Explore the fundamental principles of genetics with these concise notes tailored for Year 1 students in the Introduction to Genetics (BIOL0003) module at University College London. This document focuses on the basic Mendelism chapter, covering essential concepts like basic Mendelism, Mendel's secon...
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
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