Transcript Sex Linked Inheritance

Sex Linked Inheritance
• A human female, has 23 pair of
chromosomes
• A human male, has 22 similar pairs and
one pair consisting of two chromosomes
that are dissimilar in size and structure.
• The 23 rd pair in both the sexes is called
sex chromosomes
• the female, XX. the male, XY
X-linked diseases
• X-linked diseases are those for which
the gene is present on the X
chromosome.
• X-linked genes are never passed from
father to son.
• The Y chromosome is the only sex
chromosome that passes from father to
son.
• Males are never carriers – if they have a
mutated gene on the X chromosome, it
will be expressed.
X-linked dominant
• Hereditary pattern in which a dominant gene on the X
chromosome causes a characteristic to be
manifested in the offspring.
• X-linked dominant diseases are those that are
expressed in females when only a single copy of the
mutated gene is present.
•
Very few X-linked dominant diseases have been
identified (e.g. hypophosphatemic rickets, Alport
syndrome, diabetes insipidus)
– hypophosphatemic rickets or vitamin D resistant
rickets >>>low serum phosphorus, skeletal
abnormalities
– Alport syndrome, which involves progressive
hearing loss and progressive kidney problems.
Characteristics of X-linked
dominant diseases include:
• Never passed from father to son.
• Affected males produce only affected females. An affected
male only has one X chromosome to pass on to his
daughters
• Affected females produce 50% normal and 50% affected
offspring.. >>>> heterozygous
• Males are usually more severely affected than females.
Some X-linked dominant traits may even be lethal to males.
• Females are more likely to be affected. Since females have
2 X chromosomes, they have 2 “chances” to inherit the
mutated allele.
The pattern for the pedigree of Xlinked dominant inheritance
Pattern for inheritance
• Mating A
Mating B
Pattern for inheritance
• Mating A
Mating B
X-linked recessive
• hereditary pattern in which a recessive gene
on the X chromosome results in the
manifestation of characteristics in male
offspring and a carrier state in female
offspring
• X-linked recessive diseases are those in
which a female must have two copies of the
mutant allele in order for the mutant
phenotype to develop.
• Many X-linked recessive disorders are wellknown, including color blindness,
hemophilia, and Duchenne muscular
dystrophy.
The pattern for the pedigree of Xlinked recessive inheritance
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www.tylermedicalclinic.com/ pgd-presentation18...
Pattern of x linked recessive inheritance
staff.um.edu.mt/ acus1/02Monogenic.htm
Hemophilia
• The blood fails to clot normally
• Lacking a blood clotting factor
VIII(antihemophilic globulin, AHG),IX
• bleeding from even minor cuts
• in 1,500 newborn males. Most (75%) have
hemophilia A, a lack of clotting factor VIII.
• Hemophilia B- "Christmas Disease" is a defect in
clotting factor IX.
• Transfusions of fresh whole blood or plasma or
factor concentrates control bleeding
Hemophilia A and B. Coagulation system
www.emedicine.com/.../ 14801480ped0962-01.jpg
Inheritance of hemophilia
www.hemophilia.ca/ en/images/figure5.gif
A Pedigree of Hemophilia in the Royal
Families of Europe
Typical features of X-linked
recessive inheritance
• Never passed from father to son.
• Males are much more likely to be affected because they only
need one copy of the mutant allele to express the phenotype.
•
• Affected males get the disease from their mothers and all of
their daughters are obligate carriers.
• Sons of heterozygous females have a 50% chance of receiving
the mutant allele.
• These disorders are typically passed from an affected
grandfather to 50% of his grandsons.