BIOLOGY CONCEPTS & CONNECTIONS Fourth Edition Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Neil A. Campbell Jane B. Reece Lawrence G. Mitchell Martha R. Taylor From PowerPoint ® Lectures for Biology: Concepts & Connections CHAPTER 8 The Cellular Basis of Reproduction and Inheritance Modules 8.19 – 8.23

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings To study human chromosomes microscopically, researchers stain and display them as a karyotype –A karyotype usually shows 22 pairs of autosomes and one pair of sex chromosomes ALTERATIONS OF CHROMOSOME NUMBER AND STRUCTURE 8.19 A karyotype is a photographic inventory of an individual’s chromosomes

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Preparation of a karyotype Figure 8.19 Blood culture 1 Centrifuge Packed red And white blood cells Fluid 2 Hypotonic solution 3 Fixative White Blood cells Stain 45 Centromere Sister chromatids Pair of homologous chromosomes

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings This karyotype shows three number 21 chromosomes An extra copy of chromosome 21 causes Down syndrome 8.20 Connection: An extra copy of chromosome 21 causes Down syndrome Figure 8.20A, B

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The chance of having a Down syndrome child goes up with maternal age Figure 8.20C

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Abnormal chromosome count is a result of nondisjunction –Either homologous pairs fail to separate during meiosis I 8.21 Accidents during meiosis can alter chromosome number Figure 8.21A Nondisjunction in meiosis I Normal meiosis II Gametes n + 1 n – 1 Number of chromosomes

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings –Or sister chromatids fail to separate during meiosis II Figure 8.21B Normal meiosis I Nondisjunction in meiosis II Gametes n + 1n – 1nn Number of chromosomes

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Fertilization after nondisjunction in the mother results in a zygote with an extra chromosome Figure 8.21C Egg cell Sperm cell n + 1 n (normal) Zygote 2n + 1

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Nondisjunction can also produce gametes with extra or missing sex chromosomes –Unusual numbers of sex chromosomes upset the genetic balance less than an unusual number of autosomes 8.22 Connection: Abnormal numbers of sex chromosomes do not usually affect survival

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Table 8.22

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings A man with Klinefelter syndrome has an extra X chromosome Figure 8.22A Poor beard growth Under- developed testes Breast development

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings A woman with Turner syndrome lacks an X chromosome Figure 8.22B Characteristic facial features Web of skin Constriction of aorta Poor breast development Under- developed ovaries