chapter 9

Question 1

alleles

Answer 1

are alternative versions of genes that account for variations in inherited characters.
2. For each characteristic, an organism inherits two alleles, one from each parent. The alleles can be the same or different.

Question 2

Genetics

Answer 2

s the scientific study of heredity

Question 3

dominant allele

Answer 3

If the alleles of an inherited pair differ, then one determines the organism’s appearance

Question 4

recessive allie

Answer 4

has no noticeable effect on the organism’s appearance

Question 5

homozygous

Answer 5

notype has identical alleles

Question 6

heterozygous

Answer 6

genotype has two different alleles

Question 7

hybrid

Answer 7

The offspring of two different varieties

Question 8

true-breeding

Answer 8

arieties result when self-fertilization produces offspring all identical to the parent.

Question 9

phenotype

Answer 9

he appearance or expression of a trait.

Question 10

genotype

Answer 10

genetic makeup of a trait.

Question 11

P Generation

Answer 11

true-breeding parental plants

Question 12

F1 Generation

Answer 12

Hybrid offspring

Question 13

F2 generation

Answer 13

A cross of F1 plants produces an F2 generation.

Question 14

Punnett square

Answer 14

shows the four possible combinations of alleles that could occur when these gametes combine.

Question 15

monohybrid cross

Answer 15

A cross between two individuals differing in a single character

Question 16

The Law of segregation

Answer 16

sperm or egg carries only one allele for each inherited character because allele pairs separate (segregate) from each other during the production of gametes

Question 17

dihybrid cross

Answer 17

s a mating of parental varieties that differ in two characters.

Question 18

The Law of independent Assortment

Answer 18

uggested that the inheritance of one character has no effect on the inheritance of another,
suggested that the dihybrid cross is the equivalent to two monohybrid crosses

Question 19

Testcross

Answer 19

s the mating between an individual of unknown genotype and a homozygous recessive individual.
A testcross can show whether the unknown genotype includes a recessive allele.
Mendel used testcrosses to verify that he had true-breeding genotypes.
The following figure demonstrates how a testcross can be performed to determine the genotype of a Lab with normal eyes.

Question 20

complete dominance.

Answer 20

Mendel’s pea crosses always looked like one of the parental varieties

Question 21

in codominance,

Answer 21

neither allele is dominant over the other and
expression of both alleles is observed as a distinct phenotype in the heterozygous individual.
AB blood type is an example of codominance.

Question 22

codominance

Answer 22

The A and B alleles are both expressed in heterozygous individuals, a condition

Question 23

The four human blood groups

Answer 23

A, B, AB, and O

Question 24

Pleiotropy

Answer 24

occurs when one gene influences many characteristics.

Question 25

Sickle-cell disease

Answer 25

affects the type of hemoglobin produced and the shape of red blood cells and
causes anemia and organ damage.
Sickle-cell and nonsickle alleles are codominant.
Carriers of sickle-cell disease are resistant to malaria.

Question 26

Most sex-linked human disorders

Answer 26

due to recessive alleles and

seen mostly in males.