Genes and Alleles Genes DNA in chromosomes have

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.