chapter 4: heredity and evolution

Question 1

selective breeding

Answer 1

a practice whereby animal or plant breeders choose which individual animals or plants will be allowed to mate based on the traits (ex: body size) they hope to produce in the offspring; animals or plants that don’t have 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; 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; the allele that governs the trait; to be expressed, an individual must have two copies of it (homozygous)

Question 5

dominant

Answer 5

describing a trait governed by an allele that’s expressed in the presence of another allene (heterozygotes); prevent the expression of recessive alleles in heterozygotes (complete dominance)

Question 6

locus

Answer 6

the position on a chromosome where a given gene occurs; aka gene

Question 7

alleles

Answer 7

alternate forms of a gene; occur at the same locus on both members of a pair of chromosomes, and they influence the same trait; action may result in different expressions of that trait because they are slightly different; aka gene

Question 8

homozygous

Answer 8

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

Question 9

heterozygous

Answer 9

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

Question 10

genotype

Answer 10

the genetic makeup of an individual; can refer to an organism’s entire genetic makeup or to the alleles at a particular locus

Question 11

phenotypes

Answer 11

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

Question 12

principle of independent assortment

Answer 12

the distribution of one pair of alleles into gametes does not influence the distribution of another pair; genes controlling different traits are inherited independently of one another

Question 13

random assortment

Answer 13

the chance distribution of chromosomes to daughter cells during meiosis; along with recombination, it is an important source of genetic variation (but not new alleles)

Question 14

mendelian traits

Answer 14

characteristics that are influenced by alleles at only one genetic locus; ex: blood types, genetic disorders (sickle-cell anemia & tay-sachs)

Question 15

antigens

Answer 15

large molecules found on the surface of cells; ex: red and white blood cells

Question 16

codominance

Answer 16

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

Question 17

polygenic

Answer 17

traits that are influenced by genes at two or more loci; ex: stature, skin color, eye color, hair color; many (but not all) are influenced by environmental factors (ex: nutrition and sunlight exposure)

Question 18

pigment

Answer 18

a molecule that influences the color of skin, hair, and eyes

Question 19

modern synthesis

Answer 19

a synthesis of multuple lines of evidence to integrate mendelian genetics and natural selection within evolutionary theory

Question 20

variation

Answer 20

inherited differences among individuals; the basis of all evolutionary change

Question 21

allele frequency

Answer 21

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

Question 22

population

Answer 22

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

Question 23

gene pool

Answer 23

all of the genes shared by reproductive members of a population

Question 24

microevolution

Answer 24

small changes occurring within species; ex: changes in allele frequencies)

Question 25

macroevolution

Answer 25

changes produced only after many generations; ex: appearance of a new species

Question 26

gene flow

Answer 26

exchange of genes between populations

Question 27

genetic drift

Answer 27

evolutionary changes, or changes in allele frequencies, that are produced by random factors in small populations; 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, or are remnants of, larger populations

Question 29

sickle-cell trait

Answer 29

heterozygous condition in which a person has one hba allele and one hbs allele and thus some normal hemoglobin

Question 30

sickle-cell anemia

Answer 30

a severe inherited hemoglobin disorder in which rbc collapse when deprived of oxygen’ results from inheriting two copies of a mutant allele; allele caused by a single base substitution in the dna