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CHROMOSOMAL BASIS OF INHERITANCE.pptx
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- 2. LEARNING OBJECTIVES ▪ Distinguishamong sex limited, sex influenced, and sex linked traits. ▪ Explain the chromosomal basis for genetic linkage and demonstrate how the chromosomal locations of linked genes can be mapped. ▪ Identify the specific patterns of inheritance that are characteristic of sex-linked traits. ▪ Know some human diseases or disorders caused by chromosomal alteration.
- 3. TOPICS ▪ Chromosome Theoryof Heredity ▪ Gene Dosage and Compensation ▪ Chromosome Mutation ▪ Changes in Chromosome Number ▪ Changes in Chromosome Structure ▪ Chromosomal Alterations in Human Disease/Disorders
- 4. CHROMOSOMES ▪ Threadlike structureswithin nucleus. ▪ A very long DNA molecule and associated proteins, that carry portions of the hereditary information of an organism.
- 5. Thomas H. Morgan ▪Defined the relationships between chromosomes and heredity. ▪ Morgan's first papers dealt with the demonstration of sex linkage of the gene for white eyes in the fly, the male fly being heterogametic.
- 6. CHROMOSOMES THEORY OF HEREDITY Itsays that genes are located on chromosomes.
- 7. CHROMOSOME MAPPING Lists the sequencesof genetic loci along a particular chromosome
- 8. HUMAN CHROMOSOMES Sex Chromosomes– X and Y chromosomes Autosomes – 22 pairs of chromosomes except the sex chromosomes.
- 9. NORMAL KARYOTYPES FEMALE NORMALKARYOTYPE MALE NORMAL KARYOTYPE
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- 11. Sex-Limited Inheritance Inheritance inwhich a trait or phenotype is expressed in one sex only Example: A man may inherit his beard type from his mother rather than from his father. Both sexes transmit the genes although only one sex normally expresses the trait.
- 12. Sex-Influenced Inheritance Inheritance thatis autosomal but has a different intensity of expression in the two sexes Example: In humans, baldness occurs in males with a single copy or the allele. A woman will lose her hair only if she is homozygous for the alleles.
- 13. Sex-Linked Inheritance Inheritance thatmay result from a mutant gene located on either the X- or Y-chromosome. Example: Color Blindness – mild disorder Hemophilia – Any of several hereditary blood-coagulation disorders, manifested almost exclusively in males, in which the blood fails to clot normally because of a deficiency or an abnormality of one of the clotting factors.
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- 15. GENE DOSAGE COMPENSATION ▪In mammals, only one X chromosome if fully active in most diploid cells. ▪ In females, one of the two X chromosomes is inactivated during embrayonic development.
- 16. GENE DOSAGE COMPENSATION ▪The inactive X chromosome contracts into a dense object, called a BARR BODY, which lies along the inside of the nuclear envelope in cells of females. ▪ Most of the genes of the X chromosomes that forms the BARR BODY are not expressed, although small regions of that chromosomes remain active.
- 17. CHROMOSOMES MUTATIONS ▪ Majorchanges in the chromosomes of a cell may occur as a result of errors during meiosis, mitosis or because of MUTAGENS. ▪ CHROMOSOME MUTATIONS – changes in genetic material that involve entire chromosomes or pieces of them.
- 18. CHROMOSOMES MUTATIONS ▪ Changesin chromosome structure (chromosomal mutations) are of great importance. ▪ Chromosomal mutations are used as tools in genetic experiments. ▪ In addition, many human diseases including many types of cancer are caused by chromosomal rearrangements.
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- 20. NONDISJUNCTION An accident ofmeiosis or mitosis in which both members of a pair of homologous chromosomes or both sister chromatids fail to separate properly
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- 22. ANEUPLOIDY A chromosomal aberrationin which certain chromosomes are present in extra copies or deficient in number a. trisomy- cell has an extra chromosome (2N + 1) b. monosomy- cell is missing a chromosome (2N-1)
- 23. POLYPLOIDY When an organismhas more than two complete chromosome sets a. Triploids – three complete sets b. Tetraploids – four sets
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- 25. CHANGES IN CHROMOSOMESTRUCTURE DELETION - The simple loss of a chromosomal segment DUPLICATION -The presence of two copies of a chromosomal region
- 26. CHANGES IN CHROMOSOMESTRUCTURE INVERSION -A segment of a chromosome can rotate 180 degrees and rejoin the chromosome, resulting in a chromosomal mutation TRANSLOCATION - two nonhomologous chromosomes can exchange parts to produce a chromosomal mutation
- 27. MECHANISMS OF CHANGE ▪breakage of a chromosome can lead to a variety of rearrangements affecting the gene ▪ fragments without centromeres are usually lost when the cell divides. the chromosome from which the fragment originated will then be missing certain genes, an alteration called deletion ▪ in some cases, the fragment may join a homologous chromosome, producing a duplication
- 28. MECHANISMS OF CHANGE ▪it may reattach to the original chromosome, but in reverse (called inversion) ▪ it may join a non-homologous chromosome (called translocation) ▪ a homozygous deletion (or a single X in a male) is usually lethal ▪ position effect- a gene's expression can be influenced by its location among neighboring genes
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- 30. DOWN SYNDROME ▪ isthe most common serious birth defect in the US (1:700) ▪ is the result of aneuploidy- extra chromosome 21 ▪ therefore, each body cell has a total of 47 chromosomes ▪ the chances of having a DS child increase with age (usually due to age of eggs)
- 31. PATAU SYNDROME ▪ causedby trisomy for chromosome 13 ▪ characterized by serious eye, brain, and circulatory defects, as well as harelip and cleft palate ▪ occurs one in every 5000 live births
- 32. EDWARD SYNDROME ▪ trisomyof chromosome 18 ▪ affects almost every organ system in the body ▪ one in 10000 ▪ most victims survive in less than a year
- 33. KLINEFELTER SYNDROME ▪ anextra X chromosome in a male (XXY) ▪ one in every 2000 births ▪ have abnormally small testes and is sterile ▪ can lead to breast enlargement and other feminine body contours. ▪ the affected individual is usually of normal intelligence.
- 34. TURNER SYNDROME ▪ monosomy-female is XO ▪ is the only known viable human monosomy ▪ individuals with this syndrome are phenotypically female but their sex organs do not mature at adolescence, and secondary sexual characteristics fail to develop. ▪ they are sterile and short but usually have no mental deficiency. Source: http://www.turner-syndrome-us.org/resource/faq.html
- 35. METAFEMALES ▪ females withthree X chromosomes ▪ they have limited fertility and may be mentally retarded.
- 36. CRI DU CHAT(“CRY OF THE CAT”) SYNDROME ▪ A human disorder caused by specific deletion in chromosome 5. ▪ An individual with this syndrome is mentally retarded and has a small head with unusual facial features and a cry that sounds like the mewing of a distressed cat. ▪ Death usually occurs in infancy or early childhood.