1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 18 Patterns of Chromosome Inheritance Lecture Outline Part 4 Human Biology Sylvia S. Mader Michael Windelspecht

2 Mitosis vs. Meiosis Growth and repair of cells Occurs in body cells 1 division Results in 2 diploid, genetically identical cells Formation of gametes Occurs in sex cells 2 divisions Results in 4 haploid, genetically different cells 18.5 Comparison of Meiosis and Mitosis

3 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. MEIOSIS I MITOSIS Prophase I Synapsis and crossing-over occur. 2n = 4 Metaphase I Homologous pairs align independently at the equator. Anaphase I Homologous chromosomes separate and move towards the poles. Prophase 2n =4 Metaphase Chromosomes align at the equator. Anaphase Sister chromatids separate and become daughter chromosomes. Figure A comparison of meiosis and mitosis Comparison of Meiosis and Mitosis Comparing meiosis and mitosis

4 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Daughtercells Telophase I Daughter cells are forming and will go on to divide again. MEIOSIS I cont'd MEIOSIS II n = 2 Sister chromatids separate and become daughter chromosomes. Daughter cells Four haploid daughter cells: Their nuclei are genetically different from the parent cell. n = 2 Two diploid daughter cells: Their nuclei are genetically identical to the parent cell. Telophase Daughter cells are forming. MITOSIS cont'd Figure A comparison of meiosis and mitosis Comparison of Meiosis and Mitosis Comparing meiosis and mitosis

5 Changes in chromosome number ______________ occurs when both members of a homologous pair go into the same daughter cell during meiosis I, or when sister chromatids fail to separate in meiosis II. Results of nondisjunction –_________: cell has only 1 copy of a chromosome e.g., Turner syndrome (only 1 X chromosome) –__________: cell has 3 copies of a chromosome e.g., Down syndrome (3 copies of chromosome 21) 18.6 Chromosome Inheritance

6 Nondisjunction Figure The consequences of nondisjunction of chromosomes during oogenesis Chromosome Inheritance Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. pair of homologous chromosomes normal meiosis I normal meiosis IInondisjunction Egg will have either one extra or one less chromosome. Egg will have normal number of chromosomes. a. pair of homologous chromosomes nondisjunction meiosis II Egg will have one less chromosome. Egg will have one extra chromosome. b.

7 Changes in chromosome number Figure Down syndrome Chromosome Inheritance Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. extra chromosome 21 Gart gene b.a. 21 a: © Scott Wintrow/Getty Images; b (left): © CNRI/SPL/Photo Researchers

8 Changes in sex chromosome number ______________ (XO) – short stature, broad- shouldered, with folds of skin on the neck, underdeveloped sex organs and breasts Klinefelter syndrome (____) – underdeveloped sex organs, breast development, large hands, and long arms and legs 18.6 Chromosome Inheritance

9 Changes in sex chromosome number Poly-X females (XXX, XXXX) –XXX tend to be tall and thin but do not usually have mental retardation –XXXX have severe mental retardation _______ syndrome (XYY) – tall, persistent acne, speech and reading problems 18.6 Chromosome Inheritance

10 Barr bodies and X inactivation Females have 2 copies of X genes; males have 1. In female embryos, 1 X chromosome becomes inactivated (Barr body) in each cell Chromosome Inheritance

11 Changes in chromosome structure ___________ – loss of a piece of the chromosome (e.g., Williams syndrome) Translocation – movement of chromosome segments from one chromosome to another nonhomologous chromosome (Alagille syndrome) _________ – presence of a chromosome segment more than once in the same chromosome Inversion – a segment of a chromosome is inverted 180 degrees 18.6 Chromosome Inheritance

12 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. a b c d e f g a b c d e f g a b c d e f g h l m n o p q r a b c d e f g h l m n o p q r a b c d e f g a b c d e d e f g + a b c d e f g a b c d e f g a. Deletionb. Duplicationc. Inversiond. Translocation Figure The various types of chromosomal mutations Chromosome Inheritance Changes in chromosome structure

13 Chromosomal inversion Figure A chromosomal inversion Chromosome Inheritance Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. A A A B B B C C C D D D E E E F F F G G G a a a b b b e e e d d d c c c f f f g g g inverted segment region of crossing-over homologous chromosomes duplication and deletion in both

14 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. + a b c d e f g h a b c d e f g h deletionlost a b c d e f g h s t u v w x y z a b c d e f g h s t u v w x y z translocation Figure A chromosomal deletion.Figure A chromosomal translocation Chromosome Inheritance Changes in chromosome structure