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= Altitude Sickness Adaptation =

Causes
Altitude sickness occurs at high altitudes where the partial pressure of oxygen is low. This results in a low partial pressure of oxygen in the lungs, which lessens arterial oxygen content. In an attempt to restore arterial oxygen content, the body increases hemoglobin concentration and cardiac output. The initial symptom of altitude sickness is a headache. This can lead to other symptoms, but the mechanism behind the headache is unknown.

Ethiopians
The adaptive mechanism of Ethiopian highlanders is quite different. This is probably because their migration to the highland was relatively earlier; for example, the Amhara have inhabited altitudes above 2,500 metres (8,200 ft) for at least 5,000 years and altitudes around 2,000 metres (6,600 ft) to 2,400 metres (7,900 ft) for more than 70,000 years.[61]Genomic analysis of two ethnic groups, Amhara and Oromo, revealed that gene variations associated with haemoglobin difference among Tibetans or other variants at the samegene location do not influence the adaptation in Ethiopians.[62] Identification of specific genes further reveals that several candidate genes are involved in Ethiopians, including CBARA1, VAV3, ARNT2 and THRB.[63] Two of these genes (THRB and ARNT2) are known to play a role in the HIF-1 pathway, a pathway implicated in previous work reported in Tibetan and Andean studies. This supports the concept that adaptation to high altitude arose independently among different highlanders as a result of convergent evolution.

'''Identification of specific genes further revealed several candidate genes potentially involved in Ethiopians, including CBARA1, VAV3, ARNT2, THRB, BHLHE41, CIC, LIPE, and PAFAH1B3. Many of these genes (THRB, ARNT2, and BHLHE41) are known to play a role in the HIF-1 pathway, a pathway implicated in previous Tibetan and Andean studies. When orthologs of CIC, LIPE, and PAFAH1B3 were knocked down in Drosophila, increased survival in low oxygen conditions was observed.'''

* Note to graders: Our edits to this wikipedia page, "High Altitude Adaptation in Humans ," is in bold.

Tibetan Grey Wolf
The Tibetan grey wolf (Canis lupus chanco) shows positive selection in three genes related to hypoxia adaptation: EPAS1, ANGPT1 and RYR2. The EPAS1 and ANGPT1 genes are responsible for increased oxygen flow to tissues while RYR2 is involved in increased cardiac function. These genes are known to be selected for in humans living at high-altitudes. EPAS1 and ANGPT1 was found to be selected for in Tibetans while RYR2 was found in high-altitude dwelling Ethiopians.

Tibetan Chicken
Tibetan chickens (Gallus gallus domesticus) are characterized by smaller size and more efficient blood oxygen-carrying capacity compared to low-altitude chickens. A genetic comparison between Tibetan chickens and their lowland counterparts found not only significant admixture between the two populations but also noticeable differences in genes related to high-altitude adaptation. In Tibetan chickens, genes related to increased angiogenesis were determined to be positively selected for; specifically, HIF-1a and VEGF, important for blood vessel formation, are upregulated. Researchers also found variation in genes associated with UV radiation protection and DNA repair between the two populations.

Adaptation in Plants
Alpine plant species are able to attain relatively greater carbon gains in abundant CO2 atmosphere than lowland plants. High altitude plants display adaptations that allow them to increase their CO2 uptake and retain photosynthetic efficiency under elevated CO2 conditions compared to lowland plants.

There is a significant difference in variation between high-altitude plants and lowland plants. The latter displays high variation in growth responses, whereas the former group rely on dominant plants that prevail at high altitudes. Growing conditions in lowland plants favors phenotypic plasticity, while selective pressures at high altitude promote directional selection. Further phylogenetic research on plant diversification may provide new insights on environmental processes that characterize plant diversity and evolution.