Concept explainers
CASE STUDY| One foot or another
In humans the HOXD homeotic gene cluster plays a critical role in limb development. In one large family, 16 of 36 members expressed one of two dominantly inherited malformations of the feet known as rocker bottom foot (CVT) or claw foot (CMT). One individual had one foot with CVT and the other with CMT. Genomic analysis identified a single missense mutation in the HOXD10 gene, resulting in a single amino acid substitution in the homeodomain of the encoded transcription factor. This region is crucial for making contact and binding to the target genes controlled by this protein. All family members with the foot malformations were heterozygotes; all unaffected members were homozygous for the normal allele.
What might we learn about the control of developmental processes from an understanding of how this mutation works?
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- Explore chromosomal defects among humans in Ensembl at https://www.ensembl.org/index.html?redirect=no(Links to an external site.) Take a screenshot of one of your findings and describe the type of aberration and its associated phenotype. Identify the locus of gene variant(s) responsible for the disorder. Screenshot Name of chromosomal defect Type of aberration and locus of gene variant(s) Phenotype References:arrow_forwardThe Drosophila gene Sex lethal (Sxl) is deserving of itsname. Certain alleles have no effect on XY animals butcause XX animals to die early in development. Other alleles have no effect on XX animals but cause XY animals to die early in development. Thus, some Sxl allelesare lethal to females, while others are lethal to males.a. Would you expect a null mutation in Sxl to causelethality in males or in females? b. Why do Sxl alleles of either type cause lethality ina specific sex?The gene transformer (tra) gets its name from sexualtransformation, as some tra alleles can change XXanimals into morphological males, while other traalleles can change XY animals into morphologicalfemales.c. Which of these sex transformations would becaused by null alleles of tra and which would becaused by constitutively active alleles of tra?d. In contrast with Sxl, null tra mutations do notcause lethality either in XX or in XY animals.However, the Sxl protein regulates the productionof the Tra protein. Why…arrow_forwardEXTRANUCLEAR INHERITANCE In drosophila, a recessive mutation (m-) of a maternal effect gene (MEG) results in an abnormal phenotype wherein homozygous (m-m-) females produce eggs that cannot support embryonic development. Homozygous (m-m-) males, however, can still produce viable sperm. Using m+ to denote a normal gene, determine the genotypes and phenotypes of the F1s produced by a cross between a heterozygous female and a recessive male. From the offspring, backcross the recessive female with the paternal strain. What are the genotypes and phenotypes of the F2s? with COMPLETE cross for both cases.arrow_forward
- In drosophila, a recessive mutation (m-) of a maternal effect gene results in an abnormal phenotype wherein homozygous (m-m-) females produce eggs that cannot support embryonic development. Homozygous (m-m-) males, however, can still produce viable sperm. Using m+ to denote a normal gene, determine the genotypes and phenotypes of the F1s produce by a cross between a heterozygous female and a recessive male. From the offspring, backcross the recessive female with the paternal strain. What are the genotypes and phenotypes of the F2s? Show COMPLETE cross for both cases. If m-m- females produce useless eggs, then how are m-m- produced?arrow_forward2. a. You want to create a genetic construct that will express GFP in Drosophila. In addition to the GFPcoding sequence, what DNA element(s) must youinclude in order to express this protein in flies if theconstruct were integrated into the Drosophila genome? Where should such DNA element(s) be located? How would you ensure that GFP is expressedonly in certain tissues of the fly, such as the wing?b. Suppose you insert the GFP coding region plus allof the DNA elements required by the answer to part(a)—except the enhancer—between inverted repeatsfound at the ends of a particular transposable element.Because all of the DNA sequences located betweenthese inverted repeats can move from place to placein the Drosophila genome, you can generate manydifferent fly strains, each with the construct integrated at a different genomic location. You now examine animals from each strain for GFPfluorescence. Animals from different strains showdifferent patterns: some glow green in the eyes,others in…arrow_forwardFlies homozygous for recessive null mutations in thesevenless (sev) or bride-of-sevenless (boss) genes have the same mutant phenotype: Every ommatidium(facet) in their eyes lacks photoreceptor cell 7 (R7).The R7 cells enable flies to detect UV light.a. Given that flies normally move toward light, suggest a screening method that would enable you toidentify mutations in additional genes required forR7 determination.b. Would you be able to recover mutations in everygene required for R7 development with yourmethod? Explain.c. How could you tell whether any of the new mutationsyou found in your screen are alleles of sev or boss?d. Suppose you found one recessive mutant allele ofa gene not previously known to be involved in eyedevelopment. How could you use this allele in anew mutagenesis screen to find additional allelesof this gene? Why might you want additional mutant alleles to study the process?arrow_forward
