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Chapter 4: Problem 30

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, illustrating maternal effect. How do such mutations vary from those involved in organelle heredity that illustrate extranuclear inheritance? Devise a set of parallel crosses and expected outcomes involving mutant genes that contrast maternal effect and organelle heredity.

Short Answer

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Short Answer: Maternal effect inheritance is when an organism's phenotype is determined by the genotype of its mother, usually due to gene products in the egg cytoplasm, whereas organelle heredity involves the inheritance of cytoplasmic organelles such as mitochondria and chloroplasts and their DNA. Both inheritance types involve maternal inheritance, but the maternal effect is related to gene products while organelle heredity is related to organelle DNA.

Step by step solution

01

Understand maternal effect and organelle heredity

Maternal effect is a type of inheritance where an organism shows the phenotypic effect of a gene present in its mother, regardless of the organism's own genotype. This is usually due to the presence of the gene products in the egg cytoplasm. Organelle heredity, or extranuclear inheritance, is a type of inheritance where traits are passed from parents to offspring via cytoplasmic organelles such as mitochondria and chloroplasts instead of nuclear genes. These organelles have their own DNA, which is passed to offspring primarily through the maternal line.
02

Devise a set of parallel crosses for maternal effect

Let's consider two homozygous lines of Drosophila, one with a wild-type phenotype for the anterior-posterior axis (A), and the other with a mutant phenotype for the axis (a). Here, A represents the dominant wild type, and a represents the recessive maternal-effect mutation. We can represent the crosses as follows: 1. AA (鈾�) x AA (鈾�) - Results in all offspring with a wild-type phenotype 2. aa (鈾�) x AA (鈾�) - Results in all offspring with mutant phenotypes due to the maternal effect 3. AA (鈾�) x aa (鈾�) - Results in all offspring with wild-type phenotypes
03

Devise a set of parallel crosses for organelle heredity

Now let's consider two homozygous lines of Drosophila, one with healthy mitochondria, represented by (+) and the other with mutant mitochondria, represented by (m). We will represent the crosses as follows: 1. (+) (鈾�) x (+) (鈾�) - Results in offspring with healthy mitochondria due to maternal inheritance 2. (m) (鈾�) x (+) (鈾�) - Results in offspring with mutant mitochondria due to maternal inheritance 3. (+) (鈾�) x (m) (鈾�) - Results in offspring with healthy mitochondria due to maternal inheritance
04

Comparison of Expected Outcomes

In the maternal effect crosses, we notice that the mother's genotype directly affects the offspring's phenotype, while in organelle heredity crosses, offspring inherit their mitochondria only from the mother, leading to the expression of the phenotype associated with the mother's mitochondrial genotype. In both cases, paternal contribution does not affect the offspring's phenotype, which highlights the importance of maternal inheritance. However, they differ in that maternal effect involves gene products stored in the egg cytoplasm, whereas organelle heredity involves inheritance of cytoplasmic organelles and their DNA.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Organelle Heredity
Organelle heredity, also known as extranuclear inheritance, is a fascinating biological concept. It refers to how traits are transmitted from parents to offspring through cytoplasmic organelles like mitochondria and chloroplasts. Unlike the inheritance of nuclear genes, which involves contributions from both parents, organelle heredity predominantly involves the maternal line.

This is because these organelles contain their own DNA and are typically inherited from the egg cell provided by the mother. Mitochondria, for example, have a small circular DNA, which can harbor mutations that contribute to unique phenotypes. These phenotypes will manifest in the offspring if mutations are present in the mitochondria inherited from the mother.
  • Mitochondrial DNA is passed almost exclusively through the maternal line.
  • Traits associated with organelle heredity do not follow traditional Mendelian inheritance.
  • Chloroplasts in plants also exhibit organelle heredity.
Therefore, when studying organelle heredity, one focuses on non-nuclear genetic material which can influence traits and characteristics across generations in distinctive ways.
Drosophila Genetics
Drosophila, commonly known as fruit flies, have become a staple in genetic research due to their simplistic genetic make-up and easy cultivation. Their genetic structure provides a clearer view of both classic and non-Mendelian inheritance patterns.

