Question

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?

Short answer

Answer: The key factors that distinguish extranuclear inheritance from Mendelian autosomal inheritance are chromosomal vs. non-chromosomal DNA, uniparental vs. biparental inheritance, genotype-phenotype relationship, and Mendelian ratios. The key factors that distinguish extranuclear inheritance from X-linked inheritance are chromosomal location, uniparental vs. biparental inheritance, sex-related phenotypes, and Mendelian ratios and sex-linkage.

Step-by-step solution

Distinguishing extranuclear inheritance from Mendelian autosomal inheritance

In order to distinguish between extranuclear inheritance and Mendelian autosomal inheritance, consider the following factors: 1. Chromosomal vs. non-chromosomal DNA: Extranuclear inheritance involves the inheritance of genetic material from organelles outside of the nucleus, such as mitochondria and chloroplasts. In contrast, Mendelian autosomal inheritance is the inheritance of genetic material present in the nucleus, specifically on non-sex chromosomes (autosomes). 2. Uniparental vs. biparental inheritance: In extranuclear inheritance, the genetic material is typically inherited from one parent, usually the mother. In Mendelian autosomal inheritance, genetic material is inherited from both parents, as each parent contributes one set of autosomes to their offspring. 3. Genotype-phenotype relationship: In extranuclear inheritance, there is often a direct relationship between the genotype and the phenotype of an organism. For example, in cytoplasmic male sterility in plants, a specific mitochondrial DNA genotype leads to male sterility. However, in Mendelian autosomal inheritance, traits can be affected by multiple genes present on the autosomes, leading to a more complex relationship between genotype and phenotype. 4. Mendelian ratios: Mendelian autosomal inheritance follows Mendel's Laws, including the Law of Segregation and the Law of Independent Assortment. As a result, traits inherited in this manner often display characteristic Mendelian inheritance ratios (i.e., 3:1, 9:3:3:1). In contrast, extranuclear inheritance does not follow these ratios.

Distinguishing extranuclear inheritance from X-linked inheritance

To distinguish between extranuclear inheritance and X-linked inheritance, consider the following factors: 1. Chromosomal location: Extranuclear inheritance involves genetic material inherited from non-nuclear DNA found in organelles such as mitochondria and chloroplasts. In contrast, X-linked inheritance is the inheritance of genetic material located on the X chromosome, one of the sex chromosomes found in the nucleus. 2. Uniparental vs. biparental inheritance: In extranuclear inheritance, genetic material is typically inherited from one parent, usually the mother. In X-linked inheritance, genetic material can be inherited from either parent, but the father typically passes the X chromosome to his daughters, whereas the mother can pass the X chromosome to both sons and daughters. 3. Sex-related phenotypes: In extranuclear inheritance, the trait may not be specifically linked to the sex of the organism. However, X-linked inheritance often results in sex-related phenotypes, as males (XY) and females (XX) have a different number of X chromosomes. One example is color blindness, which is more common in males due to its X-linked inheritance pattern. 4. Mendelian ratios and sex-linkage: X-linked inheritance follows Mendelian inheritance patterns, but the patterns may be sex-specific or show differences between males and females. For example, X-linked recessive traits appear more frequently in males, who have only one X chromosome, as opposed to females, who have two X chromosomes and may be carriers without expressing the trait. In contrast, extranuclear inheritance does not follow Mendelian ratios and is not sex-linked in the same way.