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Chapter 11 Germ cells, fertilization and sex Determination of the sexual phenotype Sex chromosomes Chapter 14— Sex determination Developmental Biology.

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Presentation on theme: "Chapter 11 Germ cells, fertilization and sex Determination of the sexual phenotype Sex chromosomes Chapter 14— Sex determination Developmental Biology."— Presentation transcript:

1 Chapter 11 Germ cells, fertilization and sex Determination of the sexual phenotype Sex chromosomes Chapter 14— Sex determination Developmental Biology by Scott Gilbert

2 The sex chromosome in humans Fig Mammals : Y chromosome Alligator : environmental temperature Fish: switch sex Drosophila: chromosome content Compensation of chromosomal composition

3 Figure 14.1 Sex determination in mammals (Part 1)

4 Development of the gonads Fig SRY--Testes—Mullerian-inhibiting substance —suppress female reproductive organ and induce cells to be Leydig cells— secrets testosterone Sex phenotypes controlled by hormone

5 Figure 14.1 Sex determination in mammals (Part 2)

6 Figure 14.2 Differentiation of human gonads shown in transverse section (Part 1)

7 Figure 14.2 Differentiation of human gonads shown in transverse section (Part 2) Sertoli cells Sperm

8 Figure 14.2 Differentiation of human gonads shown in transverse section (Part 3) GC-ova Granulosa and thecal cells follicle

9 Figure 14.4 Possible mechanism for the initiation of primary sex determination in mammals Sox9/Fgf9 Wnt4/  -catenin

10 Sex reversal in humans Fig Y chromosome—embryo’s gonads —develop into testes Single gene—sex-determining region of the Y chromosome (SRY) Klinefelter syndrome: XXY —males but infertile Turner syndrome: XO—female but no eggs XY females XX males Corssing over XX+SRY gene-infertile male

11 Figure 14.6 An XX mouse transgenic for Sry is male

12 Figure 14.7 Ability of Sox9 to generate testes

13 Figure Model for the formation of external genitalia

14 Figure Organization of brain development by hormones

15 Figure Masculinization of the brain by hormones (Part 1)

16 Figure Masculinization of the brain by hormones (Part 2)

17 Genitalia Sex comb Pigmentation Small wing Fig XX female XY male XXY female X male

18 Sex determining signal--- Sex-lethal (X chromosome) Sex-specific RNA splicing Transformer-spliced + transformer 2 transformer doublesex

19 Figure Proposed regulatory cascade for Drosophila somatic sex determination (Part 1)

20 Figure Proposed regulatory cascade for Drosophila somatic sex determination (Part 2)

21 Dosage compensation Barr body Xist-non-coding RNA Male specific gene Repressed by Sxl

22 2X higher numerator—binding to Pe Repression by autosome Autoregulatory loop Post-transcriptional levels

23 Figure Sex-specific RNA splicing in four major Drosophila sex-determining genes

24 Figure Roles of Dsx M and Dsx F proteins in Drosophila sexual development (Part 1)

25 Figure Roles of Dsx M and Dsx F proteins in Drosophila sexual development (Part 2)

26 Mating in fruit flies

27 Figure Subsets of neurons expressing the male-specific form of fruitless

28

29 2006 WINNER A cluster of Fruitless-expressing neurons in the Drosophila brain has been found to differ between male and females. This difference is produced by active elimination of neuronal precursor cells in females. The male-specific Fruitless protein inhibits programmed cell death in a cluster of neurons, allowing them to form a neural circuit that directs males to court females and not males. This research shows how a single gene can direct brain development and subsequently a sex-specific behavior. In this framework, sexual orientation can be understood in relation to an identified neuronal circuit and defined actions of a sex-determination gene. This figure shows the projection pattern of sexually dimorphic mAL (medially located, just above Antennal Lobe) neurons in the brain of a female (left) and a male (right). Kimura, K.-I., Ote. M, Tazawa, T and Yamamoto, D. Fruitless specifies sexually dimorphic neural circuitry in the Drosophila brain. Nature, vol. 438, (2005).

30 C. elegans Self-fertilizing-limited amount of sperm XO lethal(xol-1)—repressed by SEX-1 on X chromosome

31 Somatic sex determination pathway in C elegans Egl-1—death of neurons associated in the hermaphrodite with egg laying

32 Signals specify germ-cell sex in mammals

33 Determination of germ-cell sex in the hermaphrodite gonad Tips: germ cell multiply Meiosis--sperm Adult: proliferative zone--oocytes

34 Figure Temperature-dependent sex determination in three species of reptiles

35 Figure the feminization of male frogs and the decline of frog populations in regions where atrazine has been used to control weed populations Atrasine


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