Human Genetics

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One of two or more alternative forms of a gene that arise by mutation and are found at the same place on a chromosome.

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Alleles

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What are the two different kinds of alleles?

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Dominant - D and recessive - d

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Having identical pairs of genes for any given pair of hereditary characteristics.

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Homozygous

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Having identical pairs of genes for any given pair of hereditary characteristics.

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Heterozygous

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The appearance of an organism resulting from the interaction of the genotype and the environment.

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Phenotype

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In genetics, a type of grid used to show the gametes of each parent and their possible offspring; a type of grid that can indicate all the possible outcomes of a genetic cross; also called checkerboard.

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Punnett square

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A dominantly inherited genetic disorder characterized by flat brown patches on the skin, neurofibromas of the skin and internal organs,and in some cases skeletal deformity.

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Neurofibromatosis

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A hereditary chronic disease of the exocrine glands, characterized by the production of viscid mucus that obstructs the pancreatic ducts and bronchi, leading to infection and fibrosis.

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Cystic fibrosis

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Who is a carrier of cystic fibrosis?

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A carrier is an individual that appears to be normal but carries a recessive allele for a genetic disorder.

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A hereditary disease of the central nervous system characterized by brain deterioration and loss of control over voluntary movements, the symptoms usually appearing in the fourth decade of life.

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Huntington disease

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An inherited disease due to faulty metabolism of phenylalanine,characterized by phenylketones in the urine and usually first noted by signs of mental retardation in infancy.

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Phenylketonuria

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A rare fatal hereditary disease, occurring chiefly in infants and children, especially of eastern European Jewish origin, characterized by a red spot on the retina, gradual blindness, and paralysis.

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Tay-Sachs disease

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Inability to distinguish one or several chromatic colors, independent of the capacity for distinguishing light and shade.

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Color blindness

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Any of several X-linked genetic disorders, symptomatic chiefly in males, in which excessive bleeding occurs owing to the absence or abnormality of a clotting factor in the blood.

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Hemophilia

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Any one of a series of three or more alternative or allelic forms of a gene, only two of which can exist in any normal, diploid individual.

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Multiple alleles

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The chromosomes of a cell, usually displayed as a systematized arrangement of chromosome pairs in descending order of size.

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Karyotype

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A genetic disorder, associated with the presence of an extra chromosome 21, characterized by mild to severe mental impairment,weak muscle tone, shorter stature, and a flattened facial profile.

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Down syndrome

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An abnormal congenital condition resulting from a defect on or absence of the second sex chromosome, characterized by retarded growth of the gonads.

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Turner's syndrome

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Characterized by the presence of an additional X chromosome in each of a female's cells.

Although females with this condition may be taller than average, this chromosomal change typically causes no unusual physical features.

Most females with triple X syndrome have normal sexual development and are able to conceive children.

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poly-X syndrome

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An abnormal condition in which at least one extra X chromosome is present in a male: characterized by reduced or absent sperm production, small testicles, and in some cases enlarged breasts.

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Klinefelter syndrome