variation-2

variation-2 - 1 Sources of heritable variation There are...

Info iconThis preview shows pages 1–12. Sign up to view the full content.

View Full Document Right Arrow Icon
1
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
There are two principal ways in which heritable variations can be acquired Independent assortment of genes Mutation Sources of heritable variation 2
Background image of page 2
Independent assortment arises as a result of meiosis and fertilisation The separation of parental chromosomes at meiosis and their recombination at fertilisation introduces the possibility of new combinations of genes In the example which follows, the parental types have each inherited one set of chromosomes from the father (blue) and one set from the mother (red) Independent assortment of genes 3
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Phenotype : brown eyes,straight hair Genotype : Bbcc Male sperm mother cell Phenotype : blue eyes, curly hair Female ovum mother cell Genotype : bbCc Meiosis ; the homologous chromosomes are separated in the gametes B b c c B c b c c b b C b C c b X 4
Background image of page 4
Bc bc bC bc Bb Cc bb Cc Bb cc bb cc ova sperms Possible recombinations at fertilisation Bbcc Brown eyes, straight hair – like father bbCc Blue eyes, curly hair – like mother BbCc Brown eyes, curly hair – new variation Bbcc Blue eyes, straight hair – new variation 5
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
BBUU bbuu X BbUu BbUu BbUu BbUu A black ( B ) uniformly coloured ( U ) bull is crossed with a red ( b ) spotted ( u ) cow The alleles B and U are dominant so all the calves are uniformly black F1 offspring 6
Background image of page 6
An F 1 bull is mated with an F 1 cow BbUu BbUu Parental type Parental type New variety New variety X Possible offspring 7
Background image of page 7

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
The next slide offers a blank Punnett square which can be printed out and filled in to show the genotypes and expected number of phenotypes from a cross between the F 1 black, uniform, cattle 8
Background image of page 8
Enter female gametes here Enter male gametes here BbUu x BbUu genotypes phenotypes Black uniform Black spotted Red spotted Red uniform 9
Background image of page 9

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
If you worked out the genotypes from the Punnett square, you will realise that the only cattle which will breed true are the ones homozygous for both characteristics BBUU BBuu bbUU bbuu Other crosses are likely to result in some offspring which do not resemble either parent For this reason, all possible variations will keep cropping up in a breeding population If, however, either of the homozygotes BBUU or bbuu were to be more successful* than the others, they might become established as a stable population 10
Background image of page 10
B b C c If the genes for eye colour and hair curliness occurred on the same chromosome, they would be said to be
Background image of page 11

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 12
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 40

variation-2 - 1 Sources of heritable variation There are...

This preview shows document pages 1 - 12. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online