Biology

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many genes working together

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polygenes

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allele that is expressed when present in either the heterozygous or homozygous condition

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dominant

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lost one copy of an autosome

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monosomics

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the genetic constitution underlying a single trait or set of traits

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genotype

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when expressed causes death of an organism; some recessive, some dominant

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lethal alleles

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the realized expression of the genotype, the physical appearance or functional expression of a trait

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phenotype

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any eukaryotic chromosone that is not a sex chromosome; present in the same number and kind in both males and females

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autosomes

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mating between a phenotypically dominant individual of unknown genotype and a homozygous "tester"; is done to test whether is homo. or hetero.

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testcross

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consists of two similar chromosomes in females and two dissimilar chromosomes in males

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sex chromosomes

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the union of egg and sperm produced by a single hermaphroditic organism

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self-fertilization

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when a couple is expecting a child and pedigree analysis indicates that both of them have a significant probability of being heterozygous carriers of a recessive alleles responsibile for a genetic disorder

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high risk pregnancy

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diagram that show the possibilities after fertilization

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Punnett square

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a deeply, staining structure, seen in the interphase nucleus of a cell of an individual with more than one X chromosome

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Barr body

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process by which alternative forms of traits are expressed in offspring rather than blending each trait of the parents in the offspring

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segregation

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gained an extra autosome

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trisomics

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one of two or more alternative states of a gene

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alleles

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a congenital symdrome caused by the presence of an extra copy of chromosome 21

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Down's syndrome

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having two identical alleles of the same gene

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homozygous

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the physician removes cells from the chorion and is done in the eighth week of pregnancy

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chorionic villi sampling

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the position on a chromosome where a gene is located

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locus

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failure of chromosomes to separate properly at meiosis I

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primary nondisjunction

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allele that is only expressed when present in the homozygous condition, while being hidden in the heterozygous by dominant

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recessive

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a emembranous part of the placenta that nourishes the fetus

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chorion

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alternative alleles of a character segregate from each other in heterozygous individuals and remain distinct

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Mendel' First Law of Heredity or the Law of Segregation

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recognize very specific DNA sequences

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restriction enzymes

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basic unit of heredity

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genes

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a hereditary condition caused by a dominant allele that leads to the progressive deterioration of brain cells

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Huntington's disease

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having two different alleles of the same gene

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heterozygous

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states that genes located on different chromosomes assort independently

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Mendel's second law of heredity or law of independent assortment

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genes are close enough together on a chromosome that they do not assort independently are said to be

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linked

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when a detrimental allele occurs at a significant frequency in a population, the harful effect it produces is

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a gene disorder

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most common genetic disorder among whites; fatal disease in which the body cells secrete a thick mucus that clogs the airways of the lungs

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cystic fibrosis

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caused by a single-nucleotide change in the gene for hemoglobin, producing a protein with a nonpolar amino acid on its surface that tends to make the molecules clump together

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sickle cell anemia

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genetic changes of character involve the physical exchange of chromosome arms

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crossing over

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individuals heterozygous for both genes

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dihybrid

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measures distance between genes in terms of the frequency of recombination

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genetic map

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many genes that act sequntially or jointly

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polygenes

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a cross involving three linked genes is called a

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three-point cross

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interaction between 2 nonallelic genes in which one of them modifies the phenotypic expression of the other

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epistasis

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a "map unit" defined as the distance within which a crossover event is expected to occur in an average of 1% of gamates

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centimorgan

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hereditary disorder in which the nervous system deteriorates

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Tay-Sachs disease

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trait determined by a gene on the X chromosome

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sex-linked

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a hereditary disorder in which the blood is slow to clot or does not clot at all

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hemophilia

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a mutated gene; an organism carrying a gene that has undergone a mutation

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mutant

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the most common allele of a gene is often denoted with the symbol "+" and is designated as

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wild type