Final answer:
Incomplete dominance occurs when neither allele is completely dominant or recessive, codominance means both alleles contribute to the phenotype, sex-linked traits are controlled by genes on the sex chromosomes, multiple alleles refer to having more than two alleles for a gene.
Step-by-step explanation:
A. Incomplete Dominance: In incomplete dominance, neither allele is completely dominant or recessive, and the heterozygous individual shows a phenotype that is intermediate between the two homozygous genotypes. For example, in snapdragons, the red and white alleles for flower color exhibit incomplete dominance, resulting in pink flowers when a red and white genotype is present.
B. Codominance: In codominance, both alleles contribute to the phenotype and are fully expressed. An example of codominance is the blood type system in humans, where the A and B alleles are codominant, resulting in individuals with type AB blood expressing both A and B antigens on their red blood cells.
C. Sex-linked Traits: Sex-linked traits are controlled by genes located on the sex chromosomes, usually the X chromosome. Conditions like color blindness and hemophilia are examples of sex-linked traits, where the genes are more commonly inherited by males because they only have one X chromosome.
D. Multiple Alleles: Multiple alleles refer to the existence of more than two alleles for a particular gene. An example is the ABO blood group system in humans, which involves three alleles: A, B, and O. Each individual can have two of these three alleles, resulting in various blood types.
E. Polygenic Traits: Polygenic traits are controlled by multiple genes, and the phenotype typically shows a continuous range of variation. Height, skin color, and eye color are examples of polygenic traits, influenced by the combined effects of several genes.
F. Environmental Influence: Environmental influences can affect gene expression and phenotype. For example, exposure to sunlight can affect the expression of genes involved in skin pigmentation, resulting in a tan. Additionally, nutritional factors, temperature, and stress can also influence gene expression.
G. Gene Linkage and Gene Maps: Gene linkage refers to the tendency of genes located close together on a chromosome to be inherited together. Gene maps are created to determine the relative positions of genes on a chromosome. These maps are based on the frequency of recombination events that occur during the crossing over of homologous chromosomes during meiosis.
H. Pedigrees: Pedigrees are diagrams that show the inheritance of traits within a family. They can be used to track the presence and pattern of genetic disorders and traits through generations. Pedigrees provide information about the mode of inheritance, whether it is autosomal dominant, autosomal recessive, or sex-linked.