10.2: InheritanceHL only

Prediction practice - unlinked A farmer has rabbits with two particular traits, each

controlled by a separate gene. Coat colour brown is completely dominant to white. Tailed is completely dominant to tail-less. A brown, tailed male rabbit that is heterozygous at both loci is crossed with a white, tail-less female rabbit. A large number of offspring is produced with only two phenotypes: brown and tailed, white and tail-less, and the two types are in equal numbers. State the parents genotypes and the gametes that are

produced by each during the process of meiosis. Predict the genotypic and phenotypic ratios of the F2

generation. Show your workings.

Male genotype = BbTt Male gametes = BT, Bt, bT, bt Female genotype = bbtt Female gamete = bt

BT Bt bT bt

bt BbTt

Brown, tailed

25%

Bbtt

Brown, tail-less

25%

*recombinant

bbTt

White, tailed

25%

* recombinant

bbtt

White, tail-less

25%

Genes…

Genes on different chromosomes are unlinked therefore segregate independently during meiosis

Genes on the same chromosome are linked and therefore do not segregate independently during meiosis.

Thomas Hunt Morgan

Experimented with Drosphilia melanogaster (fruit flies) to prove non-Mendelian ratios of inheritance.

He believed variation in a population was more likely to be due to environmental effects.

His studies largely supported Mendels theories, so he had to reconsider his own, but he did prove that there are exceptions to Mendels theory of independent assortment.

Fruit flies (Drosophila)

https://www.youtube.com/watch?v=-_UcDhzjOio

http://www.dnaftb.org/10/animation.html

Linked genes

Genes found on the same chromosome

Groups of inherited genes are called linkage groups. Applies to autosomes & sex chromosomes.

Linked genes are the exception to the law of independent assortment. Linked groups can give a much wider variety of ratios - not just 9:3:3:1

Fruit flies (Drosophila)

G – grey bodyg – black bodyL – long wingsl – short wings

What are the genotypes for the true breeding parents?

GGLL, ggll

These are linked genes. Represented by:

GL

G

Lg l

g

l

The bars represent homologous

chromosomes

If you crossed a homozygous dominant true breeding fruit fly with a homozygous recessive true breeding fruit fly. What would your offspring be?

If you do not know the genotype of the parent, test crosses would be used to determine homo/heterozygous genotype.

If you crossed a grey, long winged fly (heterozygote) with a black short winged fly what off spring would you have?

g l

G

L g l

g

l

X

GL Gl gL gl

gl GgLl Ggll ggLl ggll

g

l

G

Lg

l

G

lg

l

g

Lg

l

g

lR R

R = recombinants (new genotypes result of crossing

over. Creates variety in a population)

Practice problems

http://www.k-state.edu/biology/pob/genetics/linked.htm

http://bcs.whfreeman.com/thelifewire/content/chp10/1002s.swf