autosomal and sex linked inheritance

1. AUTOSOMAL
AND SEX
LINKED
INHERITANCE

2. 2
Characteristics of an autosomal
dominant trait:
1. Every affected individual should have at least one affected parent.
2. An affected individual has a 50% chance of transmitting the trait
3. Males and females should be affected with equal frequency
4. Two affected individuals may have unaffected children
5. No skipping of generations

3. Autosomal dominant pedigree chart

4. Characteristics of an autosomal
recessive trait:
Every affected individual may/may not have affected parent.
Males and females should be affected with equal frequency
skipping of generations

5. Autosomal recessive pedigree chart

6. Sex linked Inheritance
 X-linked genes : r called sex linked genes
: localized on non- homologous sections of X – chr.
 Y – linked genes : holandric genes
: localized on non- homologous sections of Y – chr.
 X Y –linked genes : localized on homologous regions of X and Y chr.

8. Characteristics of a X-linked trait:
Dominant and Recessive
X-linked DOMINANT : more in females as compared to males
: females pass to ½ of sons and ½ of daughters
: males pass to daughters only; never to sons
X-linked RECESSIVE : Hemizygous : males
Homozygous : females
Phenotypic expression is much more common in males than in
females.
Affected males transmit the gene to all daughters but not to any sons
no offspring of affected male is affected
Daughters of affected males will usually be heterozygous (carriers)
and unaffected.
Sons of heterozygous females have a 50% chance of receiving the
recessive gene.

10. 26-10
X-linked recessive pedigree chart

11. Characteristics of a Y-linked trait
Genes on non- homologous regions of Y- chr.
Direct transmission to all sons.
No female affected .
E.g –procupine man : Edward Lambert 1717
: thick skin like bark
: shedding perodically
: quill like hairs
: passed on the trait to all sons

12. Autosomal recessive disorders
 Tay-sachs disease
 Jewish people in U.S. of central and eastern European descent
 Lack of hexosaminidase A
 Glycosphingolipid stored in lysosomes
 Build up in brain cells-loss of function
 Symptoms appear in infancy
 Cystic fibrosis
 Most common genetic disorder in Caucasians in U.S.
 Defect in chloride channel proteins in cells
 Thick, abnormal mucus production
 Lungs, bronchial tubes, pancreatic ducts affected

13.  Autosomal recessive disorders cont’d.
 Phenylketonuria
 Lack enzyme for phenylalanine metabolism
 Affects nervous system development
 Sickle-cell anemia
 Irregular red blood cells caused by abnormal hemoglobin
 Clog vessels- poor circulation
 Internal hemorrhaging
 Heterozygous individuals are normal unless dehydrated or experience mild
oxygen deprivation

14.  Autosomal dominant disorders
 Marfan syndrome
 Defect in fibrillin-protein in elastic connective tissue
 Long limbs and fingers, weakened arteries, dislocated lenses in the eyes
 Huntington disease
 Progressive degeneration of brain cells
 Gene for defective protein called Huntington
 Too many copies of the amino acid glutamine

15. 26-15
 X-linked recessive disorders
 Color blindness
 About 8% of Caucasian males have red-green colorblindness
 Duchene's muscular dystrophy
 Absence of a protein called dystrophin
 Causes calcium to leak into muscle cells which actives enzymes that break down
the cells
 Hemophilia
 Hemophilia A is due to a lack of clotting factor VIII
 Hemophilia B is due to a lack of clotting factor IX
 Blood clots slowly or not at all

16. X-linked dominant disorders
 Rett syndrome
- abnormal dev. of brain
 Hypo phosphatemic rickets
- abn. with bones
- no response to high doses of vit D
 Aicardi syndrome
- corpus callosum absent
- brain dev. abnormal