The specification of the anterior–posterior axis in Drosophila embryos is initially controlled by various gene products that are synthesized and stored in the mature egg following oogenesis. Mutations in these genes result in abnormalities of the axis during embryogenesis. These mutations illustrate maternal effect. How do such mutations vary from those produced by organelle heredity? Devise a set of parallel crosses and expected outcomes involving mutant genes that contrast maternal effect and organelle heredity.

Verified step by step guidance

1. Understand the concept of maternal effect: Maternal effect refers to the phenomenon where the phenotype of the offspring is determined by the genotype of the mother, due to gene products deposited in the egg during oogenesis. These gene products influence early embryonic development, such as the anterior-posterior axis specification in Drosophila.
2. Understand organelle heredity: Organelle heredity involves the inheritance of genetic material from organelles such as mitochondria or chloroplasts. This type of inheritance is non-Mendelian and typically maternal, as organelles are passed to offspring through the cytoplasm of the egg.
3. Devise parallel crosses for maternal effect: For maternal effect, cross a homozygous mutant female (e.g., for a gene affecting axis specification) with a wild-type male. The offspring will exhibit the mutant phenotype regardless of their own genotype, as the mother's genotype determines the phenotype.
4. Devise parallel crosses for organelle heredity: For organelle heredity, cross a female with mutant organelle DNA (e.g., mitochondrial mutation) with a wild-type male. The offspring will inherit the mutant organelle DNA and exhibit the mutant phenotype, as organelle DNA is maternally inherited.
5. Compare expected outcomes: In maternal effect, the offspring's phenotype is determined by the mother's genotype, not their own. In organelle heredity, the offspring's phenotype is determined by the organelle DNA inherited from the mother. These mechanisms differ in the source of the genetic material influencing the phenotype.

Key Concepts

Maternal Effect Genes

Maternal effect genes are genes expressed in the mother that produce products (like RNA or proteins) that are deposited into the egg during oogenesis. These products influence the development of the embryo, particularly in establishing body axes. Mutations in these genes can lead to developmental defects in the offspring, regardless of the genotype of the offspring, as they rely on maternal contributions for early development.

Organelle Heredity

Organelle heredity refers to the inheritance of traits determined by genes located in organelles, such as mitochondria or chloroplasts, rather than nuclear DNA. This type of inheritance is often maternal, as organelles are typically passed down from the mother’s egg. Mutations in organelle DNA can lead to specific phenotypic traits, but these traits are inherited differently than those influenced by maternal effect genes, as they depend on the organelle's genetic material.

Genetic Crosses

Genetic crosses are experimental methods used to study inheritance patterns by mating individuals with known genotypes. In the context of maternal effect and organelle heredity, parallel crosses can be devised to observe the outcomes of offspring from parents with mutations in maternal effect genes versus those with mutations in organelle genes. By analyzing the phenotypes of the offspring, researchers can distinguish the effects of maternal contributions from those of organelle inheritance.