Maternal effect: Difference between revisions
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! colspan="4"|Maternal effect |
! colspan="4"|Maternal effect |
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! colspan="2"|All offspring show the wild-type phenotype |
! colspan="2"|All offspring show the wild-type phenotype |
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! colspan="2"|All offspring show the mutant phenotype |
! colspan="2"|All offspring show the mutant phenotype |
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|+ style="caption-side: bottom; font-weight: normal; margin-top: 1em;"|Genetic crosses involving a maternal effect recessive mutation, ''m''. The maternal genotype determines the phenotype of the offspring. |
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Maternal effects often occur because the mother supplies a particular [[mRNA]] or [[protein]] to the oocyte, hence the maternal genome determines whether the molecule is functional. Maternal supply of mRNAs to the early embryo is important, as in many organisms the embryo is initially transcriptionally inactive.<ref>{{cite journal |author=Schier AF |title=The maternal-zygotic transition: death and birth of RNAs |journal=Science |volume=316 |issue=5823 |pages=406–7 |year=2007 |month=April |pmid=17446392 |doi=10.1126/science.1140693 |url=}}</ref> Because of the inheritance pattern of maternal effect mutations, special [[genetic screen]]s are required to identify them. These typically involve examining the phenotype of the F3 generation, as their (F2) mothers will potentially be homozygous for maternal effect mutations.<ref>{{cite journal |author=Jorgensen EM, Mango SE |title=The art and design of genetic screens: ''Caenorhabditis elegans'' |journal=Nat. Rev. Genet. |volume=3 |issue=5 |pages=356–69 |year=2002 |month=May |pmid=11988761 |doi=10.1038/nrg794 |url=}}</ref><ref>{{cite journal |author=St Johnston D |title=The art and design of genetic screens: ''Drosophila melanogaster'' |journal=Nat. Rev. Genet. |volume=3 |issue=3 |pages=176–88 |year=2002 |month=March |pmid=11972155 |doi=10.1038/nrg751 |url=}}</ref> |
Maternal effects often occur because the mother supplies a particular [[mRNA]] or [[protein]] to the oocyte, hence the maternal genome determines whether the molecule is functional. Maternal supply of mRNAs to the early embryo is important, as in many organisms the embryo is initially transcriptionally inactive.<ref>{{cite journal |author=Schier AF |title=The maternal-zygotic transition: death and birth of RNAs |journal=Science |volume=316 |issue=5823 |pages=406–7 |year=2007 |month=April |pmid=17446392 |doi=10.1126/science.1140693 |url=}}</ref> Because of the inheritance pattern of maternal effect mutations, special [[genetic screen]]s are required to identify them. These typically involve examining the phenotype of the F3 generation, as their (F2) mothers will potentially be homozygous for maternal effect mutations.<ref>{{cite journal |author=Jorgensen EM, Mango SE |title=The art and design of genetic screens: ''Caenorhabditis elegans'' |journal=Nat. Rev. Genet. |volume=3 |issue=5 |pages=356–69 |year=2002 |month=May |pmid=11988761 |doi=10.1038/nrg794 |url=}}</ref><ref>{{cite journal |author=St Johnston D |title=The art and design of genetic screens: ''Drosophila melanogaster'' |journal=Nat. Rev. Genet. |volume=3 |issue=3 |pages=176–88 |year=2002 |month=March |pmid=11972155 |doi=10.1038/nrg751 |url=}}</ref> |
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Revision as of 23:32, 30 June 2009
A maternal effect is a situation where the phenotype of an organism is determined not only by the environment it experiences and its genotype, but also by the environment and phenotype of its mother. In genetics, maternal effects occur when an organism shows the phenotype expected from the genotype of the mother, irrespective of its own genotype, often due the mother supplying mRNA or proteins to the egg. Maternal effects can also be caused by the maternal environment independent of genotype, sometimes controlling the size, sex, or behaviour of the offspring. It has been proposed that maternal effects are important for the evolution of adaptive responses to environmental heterogeneity.
