**1.2 Marsupial BAC libraries**

Marsupials, a diverse group of mammals with over 300 extant species found in the Americas and Australasia, diverged from eutherian mammals approximately 147 mya (Bininda-Emonds et al., 2007) (Fig. 1). They are renowned for their mode of reproduction, giving birth to altricial young that usually develop in a pouch. Three species of marsupials were chosen as 'model' species for genetics and genomics studies 20 years ago: the grey short-tailed South American opossum (*Monodelphis domestica*) representing the Family Didelphidae, the tammar wallaby (*Macropus eugenii*) from the kangaroo family Macropodidae and the fat-tailed dunnart (*Sminthopsis macroura*) as a member of the speciose Family Dasyuridae (Hope & Cooper, 1990). The opossum, the first marsupial to have its genome sequenced (Mikkelsen et al., 2007), is considered a laboratory marsupial and has been used as a biomedical model for studying healing of spinal cord injuries and ultraviolet (UV) radiation induced melanoma (Samollow, 2006). The tammar wallaby has also recently had its genome sequence (Renfree et al., 2011) and has been extensively used for research into genetics, reproduction and physiology. Although there have been a few studies carried out on the fat-tailed dunnart, the recent emergence of the fatal devil facial tumour disease (DFTD) has led to the Tasmanian devil replacing it as the model dasyurid, with many resources being made available, including genome (Miller et al., 2011) and transcriptome sequence (Murchison et al., 2010). These model species represent three distantly related marsupial orders, with comparisons between these species being valuable for discerning the features that are shared among marsupials and those that are specific to certain lineages. BAC libraries have been made for all four species mentioned above and are summarized in Table 2. The three current model species will herein be referred to simply as opossum, wallaby and devil.

In addition to the model species, BAC libraries have also been constructed for the Virginia opossum (*Didelphis virginiana*), another member of the Family Didelphidae and the Northern brown bandicoot (*Isoodon macrourus*) (Table 2) from the Family Peramelidae. The phylogenetic position of the bandicoots, located at the base of the Australian marsupial radiation, and some of their more unique features make them interesting animals to study (Deakin, 2010). They possess the most invasive placentas among marsupials, with an allantoic placenta more like that found in eutherians, which would make them a valuable species in which to study genomic imprinting. They also deal with dosage compensation in an unusual way by eliminating one sex chromosome in somatic cells (Hayman & Martin, 1965; Johnston et al., 2002).


Table 2. Marsupial BAC libraries

2 Bacterial Artificial Chromosomes

Monotremes are the most basal lineage of mammals (Fig. 1), diverging from therian mammals (marsupials and eutherians) around 166 million years ago (mya) (Bininda-Emonds et al., 2007). Like all other mammals, they suckle their young and possess fur, but their oviparous mode of reproduction and their rather unique sex chromosome system are two features of most interest to comparative genomicists. BAC libraries have been made for two of the five extant species of monotremes, the platypus (*Ornithorhynchus anatinus*) and the short-beaked echidna (*Tachyglossus aculeatus*). These species last shared a common ancestor approximately 70 mya. The platypus genome, consisting of 21 pairs of autosomes and 10 pairs of sex chromosomes, has been sequenced (Warren et al., 2008) and a male and a female BAC library constructed (see Table 1). Similarly, the echidna genome has nine sex chromosomes and 27 pairs of autosomes,

Platypus CHORI\_236 Female 147 327,485 Platypus Oa\_Bb Male 143 230,400 Short-beaked echidna Ta\_Ba Male 145 210,048

Marsupials, a diverse group of mammals with over 300 extant species found in the Americas and Australasia, diverged from eutherian mammals approximately 147 mya (Bininda-Emonds et al., 2007) (Fig. 1). They are renowned for their mode of reproduction, giving birth to altricial young that usually develop in a pouch. Three species of marsupials were chosen as 'model' species for genetics and genomics studies 20 years ago: the grey short-tailed South American opossum (*Monodelphis domestica*) representing the Family Didelphidae, the tammar wallaby (*Macropus eugenii*) from the kangaroo family Macropodidae and the fat-tailed dunnart (*Sminthopsis macroura*) as a member of the speciose Family Dasyuridae (Hope & Cooper, 1990). The opossum, the first marsupial to have its genome sequenced (Mikkelsen et al., 2007), is considered a laboratory marsupial and has been used as a biomedical model for studying healing of spinal cord injuries and ultraviolet (UV) radiation induced melanoma (Samollow, 2006). The tammar wallaby has also recently had its genome sequence (Renfree et al., 2011) and has been extensively used for research into genetics, reproduction and physiology. Although there have been a few studies carried out on the fat-tailed dunnart, the recent emergence of the fatal devil facial tumour disease (DFTD) has led to the Tasmanian devil replacing it as the model dasyurid, with many resources being made available, including genome (Miller et al., 2011) and transcriptome sequence (Murchison et al., 2010). These model species represent three distantly related marsupial orders, with comparisons between these species being valuable for discerning the features that are shared among marsupials and those that are specific to certain lineages. BAC libraries have been made for all four species mentioned above and are summarized in Table 2. The three current model species will herein be

**Average insert size (kb)** 

**Number of Clones** 

**1.1 Monotreme BAC libraries** 

with a male BAC library available for this species (Table 1).

Table 1. Available monotreme BAC libraries

referred to simply as opossum, wallaby and devil.

**1.2 Marsupial BAC libraries** 

**Species Library Name Sex** 
