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Summary Summarised genetics notes
Summarised and easy to follow genetics notes which follow the SAGS with diagrams to make reference to
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GeneticsHeredity:
The passing of traits from parents to their offspring
Gregor Mendel: The Father of Genetics
● 1822-1884
● Austrian monk
● Responsible for first major breakthrough in study of heredity
● Investigated the transfer of characteristic from one generation to the next
● “Something” (genes) is passed on from parent to offspring
● Sexual reproduction combines these “somethings” (genes) from each parent to produce offspring which
are:
○ Unique
○ Yet the same
● 1866 → published his work
NOTE:
Chromosomes = believed to carry the hereditary factors (genes) that Mendal referred to
What is a gene:
Gene:
Short section of DNA with nucleotides in a particular order that codes for a hereditary
characteristic/ trait
● Basic unit of heredity (inheritance)
● Each chromosome:
○ 100’s - 1000’s of genes
● Each chromatid → made up of one helical DNA molecule
● Each DNA molecule
○ Made up of series of genes
● Somatic cell:
○ Exact copy of all genes in that org
● Two of each kind of chromo
○ Paternal & maternal
○ Each cell contains two of each kind of gene (before replication)
○ These versions of gene → alleles
Allele:
Version of a gene (that results in expression of the characteristics) found in the same locus on
a homologous chromosome
● Different forms of the same gene
● Responsible for controlling different version of a trait found in the same locus on homologous
chromosome
● One from mother & other from father
, ● Represented by: capital letter for dominant allele
○ Lower case: recessive allele
How are alleles passed from parent to offspring:
● By chromosomes in gametes
○ Gametes: made by meiosis in sex organs
● Somatic cells:
○ Diploid
○ Pairs of homo chromom
○ With two alleles for each characteristic
○ May be the same/ different
● Gametes:
○ Haploid
○ One pair of homo chromo
○ One of each pair of alleles
1. DURING FERTILISATION Male gamete (n) fuses with female (n) gamete to
form zygote (2n)
2. ZYGOTE DIVIDES By mitosis to form new org
3. EACH CELL SAME SET OF CHROMO Therefore: same alleles as in the zygote
Gene pool:
● Set of all genes/ genetic information in a population of sexually reproducing organisms
● Large gene pool:
○ High genetic diversity
○ Incr chances of survival
● Small gene pool:
○ Low genetic diversity
○ Incr chance of extinction
Genotype:
All the genes an organism carries on its chromosomes which it has inherited from its parents
Phenotype:
The physical appearance of an organism
Determined by the genotype & external factors (genes determine)
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