Introduction to Genetics (BIOL0003) Notes - Basic Mendelism

Basic Mendelism
Basic Mendelism
 23000 genes
 Charles Darwin – 1837
o Studied evolution
 Family tree
 Gregor Mendel
o Interested in inheritance
o Worked on the hermaphrodite pea flower
 Hermaphrodite = flower is both male and female
 Ovary – contains egg cells (female cells)
 Stigma – contains pollen (male cells)
 Can fertilise itself – egg and pollen from same flower can produce new flower
 Brush stigma over ovary – to produce new flower




o
 Mendel made crosses between them
st
o 1 experiment
 P1 – crossed Yellow X Green (parental generation)
 P1 = parental generation
 F1 – cross produced All Yellow (first filial generation)
 F1 = first filial generation = 1st son generation produced from parental cross
 F2 – ratio of 3 Yellow to 1 Green
 F2 = second filial generation
o Mendel’s interpretation of his 1st experiment
 P1 – YY x GG
 Make Y, or G, pollen and egg
 F1 – All YG = yellow colour
 Yellow is dominant to Green – hinds green effects
 F2 – ratio of 3 Yellow to 1 Green (phenotypes)
 1YY: 2YG: 1GG (genotypes)
 Genetical terminology
o Gamete
 Organism’s reproductive cells (sex cells)
 Female gametes – egg cells
 Male gametes – sperm / pollen
 Produced by meiosis
 Contains 1n number of chromosomes

, Basic Mendelism
o Zygote
 Normal body cells
 Produced in mitosis
 Gamete + gamete = zygote
 Contains 2n number of chromosomes
o Locus
 Position of a gene in the genome that codes for a particular characteristic
o Allele
 Different forms of a gene
o Dominant
 Variation of a gene that will be expressed in the phenotype if at least 1 copy is present
o Recessive
 Variation of a gene that will only be expressed in the phenotype if two copies are present
o Homozygote
 An individual having two identical alleles of a particular gene
o Heterozygote
 An individual having two different alleles of a particular gene
 Pedigrees – diagram showing the biological relationships between an organism and its ancestors




o
 Consanguineous marriage = mating between two people descended from the same ancestor
o E.g.
 Brachydactyly with three generation dominant pedigree





o Huntington’s disease = dominant
 Cannot skip generations