10.2:
Inheritance
HL 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
Bbtt
bbTt
bbtt
Brown,
tailed
Brown, tail-less
White, tailed
25%
25%
White, tailless
*recombinant
* recombinant
25%
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 nonMendelian 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 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:
G L
g l
The bars represent
G L
g l
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
X
g l
R = recombinants (new genotypes
result of crossing over. Creates variety
in a population)
g l
gl
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
Practice problems
 http://www.k-
state.edu/biology/pob/genetics/linked.ht
m
 http://bcs.whfreeman.com/thelifewire/co
ntent/chp10/1002s.swf