Theoretical Genetics Essay, Research Paper

Define: Genotype The alleles possessed by an organism Phenotype All the characteristics of an organism Dominant allele An allele which has the same effect on the phenotype whether it is present in

the homozygous or heterozygous state Recessive allele An allele which only has an effect on the phenotype when present in

homozygous state Codominant alleelle Allelees which have a partial effect on the phenotype when present in

heterozygotes but a greater effect in homozygotes Locus The particular position on homologous chromosomes of a gene Homozygous Having two identical alleles of a gene Heterozygous Having two different alleles of a gene Carrier An individual that has a recessive allele of a gene that does not have an

effect on the phenotype Test Cross Testing a suspected heterozygote by crossing with a known homozygous

recessive Punnet Grid Pedigree Chart a record of ancestry or purity of breed State that some genes have more than two alleles Describe ABO blood groups as an example of co-dominance and multiple

alleles Co-dominant alleles- alleles which have a partial effect on the phenotype when present in heterozygous state but have a greater effect in homozygotes. An example is in the alleles controlling the BO blood group system in

humans. The ABO system is controlled by 3 alleles; I , I and I . I produces A antigens I produces B antigens I produces no antigens There are 2 such alleles present in each person and therefore 6

combinations, which are: I I = A I I = A The I and I alleles show equal dominance I I = B with respect to one another (i.e. the are I I = AB co-dominant), but each is dominant to I . I I = O Inheritance follows normal Mendelian I I = B patterns. Outline how the sex chromosomes determine gender by referring to the

inheritance of x and y chromosomes of humans Xy = male Xx = female State that some genes are present on the x chromosome and absent from the

shorter y chromosome Define sex linkage Genes carried on sex chromosomes State two examples of sex linkage Colour Blindness

Haemophilia

State that a human female can be heterozygous or homozygous, with respect to

sex-linked genes Explain that female carriers are heterozygous for x-linked alleles Calculate and predict the genotypic and phenotypic ratios of offspring of

monohybrid crosses involving any of the above patterns of inheritance Deduce the genotypes or phenotypes of individuals in pedigree

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