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Chapter 5: Problem 25

What is extranuclear inheritance? Describe three examples.

Short Answer

Expert verified
Extranuclear inheritance refers to the transmission of genes that occur outside the nucleus. Examples are mitochondrial inheritance where the DNA within the mitochondria is passed on (i.e., LHON), chloroplast inheritance where DNA within the chloroplasts is passed down (e.g., four-o'clock plant color variations), and the maternal effect where the phenotype is determined by the genotype of the mother (e.g., snail shell coiling).

Step by step solution

01

Understanding Extranuclear Inheritance

Extranuclear inheritance, also known as cytoplasmic inheritance, refers to the transmission of genes that occur outside the nucleus. It is the non-Mendelian form of inheritance. These genes are found in the cytoplasmic organelles which are structures inside the cells that are responsible for energy production and protein synthesis, namely the mitochondria and chloroplasts.
02

Example 1: Mitochondrial Inheritance

Mitochondrial inheritance is an example of extranuclear inheritance where the DNA within the mitochondria, inherited almost exclusively from the mother, is passed on. A prime example of this, in humans, relates to Leber's Hereditary Optic Neuropathy (LHON), a condition that leads to vision loss.
03

Example 2: Chloroplast Inheritance

Chloroplast inheritance, most common in algae and plants, is another instance of this type of inheritance. Here, the DNA within the chloroplasts, inherited often through the female parent, is passed down. An instance is the variegated leaf color observed in the four-o'clock plant (Mirabilis jalapa).
04

Example 3: Maternal Effect

The maternal effect is another example of extranuclear inheritance where the phenotype of an organism is determined not by its own genotype, but by the genotype of its mother. For instance, in snail shell coiling, the direction of coiling (left-handed or right-handed) is determined by the mother's genes.

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Most popular questions from this chapter

Describe when X-chromosome inactivation occurs and how this leads to phenotypic results at the organism level. In your answer, you should explain why XCI causes results such as variegated coat patterns in mammals. Why do two different calico cats have their patches of orange and black fur in different places? Explain whether or not a variegated coat pattern due to \(\mathrm{XCI}\) could occur in marsupials.

Describe the molecular process of X-chromosome inactivation. This description should include the three phases of inactivation and the role of the Xic. Explain what happens to the X chromosomes during embryogenesis, in adult somatic cells, and during oogenesis.

Explain why maternal effect genes exert their effects during the early stages of development.

Suppose a maternal effect gene exists as a functional dominant allele and a nonfunctional recessive allele. A mother who is phenotypically abnormal produces all normal offspring. Explain the genotype of the mother.

Describe the inheritance pattern of maternal effect genes. Explain how the maternal effect occurs at the cellular level. What are the expected functional roles of the proteins that are encoded by maternal effect genes?
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