Ch. 4

Question 0

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.

Answer 0

Selective breeding

Question 1

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

Answer 1

Hybrids

Question 2

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.

Answer 2

Principle of segregation

Question 3

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).

Answer 3

Recessive

Question 4

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.)

Answer 4

Dominant

Question 5

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

Answer 5

Homozygous

Question 6

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

Answer 6

Heterozygous

Question 7

The genetic makeup of an individual. Genotype usually refers to an organism’s genetic makeup (or alleles) at a particular locus.

Answer 7

Genotype

Question 8

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

Answer 8

Phenotypes

Question 9

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.

Answer 9

Principle of independent assortment

Question 10

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).

Answer 10

Random assortment

Question 11

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.

Answer 11

Mendelian traits

Question 12

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.)

Answer 12

Antigens

Question 13

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

Answer 13

Codominance

Question 14

A diagram showing family relations. It’s used to trace the hereditary pattern of particular genetic (usually Mendelian) traits.

Answer 14

Pedigree chart

Question 15

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.

Answer 15

Polygenic

Question 16

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

Answer 16

Pigment

Question 17

A situation where the action of one gene affects several different traits.

Answer 17

Pleiotropy

Question 18

In genetics, inherited differences among individuals; the basis of all evolutionary change.

Answer 18

Variation

Question 19

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

Answer 19

Allele frequency

Question 20

Within a species, a community of individuals where mates are usually found.

Answer 20

Population

Question 21

All of the genes shared by the reproductive members of a population.

Answer 21

Gene pool

Question 22

Small changes occurring within species, such as changes in allele frequencies.

Answer 22

Microevolution

Question 23

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

Answer 23

Macroevolution

Question 24

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

Answer 24

Tandem repeats

Question 25

Exchange of genes between populations.

Answer 25

Gene flow

Question 26

Evolutionary changes, or changes in allele frequencies, produced by random factors in small populations. Genetic drift is a result of small population size.

Answer 26

Genetic drift

Question 27

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.

Answer 27

Founder effect

Question 28

Heterozygous condition where a person has one HbA allele and one HbS allele. Thus they have some normal hemoglobin.

Answer 28

Sickle-cell trait