SBI3U – Unit 2: Genetics
Date: ___________________
6.2 Inheritance of Linked Genes
Some genes are ______________________. Genes that are the same chromosome and that tend to be
inherited together are linked. Genes do not assort independently in meiosis if linked.
Crossing Over & Inheritance of Linked Genes
 Linked genes do not always stay together due to the process of crossing over.
 Crossing over is a random event and it occurs infrequently
 When it occurs it results in recombined alleles
SBI3U – Unit 2: Genetics
Date: ___________________
Sex-Linked Inheritance
Sex-Linked Traits 
_____________________________________________________________________________________
_____________________________________________________________________________________
X and Y Sex-linked Genes
o X and Y chromosomes are not completely homologous pairs, although they act like it during
meiosis
o X and Y have only a few genes in common
o X chromosome has ~ ________________
o Y chromosome has less than ~ ________________
Genes on ‘X’ are called ____________________________.
Genes on “Y” are called ____________________________.
For sex-linked traits:
 The allele on the sex chromosome is shown as a superscript to an X or a Y.
o E.g. _____________________
Morgan and Sex-linked Inheritance
o Thomas Morgan  ___________________________________________________________
o Observed very few white-eyed males among many red-eyed flies (male and female)
o Concluded that the ___________________________does not carry the gene for eye colour, it is
the ________________________
Morgan’s F1 Crosses
Mated a white-eyed male XrY with a red-eyed female XRXR
F1 Results:
SBI3U – Unit 2: Genetics
Date: ___________________
Morgan’s F2 Crosses
Mated a red-eyed male XRY with a red-eyed female XRXr from F1
F2 Results:
Sex-linked Traits in Humans
Many genetic disorders are sex-linked.
Examples: ___________________________________________________________________________
X-Linked Dominant
Affected males pass the allele only to daughters, who have a ______________ chance of having the
disorder.
Females can pass the allele to both sons and daughters, all of whom will have the disorder.
X-Linked Recessive
Most sex-linked inherited traits in humans are _______________________________________.
The male only needs to inherit one allele to be affected, the female
________________________________________________________________.
∴ X-linked recessive traits affect more males than females in a family.
Example: Colour Vision Deficiency (recessive)
SBI3U – Unit 2: Genetics
Date: ___________________
Ex. 1: Determine the probability that a woman who is a carrier for hemophilia and a man without
hemophilia will have a child with hemophilia.
 Define given:
 X-linked recessive
 Woman XRXr , Male XRY
 Use a punnett square
F1 Phenotypes:
Ex. 2: Identify the genotype of each family member represented in the pedigree that shows the
inheritance of red-green CVD. How does the inheritance pattern in the pedigree support X-linked
inheritance?
To do:
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Section 6.2 Pg. 253 #7-12
Pg. 258 #11-16 (Practice Problems)
Read p. 258 on ‘Barr Bodies’
Section 6.2 p. 259 #2 – 10, 12, 13