by hafiz m Waseem university of education Lahore

2. HAFIZ M WASEEM

3. SUBJECT : GENETICS
TOPIC: SEX LINKAGE

4.  SEX LINKAGE
 HISTORY
 TYPES OF SEX LINKAGE
 SEX LINKAGE IN HUMAN
 COLOUR BLINDNESS
 CAUSES OF COLOUR BLINDNESS
 TYPE OF COLOUR BLINDNESS
 EXAPLE OD COLOUR BLINDNESS
 TEST CROSS
 SYPTOMS
 DETECTION
 EFFECTS
 SEX INFLUENCED TRAIT
 SEX LIMITED TRAIT
 CONCLUSION

5. DEFINITION:
Sex linkage is the phenotypic expression of
an allele that is independent on he gender of the
individual and is directly tied to sex chromosome.
HISTORY:
THOMAS MORGAN:
Sex linkage was first discovered by Thomas Morgan in 1910
who observed a disproportionate percentage of white- eye male fruits
flies. This experiment involved crossing purebred red-eyed female
fruit flies with these mutant white – eyed males. The result was
exclusively red – eyed individuals of both sexes.

7. There are some examples of sex linkage.
1. Hemophilia
2. Red- green colour blindness
3. Congenital night blind ness
4. Some high blood pressure genes
5. Fragile X syndrome

8. HEMOPHILIA
CONGENITAL NIGHT
BLINDNESS

9.  Twenty genes are sex linked.
 Red green colour blindness and hemophilia
 Both these disease are sex linked recessive trait.

10.  DEFINITION
Colour blindness is a condition in which
individuals have difficulty in distinguishing red
from green.

12.  Cats and Dogs
To see in full colour as we know it,
humans use three cones red, blue, and green.
However cats and dogs have only blue and green
cones. This means they have much more muted
perception of colour, which akin to colour
blindness in humans.

13.  There are three types of colour blindness.
 Protanolay:
 It is a type of o colour blind ness which reduce to red
colour.
 Deuteranomaly
Which reduce sensitivity to green color.
Tritanomaly
Which reduce sensitivity to blue colour.

14.  E.B Wilson firstly discovered facts about
hereditary color blindness
 It is genetic disease and inherited from mother
to child
 Gene for colour blindness present on X
chromosome
 Colour blindness occurs in about 8% males and
only 0.5% in females
 Some people become colour blind due to other
disease like diabetes and medication and
multiple sclerosis.

15.  Why blindness colour is occur more in males
instead of females.
 Father transfer his x chromosomes to all
daughter and mother transfer her x
chromosome.
 Son will be colour blind and daughter will be
normal if his mother is carrier father is normal
 Colour blind daughter will be produce only
produce only when his father is colour blind
and mother is carrier or colour blind.
 Since such marriages are very rare.

16.  If mother is normal father is colour blind
 Then son will be normal and daughter will be
carrier.

18. TEST CROSS-2
If mother is carrier
and father is colour
blind.
50 percent chances
daughter may be
colour blind or
carrier.
50 percent chances
son will be normal
or colour blind.

19. TEST CROSS -3
If mother is colour
blind and father is
normal.
All sons will be
colour blind and all
daughter will be
carriers.

20.  Symptoms of colour blindness could range
from mild to severe.
 Example would be difficult distinguishing
between colors, or inability to see shades of the
same color.
 Rapid eye movement could occur in rare cases,
and sensitivity of bright light.
 They could also suffer from having trouble
seeing the brightness of color in the usual way.
 Inability to tell the difference between the
shades of same or similar colors.
 Particularly red and green or blue or yellow.

21.  It can be detected by using special charts made up of coloured
dots
 These dots are so arranged that coloured blind person can see a
different patterns
 Sex linked traits in other animals:
 White eyes in drosophila melanogaster flies – the first sex linked
gene discovered.
 Fur colour in domestic cats : the gene that causes orange pigment
is on the X chromosome; thus a calico or tortoiseshell cat, with
both black and orange pigment, is nearly always female.
 The first sex- linked gene ever discovered was the lacticolor X
linked recessive gene in the moth.

22.  Sex – influenced traits :
 Sex influenced or sex conditioned traits are
phenotypes affected by whether they appear in
a male or female body. Even in a homozygous
dominant or recessive female the condition
may not be expressed fully.
 Example :
The baldness in humans.
 Sex limited traits:
These are characters only expressed in
one sex. They may be caused by gene on either
autosomal or sex chromosome

23. BALDNESS IN HUMANS
POLYMORPHISM IN
HONEY BEES

24.  There are no treatments for most types of color
vision difficulties, unless the colour vision
problem is related to the use of certain
medicine or eye condition.
 Discontinuing the medication causing your
vision problem or treating the underlying eye
disease may result in better color vision.

25.  Morgan’s conclusion was the trait for eye
color must be encoded on the X chromosome,
and that white eyes must represent the
recessive allele.

26.  References:
 Morgan, Thomas 1919. The physical basis of hereditary
 Genetics home reference (2006), genetic condition illustration,
national library of medicine
 Don caster L.& Raynor G.H 1906. Breeding experiments with
Lepidoptera. Proceeding of the zoological society of London.
 Ford E.B (1965) Genetics polymorphism. p17 – 25.MIT Press1965.
 Mallet J. Joron M. (1999) the evolution diversity in warning color
and mimicry polymorphisms, shifting balance, and speciation.
 Zirkle, Conway (1946). The discovery of sex influenced , sex
limited and sex linked hereditary .
 Joron M, Papa R, Beltran M, et al (2006). A conserved supergene
locus controls colour patterns diversity in Heliconius Butterfly.
 www.sciencehub.com
 www.ilamkidunya.com