Chapter 4 Flashcards
selective breeding
practice where 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
hybrids
offspring of parents who differ from each other with regard to certain traits or certain aspects of genetic makeup; also known as heterozygotes
principle of segregation
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
recessive
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)
dominant
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 (complete dominance)
homozygous
having the same allele at the same locus on both members of a pair of chromosomes
heterozygous
having different alleles at the same locus on members of a different pair of chromosomes
genotype
the genetic makeup of an individual, usually refers to an organism’s genetic makeup (or alleles) at a particular locus
phenotypes
the observable or detectable physical characteristics of an organism; the detectable expressions of genotypes, frequently influenced by environmental factors
principle of independent assortment
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
random assortment
the chance distribution of chromosomes to daughter cells during meiosis; along with recombination, random assortment is an important source of genetic variation (but not new alleles)
Mendelian traits
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
antigens
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)
codominance
the expression of two alleles in heterozygotes; in this situation, neither allele is dominant or recessive, so they both influence the phenotype
pedigree chart
a diagram showing family relationships; it’s used to trace the hereditary pattern of particular genetic (usually Mendelian) traits
polygenic
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
pigment
in this context, molecules that influence the color of skin, hair, and eyes
pleiotropy
a situation where the action of one gene affects several different traits
variation
inherited differences among individuals; the basis of all evolutionary change
allele frequency
in a population, the percentage of all the alleles at a locus accounted for by one specific allele
population
within a species, a community of individuals where mates are usually found
gene pool
all the genes shared by the reproductive members of a population
microevolution
small changes occurring within species, such as changes in allele frequencies
macroevolution
changes produced only after many generations, such as the appearance of a new species
tandem repeats
short, adjacent segments of DNA within a gene that are repeated several times
gene flow
exchange of genes between populations
genetic drift
evolutionary changes, or changes in allele frequencies, produced by random factors in small populations; genetic drift is a result of small population size
founder effect
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
sickle-cell trait
heterozygous condition where a person has one HbA allele and one HbS allele; thus they have some normal heboglobin
