Chapter 20: Genetics and Human Inheritance (Vocabulary) Flashcards
A segment of DNA on a chromosome that directs the synthesis of a specific polypeptide that will play a structural or functional role in the cell. Some have regulatory regions of DNA within their boundaries. Also, some code for RNA molecules that are needed for the production of the polypeptide but are not part of it.
gene
A phenotypically expressed characteristic.
trait
An alternative form of a gene. One of two or more slightly different versions of a gene that code for different forms of the same trait.
allele
The condition of having two identical alleles for a particular gene.
homozygous
The condition of having two different alleles for a particular gene.
heterozygous
The allele that is fully expressed in the phenotype of an individual who is heterozygous for that gene. It usually produces a functional protein, whereas the recessive allele does not.
dominant allele
The allele whose effects are masked in the heterozygous condition. It often produces a nonfunctional protein.
recessive allele
The genetic makeup of an individual. It refers to precise alleles that are present.
genotype
The observable physical and physiological traits of an individual. It results from the inherited alleles and their interactions with the environment.
phenotype
A diagram showing the genetic connections among individuals in an extended family that is often used to trace the expression of a particular trait in that family.
pedigree
An individual who displays the dominant phenotype but is heterozygous for a trait and can therefore pass the recessive allele to descendants.
carrier
In genetic inheritance, the dominant allele in a heterozygote completely masks the effect of the recessive allele. It often occurs because the dominant allele produces a functional protein and the recessive allele produces a less functional protein or none at all.
complete dominance
The condition in which the effects of both alleles are separately expressed in a heterozygote.
codominance
In genetic inheritance, expression of the trait in a heterozygous individual is somewhere in between expression of the trait in a homozygous dominant individual and homozygous recessive individual.
incomplete dominance
This describes a gene on one of the non-sex chromosomes; i.e. neither on the X or the Y chromosome.
autosomal
The ability to duplicate genetically identical individuals. Researchers often use genes or whole chromosomes to produce identical clones. Vegetative reproduction of plants (as in the use of cuttings of shrubs) is a type of cloning.
Cloning
Having both homologous partners. A homologous pair is two chromosomes of similar size, shape, and gene location. One receives one homologue from one parent and the other from the other parent. The oddest homologous partnership is between the X and the Y chromosome because they are neither the same size nor the same shape, In meiosis, however, because of a few similar genes, they do behave as homologues.
Diploid
The allele (or alternative of two genes) that will be read in the DNA. For example, if you had on one homologue the gene for freckles and on the other homologue the gene for the non-freckled condition, you would have freckles. The freckle characteristic is dominant.
Dominant
The places on the chromosome. For example the locus (the singular of loci) for hemophilia A is a certain place on the X chromosome. You can go the the Human Genome web site and find the specific locus for hemophilia. Finding these specific locations is called genen mapping. There is a great deal of interest in gene mapping because this allows genetic councilors to determine if a person is carrying a deleterious or lethal gene. Such a person may then choose not to reproduce and thus spread that gene to future generations. As Volpe notes, this has been an extremely useful method for limiting the incidence of Tay-Sachs disease.
Loci
Genetic testing for more than one characteristic at the same time.
Multiplex testing
The sex determining chromosome. With some minor exceptions, mammals (including people) with no Y’s are female (as in XX) and people with at least one Y (as in XY) are male.
Sex chromosomes
The alternative gene that the cell will not read.
Recessive
A gene that is on either the X or Y chromosome. There are very few proven structural genes on the Y chromosome so the term sex-linked mostly refers to genes on the X chromosome such as color blindness and hemophilia A and B.
Sex-linked
A gene that has the information to make a single portion of a protein. The information from structural genes is used to make the messenger RNA.
Structural Gene
