Chapter 4

Question 1

selective breeding

Answer 1

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

Question 2

hybrids

Answer 2

offspring of parents who differ from each other with regard to certain traits or certain aspects of genetic makeup; also known as heterozygotes

Question 3

principle of segregation

Answer 3

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

Question 4

recessive

Answer 4

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)

Question 5

dominant

Answer 5

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)

Question 6

homozygous

Answer 6

having the same allele at the same locus on both members of a pair of chromosomes

Question 7

heterozygous

Answer 7

having different alleles at the same locus on members of a different pair of chromosomes

Question 8

genotype

Answer 8

the genetic makeup of an individual, usually refers to an organism’s genetic makeup (or alleles) at a particular locus

Question 9

phenotypes

Answer 9

the observable or detectable physical characteristics of an organism; the detectable expressions of genotypes, frequently influenced by environmental factors

Question 10

principle of independent assortment

Answer 10

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

Question 11

random assortment

Answer 11

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)

Question 12

Mendelian traits

Answer 12

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

Question 13

antigens

Answer 13

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)

Question 14

codominance

Answer 14

the expression of two alleles in heterozygotes; in this situation, neither allele is dominant or recessive, so they both influence the phenotype

Question 15

pedigree chart

Answer 15

a diagram showing family relationships; it’s used to trace the hereditary pattern of particular genetic (usually Mendelian) traits

Question 16

polygenic

Answer 16

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

Question 17

pigment

Answer 17

in this context, molecules that influence the color of skin, hair, and eyes

Question 18

pleiotropy

Answer 18

a situation where the action of one gene affects several different traits

Question 19

variation

Answer 19

inherited differences among individuals; the basis of all evolutionary change

Question 20

allele frequency

Answer 20

in a population, the percentage of all the alleles at a locus accounted for by one specific allele

Question 21

population

Answer 21

within a species, a community of individuals where mates are usually found

Question 22

gene pool

Answer 22

all the genes shared by the reproductive members of a population

Question 23

microevolution

Answer 23

small changes occurring within species, such as changes in allele frequencies

Question 24

macroevolution

Answer 24

changes produced only after many generations, such as the appearance of a new species

Question 25

tandem repeats

Answer 25

short, adjacent segments of DNA within a gene that are repeated several times

Question 26

gene flow

Answer 26

exchange of genes between populations

Question 27

genetic drift

Answer 27

evolutionary changes, or changes in allele frequencies, produced by random factors in small populations; genetic drift is a result of small population size

Question 28

founder effect

Answer 28

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

Question 29

sickle-cell trait

Answer 29

heterozygous condition where a person has one HbA allele and one HbS allele; thus they have some normal heboglobin