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Chromosomal Patterns of Inheritance

Chromosomal Patterns of Inheritance

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Chromosomal Patterns of Inheritance

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  1. Chromosomal Patterns of Inheritance Mader: Biology 8th Ed.

  2. Outline • X-Linked Alleles • Human X-Linked Disorders • Gene Linkage • Crossing-Over • Chromosome Map • Changes in Chromosome Number • Changes in Chromosome Structure • Human Syndromes Mader: Biology 8th Ed.

  3. Chromosomal Inheritance • All but one pair of chromosomes in males and females are the same. • Autosomes - Nonsex chromosomes • The different pair, sex chromosomes, determines the sex of an individual. • X-linked (sex-linked) is the term used for genes carried on the X chromosome. Mader: Biology 8th Ed.

  4. X-Linked Alleles • X-linked alleles have a different pattern of inheritance than alleles on autosomes because the Y chromosome is blank for these alleles. • Inheritance of a Y chromosome cannot offset the inheritance of an X-linked recessive allele. Mader: Biology 8th Ed.

  5. Drosophila Mader: Biology 8th Ed.

  6. Human X-Linked Disorders • Color Blindness • In humans, color vision receptors in the retina are three different classes of cone cells. • Only one type of pigment is present in each class of cone cell. • The allele for blue-sensitive is autosomal, but the red- and green-sensitive proteins are on the X chromosome. Mader: Biology 8th Ed.

  7. Human X-Linked Disorders • Muscular Dystrophy • Absence of protein dystrophin allows calcium to leak into muscle cells. • Hemophilia • Hemophilia A due to lack of clotting factor IX and hemophilia B due to lack of clotting factor VIII. Mader: Biology 8th Ed.

  8. Hemophilia Pedigree Mader: Biology 8th Ed.

  9. Gene Linkage • The existence of several alleles on the same chromosome. • Alleles on the same chromosome form a linkage group because they tend to be inherited together. • Can be used to build a linkage map. Mader: Biology 8th Ed.

  10. Constructing a Chromosome Map • A linkage map can also be called a chromosome map because it tells the order of gene loci on chromosomes. • If crossing-over occurs between two linked alleles of interest, a dihybrid produces four types of gametes instead of two. Mader: Biology 8th Ed.

  11. Crossing-Over Mader: Biology 8th Ed.

  12. Linkage Data • The percentage of recombinant phenotypes can be used to map chromosomes because there is a direct relationship between the frequency of crossing-over and the distance between alleles. • Assumed 1% crossing-over equals 1 map unit. Mader: Biology 8th Ed.

  13. Changes in Chromosome Number • Polyploidy • Occurs when eukaryotes have more than 2n number of chromosomes. • Named according to number of sets of chromosomes. • Major evolutionary force in plants. • Some estimate 47% of flowering plants are polyploids. Mader: Biology 8th Ed.

  14. Changes in Chromosome Number • Monosomy and Trisomy • Monosomy (2n - 1) occurs when an individual has only one of a particular type of chromosome. • Trisomy (2n + 1) occurs when an individual has three of a particular type of chromosome. Mader: Biology 8th Ed.

  15. Down Syndrome • Down syndrome (Trisomy 21) is caused by three copies of chromosome 21. Mader: Biology 8th Ed.

  16. Changes in Sex Chromosome Number • An abnormal sex chromosome number is the result of inheriting too many or too few X or Y chromosomes. • Nondisjunction during oogenesis or spermatogenesis. Mader: Biology 8th Ed.

  17. Sex Chromosome Syndromes • Turner Klinefelter (XO) (XXY) Mader: Biology 8th Ed.

  18. Sex Chromosome Syndromes • Poly-X Females • More than two X chromosomes and extra Barr bodies in the nucleus. • Range from tall and thin to tall and severely retarded depending on number of X chromosomes. • Jacobs Syndrome • XXY due to nondisjunction during spermatogenesis. • Taller than average Mader: Biology 8th Ed.

  19. Changes in Chromosome Structure • Deletion • End of a chromosome breaks off, or two simultaneous breaks lead to loss of an internal segment. • Translocation • Movement of a chromosome segment from one chromosome to another, non-homologous chromosome. Mader: Biology 8th Ed.

  20. Changes in Chromosome Structure Mader: Biology 8th Ed.

  21. Changes in Chromosome Structure • Duplication • Presence of chromosomal segment more than once in the same chromosome. • Known to occur as a result of an inversion in which segment is turned 180o. Mader: Biology 8th Ed.

  22. Changes in Chromosome Structure Mader: Biology 8th Ed.

  23. Human Syndromes • Deletion Syndromes • Williams syndrome - Loss of segment of chromosome 7. • Cri du chat syndrome (cat’s cry) - Loss of segment of chromosome 5. Mader: Biology 8th Ed.

  24. Review • X-Linked Alleles • Human X-Linked Disorders • Gene Linkage • Crossing-Over • Chromosome Map • Changes in Chromosome Number • Changes in Chromosome Structure • Human Syndromes Mader: Biology 8th Ed.

  25. Mader: Biology 8th Ed.