Question

(a) What are maternal-effect genes? (b) When are gene products from these genes made, and where are they located? (c) What aspects of development do maternal-effect genes control? (d) What is the phenotype of maternal-effect mutations?

Short answer

In summary, maternal-effect genes are crucial for early embryo development, as they directly affect the offspring's phenotype, regardless of the genes inherited by the offspring. The gene products from these maternal-effect genes are made during oogenesis and become available for use during embryonic development. Maternal-effect genes play significant roles in various aspects of development, such as establishing body axes, cell cleavage patterns, and cellular differentiation. Mutations in these genes can lead to abnormal development and embryonic lethality.

Step-by-step solution

(a) Define Maternal-Effect Genes

Maternal-effect genes are genes found in the mother's genome that affect the characteristics of her offspring, independent of the genes inherited by the offspring themselves. These genes often encode mRNAs and proteins, which are deposited in the egg during oogenesis and, later, play a crucial role in the early stages of embryo development.

(b) Timing and Location of Gene Products

The gene products of maternal-effect genes (mRNAs and proteins) are made during oogenesis (egg formation) in the mother's ovaries. Once produced, they are located within the egg cytoplasm and become available for use during early embryonic development, prior to the activation of the embryo's own genome.

(c) Aspects of Development Controlled by Maternal-Effect Genes

Maternal-effect genes regulate various aspects of development, including the establishment of body axes (anterior-posterior and dorsal-ventral), cell cleavage patterns, and cellular differentiation during the early stages of embryogenesis. They are particularly important in setting up initial gradients and signaling events that guide the development of the embryo.

(d) Phenotype of Maternal-Effect Mutations

The phenotype of maternal-effect mutations depends on the specific gene affected. Generally, they result in abnormal embryo development, leading to embryonic lethality or distinctive aberrations in the offspring's body plan. It's essential to note that the offspring's phenotype is determined by the mother's genotype for these genes, meaning that changes in the mother's genes can affect the offspring's phenotype, even if the offspring does not inherit the same mutation.