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 genetic criteria that distinguish extranuclear inheritance from Mendelian autosomal inheritance and X-linked inheritance include the locations of genes, patterns of trait transmission, and sex-dependence. In extranuclear inheritance, genes are located outside the cell nucleus and often exhibit a maternal pattern of inheritance, while in Mendelian autosomal inheritance, genes are located on the autosomes within the cell nucleus and follow Mendel's laws. In X-linked inheritance, genes are located on the X chromosome within the cell nucleus, and inheritance is sex-dependent.

Step-by-step solution

Define the types of inheritance

Extranuclear inheritance: It is a type of genetic inheritance that occurs outside the cell nucleus involving the transmission of traits through non-chromosomal genetic elements, such as mitochondrial DNA or chloroplast DNA. Mendelian autosomal inheritance: It refers to the transmission of traits controlled by genes located on the autosomes, the non-sex chromosomes. Mendel's laws of segregation and independent assortment apply to this type of inheritance. X-linked inheritance: It refers to the transmission of traits controlled by genes located on the X chromosome. This mode of inheritance is different because males have only one X chromosome, and females have two.

Compare extranuclear inheritance with Mendelian autosomal inheritance

1. Locus of genes: In extranuclear inheritance, genes are present outside the cell nucleus (e.g., in mitochondria or chloroplasts), while in Mendelian autosomal inheritance, genes are present on the autosomes within the cell nucleus. 2. Transmission of traits: Extranuclear inheritance typically exhibits a non-Mendelian pattern. In many cases, traits are maternally inherited due to the transmission of mitochondria or chloroplasts through the egg cells. Mendelian autosomal inheritance follows Mendel's laws, and traits are inherited from both parents. 3. Chromosome segregation: In extranuclear inheritance, segregation is not based on chromosomes, whereas in Mendelian autosomal inheritance, chromosome segregation follows Mendel's first law of segregation.

Compare extranuclear inheritance with X-linked inheritance

1. Locus of genes: In extranuclear inheritance, genes are present outside the cell nucleus, while in X-linked inheritance, genes are located on the X chromosome within the cell nucleus. 2. Transmission of traits: Extranuclear inheritance often shows a maternal pattern of inheritance, as the transmission occurs through the cytoplasm of egg cells. In contrast, X-linked inheritance exhibits different patterns in males and females. Males inherit their X chromosome from their mother, while females inherit one X chromosome from each parent. 3. Sex-dependence: Extranuclear inheritance is not sex-dependent, as both males and females inherit the extranuclear genetic material from their mother. In contrast, X-linked inheritance is sex-dependent, as males are hemizygous (having only one copy) for X-linked genes, while females are diploid (having two copies). By comparing the characteristics of extranuclear, Mendelian autosomal, and X-linked inheritance, we can identify the key distinguishing genetic criteria for each mode of inheritance. These differences include the locations of genes, patterns of trait transmission, and sex-dependence.