Within Drosophila genetics, new insights have emerged regarding maternal effect genes, which control the development of specific traits in offspring. The anterior-posterior axis in Drosophila is a well-studied genetic axis showcasing maternal effect. Here, the genotype of the mother affects the phenotype of the offspring, regardless of the offspring's own genetic make-up.
  • Maternal effect genes are vital for early embryonic development.
  • Mutations in these genes can lead to developmental abnormalities.
  • Drosophila are used to study both nuclear and extranuclear inheritance.
By understanding Drosophila genetics, researchers can dissect complex inheritance patterns and evaluate the role of both nuclear and extranuclear elements in trait development.
Extranuclear Inheritance
Extranuclear inheritance, often synonymous with cytoplasmic inheritance, describes how genetic material outside the nucleus can determine inherited traits. Organelle heredity, concerning mitochondria and chloroplasts, falls under this broader category.

In this form of inheritance, the genetic material housed in organelles is transmitted to offspring, often showing maternal lineage dominance. It diverges from Mendelian inheritance patterns, where nuclear DNA from both parents combine to shape offspring traits. In extranuclear inheritance, only the maternal organelles influence traits.
  • Includes both mitochondria and chloroplasts' inheritance.
  • Maternally inherited, reducing paternal genetic impact on offspring organelle traits.
  • Involves unique DNA that can create distinct phenotypes.
Understanding extranuclear inheritance allows for deeper insight into how various factors contribute to trait expression beyond traditional genetic rules. This knowledge provides a window into how complex genetic interactions influence biological diversity and species evolution.

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Most popular questions from this chapter

Pigment in the mouse is produced only when the \(C\) allele is pres- ent. Individuals of the ce genotype have no color, If color is present, it may be determined by the \(A\) and \(a\) alleles. AA or Aa results in agouti color, whereas aa results in black coats. (a) What \(\mathrm{F}_{1}\) and \(\mathrm{F}_{2}\) genotypic and phenotypic ratios are obtained from a cross between \(A A C C\) and aace mice? (b) In the three crosses shown here between agouti females whose genotypes were unknown and males of the aacc genotype, what are the genotypes of the female parents for each of the following phenotypic ratios? (1) 8 agouti (2) 9 agouti (3) 4 agouti 8 colorless 10 black \(\quad 5\) black 10 colorless

What genetic criteria distinguish a case of extranuclear inheritance from (a) a case of Mendelian autosomal inheritance; (b) a case of \(\mathrm{X}\) -linked inheritance?

While vermilion is X-linked in Drosophila and causes eye color to be bright red, brown is an autosomal recessive mutation that causes the eye to be brown. Flies carrying both mutations lose all pigmentation and are white-eyed. Predict the \(\mathrm{F}_{1}\) and \(\mathrm{F}_{2}\) results of the following crosses: (a) vermilion females \(\times \quad\) brown males (b) brown females \(\times\) vermilion males (c) white females \(\times\) wild males

In four o'clock plants, many flower colors are observed. In a cross involving two true-breeding strains, one crimson and the other white, all of the \(\mathrm{F}_{1}\) generation were rose color. In the \(\mathrm{F}_{2}\) four new phenotypes appeared along with the \(P_{1}\) and \(F_{1}\) parental colors. The following ratio was obtained: \(1 / 16\) crimson \(4 / 16\) rose \(2 / 16\) orange \(\quad 2 / 16\) pale yellow 1/16 yellow \(\quad 4 / 16\) white \(2 / 16\) magenta Propose an explanation for the inheritance of these flower colors.

Hemophilia is an X-linked recessive mutation In humans that causes delayed blood clotting. What kinds of \(\mathrm{F}_{1}\) and \(\mathrm{F}_{2}\) offspring would be expected from matings between (a) a hemophilic female and a normal male, and (b) a hemophilic male and a normal female? Compare these results to those that would be obtained if the hemophilic gene was autosomal.
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