(1) Normal development depends on both the timing of the expression of the toolkit genes and
the spatial pattern of expression (i.e. when and where those genes are expressed).
1a. What is the spatial pattern of gene expression for maternal-effect genes such as bicoid? How
is this pattern achieved in the embryo?
1b. Explain why “maternal-effect genes” have this name. What is distinct about how maternal-
effect genes function relative to the other classes of developmental tool-kit genes? Why do the
phenotypic effects of mutations in maternal-effect genes that appear in the embryo depend on the
mother’s genotype and not the zygote’s genotype?
Solution
1.a.The pattern of bicoid gene expression during embryogenesis of Drosophila is at the anterior
end of the embryo that results in formation of anterior-posterior axis.The bicoid mRNAs
associate with microtubules and accumulate at the anterior end of the drosophila eggs.As these
bicoid mRNAs are translated ,a gradient of bicoid protein is formed at the anterior end of the
egg.After fertilisation,there occurs a gradient of bicoid protein at the anterior end.Bicoid protein
now blocks the translation of caudal mRNA that that the concentration of caudal protein is low at
the anterior end while high at the posterior end.
1.b.Maternal effects genes have this name becuase it is the genes from the genome of the
mothers whose expression results in proteins that are required for the development of the embryo
at its early stages i.e for example polarity establishment in the embryo.The distinct part is that
maternal effect genes function by supplying the egg with its own mRNAs and proteins and
introduces phenotype plasticity in relation to other classes of development tool kit genes.The
phenotypic effects of mutations in maternal-effect genes that appear in the embryo depend on the
mother’s genotype and not the zygote’s genotype because mutations in the maternal effect genes
are usually homozygous..
(1) Normal development depends on both the timing of the expression .pdf
1. (1) Normal development depends on both the timing of the expression of the toolkit genes and
the spatial pattern of expression (i.e. when and where those genes are expressed).
1a. What is the spatial pattern of gene expression for maternal-effect genes such as bicoid? How
is this pattern achieved in the embryo?
1b. Explain why “maternal-effect genes” have this name. What is distinct about how maternal-
effect genes function relative to the other classes of developmental tool-kit genes? Why do the
phenotypic effects of mutations in maternal-effect genes that appear in the embryo depend on the
mother’s genotype and not the zygote’s genotype?
Solution
1.a.The pattern of bicoid gene expression during embryogenesis of Drosophila is at the anterior
end of the embryo that results in formation of anterior-posterior axis.The bicoid mRNAs
associate with microtubules and accumulate at the anterior end of the drosophila eggs.As these
bicoid mRNAs are translated ,a gradient of bicoid protein is formed at the anterior end of the
egg.After fertilisation,there occurs a gradient of bicoid protein at the anterior end.Bicoid protein
now blocks the translation of caudal mRNA that that the concentration of caudal protein is low at
the anterior end while high at the posterior end.
1.b.Maternal effects genes have this name becuase it is the genes from the genome of the
mothers whose expression results in proteins that are required for the development of the embryo
at its early stages i.e for example polarity establishment in the embryo.The distinct part is that
maternal effect genes function by supplying the egg with its own mRNAs and proteins and
introduces phenotype plasticity in relation to other classes of development tool kit genes.The
phenotypic effects of mutations in maternal-effect genes that appear in the embryo depend on the
mother’s genotype and not the zygote’s genotype because mutations in the maternal effect genes
are usually homozygous.
