Ch. 4 Flashcards
A practice whereby animal or plant breeders choose which individual animals or plants will be allowed to mate based on the traits (such as coat color or body size) they hope to produce in the offspring. Animals or plants that don’t have the desirable traits aren’t allowed to breed.
Selective breeding
Offspring of parents who differ from each other with regard to certain traits or certain aspects of genetic makeup; also known as heterozygous.
Hybrids
Genes (alleles) occur in pairs because chromosomes occur in pairs. During gamete formation, the members of each pair of alleles separate, so that each gamete contains one member of each pair.
Principle of segregation
Describing a trait that isn’t expressed in heterozygotes; it also refers to the allele that governs the trait. For a recessive allele to be expressed, an individual must have two copies of it (i.e., the individual must be homozygous).
Recessive
In genetics, describing a trait governed by an allele that’s expressed in the presence of another allele (i.e., in heterozygotes). Dominant alleles prevent the expression of recessive alleles in heterozygotes. (This is the definition of complete dominance.)
Dominant
Having the same allele at the same locus on both members of a pair of chromosomes.
Homozygous
Having different alleles at the same locus on members of a pair of chromosomes.
Heterozygous
The genetic makeup of an individual. Genotype usually refers to an organism’s genetic makeup (or alleles) at a particular locus.
Genotype
The observable or detectable physical characteristics of an organism; the detectable expressions of genotypes, frequently influenced by environmental factors.
Phenotypes
The distribution of one pair of alleles into gametes does not influence the distribution of another pair. The genes controlling different traits are inherited independently of one another.
Principle of independent assortment
The chance distribution of chromosomes to daughter cells during meiosis. Along with recombination, random assortment is important source of genetic variation (but not new alleles).
Random assortment
Characteristics that are influenced by alleles at only one genetic locus. Examples include many blood types, such as ABO. Many genetic disorders, including sickle-cell anemia and Tay-Sachs disease, are also Mendelian traits.
Mendelian traits
Large molecules found on the surface of cells. Several different loci govern various antigens on red and white blood cells. (Foreign antigens provoke an immune response.)
Antigens
The expression of two alleles in heterozygotes. In this situation, neither allele is dominant or recessive, so they both influence the phenotype.
Codominance
A diagram showing family relations. It’s used to trace the hereditary pattern of particular genetic (usually Mendelian) traits.
Pedigree chart
Referring to traits influenced by genes at two or more loci. Examples include stature, skin color, eye color, and hair color. Many polygenic traits are influenced by environmental factors such as nutrition and exposure to sunlight.
Polygenic
In this context, molecules that influence the color of skin, hair, and eyes.
Pigment
A situation where the action of one gene affects several different traits.
Pleiotropy
In genetics, inherited differences among individuals; the basis of all evolutionary change.
Variation
In a population, the percentage of all the alleles at a locus, accounted for by one specific allele.
Allele frequency
Within a species, a community of individuals where mates are usually found.
Population
All of the genes shared by the reproductive members of a population.
Gene pool
Small changes occurring within species, such as changes in allele frequencies.
Microevolution
Changes produced only after many generations, such as the appearance of a new species.
Macroevolution
Short, adjacent segments of DNA within a gene that are repeated several times.
Tandem repeats
Exchange of genes between populations.
Gene flow
Evolutionary changes, or changes in allele frequencies, produced by random factors in small populations. Genetic drift is a result of small population size.
Genetic drift
A type of genetic drift in which allele frequencies are altered in small populations that are taken from larger populations or are remnants of the latter.
Founder effect
Heterozygous condition where a person has one HbA allele and one HbS allele. Thus they have some normal hemoglobin.
Sickle-cell trait
