Patterns of inheritance
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This document discusses various patterns of inheritance including autosomal dominant, autosomal recessive, X-linked dominant, and Y-linked recessive inheritance. It provides examples for each pattern and describes their characteristics such as whether males and females are equally affected, the chance of offspring being affected, and common diseases that follow each pattern of inheritance. The document also briefly discusses non-Mendelian inheritance including mosaicism, imprinting, triplet repeats, and mitochondrial inheritance.
Patterns of inheritance
- 2. PATTERNS OF INHERITANCE Observations of the way traits, or characteristics, are passed from one generation to the next in the form of identifiable phenotypes probably represent the oldest form of genetics. The various ways in which genes are transmitted are Autosomal Dominant Autosomal Recessive X-linked dominant Y-linked Recessive
- 3. I.AUTOSOMAL DOMINANT Affected parent Normal parent Gamete A a a Aa aa a Aa aa • Males and females are affected equally • Affected individual has affected parent unless caused by fresh mutation. • Half the children are heterozygous • Affected parent will posses defective gene. • Unaffected children of affected parents will have unaffected children. Ex: breast and ovarian cancers • Alzheimer's , Huntington's disease, hypercholesteremia
- 4. II.AUTOSOMAL RECESSIVE INHERITANCE Heterozygous Parent A/a Hetero zygous Gamete A a A AA Aa CARRIER a Aa CARRIER aa • Males and females are affected equally • Affected individual has unaffected parents who are heterozygous for the trait. • There is 1 in 4 chance that any child of 2 unaffected heterozygous parents will be affected. • 2 affected parents will have affected children exclusively • PKU,SCA,Albinism, Cystic fibrosis
- 5. III.X-LINKED DOMINANT INHERITANCE NORMAL MOTHER Affected father Gamete X X XA XAx XAx Y XY XY AFFECTED MOTHER NORMAL FATHER Gamete XA X X XAx Xx Y XAY XY
- 6. Affected individuals have an affected parent All the daughters but none of the sons of an affected male will be affected. Half the sons and half the daughters of an affected female will be affected. Normal children of an affected parent will have normal offspring . There are no carriers. Ex: fragile X syndrome, ADHD, MR III.X-LINKED DOMINANT INHERITANCE
- 7. IV.Y-LINKED RECESSIVE INHERITANCE NORMAL MOTHER Affected father Gamete X X XA Xax (carrier) Xax (carrier) Y XY XY CARRIER MOTHER NORMAL FATHER Gamete XA X X Xax Carrier daughter Xx Y XAY Affected son XY
- 8. Affected individuals are principally males Affected individuals have unaffected parents Half of female siblings of an affected will be carriers. Ex: Hemophilia A & B, Duchenne Muscular dystrophy IV.Y-LINKED RECESSIVE INHERITANCE
- 9. NON MENDELIAN INHERITANCE Mosaicism Imprinting Prader willi Angelman syndrome Triplet repeats Fragile X syndrome Myotonic dystrophy Mitochondrial inheritance
- 10. MOSAICISM It refers to the presence of 2 or more distinct cell lines, one normal and one abnormal . This was first recognized in chromosomal disorders. Ex: segmental Neurofibromotosis (NF) - only certain areas of body were affected. Cells from affected areas were shown to have the gene coding of NF’s. Cells from unaffected areas had the normal gene. As his gonads were involved, he passed the NF gene onto his children who were in turn fully affected.
- 11. IMPRINTING It refers to modification of the gene as it is transmitted through father and mother. Ex: Prader Willi , Angleman, Obesity, Intellectual disability. Both conditions are due to deletion of a chromosomal segment. If the deleted chromosome 15 is paternal in origin-PWS If its maternal in origin -AMS
- 12. TRIPLET REPEATS It is a condition where 3 base repeats CTG,CGG,CAG are abnormally repeated in a genome. This triplet repeats are found close to the beginning within or close to the end of the gene. The function of these repeated DNA sequences is not clearly defined. As they are passed onto subsequent generation it can undergo expansion in size and result in various genetic diseases. Ex: fragile X syndrome: CGG is repeated. Normally 6-40 repeats are present. Unaffected carriers have 50-200 pairs affected have 200-1000 repeats.
- 13. MITOCHONDRIAL INHERITANCE Mitochondria are power houses of the cell which provides energy by oxidative phosphorylation. The number of mitochondria varies from species to species and even among cells of different tissues. The genectic conditions due to abnormal mitochondrial DNA are very rare . This follows vertical pattern which means only mother can contribute her mitochondria to the zygote. Ex: Lactic acidosis