(a) How would you find out that a particular disease/disorder is inherited and, if so, in which manner? Elaborate with suitable…

How this answer will be evaluated

Evaluation rubric

Each sub-part is marked on its own, against the marks and word limit printed on the paper.

1. (a) Two linked demands: the methods by which one establishes that a disorder is genetically determined, and then the identification of its mode of inheritance, each illustrated with named disorders - first whether it is inherited, then in what manner. 20 marks

   Must cover

   • pedigree analysis, proband, segregation analysis
   • twin concordance (MZ vs DZ) and heritability; adoption studies
   • consanguinity as evidence of autosomal recessive inheritance
   • linkage analysis and LOD score; GWAS
   • Huntington disease, achondroplasia, Marfan syndrome (autosomal dominant)
   • sickle-cell anaemia, beta-thalassaemia, phenylketonuria, cystic fibrosis (autosomal recessive)
   • haemophilia (A and B), Duchenne muscular dystrophy, colour blindness, G6PD deficiency (X-linked recessive)
   • mitochondrial inheritance - LHON or MELAS; multifactorial threshold traits; imprinting (Prader-Willi and Angelman)

   Loses marks

   • Listing modes of inheritance only, and never answering the first half of the question about how one establishes that a disorder is inherited at all
   • Omitting twin and adoption studies, which are the classic anthropological tools for separating heredity from environment
   • Assigning disorders to the wrong mode - most often calling haemophilia autosomal, or sickle-cell dominant
   • Claiming male-to-male transmission for an X-linked recessive trait, which is the defining impossibility of that pattern
   • Ignoring multifactorial inheritance, so that common disorders such as diabetes and hypertension are forced into Mendelian categories

   Earns more

   • Describes molecular and cytogenetic confirmation: linkage analysis with LOD scores, where a score of 3 or more is conventionally taken as significant following Morton (1955); association studies and genome-wide association studies for complex traits; candidate gene testing and exome or whole-genome sequencing; karyotyping, banding, FISH and chromosomal microarray where a chromosomal cause is suspected; and biochemical or enzyme assays for metabolic disorders
   • Sex-linked and mitochondrial patterns: X-linked recessive inheritance with predominantly affected males, carrier mothers, absence of male-to-male transmission and criss-cross inheritance from maternal grandfather to grandson, illustrated by haemophilia (the royal haemophilia of Queen Victoria's descendants, identified in 2009 as haemophilia B), Duchenne muscular dystrophy, red-green colour blindness and G6PD deficiency; X-linked dominant inheritance in which an affected father transmits to all daughters and no sons, illustrated by vitamin D-resistant hypophosphataemic rickets and Rett syndrome; Y-linked or holandric transmission from father to all sons; and mitochondrial inheritance in which an affected mother transmits to all her children while affected fathers do not transmit, illustrated by Leber's hereditary optic neuropathy and MELAS
   • Non-Mendelian complications and application: multifactorial and polygenic inheritance with a liability-threshold model, seen in type 2 diabetes, hypertension, coronary artery disease, cleft lip and palate and neural tube defects, where empirical rather than Mendelian recurrence risks are used; genomic imprinting, with Prader-Willi and Angelman syndromes arising from the same 15q11-13 region according to parental origin; anticipation in trinucleotide repeat disorders such as fragile X from FMR1 CGG expansion and myotonic dystrophy; and the use of all this in genetic counselling, carrier screening and prenatal diagnosis

   Extra mark

   • Indian relevance: high sickle-cell and beta-thalassaemia carrier frequencies in tribal and some caste populations, and the National Sickle Cell Anaemia Elimination Mission (2023)
   • South Indian uncle-niece and cross-cousin marriage cited as raising the frequency of autosomal recessive disorders
2. (b) The directive is 'critically discuss', anchored to Leslie White's theory. The answer must expound White's account of culture as a determinant of human behaviour and then evaluate it - a purely expository answer forfeits the critical marks. 15 marks

   Must cover

   • Leslie A. White; 'The Science of Culture' (1949); 'The Evolution of Culture' (1959)
   • culturology; culture as superorganic and sui generis
   • symboling; 'The Symbol' (1940)
   • White's Law: energy harnessed per capita per year x efficiency of technology
   • technological, sociological and ideological subsystems; technological determinism
   • general evolution vs Steward's multilinear evolution
   • critique: absence of agency, crudeness of energy measure, neglect of meaning and history
   • counter-positions: Geertz, Bourdieu, Sahlins

