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Chapter 11 Germ cells, fertilization and sex. Determination of the sexual phenotype Sex chromosomes. Chapter 14— Sex determination Developmental Biology by Scott Gilbert. The sex chromosome in humans. Mammals : Y chromosome Alligator : environmental temperature Fish: switch sex
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Chapter 11 Germ cells, fertilization and sex Determination of the sexual phenotype Sex chromosomes Chapter 14— Sex determination Developmental Biology by Scott Gilbert
The sex chromosome in humans Mammals : Y chromosome Alligator : environmental temperature Fish: switch sex Drosophila: chromosome content Compensation of chromosomal composition Fig. 11-16
Development of the gonads SRY--Testes—Mullerian-inhibiting substance —suppress female reproductive organ and induce cells to be Leydig cells— secrets testosterone Sex phenotypes controlled by hormone Fig. 11-18
Figure 14.2 Differentiation of human gonads shown in transverse section (Part 1)
Figure 14.2 Differentiation of human gonads shown in transverse section (Part 2) Sertoli cells Sperm
Figure 14.2 Differentiation of human gonads shown in transverse section (Part 3) GC-ova Granulosa and thecal cells follicle
Figure 14.4 Possible mechanism for the initiation of primary sex determination in mammals Sox9/Fgf9 3 1 2 Wnt4/b-catenin
Sex reversal in humans 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 Fig. 11-17
Figure 14.15 Masculinization of the brain by hormones (Part 1)
Figure 14.15 Masculinization of the brain by hormones (Part 2)
Genitalia Sex comb Pigmentation Small wing XX female XY male XXY female X male Fig. 11-20
Sex determining signal--- Sex-lethal (X chromosome) Sex-specific RNA splicing doublesex transformer Transformer-spliced + transformer 2
Figure 14.17 Proposed regulatory cascade for Drosophila somatic sex determination (Part 1)
Figure 14.17 Proposed regulatory cascade for Drosophila somatic sex determination (Part 2)
Dosage compensation Barr body Xist-non-coding RNA Male specific gene Repressed by Sxl
Repression by autosome 2X higher numerator—binding to Pe Autoregulatory loop Post-transcriptional levels
Figure 14.18 Sex-specific RNA splicing in four major Drosophila sex-determining genes
Figure 14.20 Roles of DsxM and DsxF proteins in Drosophila sexual development (Part 1)
Figure 14.20 Roles of DsxM and DsxF proteins in Drosophila sexual development (Part 2)
Figure 14.21 Subsets of neurons expressing the male-specific form of fruitless
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, 229-233 (2005).
C. elegans Self-fertilizing-limited amount of sperm XO lethal(xol-1)—repressed by SEX-1 on X chromosome
Somatic sex determination pathway in C elegans Egl-1—death of neurons associated in the hermaphrodite with egg laying
Determination of germ-cell sex in the hermaphrodite gonad Tips: germ cell multiply Meiosis--sperm Adult: proliferative zone--oocytes
Figure 14.22 Temperature-dependent sex determination in three species of reptiles
Figure 14.24 the feminization of male frogs and the decline of frog populations in regions where atrazine has been used to control weed populations Atrasine
