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In this third article in the series, two further hypothetical scenarios are used to provide guidance on supporting breastfeeding mothers when the baby has a craniofacial anomaly or a cardiac defect. Successful breastfeeding in such circumstances has a positive effect on maternal confidence and attachment, and appears in itself to have healing potential. Unexpected benefits of breastfeeding critically ill babies include enhanced immunity and feeding tolerance in babies undergoing chemotherapy. A structured breastfeeding support service can assist staff in promoting successful breastfeeding in the paediatric environment. Expert, experiential knowledge of overcoming challenges in breastfeeding for mothers of critically ill babies can be applied in the absence of research evidence.

The first article in this series highlighted the challenges that mothers face in establishing breastfeeding (Wallis and Harper 2007). Breastfeeding a sick infant in hospital presents additional challenges such as small, sleepy babies, babies who may be nil by mouth for prolonged periods and babies who may find breastfeeding difficult due to mechanical problems. There is very little published abut the needs of babies with complex medical or surgical conditions who may have had significant delays in their feeding or numerous starts and stops along the way. This article and Part 2b in the November issue illustrate some of the common challenges and propose principles of care that are transferable to caring for other sick babies with similar problems.

Breastfeeding makes a vital contribution to the health and development of babies, as well as to long term health. Establishing breastfeeding may not be easy even for mothers with healthy full-term babies. Mothers in the paediatric environment experience additional challenges: sick babies, delayed onset of breastfeeding and having to establish and maintain breastfeeding in situations where privacy may be limited and anxiety levels high. This first part of a two-part article describes the development of a breastfeeding support service in a tertiary children's hospital. Institutional support, a dedicated post and a planned programme of training and education, with the development of specific resource materials, have resulted in a service that closely matches the expressed needs of mothers.

The duck-billed platypus has five pairs of sex chromosomes, but there is no information about the primary sex-determining switch in this species. As there is no apparent SRY orthologue in platypus, another gene must acquire the function of a key regulator of the gonadal male or female fate. SOX9 was ruled out from being this key regulator as it maps to an autosome in platypus. To check whether other genes in mammalian gonadogenesis could be the primary switch in monotremes, we have mapped a number of candidates in platypus. We report here the autosomal location of WT1, SF1, LHX1, LHX9, FGF9, WNT4 and RSPO1 in platypus, thus excluding these from being key regulators of sex determination in this species. We found that GATA4 maps to sex chromosomes Y1 and X2; however, it lies in the pairing region shown by chromosome painting to be homologous, so is unlikely to be either male-specific or differentially dosed in male and female.

Sex determination in vertebrates is accomplished through a highly conserved genetic pathway. But surprisingly, the downstream events may be activated by a variety of triggers, including sex determining genes and environmental cues. Amongst species with genetic sex determination, the sex determining gene is anything but conserved, and the chromosomes that bear this master switch subscribe to special rules of evolution and function. In mammals, with a few notable exceptions, female are homogametic (XX) and males have a single X and a small, heterochromatic and gene poor Y that bears a male dominant sex determining gene SRY. The bird sex chromosome system is the converse in that females are the heterogametic sex (ZW) and males the homogametic sex (ZZ). There is no SRY in birds, and the dosage-sensitive Z-borne DMRT1 gene is a credible candidate sex determining gene. Different sex determining switches seem therefore to have evolved independently in different lineages, although the complex sex chromosomes of the platypus offer us tantalizing clues that the mammal XY system may have evolved directly from an ancient reptile ZW system. In this review we will discuss the organization and evolution of the sex chromosomes across a broad range of mammals, and speculate on how the Y chromosome, and SRY, evolved.

A comparative study of the karyotype of the short-beaked echidna shows that monotremes appear to have a unique XY sex chromosome system that shares some homology with the avian Z., Background Sex-determining systems have evolved independently in vertebrates. Placental mammals and marsupials have an XY system, birds have a ZW system. Reptiles and amphibians have different systems, including temperature-dependent sex determination, and XY and ZW systems that differ in origin from birds and placental mammals. Monotremes diverged early in mammalian evolution, just after the mammalian clade diverged from the sauropsid clade. Our previous studies showed that male platypus has five X and five Y chromosomes, no SRY, and DMRT1 on an X chromosome. In order to investigate monotreme sex chromosome evolution, we performed a comparative study of platypus and echidna by chromosome painting and comparative gene mapping. Results Chromosome painting reveals a meiotic chain of nine sex chromosomes in the male echidna and establishes their order in the chain. Two of those differ from those in the platypus, three of the platypus sex chromosomes differ from those of the echidna and the order of several chromosomes is rearranged. Comparative gene mapping shows that, in addition to bird autosome regions, regions of bird Z chromosomes are homologous to regions in four platypus X chromosomes, that is, X1, X2, X3, X5, and in chromosome Y1. Conclusion Monotreme sex chromosomes are easiest to explain on the hypothesis that autosomes were added sequentially to the translocation chain, with the final additions after platypus and echidna divergence. Genome sequencing and contig anchoring show no homology yet between platypus and therian Xs; thus, monotremes have a unique XY sex chromosome system that shares some homology with the avian Z.