The Cellular and Molecular Basis of Inheritance

1. The Cellular andMolecular Basis ofInheritance

2. Components of Inheritance • Cell • Nucleus • Cytoplasm • DNA • Composition • Structure • Replication • Transcription • Chromosomes

3. Chromosome Structure Image from: Emery's Elements of Medical Genetics, 14th Edition, by Peter D. Turnpennyand Sian Ellard, (2012)

4. Cell Cycle / Mitosis Image from: An Introduction To Human Molecular Genetics Second Edition by Jack J. Pasternak, Published by John Wiley & Sons, Inc., Hoboken, New Jersey 2005.

5. Meiosis Image from: An Introduction To Human Molecular Genetics Second Edition by Jack J. Pasternak, Published by John Wiley & Sons, Inc., Hoboken, New Jersey 2005.

6. The Human Genome • The nuclear genome • Approximately 3 200 000 000 nucleotides of DNA • Either 23 or 24 different types of chromosomal DNA Molecules • About 23 000 genes • The mitochondrial genome • 16 569 nucleotides • A small circular DNA • 37 genes

7. The Human Genome Image from: Human Molecular Genetics 4thEdition Tom Strachan, Andrew Read, Published by Garland Science (2011).

8. Types of DNA Sequence • Nuclear Genes • Unique single copy • Multigene families • Classicgenefamilies • Gene superfamilies • Pseudogenes • Extragenic DNA • Tandem repeat • Satellite • Minisatellite • Telomeric • Hypervariable • Microsatellite • Interspersed • Short interspersed nuclear elements • Long interspersed nuclear elements • Mitochondrial

9. Nuclear Genes / Unique Single Copy Most human genes are unique single-copy genes coding for polypeptides Include enzymes, hormones, receptors, and structural and regulatory proteins. Image from: Emery's Elements of Medical Genetics, 14th Edition, by Peter D. Turnpennyand Sian Ellard, (2012)

10. Nuclear Genes / Multigene Families 16p13 11p15 Have similar functions, arisen through gene duplication events Some are found physically close together in clusters; for example, the αand βglobin gene clusters on chromosomes 16 and 11. Image from: Human Molecular Genetics 4thEdition Tom Strachan, Andrew Read, Published by Garland Science (2010).

11. Nuclear Genes / Multigene Families Others are widely dispersed throughout the genome occurring on different chromosomes, such as the HOX home box gene family Image from: Emery's Elements of Medical Genetics, 14th Edition, by Peter D. Turnpennyand Sian Ellard, (2012)

12. Multigene Families Classic gene families ribosomal RNAs transfer RNA high degree of sequence homology Limited sequence homology functionally related, similar structural domains Gene superfamilies T-cell receptor genes Human Leukocyte Antigen (HLA)

13. Pseudogenes • Closely resemble known structural genes but, in general, are not functionally expressed. • Thought to have arisen in two main ways: • By genes undergoing duplication events • As the result of the insertion of complementary DNA sequences

14. Tandem Repeated DNA Sequences • Satellite DNA (20 kb to many hundreds of kilobases) • Approximately 10% to 15% of the repetitive DNA sequences of the human genome • located at centromeres and some other heteochromatic regions • MinisatelliteDNA (100 bp to 20 kb) • Telomeric DNA: contains 10 to 15 kb of tandem repeats of a 6-base pair (bp) DNA sequence • Hypervariableminisatellite DNA: made up of highly polymorphic DNA sequences consisting of short tandem repeats of a common core sequence • Microsatellite DNA (fewer than 100 bp) • Consists of tandem single, di-, tri-,and tetra-nucleotide repeat base-pair sequences located throughout the genome

15. Highly Repeated Interspersed Repetitive DNA Sequences Approximately one-third of the human genome is made up of two main classes of short and long repetitive DNA Short Interspersed Nuclear Elements (SINEs) About 5% of the human genome consists of some 750,000 copies The most common are DNA sequences of approximately 300 bp (Alu) Long Interspersed Nuclear Elements (LINEs) About 5% of the DNA of the human genome The most common, LINE-l , consists of more than 100,000 copies of a DNA sequence of up to 6000 bpthat encodes a reverse transcriptase

16. Mitochondrial DNA • The mtDNA genome is very compact, containing little repetitive DNA • Codes for 37 genes, which include • Two types of ribosomal RNA • 22 transfer RNAs • 13 proteins • Inherited almost exclusively from the oocyte leading to the maternal pattern of inheritance

17. Mitochondrial DNA Image from: Human Molecular Genetics 4thEdition Tom Strachan, Andrew Read, Published by Garland Science (2011).

18. From DNA to Protein

19. Transcription The process whereby genetic information is transmitted from DNA to RNA messenger RNA, by RNA polymerase II The template strand, antisense and sense strand mRNA splicing Capping Polyadenylation

21. Alternative Splicing

22. Capping After 20 to 30 nucleotides have been transcribed, the nascent mRNA is modified by the addition of a guanine nucleotide to the 5' end of the molecule by an unusual 5' to 5' triphosphate linkage. A methyltransferaseenzyme then methylates the N7 position of the guanine, giving the final 5' cap. Protect the RNA transcript from degradation by endogenous cellular exonucleases Facilitate transport of the mRNA to the cytoplasm and attachment to the ribosomes

23. Polyadenylation Approximately 200 adenylate residues-the so-called poly(A) tail-are added to the mRNA, Facilitates nuclear export and translation

24. Regulation of Gene Expression • Housekeeping genes • Many other genes only express in specific cells or stage of cell development • Control of gene expression • Control of Transcription • Post- Transcriptional Control

25. Control of Transcription • Can be affected permanently or reversibly by a variety of factors, both environmental (e.g., hormones) and genetic (cell signaling). • All mechanisms ultimately affect transcription through the binding of the transcription factors to short specific DNA promoter elements

26. Transcription Factors Proteins involved in the regulation of gene expression. have a transcriptional activation domain and a DNA-binding domain.

27. Control of Transcription

28. Post- Transcriptional Control of Gene Expression • Regulation of expression of most genes occurs at the level of transcription but can also occur at the levels of RNA processing, RNA transport, mRNA degradation and translation. • RNA-Mediated Control of Gene Expression • Small interfering RNAs (siRNAs) were discovered in 1998 and are the effector molecules of the RNA interference pathway (RNAi) • MicroRNAs (miRNAs) also bind to mRNAs in a sequence-specific manner.

29. Mutations Heritable alteration or change in the genetic material Mutations can arise through exposure to mutagenic agents, but the vast majority occur spontaneously through errors in DNA replication and repair. Somatic mutations may cause adult-onset disease, such as cancer, but cannot be transmitted to offspring. It is estimated that each individual carries up to six lethal or semilethal recessive mutant alleles

30. Types of Mutation Substitution Deletion Insertion

31. Substitution

32. Substitution/Missense

33. Deletion

34. Insertion

35. Frameshift Mutation

36. Mutation Nomenclature

37. Functional Effects of Mutations on the Protein • Loss-of-Function Mutations: • Either reduced activity or complete loss of the gene product • Usually inherited in an recessive manner • Haplo-insufficiency • Gain-of-Function Mutations: • Either increased levels of gene expression or the development of a new function(s) of the gene product. • Dominant-Negative Mutations

38. DNA Repair Base excision repair (BER) Nucleotide excision repair (NER) Post-replication repair Mismatch repair (MMR)