Concepts of Genetics Ninth Edition Klug, Cummings, Spencer, Palladino

Transcription

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

2 Section 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

3 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.

4 Figure 7.1

5 Figure 7.2

6 Section 7.1 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

7 Figure 7.3.2

8 Section 7.1 The nematode worm Caenorhabditis elegans has 2 sexual phenotypes: Males, which have only testes Hermaphrodites, which have both testes and ovaries

9 Figure 7.4

10 Section 7.2 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 mals/insects/butterflies/papilio_prot enor2.jpg

11 Figure 7.5a

12 Section 7.2 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

13 Figure 7.5b

14 Section 7.2 ZZ/ZW sex determination: females are the heterogametic (ZW) sex males are the homogametic (ZZ) sex

15 Section The 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

16 Normal Human Karyotypes Figure 7.6

17 Section 7.3 Persons with Klinefelter syndrome have: male genitalia more than one X chromosome (usually XXY, or a 47,XXY karyotype)

18 Figure 7.7a

19 Section 7.3 Persons with Turner syndrome usually have: a single X chromosome no Y chromosome (45,X karyotype) female genitalia

20 Figure 7.7b

21 Section , 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.

22 Section , XYY Jacobs Syndrome Males are usually over 6 feet tall.

23 Figure 7.8

24 Section 7.3 The Y chromosome contains far fewer genes than the X chromosome.

25 Section 7.3 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

26 Section 7.3 Y chromosome contains: the malespecific region of the Y (MSY) a sexdetermining region of the Y (SRY)

27 Section 7.3 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

28 Section The 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.

29 Section Dosage 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.

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

31 Figure 7.11

32 Section 7.5 The Lyon hypothesis states that X-inactivation occurs randomly in somatic cells. This is evident in the calico cat (Figure 7.12).

33 Lyonization in Humans: - Red-green color blindness - Anhidrotic ectodermal dysplasia Figure 7.13

34 Section 7.5 The X-inactivation center (Xic) is active on the inactive X. It consists of the X-inactive specific transcript (XIST) gene.

35 7.6 The Ratio of X Chromosomes to Sets of Autosomes Determines Sex in Drosophila

36 Figure 7.15

37 7.7 Temperature Variation Controls Sex Determination in Reptiles

38 Section 7.7 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.

39 Section 7.7 There are three different patterns of temperature sex determination in reptiles (Figure 7.18).

40 Figure 7.18