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