11. Mendel and the Gene Idea

Question 1

character

Answer 1

An observable heritable feature that may vary among individuals (ex. flower color).

Question 2

trait

Answer 2

One of two or more detectable variants in a genetic character (ex. white or purple flowers).

Question 3

true-breeding

Answer 3

Referring to organisms that produce offspring of the same variety over many generations of self-pollination.

Question 4

hybridization

Answer 4

In genetics, the mating, or crossing, of two true-breeding varieties.

Question 5

P generation

Answer 5

The true-breeding (homozygous) parent individuals from which F1 hybrid offspring are derived in studies of inheritance; P stands for “parental.”

Question 6

F1 generation

Answer 6

The first filial, hybrid (heterozygous) offspring arising from a parental (P generation) cross.

Question 7

F2 generation

Answer 7

The offspring resulting from interbreeding (or self-pollination) of the hybrid F1 generation.

Question 8

allele

Answer 8

Any of the alternative versions of a gene that may produce distinguishable phenotypic effects.

Question 9

dominant allele

Answer 9

An allele that is fully expressed in the phenotype of a heterozygote.

Question 10

recessive allele

Answer 10

An allele whose phenotypic effect is not observed in a heterozygote.

Question 11

Law of Segregation

Answer 11

Mendel’s first law, stating that the two alleles in a pair separate from each other into different gametes during gamete formation.

Question 12

Punnett square

Answer 12

A diagram used in the study of inheritance to show the predicted genotypic results of random fertilization in genetic crosses between individuals of known genotype.

Question 13

homozygous

Answer 13

Having two identical alleles for a given gene.

Question 14

heterozygous

Answer 14

Having two different alleles for a given gene.

Question 15

phenotype

Answer 15

The observable physical and physiological traits of an organism, which are determined by its genetic makeup.

Question 16

genotype

Answer 16

The genetic makeup, or set of alleles, of an organism.

Question 17

testcross

Answer 17

Breeding an organism of unknown genotype with a homozygous recessive individual to determine the unknown genotype. The ratio of phenotypes in the offspring reveals the unknown genotype.

Question 18

monohybrid

Answer 18

An organism that is heterozygous with respect to a single gene of interest. All the offspring from a cross between parents homozygous for different alleles are monohybrids. For example, parents of genotypes AA and aa produce a monohybrid of genotype Aa.

Question 19

monohybrid cross

Answer 19

A cross between two organisms that are heterozygous for the character being followed (or the self-pollination of a heterozygous plant).

Question 20

dihybrid

Answer 20

An organism that is heterozygous with respect to two genes of interest. All the offspring from a cross between parents doubly homozygous for different alleles are dihybrids. For example, parents of genotypes AABB and aabb produce a dihybrid of genotype AaBb.

Question 21

dihybrid cross

Answer 21

A cross between two organisms that are each heterozygous for both of the characters being followed (or the self-pollination of a plant that is heterozygous for both characters).

Question 22

Law of Independent Assortment

Answer 22

Mendel’s second law, stating that each pair of alleles segregates, or assorts, independently of each other pair during gamete formation; this applies when genes for two characters are located on different pairs of homologous chromosomes or when they are far enough apart on the same chromosome to behave as though they are on different chromosomes.

Question 23

multiplication rule

Answer 23

A rule of probability stating that the probability of two or more independent events occurring together can be determined by multiplying their individual probabilities.

Question 24

addition rule

Answer 24

A rule of probability stating that the probability of any one of two or more mutually exclusive events occurring can be determined by adding their individual probabilities.

Question 25

complete dominance

Answer 25

The situation in which the phenotypes of the heterozygote and dominant homozygote are indistinguishable.

Question 26

incomplete dominance

Answer 26

The situation in which the phenotype of heterozygotes is intermediate between the phenotypes of individuals homozygous for either allele.

Question 27

codominance

Answer 27

The situation in which the phenotypes of both alleles are exhibited in the heterozygote because both alleles affect the phenotype in separate, distinguishable ways.

Question 28

Tay-Sachs disease

Answer 28

A human genetic disease caused by a recessive allele for a dysfunctional enzyme, leading to accumulation of certain lipids in the brain. Seizures, blindness, and degeneration of motor and mental performance usually become manifest a few months after birth, followed by death within a few years.

Question 29

pleiotropy

Answer 29

The ability of a single gene to have multiple effects.

Question 30

epistasis

Answer 30

A type of gene interaction in which the phenotypic expression of one gene alters that of another independently inherited gene.

Question 31

quantitative character

Answer 31

A heritable feature that varies continuously over a range rather than in an either-or fashion.

Question 32

polygenic inheritance

Answer 32

An additive effect of two or more genes on a single phenotypic character. (Think of it as inverse pleiotropy, where 1 gene affects multiple phenotypic characters)

Question 33

multifactorial

Answer 33

Referring to a phenotypic character that is influenced by multiple genes and environmental factors.