   Loses marks

   • Confusing Leslie White with Julian Steward, or attributing multilinear evolution to White
   • Reproducing White's Law inaccurately - for example as energy alone, omitting the efficiency of the technological means
   • Writing a general essay on neo-evolutionism without engaging White's specific claim that culture determines behaviour
   • Giving no critique at all, when the directive is explicitly 'critically discuss'
   • Confusing White's cultural determinism with the Culture and Personality school's version in Benedict and Mead, which concerns personality formation rather than the superorganic

   Earns more

   • Sets out the three-subsystem model and technological determinism: culture comprises technological, sociological and ideological subsystems, with the technological as the primary and determining base on which social organisation and then ideology rest; and contrasts White's universal evolution of culture as a whole with Julian Steward's multilinear evolution of particular adaptive sequences
   • Delivers the critical evaluation: the theory is reductionist and deterministic, leaving no room for individual agency, creativity or resistance; energy per capita is a crude and difficult measure that cannot capture cultural complexity; ideology, meaning and symbolism are subordinated to technology despite White's own emphasis on symboling; diffusion, historical contingency and intra-cultural variation are neglected; and the scheme retains a teleological residue from nineteenth-century unilinear evolutionism; the counter-positions of Geertz's interpretive anthropology, Bourdieu's practice theory, Ortner's emphasis on agency and Sahlins's 'Culture and Practical Reason' should be invoked, as should the parallel with Marx's base and superstructure

   Extra mark

   • Sahlins and Service's 'Evolution and Culture' (1960) reconciling the two as general and specific evolution
   • Kroeber's 'The Superorganic' (1917) as precursor, or Marvin Harris's cultural materialism as successor
3. (c) Three explicit demands: define Strepsirhini, describe their geographical distribution, and state the characters distinguishing them from Haplorhini. All three must appear; the contrast with Haplorhini is separately marked and is the commonest omission. 15 marks

   Must cover

   • Strepsirhini vs Haplorhini; replacement of the Prosimii-Anthropoidea grade division
   • Lemuriformes and Lorisiformes
   • Madagascar endemism of lemurs; sub-Saharan Africa for galagos and pottos
   • Loris lydekkerianus in peninsular India; Nycticebus bengalensis in north-east India
   • rhinarium, toothcomb, grooming claw, tapetum lucidum, postorbital bar without closure
   • unfused mandibular symphysis and frontal suture
   • haplorhine features: dry nose, postorbital closure, fovea, haemochorial placenta
   • tarsiers are haplorhines despite the prosimian grade

   Loses marks

   • Equating Strepsirhini with Prosimii and therefore including tarsiers, which is the single most penalised error on this question
   • Placing lemurs in mainland Africa or in Asia rather than recognising their endemism to Madagascar and the Comoros
   • Describing only the strepsirhines and never stating the distinguishing haplorhine characters, although the question asks for them
   • Confusing the postorbital bar, which strepsirhines possess, with postorbital closure, which they lack
   • Omitting Indian species, although the slender loris and Bengal slow loris are the obvious home examples

   Earns more

   • Gives the composition of the suborder: the Malagasy lemurs including Lemuridae such as the ring-tailed lemur, Indriidae such as the indri and sifakas, Cheirogaleidae such as the mouse and dwarf lemurs, Lepilemuridae, and the aye-aye in Daubentoniidae; and the lorisiforms comprising Lorisidae - slender loris, slow loris, potto and angwantibo - and Galagidae, the bushbabies or galagos
   • Draws the contrast with Haplorhini: a dry hairy nose with a free mobile upper lip and reduced olfaction; postorbital closure by a bony plate, complete in anthropoids and partial in tarsiers; fused mandibular symphysis and fused frontal bone; loss of the toothcomb; a retinal fovea for acute vision; a haemochorial placenta; longer gestation with typically single, more slowly developing offspring; larger relative brain size and a mainly diurnal, vision-dominated adaptation in anthropoids - and notes that the tarsier, though traditionally grouped with prosimians, is a haplorhine

   Extra mark

   • Indian conservation: Kadavur Slender Loris Sanctuary (Tamil Nadu, 2022), India's first, and Schedule I protection of the slender loris under the amended Wild Life (Protection) Act
   • Notes that a large majority of lemur species are threatened on the IUCN Red List

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