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sex chromosome

one of the pair of chromosomes that determine the sex of an individual

autosome

any chromosome that is not a sex chromosome, not directly involved in determining the sex of an individual

sex-linked trait

a trait that is determined by a gene found on one of the sex chromosomes, such as the X chromosome or the Y chromosome in humans, a trait that is coded for by an allele on a sex chromosome

linked gene

one of a pair of genes that tend to be inherited together

chromosome map

a diagram of gene positions on a chromosome

map unit

in chromosome mapping, an increment of 1 percent in the frequency of crossing-over

germ-cell mutation

mutation that occurs in an organism's gametes, do not affect the organism itself but can be passed on

somatic-cell mutation

a mutation that occurs in a body cell and can affect the organism, cannot be inherited

lethal mutation

a gene or chromosomal mutation that influences the development of an organism in such a way that the organism cannot survive, causes death, often before birth

deletion

the loss of a piece of of chromosome due to breakage

inversion

a chromosomal segment breaks off, flips around backward, and reattaches

translocation

a piece of one chromosome breaks off and reattaches to a nonhomologlous chromosome

nondisjunction

the failure of homologous chromosomes to separate during meiosis. One gamete receives an extra copy and another gamete receives no copies

point mutation

a change that occurs within a single gene or other segment of DNA on a chromosome

substitution

a mutation in which one nucleotide is replaced by another nucleotide

frameshift mutation

a mutation, such as the insertion or deletion of a nucleotide in a coding sequence, that results in the misreading of the code during translation because of a change in the reading frame

insertion mutation

a mutation in which one or more nucleotides are added to a gene, which can also result in a frameshift mutation

pedigree

a diagram that shows how a trait is inherited over several generations

carrier

they have one copy of the recessive allele but do not have the disease

genetic disorder

diseases or disabling conditions that have a genetic basis

polygenic

describes a characteristic that is influenced by many genes

complex character

a character such as skin color that is influenced strongly by both genes and the environment

multiple alleles

more than two alleles (versions of the gene) for a genetic trait

codominance

a condition in which both alleles for a gene are fully expressed in the phenotype of a heterozygote

incomplete dominance

a condition in which a trait in an individual is intermediate between the phenotype of the individual's two parents because the dominant allele is unable to express itself fully

sex-influenced genes

an autosomal trait that is influenced by the presence of male or female sex hormones

Huntington's disease

an autosomal dominant condition characterized by forgetfulness and irritability

amniocentesis

a procedure used in fetal diagnosis in which amniotic fluid is removed from the uterus of the pregnant woman

chorionic villi sampling

a procedure in which the chorionic villi to are analyzed to diagnose fetal genotypes

genetic counseling

the process of testing and informing potential parents about their genetic makeup and the likelihood that they will have offspring with genetic defects or hereditary diseases

gene therapy

a technique that places a gene into a cell to correct a hereditary disease or to improve the genome

deletion mutation

one ore more nucleotides in a gene are lost

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