Modes of autosomal and sex linked inheritance
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This document discusses different modes of inheritance including autosomal dominant, autosomal recessive, X-linked recessive, and X-linked dominant inheritance. Autosomal dominant inheritance involves a 50% risk of passing on a trait with each pregnancy, affects both sexes equally, and shows no generational gaps. Autosomal recessive inheritance typically involves unaffected carrier parents who have a 25% risk of passing on the recessive trait with each pregnancy. X-linked recessive traits mainly affect males and carrier females have a 50% risk of passing the trait to sons or daughters, respectively. X-linked dominant traits affect females more than males.
Modes of autosomal and sex linked inheritance
- 1. Modes of Autosomal and Sex Linked Inheritance To MBBS/BDS 1st year 08-01-2017 By Dr. Laxman Khanal Assistant Prof. (Department of Anatomy)
- 2. Gregor Johhan Mendel: 1822-1884
- 3. Blending of characters OR Characters are discrete and do not blend Law of dominance
- 4. An important reason for studying the pattern of inheritance of disorders within families is to enable advice to be given to members of a family regarding the likelihood of their developing it or passing it on to their children (i.e.genetic counseling) Why this topic is important ?
- 5. Some definitions Gene: Sequence of nucleotides in DNA which forms specific RNA followed by protein which eventually produce some observable trait. Alleles: Different variants of gene present in specific location(locus) of homologous chromosome. Homologous chromosome: Similar chromosome inherited from father and mother containing similar genes.
- 6. Fibrillin Chromosome 15 Dominant disorders Hemoglobin Chromosome 11 Disease expression occurs Disease expression occurs Recessive disorders Which is more lethal condition ? Which is manifested earlier ?
- 7. Mode of inheritance: Definition • Its the manner in which a particular genetic trait or disorder is passed from one generation to the next. Examples: • Autosomal dominant/ recessive • Sex-linked dominant/recessive • Mitochondrial inheritance. Knowledge is important for the purpose of ‘Genetic Counselling’ 22 AA + XX/ XY
- 8. Autosomal dominant inheritance • Both parent can transmit mutant gene to both sons and daughter. • Male = female affected • Vertical transmission (no generation gap) • Myotonic muscular dystrophy • Marfan’s syndrome • Achondroplasia • Huntington’s disease • Familiar hypercholesterolemia
- 9. Autosomal dominant • Myotonic muscular dystrophy • Marfan’s syndrome • Achondroplasia • Huntington’s disease • Familiar hypercholesterolemia • Both parents can transmit mutant gene to both sons and daughter. • Male = female affected • Vertical transmission (no generation gap) 50% of offspring will be affected if one of the parent has single mutant allele.
- 11. Autosomal dominant inheritance • Only one copy of a disease allele is necessary for an individual to be susceptible to expressing the phenotype. • With each pregnancy, there is 50% chance the offspring will inherit the disease allele. • All affected individuals will have at least one parent who carries the disease allele. • Vertical inheritance involving all generations. • Male and females are equally affected.
- 12. ? Reduced penetrance 50% chance of being diseased. • Pleiotropy • Variable expressivity • Reduced penetrance
- 13. Autosomal recessive inheritance • Typically, the parents of an affected individual are not affected but are gene carriers. • With each pregnancy of carrier parents: • There is a one in four (25%) chance of having the disease. • There is a one in two (50%) chance of having carrier • There is a one in four (25%) chance of having no disease. • Proportion of affected male and female is equal.
- 14. Carrier • 25%- affected • 50%- carrier • 25%- normal
- 15. Autosomal recessive inheritance • Observed more frequently in consanguineous relationship s and in certain ethnic backgrounds. • Most of people have 1-5 mutant copy of gene for autosomal recessive disorders. • Sickle cell anemia • Cystic fibrosis • Tay-sachs disease
- 16. Sex limited disorders • Limited in one of genders • Mostly genes are in autosome • Examples Male pattern baldness Ovarian carcinoma Sex linked disorders • Either X or Y linked • Can occurs in both gender (if X linked) • Occurs only in males (if Y linked) • Genes are in sex chromosome
- 17. XY XX Y linked inheritance (Holandric inheritance) Y linked disorders • Hairy pinna • Only occurs in male
- 18. X X X Y • Father cannot transmit X linked mutant gene to sons. • Mother can transmit X linked mutant gene to both sons and daughters. xx XY xx XY X linked inheritance
- 19. X X X Y xx XY xx XY X linked recessive inheritance • 50 % of male will be affected • 50% of female will be carrier XY xx XY xx XY
- 20. X X X Y xx XY xx XY X linked recessive inheritance • 50 % of male will be affected • 50% of female will be carrier XY xx XY xx XY
- 21. X X X Y xx XY xx XY X linked recessive inheritance Rare situation Conclusion: Males>> females affected Mostly females act as carriers • Duchenne muscular dystrophy • Hemophilia A • Color blindness • G6PD deficiency
- 22. X-linked recessive inheritance • Two copies of a disease allele on the X chromosome are required for an individual with two X chromosomes (a female) to be affected. • Since males are hemizygous for X-linked genes, any male with one copy of disease allele is affected. • Females are usually carriers because they only have one copy of the disease allele. • For a carrier female, with each pregnancy there is 50% chance her sons will inherit the disease allele and 50% chance her daughters will be carriers.
- 23. X X X Y xx XY xx XY X linked dominant inheritance XY xx XY xx XY X X XY X XX X XY Females >> males affected.
- 24. X-linked recessive inheritance X-linked dominant inheritance Fragile X syndrome (!!) Vitamin D resistant rickets Charcot-Marie-Tooth disease
- 25. • Males and females are equally affected • Both father and mother can transmit the mutant gene to both sons and daughter. YESNO Autosomal inheritanceSex linked inheritance Vertical transmission +no generation gap Autosomal dominant Horizontal transmission +generation gap Autosomal recessive Father to sons transmission Y-Linked No father to sons transmission X-Linked Males >> females – X-recessive Females>> males- X-dominant