CSIR NET Life Sciences Inheritance Biology Flashcards

24 sample cards from the Inheritance Biology deck

Sampled from the end of the deck, so these are different cards from the ones shown on the syllabus page.

1. What did Benzer's fine-structure analysis of the rII region of phage T4 reveal?

   It demonstrated that the gene is divisible: the cistron is the unit of function (defined by complementation), while the recon (recombination) and muton (mutation) are smaller, down to single nucleotides — showing recombination occurs within a gene.

2. What is pedigree analysis used for?

   Pedigree analysis traces the inheritance of a trait across generations using standardized symbols to determine its mode of inheritance (autosomal/X-linked, dominant/recessive) and to assess carrier status and recurrence risk.

3. List key pedigree features of autosomal recessive vs autosomal dominant inheritance.

   Autosomal recessive: trait skips generations, affected from unaffected carrier parents, both sexes equally, often consanguinity. Autosomal dominant: every affected has an affected parent (vertical transmission), both sexes equally, no skipping.

4. What is the LOD score and the threshold for declaring linkage?

   LOD (logarithm of odds) = log10 (likelihood of data assuming linkage at recombination fraction θ / likelihood assuming no linkage, θ=0.5). A LOD score >= +3 (odds 1000:1) indicates significant linkage; <= -2 excludes linkage.

5. What is a karyotype?

   A karyotype is the complete set of chromosomes of a cell/individual arranged in order by size, centromere position, and banding pattern, used to detect numerical and structural chromosomal abnormalities.

6. Name the chromosomal basis of Down, Turner, and Klinefelter syndromes.

   Down syndrome: trisomy 21 (47,XX/XY,+21); Turner syndrome: monosomy X (45,X); Klinefelter syndrome: 47,XXY.

7. Give one example each of an autosomal recessive, autosomal dominant, and X-linked recessive genetic disorder.

   Autosomal recessive: cystic fibrosis / sickle-cell anemia; Autosomal dominant: Huntington's disease / achondroplasia; X-linked recessive: hemophilia A / Duchenne muscular dystrophy.

8. What is polygenic (quantitative) inheritance?

   Polygenic inheritance is the control of a continuously varying (quantitative) trait by many genes (polygenes), each with a small additive effect, together with environmental influence, producing a normal distribution of phenotypes.

9. Define heritability and distinguish broad-sense from narrow-sense heritability.

   Heritability is the proportion of phenotypic variance due to genetic variance. Broad-sense H^2 = VG/VP (all genetic variance); narrow-sense h^2 = VA/VP (only additive genetic variance), which predicts response to selection.

10. What is the breeder's equation relating selection to response?

    R = h^2 x S, where R is the response to selection, S is the selection differential, and h^2 is the narrow-sense heritability. Realized heritability = R/S.

11. What is QTL mapping?

    QTL (Quantitative Trait Locus) mapping locates chromosomal regions controlling quantitative traits by testing statistical association between molecular markers and trait values in a segregating population (e.g., by interval mapping, composite interval mapping).

12. What are the major types and causes of mutations?

    Types: point/gene mutations (substitutions — transitions/transversions, insertions/deletions causing frameshifts) and chromosomal mutations. Causes: spontaneous (replication errors, tautomeric shifts) or induced by mutagens (radiation, chemicals, transposons).

13. Name common methods for detecting mutations.

    Ames test (bacterial reversion for mutagens/carcinogens), CIB and attached-X methods in Drosophila, specific-locus tests in mice, replica plating for selecting bacterial mutants, and modern DNA sequencing/SSCP/DGGE.

14. Distinguish germinal from somatic mutations.

    Germinal (germ-line) mutations occur in gametes/germ cells and are heritable, transmitted to offspring; somatic mutations occur in body cells, are not inherited, and affect only the individual (e.g., a mosaic patch or cancer).

15. Classify mutant types by effect on function (loss vs gain).

    Loss-of-function: amorph (null, complete loss) and hypomorph (partial reduction). Gain-of-function: hypermorph (increased activity), neomorph (novel function), and antimorph (dominant-negative, antagonizes wild-type).

16. What is insertional mutagenesis?

    Insertional mutagenesis is gene disruption caused by integration of a DNA element (transposon, T-DNA, retrovirus) into or near a gene; the insert acts as a known molecular tag enabling cloning of the mutated gene (gene/transposon tagging).

17. Compare the four main structural chromosomal aberrations.

    Deletion: loss of a chromosome segment; Duplication: extra copy of a segment; Inversion: a segment is reversed 180 degrees; Translocation: a segment moves to a non-homologous chromosome (reciprocal or Robertsonian).

18. Differentiate paracentric from pericentric inversion and their meiotic consequences.

    Paracentric inversion excludes the centromere; a crossover within the loop yields a dicentric bridge and an acentric fragment. Pericentric inversion includes the centromere; a crossover within it yields duplication-deletion (unbalanced) recombinant chromatids. Inversions act as crossover suppressors.

19. What cytological structure forms in a heterozygote for a reciprocal translocation at meiosis, and what is its genetic consequence?

    A cross-shaped (cruciform) configuration of four chromosomes forms, segregating in alternate or adjacent patterns; adjacent segregation produces unbalanced gametes, causing semi-sterility.

20. Define ploidy variations: euploidy vs aneuploidy.

    Euploidy = variation in complete chromosome sets (monoploid n, diploid 2n, polyploid 3n/4n etc.); aneuploidy = gain or loss of individual chromosomes (e.g., monosomy 2n-1, trisomy 2n+1, nullisomy 2n-2).

21. Distinguish autopolyploidy from allopolyploidy and give the genetic implication of polyploidy.

    Autopolyploidy: multiple sets from the same species (e.g., autotetraploid); allopolyploidy: sets from two different species after hybridization + doubling (e.g., wheat, Triticale, Raphanobrassica). Odd-numbered polyploids are usually sterile due to abnormal meiotic pairing; polyploidy often increases vigor and is common in plants.

22. What is homologous recombination?

    Homologous recombination is the exchange of nucleotide sequences between two DNA molecules sharing extensive sequence similarity, mediated by strand invasion (RecA/Rad51), Holliday junction formation and resolution; it underlies crossing over and double-strand break repair.

23. What is the Holliday junction and how is it resolved?

    The Holliday junction is a four-stranded cross-shaped DNA intermediate of homologous recombination formed by reciprocal single-strand exchange; branch migration extends it, and resolvases cut it to give either crossover or non-crossover (patch/splice) products.

24. What is non-homologous recombination, and how does transposition fit in?

    Non-homologous recombination joins DNA without sequence homology — e.g., non-homologous end joining (NHEJ) of double-strand breaks and site-specific/illegitimate recombination. Transposition is a form of non-homologous (illegitimate) recombination in which transposable elements move via cut-and-paste (conservative, DNA transposons) or copy-and-paste (replicative/retrotransposons via RNA intermediate).

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