Download Genes and Alleles

Genes
 DNA in chromosomes have sections called genes.
Genes
 DNA in chromosomes have sections called genes.
 Each gene carries the genetic code for making the
particular characteristic – eg. Eye colour, hair colour.
Genes
 DNA in chromosomes have sections called genes.
 Each gene carries the genetic code for making the
particular characteristic – eg. Eye colour, hair colour.
 Genes are located at specific sites (locus) on a
chromosome.
Genes
 DNA in chromosomes have sections called genes.
 Each gene carries the genetic code for making the
particular characteristic – eg. Eye colour, hair colour.
 Genes are located at specific sites (locus) on a
chromosome.
 Genes typically have a large number of bases.
Genes
 DNA in chromosomes have sections called genes.
 Each gene carries the genetic code for making the
particular characteristic – eg. Eye colour, hair colour.
 Genes are located at specific sites (locus) on a
chromosome.
 Genes typically have a large number of bases.
 Human genome contains about 20’000 to 30’000
different genes (with approx 3 million base pairs)
Alleles
 Are alternative forms of a gene.
Alleles
 Are alternative forms of a gene.
 Alleles code for the same characteristic (eg. Eye colour)
but they have a slightly different order of bases so they
cause a different trait. (I will draw an example on the
board)
Alleles
 Are alternative forms of a gene.
 Alleles code for the same characteristic (eg. Eye colour)
but they have a slightly different order of bases so they
cause a different trait.
 Alleles produce variation in individuals.
Alleles
 Are alternative forms of a gene.
 Alleles code for the same characteristic (eg. Eye colour)
but they have a slightly different order of bases so they
cause a different trait.
 Alleles produce variation in individuals.
 Letters (upper and lower case) are used to represent
alleles of a gene.
Alleles
 Are alternative forms of a gene.
 Alleles code for the same characteristic (eg. Eye colour)
but they have a slightly different order of bases so they
cause a different trait.
 Alleles produce variation in individuals.
 Letters (upper and lower case) are used to represent
alleles of a gene.
 Because chromosomes are paired (homologous pairs),
alleles occur in pairs.
Example
Characteristic
Alleles
Traits caused by different alleles of a gene
Eye Colour
B, b
Brown eyes, blue eyes
Hair Type
C, c
Curly hair, Straight hair
Tongue roll
T, t
Tongue roller, can’t roll tongue
Alleles
 The genes for a particular characteristic are at the
identical position (the locus) on the same
chromosome pair for all individuals of that species.
 (Eg from board)
Alleles
 The genes for a particular characteristic are at the
identical position (the locus) on the same
chromosome pair for all individuals of that species.
 New alleles result from mutation in the DNA molecule
Alleles
 The genes for a particular characteristic are at the
identical position (the locus) on the same
chromosome pair for all individuals of that species.
 New alleles result from mutation in the DNA molecule
 New alleles produce variation
Alleles
 The genes for a particular characteristic are at the
identical position (the locus) on the same
chromosome pair for all individuals of that species.
 New alleles result from mutation in the DNA molecule
 New alleles produce variation
 Most mutations are harmful, but some can be
beneficial – if the mutation improves the survival of
the individual, they will pass that new allele on and
their offspring will benefit from the mutation.