1. 10.2: Inheritance
HL only

2. 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.
Taken from pg. 447, Qu. 1. Answer on the following slide

3. Male gametes = BT, Bt, bT, bt Female genotype = bbtt
Female gamete = bt BT Bt bT bt
BbTt
Brown, tailed
25%
Bbtt
Brown, tail-less
*recombinant
bbTt
White, tailed
* recombinant
bbtt
White, tail-less

4. 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.
Segregate = separate
Sometimes, linked genes which are far apart from each other on a chromosome will segregate independently, sometimes (especially after crossing over) this can cause genes to appear unlinked.

5. 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.

6. Fruit flies (Drosophila)

7. 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

8. The bars represent homologous chromosomes
Fruit flies (Drosophila)
G – grey body
g – black body
L – long wings
l – short wings
What are the genotypes for the true breeding parents?
GGLL, ggll
These are linked genes. Represented by:
HL Pairs of alleles are read vertically.
G L
g l
The bars represent homologous chromosomes
G L
g l

9. R R G L g l g l g l G L G l g L g l g l g l g l g l
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
R = recombinants (new genotypes result of crossing over. Creates variety in a population) X
g l
g l HL GL Gl gL gl
GgLl
Ggll
ggLl
ggll
G L
G l
g L
g l
g l
g l
g l
g l R R

10. Practice problems