Maternal effects in genetics
In genetics, a maternal effect occurs when the phenotype of an organism is determined by the genotype of its mother.[1] For example, if a mutation is maternal effect recessive, then a female homozygous for the mutation may appear phenotypically normal, however her offspring will show the mutant phenotype, even if they are heterozygous for the mutation.
| Maternal effect | |||
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| All offspring show the wild-type phenotype | All offspring show the mutant phenotype | ||
Maternal effects often occur because the mother supplies a particular mRNA or protein to the oocyte, hence the maternal genome determines whether the molecule is functional. Maternal supply of mRNAs to the early embryo is important, as in many organisms the embryo is initially transcriptionally inactive.[2] Because of the inheritance pattern of maternal effect mutations, special genetic screens are required to identify them. These typically involve examining the phenotype of the F3 generation, as their (F2) mothers will potentially be homozygous for maternal effect mutations.[3][4]
Example: maternal effect genes in Drosophila early embryogenesis
The formation of the anterior-posterior axis in Drosophila is created by the regional synthesis of transcription factors encoded by the hunchback & caudal genes. These genes are transcribed among nurse cells of the maternal germ line that support the growth and development of an oocyte. Maternal transcripts of the hunchback and caudal genes are transported into the oocyte to become uniformly distributed in the cytoplasm.
Although hunchback and caudal genes are evenly transcribed, their translation is regulated so that the hunchback protein is more concentrated at the anterior determination of the oocyte while the caudal protein is accumulated more in the posterior. The "bicoid" and "nanos" proteins described below are the translational regulators. Hunchback and caudal proteins act as transcription factors of many genes involved in the differentiation of an embryo along the anterior-posterior axis.
Bicoid and nanos RNAs are synthesized in the nurse cells of the maternal germ line and are transported into the oocyte.
Functions of nanos
- A transcriptional regulator - binding to the 3'OH untranslated region of hunchback RNA and causes the degradation of the RNA.
Functions of bicoid
- Acts as a transcription factor to stimulate synthesis of RNAs from several genes including hunchback. These RNAs are translated into proteins that control the formation of the anterior structures of the embryo.
- Inhibits transcription of caudal RNA by binding to sequences located in the 3'OH termini untranslated regions.
Environmental maternal effects
Paternal effect genes
In contrast, a paternal effect is when a phenotype results from the genotype of the father, rather than the genotype of the individual.[5] The genes responsible for these effects are components of sperm that are involved in fertilization and early development.[6] An example of a paternal-effect gene is the ms(3)sneaky in Drosophila, males with a mutant allele of this gene produce sperm that are able to fertilize an egg, but the snky-inseminated eggs do not develop normally. However, females with this mutation produce eggs that undergo normal development when fertilized.[7]
See also
Maternal effect dominant embryonic arrest
References
- ^ Griffiths, Anthony J. F. (1999). An Introduction to genetic analysis. New York: W.H. Freeman. ISBN 071673771X.
{{cite book}}: Cite has empty unknown parameter:|coauthors=(help) - ^ Schier AF (2007). "The maternal-zygotic transition: death and birth of RNAs". Science. 316 (5823): 406–7. doi:10.1126/science.1140693. PMID 17446392.
{{cite journal}}: Unknown parameter|month=ignored (help) - ^ Jorgensen EM, Mango SE (2002). "The art and design of genetic screens: Caenorhabditis elegans". Nat. Rev. Genet. 3 (5): 356–69. doi:10.1038/nrg794. PMID 11988761.
{{cite journal}}: Unknown parameter|month=ignored (help) - ^ St Johnston D (2002). "The art and design of genetic screens: Drosophila melanogaster". Nat. Rev. Genet. 3 (3): 176–88. doi:10.1038/nrg751. PMID 11972155.
{{cite journal}}: Unknown parameter|month=ignored (help) - ^ Yasuda GK, Schubiger G, Wakimoto BT (1995). "Genetic characterization of ms (3) K81, a paternal effect gene of Drosophila melanogaster". Genetics. 140 (1): 219–29. PMID 7635287.
{{cite journal}}: Unknown parameter|day=ignored (help); Unknown parameter|month=ignored (help)CS1 maint: multiple names: authors list (link) - ^ Fitch KR, Yasuda GK, Owens KN, Wakimoto BT (1998). "Paternal effects in Drosophila: implications for mechanisms of early development". Curr. Top. Dev. Biol. 38: 1–34. doi:10.1016/S0070-2153(08)60243-4. PMID 9399075.
{{cite journal}}: CS1 maint: multiple names: authors list (link) - ^ Fitch KR, Wakimoto BT (1998). "The paternal effect gene ms(3)sneaky is required for sperm activation and the initiation of embryogenesis in Drosophila melanogaster". Dev. Biol. 197 (2): 270–82. doi:10.1006/dbio.1997.8852. PMID 9630751.