Copyright © 2009 Pearson Education, Inc. PowerPoint ® Lecture Presentation for Concepts of Genetics Ninth Edition Klug, Cummings, Spencer, Palladino Chapter 7 Sex Determination and Sex Chromosomes Lectures by David Kass with contributions from John C. Osterman. Copyright © 2009 Pearson Education, Inc.

7.1 Life Cycles Depend on Sexual Differentiation In multicellular organisms, it is important to distinguish between: primary sexual differentiation involves only the gonads where gametes are produced secondary sexual differentiation involves the overall appearance of the organism Section 7.1

Copyright © 2009 Pearson Education, Inc. Section 7.1 Some organisms (e.g. Chlamydomonas) spend most of their life cycle in the haploid phase, asexually producing daughter cells by mitotic division.

Copyright © 2009 Pearson Education, Inc. Figure 7.1

Copyright © 2009 Pearson Education, Inc. Figure 7.2

Copyright © 2009 Pearson Education, Inc. In maize (Zea mays), the diploid sporophyte stage predominates and both male and female structures are present on the adult plant. This indicates that sex determination must occur differently in different tissues of the same plant Section 7.1

Copyright © 2009 Pearson Education, Inc. Figure 7.3.2

Copyright © 2009 Pearson Education, Inc. The nematode worm Caenorhabditis elegans has 2 sexual phenotypes: Males, which have only testes Hermaphrodites, which have both testes and ovaries Section 7.1

Copyright © 2009 Pearson Education, Inc. Figure 7.4

Copyright © 2009 Pearson Education, Inc. XX/XO (Protenor) mode of sex determination depends on random distribution of the X chromosome into half of the male gametes. Presence of two X chromosomes in the zygote = female offspring Presence of only one X chromosome = male offspring Section mals/Insects/Butterflies/Papilio_prot enor2.jpg

Copyright © 2009 Pearson Education, Inc. Figure 7.5a

Copyright © 2009 Pearson Education, Inc. XX/XY (Lygaeus) mode of sex determination: female gametes all have an X chromosome male gametes have either an X or a Y chromosome Zygotes with two X chromosomes (homogametous) = female offspring Zygotes with one X and one Y chromosome (heterogametous) = male offspring Section 7.2

Copyright © 2009 Pearson Education, Inc. Figure 7.5b

Copyright © 2009 Pearson Education, Inc. ZZ/ZW sex determination: females are the heterogametic (ZW) sex males are the homogametic (ZZ) sex Section 7.2

Copyright © 2009 Pearson Education, Inc. 7.3The Y Chromosome Determines Maleness in Humans Human karyotype revealed that one pair of chromosomes differs in males and females: females have two X chromosomes males have one X and one Y chromosome Section 7.3

Copyright © 2009 Pearson Education, Inc. Figure 7.6 Normal Human Karyotypes

Copyright © 2009 Pearson Education, Inc. Persons with Klinefelter syndrome have: male genitalia more than one X chromosome (usually XXY, or a 47,XXY karyotype) Section 7.3

Copyright © 2009 Pearson Education, Inc. Figure 7.7a

Copyright © 2009 Pearson Education, Inc. Persons with Turner syndrome usually have: a single X chromosome no Y chromosome (45,X karyotype) female genitalia Section 7.3

Copyright © 2009 Pearson Education, Inc. Figure 7.7b

Copyright © 2009 Pearson Education, Inc. 47, XXX – Trisomy X 3 X chromosomes along with a normal set of autosomes results in female differentiation. Usually normal In other cases, underdeveloped secondary sex characteristics, sterility, and mental retardation may occur. Section 7.3

Copyright © 2009 Pearson Education, Inc. 47, XYY – Jacobs Syndrome Males are usually over 6 feet tall. Section 7.3

Copyright © 2009 Pearson Education, Inc. Figure 7.8

Copyright © 2009 Pearson Education, Inc. The Y chromosome contains far fewer genes than the X chromosome. Section 7.3

Copyright © 2009 Pearson Education, Inc. Pseudoautosomal Regions (PARs) regions on Y chromosome that share homology with regions on the X chromosome synapse and recombine with it during meiosis Presence of such a pairing region is critical to segregation of the X and Y chromosomes during male gametogenesis Section 7.3

Copyright © 2009 Pearson Education, Inc. Y chromosome contains: the male- specific region of the Y (MSY) a sex- determining region of the Y (SRY) Section 7.3

Copyright © 2009 Pearson Education, Inc. Testis-determining factor (TDF) a protein encoded by a gene in the SRY that triggers testes formation. The MSY consists of three regions: X-transposed region X-degenerative region ampliconic region Section 7.3

Copyright © 2009 Pearson Education, Inc. 7.4The Ratio of Males to Females in Humans is not 1.0 Primary sex ratio reflects the proportion of males to females conceived in a population. Secondary sex ratio reflects the proportion of each sex that is born. Section 7.4

Copyright © 2009 Pearson Education, Inc. 7.5Dosage Compensation Prevents Excessive Expression of X-Linked Genes in Humans and Other Mammals Dosage compensation balances the dose of X chromosome gene expression in females and males. Section 7.5

Copyright © 2009 Pearson Education, Inc. The inactive X is highly condensed, can be observed in stained interphase cells, and are referred to as Barr bodies (Figure 7.10). Section 7.5

Copyright © 2009 Pearson Education, Inc. Figure 7.11

Copyright © 2009 Pearson Education, Inc. The Lyon hypothesis states that X-inactivation occurs randomly in somatic cells. This is evident in the calico cat (Figure 7.12). Section 7.5

Copyright © 2009 Pearson Education, Inc. Figure 7.13 Lyonization in Humans: - Red-green color blindness - Anhidrotic ectodermal dysplasia

Copyright © 2009 Pearson Education, Inc. The X-inactivation center (Xic) is active on the inactive X. It consists of the X-inactive specific transcript (XIST) gene. Section 7.5

Copyright © 2009 Pearson Education, Inc. 7.6The Ratio of X Chromosomes to Sets of Autosomes Determines Sex in Drosophila

Copyright © 2009 Pearson Education, Inc. Figure 7.15

Copyright © 2009 Pearson Education, Inc. 7.7Temperature Variation Controls Sex Determination in Reptiles

Copyright © 2009 Pearson Education, Inc. For all crocodiles, most turtles, and some lizards, sex determination is achieved according to the incubation temperature of eggs during a critical period of embryonic development. Section 7.7

Copyright © 2009 Pearson Education, Inc. There are three different patterns of temperature sex determination in reptiles (Figure 7.18). Section 7.7

Copyright © 2009 Pearson Education, Inc. Figure 7.18