Domanda del libro di testo
The bicoid gene is a coordinate maternal–effect gene. A female that is homozygous for a loss-of-function bicoid allele is mated to a wild-type male. What are the phenotypes of their progeny?
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Ch. 18 - Developmental Genetics
Sanders3rd EditionGenetic Analysis: An Integrated ApproachISBN: 9780135564172
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TOC.tableOfContents
- Ch. 1 - The Molecular Basis of Heredity, Variation, and Evolution64
- Ch. 2 - Transmission Genetics144
- Ch. 3 - Cell Division and Chromosome Heredity81
- Ch. 4 - Gene Interaction87
- Ch. 5 - Genetic Linkage and Mapping in Eukaryotes103
- Ch. 6 - Genetic Analysis and Mapping in Bacteria and Bacteriophages73
- Ch. 7 - DNA Structure and Replication71
- Ch. 8 - Molecular Biology of Transcription and RNA Processing79
- Ch. 9 - The Molecular Biology of Translation110
- Ch. 10 - Eukaryotic Chromosome Abnormalities and Molecular Organization100
- Ch. 11 - Gene Mutation, DNA Repair, and Homologous Recombination86
- Ch. 12 - Regulation of Gene Expression in Bacteria and Bacteriophage90
- Ch. 13 - Regulation of Gene Expression in Eukaryotes38
- Ch. 14 - Analysis of Gene Function via Forward Genetics and Reverse Genetics72
- Ch. 15 - Recombinant DNA Technology and Its Applications69
- Ch. 16 - Genomics: Genetics from a Whole-Genome Perspective49
- Ch. 17 - Organelle Inheritance and the Evolution of Organelle Genomes27
- Ch. 18 - Developmental Genetics43
- Ch. 19 - Genetic Analysis of Quantitative Traits66
- Ch. 20 - Population Genetics and Evolution at the Population, Species, and Molecular Levels105
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Capitolo 18, Problema 12a
In mammals, identical twins arise when an embryo derived from a single fertilized egg splits into two independent embryos, producing two genetically identical individuals.
What limits might there be, from a developmental genetic viewpoint, as to when this can occur?
Guida verificata passo dopo passo1
Understand that identical twins arise from a single fertilized egg (zygote) that splits into two embryos. This means the two embryos share the same genetic material.
Consider the stages of embryonic development: zygote, morula, blastocyst, and beyond. The timing of the split determines the developmental structures that are shared or separate between the twins.
From a developmental genetic viewpoint, the split must occur early enough for both embryos to develop independently. For example, if the split occurs at the morula stage (8-16 cells), each group of cells can still form a complete embryo.
If the split occurs too late, such as after the formation of the primitive streak (a structure that defines the body axis), the embryos may not fully separate, leading to conjoined twins. This is because the developmental pathways for body axis formation and organogenesis have already been initiated.
Developmental limits are also influenced by the ability of cells to remain totipotent (capable of forming all cell types). As cells differentiate, their potential becomes restricted, which limits the ability to form two independent embryos if the split occurs too late.
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Embryonic Development Stages
Embryonic development in mammals occurs in distinct stages, including cleavage, blastocyst formation, and gastrulation. The timing of these stages is crucial, as the potential for twinning decreases after certain developmental milestones. For instance, if the embryo has progressed too far into the blastocyst stage, the cells may have already begun to specialize, making it less likely for the embryo to split and form two viable individuals.
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Genetics of Development
Cell Differentiation
Cell differentiation is the process by which unspecialized cells become specialized into various cell types. In the context of twinning, if the cells of the embryo begin to differentiate too early, they may lose the ability to develop into two separate embryos. This differentiation typically begins after the blastocyst stage, which is why the timing of the split is critical for the formation of identical twins.
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Genetic Regulation of Development
Genetic regulation involves the control of gene expression during development, which is essential for proper embryonic growth and differentiation. Specific genes and signaling pathways dictate when and how cells divide and specialize. Disruptions or alterations in these regulatory mechanisms can affect the timing of embryo splitting, potentially limiting the occurrence of identical twins based on genetic factors.
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Pratica correlata
Domanda del libro di testo
In mammals, identical twins arise when an embryo derived from a single fertilized egg splits into two independent embryos, producing two genetically identical individuals.
The converse phenotype, fusion of two genetically distinct embryos into a single individual, is also known. What are the genetic implications of such an event?
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Domanda del libro di testo
In gain-of-function let-23 and let-60 C. elegans mutants, all of the vulval precursor cells differentiate with 1° or 2° fates. Do you expect adjacent cells to differentiate with 1° fates or with 2° fates? Explain.
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Domanda del libro di testo
Ablation of the anchor cell in wild-type C. elegans results in a vulva-less phenotype.
What about if the anchor cell is ablated in a let-23 gain-of-function mutant?
386
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Domanda del libro di testo
Ablation of the anchor cell in wild-type C. elegans results in a vulva-less phenotype.
What phenotype is to be expected if the anchor cell is ablated in a let-23 loss-of-function mutant?
444
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Domanda del libro di testo
The bicoid gene is a coordinate maternal-effect gene.
A female Drosophila heterozygous for a loss-of-function bicoid allele is mated to a male that is heterozygous for the same allele. What are the phenotypes of their progeny?
549
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