the pattern of inheritance in which traits do not segregate under with mendel's laws is called
Answer (1)
Mendel's laws, which describe the inheritance of traits linked to single genes on chromosomes in the nucleus, are based on the principle of dominance, where one allele masks the expression of another. However, there are several situations where observed phenotypic ratios deviate from the expected Mendelian ratios. Non-Mendelian inheritance encompasses a range of inheritance patterns that deviate from the classic Mendelian model. These patterns often involve multiple genes, interactions between genes, or factors outside the nuclear genome. Here are some key examples of non-Mendelian inheritance: 1. Incomplete Dominance: In this pattern, neither allele is completely dominant over the other, resulting in a blended phenotype in heterozygotes. For example, in snapdragons, a red flower (RR) crossed with a white flower (WW) produces pink flowers (RW) [3]. 2. Codominance: Both alleles are expressed equally in the heterozygote, resulting in a phenotype that exhibits both traits. For instance, in certain chicken breeds, the allele for black feathers is codominant with the allele for white feathers, producing chickens with speckled black and white feathers [3]. 3. Multiple Alleles: Many genes have more than two alleles, though an individual can only possess two alleles for each gene. This leads to a wider range of possible phenotypes. For example, the rabbit coat color gene has at least four alleles, resulting in four different coat colors [1]. 4. Polygenic Inheritance: Traits are controlled by multiple genes, often with small additive effects. This results in a continuous range of phenotypes. Human skin color is a classic example, influenced by at least four genes [1][3]. 5. Epistasis: One gene masks the expression of another gene, regardless of the alleles present at the second gene. For example, in Labrador retrievers, the presence of two recessive alleles at the "E" locus prevents the expression of coat color genes, resulting in a yellow coat, regardless of the alleles at the "B" locus for black or brown coat color [1]. 6. Sex-Linked Inheritance: Traits are determined by genes located on the sex chromosomes (X or Y). These traits often exhibit different inheritance patterns in males and females due to the difference in sex chromosome composition. For example, hemophilia is a sex-linked recessive disorder carried on the X chromosome [3]. 7. Extranuclear Inheritance: Traits are determined by genes located outside the nucleus, in organelles like mitochondria or chloroplasts. These organelles have their own DNA, which is inherited maternally. For example, mitochondrial diseases are caused by mutations in mitochondrial DNA and are passed down from mothers to their children [1][2]. 8. Genomic Imprinting: The expression of a gene depends on whether it was inherited from the mother or father. This occurs due to epigenetic modifications that affect gene expression. For instance, the insulin-like growth factor 2 (IGF2) gene is imprinted in mice, with only the paternal allele being expressed [2]. 9. Gene Conversion: During DNA repair, a piece of DNA sequence information is transferred from one DNA helix to another, altering the sequence of the recipient helix. This can result in the conversion of one allele into another, leading to non-Mendelian inheritance patterns [1][2]. 10. Infectious Heredity: Infectious particles like viruses can infect host cells and alter their phenotype. This altered phenotype can be transmitted to progeny, resulting in non-Mendelian inheritance. For example, the killer phenomenon in yeast is caused by two double-stranded RNA viruses, designated L and M, which are transmitted through mating [1][2]. Understanding non-Mendelian inheritance is crucial for comprehending the complexity of inheritance patterns and their implications for human health, agriculture, and evolution. These patterns highlight the intricate interplay of genetic and environmental factors that shape the traits of organisms.