- Gunter Korge examined several proteins that are secreted from the salivary glands of Drosophila melanogaster during larval development (G. Korge. 1975. Proceedings of the National Academy of Sciences of the United States of America 72:4550–4554). One protein, called protein fraction 4, was encoded by a gene found by deletion mapping to be located on the X chromosome at position 3C. Korge observed that, about 5 hours before the first synthesis of protein fraction 4, an expanded and puffed-out region formed on the X chromosome at position 3C. This chromosome puff disappeared before the end of the third larval instar stage, when the synthesis of protein fraction 4 ceased. He observed that there was no puff at position 3C in a special strain of flies that lacked secretion of protein fraction 4. Explain these results. What is the chromosome puff at region 3, and why does its appearance and disappearance roughly coincide with the secretion of protein fraction 4?arrow_forward12. a. You want to create a genetic construct that will express GFP in Drosophila. In addition to the GFPcoding sequence, what DNA element(s) must youinclude in order to express this protein in flies if theconstruct were integrated into the Drosophila genome? Where should such DNA element(s) be located? How would you ensure that GFP is expressedonly in certain tissues of the fly, such as the wing?b. Suppose you insert the GFP coding region plus allof the DNA elements required by the answer to part(a)—except the enhancer—between inverted repeatsfound at the ends of a particular transposable element.Because all of the DNA sequences located betweenthese inverted repeats can move from place to placein the Drosophila genome, you can generate manydifferent fly strains, each with the construct integrated at a different genomic location. You now examine animals from each strain for GFPfluorescence. Animals from different strains showdifferent patterns: some glow green in the eyes,others in…arrow_forwardInterested in exploring the genetic pathways that lead to neurological issues, you want to see if recessive mutations which generate too many neurons (tm) in flies - which many causes autistic like symptoms are in the same gene as mutations that generate too few neurons (tf) - intellectual diabilities. You cross a true-breeding homozygous tm/tm fly to a homozygous too few neuron fly tf/tf. What phenotype in the progeny would tell these mutations are in different genes?arrow_forward
- Male Drosophila expressing the autosomal recessivemutations sc (scute), ec (echinus), cv (crossveinless),and b (black) were crossed to phenotypically wildtype females, and the 3288 progeny listed wereobtained. (Only mutant traits are noted.)653 black, scute, echinus, crossveinless670 scute, echinus, crossveinless675 wild type655 black71 black, scute73 scute73 black, echinus, crossveinless74 echinus, crossveinless87 black, scute, echinus84 scute, echinus86 black, crossveinless83 crossveinless1 black, scute, crossveinless1 scute, crossveinless1 black, echinus1 echinusa. Diagram the genotype of the female parent.b. Map these loci.c. Do the data provide evidence of interference?Justify your answer with numbers.arrow_forwardQ11. One of the two genes known to be mutated in cases of Hypokalemic periodic paralysis (which is inherited in an autosomal dominant pattern but known to affect males more often than females) is the calcium voltage-gated channel subunit alpha1 S (CACNA1S). What is known about the gene is recorded here: https://www.ensembl.org/Homo_sapiens/Gene/Summary?db=core;g=ENSG00000081248;r=1:201039512-201112451 Please navigate to the link above and ensure that you click to reveal the transcript table. Then use the information in the table to answer the following question. What is the NCBI accession number (including the version) of the RefSeq Match for the first transcript (CACNA1S-201)? Answer: NCBI accession number (including the version) of the RefSeq Match for the first transcript (CACNA1S-201) is ...arrow_forwardStar eye A peculiar eye condition known as "star” is manifested as a dominant gene in Drosophila. Its recessive allele R* produces the normal eye of wild type. The expression of R can be suppressed by the dominant allele of another locus, Ru-R. Ru-R*, as the recessive allele of the said locus, has no inhibitory effect on R*. When a normal-eyed male of genotype Ru-R Ru-R RR is crossed to a homozygous wild-type female of genotype Ru-R* Ru-R* R*R*, what phenotypic ratio is expected in the F2?arrow_forward
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