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#gene mutations

8 public questions tagged with this topic.

Paracrine Factor

Which mutation in the FGFR3 gene is associated with thanatophoric dysplasia?

Thanatophoric dysplasia type I and II are neonatal lethal skeletal dysplasias caused by gain-of-function missense mutations in FGFR3 transmembrane or kinase domains, such as Arg248Cys, Tyr373Cys, Lys650Glu located in IgIII and kinase activation loop. These substitutions cause ligand-independent constitutive dimerization and activation of receptor tyrosine kinase, overactivating MAPK ERK and STAT1 pathways inhibiting chondrocyte proliferation and differentiation in growth plate, accelerating premature hypertrophy and apoptosis. Loss-of-function FGFR3 causes skeletal overgrowth tall stature opposite phenotype. Thus activating FGFR3 restricts endochondral bone growth demonstrating dosage sensitivity of RTK signaling in chondrogenesis.

Ref: Muenke & Schell, Trends Genetics: Activating FGFR3 mutations cause thanatophoric dysplasia via constitutive kinase activity.

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Drosophila -ll

Pair-rule gene mutations affect:

Pair-rule genes initiate periodic pattern where each gene's striped pattern covers every other parasegment; loss removes those parasegments causing deletion of alternate segments observed as missing denticle belts every second segment. Even-skipped mutants delete odd bands, hairy deletes complementary set. Continuous deletion characterizes gap mutants, anterior restriction characterizes head gaps. Pair-rule class links double-segment periodicity to single-segment pattern via segment polarity activation. Mechanism involves combinatorial regulation where gap proteins repress pair-rule stripes in interstripe intervals, creating precise periodic output essential for segmentation clock and metameric organization conserved across arthropod lineages and developmental timing.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 9: Pair-rule mutants affect every other segment - double-segment periodicity.

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Drosophila -ll

Gap gene mutations typically result in:

Gap genes encode transcription factors expressed in non-periodic domains defining large embryonic territories. Loss removes adjacent segment anlage covered by domain, resulting larvae missing head-thorax for hunchback, thoracic segments for Kruppel, abdominal segments for knirps or giant, producing large gaps. Phenotype contrasts with pair-rule where every other segment missing repeats, and segment polarity where polarity reversed. Duplications characterize wingless defects. Large region deletion remains diagnostic of gap function as intermediaries interpreting maternal morphogen concentrations into broad fields that later regulate periodic gene expression and establish positional values for subsequent metameric patterning during development.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 9: Gap mutants - removal of contiguous segment groups in larval cuticle.

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Drosophila -ll

Which segmentation gene mutations remove large segments?

Segmentation hierarchy subdivides embryo starting with maternal gradients regulating gap genes expressed in broad domains covering multiple adjacent segment primordia. Their proteins regulate pair-rule genes. Gap mutations delete large continuous regions, cuticle shows gap of denticle belts encompassing several segments leaving embryo shorter. Pair-rule mutations remove every other segment, segment polarity causes polarity reversals, homeotic transforms identity without loss. Therefore large deletions hallmark gap class named after conspicuous holes in larval cuticle, reflecting role integrating maternal information into regional subdivisions before periodic patterning emerges in blastoderm stage during early development.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 9: Gap genes - large region deletions and maternal gradient interpretation.

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Gene Dissection and Complementation

Complementation analysis is used to determine whether

Complementation analysis distinguishes whether recessive mutations causing same phenotype affect same functional unit or different transcriptional units. Two homozygous mutants crossed or heterokaryon formed produce trans heterozygote carrying one mutant allele from each parent on homologous chromosomes. If each genome supplies wild-type product compensating other's defect, wild-type phenotype restored indicating mutations complement and reside in different genes. Failure to restore indicates both lesions disrupt same cistron with no intact copy available, grouping mutants into single complementation group representing one gene.

Ref: Hartl & Ruvolo, Genetics, 9th ed., Chapter 7: Complementation Test for Functional Alleles and Cistrons

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ABC MODEL+PYQS

AP3/PI mutants show replacement of petals and stamens by:

Go with A — Sepals and carpels. Under ABC MODEL, this is the standard explanation you’d use in class: it names the real driver or definition, while the rest are nearby but wrong. Not these: B) Carpels only; C) Sepals only; D) Petals only. When two options sound similar, choose the one that matches the textbook definition most tightly.

Ref: Best CSIR NET Plant Physiology books: Master Unit 6 with Taiz & Zeiger and Salisbury & Ross. Crack Part C experimental questions with top textbooks.

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ABC MODEL+PYQS

Which whorls are affected in agamous (AG) mutants?

That points to C: Stamens and carpels. Compared with the other options, Stamens and carpels is the one that correctly describes the ABC MODEL concept. The wrong ones are A) Sepals and petals; B) Petals and stamens; D) Sepals and carpels. If you’re stuck, eliminate anything that contradicts a basic fact you already know for this topic.

Ref: Best CSIR NET Plant Physiology books: Master Unit 6 with Taiz & Zeiger and Salisbury & Ross. Crack Part C experimental questions with top textbooks.

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