Ch 15: Mendelian Genetics

Question 1

T/F: Although Mendel’s work was not originally considered by his contemporaries to be groundbreaking, his principles of segregation and independent assortment were “rediscovered” nearly two decades after his death.

Answer 1

True

Question 2

What made the plant hybridization studies performed by Mendel more successful than plant hybridization studies performed by others?

Answer 2

Mendel used true breeding plants that were carefully breeded to ensure the parents could be traced. He focused on traits that could be observed as phenotypes and used statistical analysis to study those phenotypes.

Question 3

What were Mendel’s two key discoveries?

Answer 3

Segregation and Independent Assortment.

Question 4

Genes that are _____ do not assort independently and are said to be _____.

Answer 4

close to each other in the same chromosome; linked

Question 5

The _____ of an individual describes the combination of _____ present, and the _____ constitutes the expression of the _____.

Answer 5

genotype; alleles; phenotype; trait

Question 6

You are given two populations of true-breeding tomato plants with two simple dominant/recessive traits that sort independently. Using the multiplication rule, how many different phenotypic combinations would you expect to see in the F2 generation? In what phenotypic ratio?

Answer 6

four; 9:3:3:1

Question 7

Genes that modify the phenotypic expression of other genes show:

Answer 7

epistasis

Question 8

A testcross involves crossing with _____ individual and is used to determine the _____ of the tested parent.

Answer 8

homozygous recessive; genotype

Question 9

The cellular mechanism that determines the independent assortment of maternal and paternal chromosomes is:

Answer 9

separation of homologous pairs at anaphase I of meiosis.

Question 10

Recall that alleles of a single gene will segregate from one another during anaphase I. When do alleles for two different genes—located in two different chromosomes—segregate?

Answer 10

anaphase I

Question 11

A true-breeding black rabbit is crossed with a true-breeding white rabbit to produce an F1 generation of 16 individuals. If the black color trait is dominant, which answer option represents the expected phenotype of an F1 generation cross?

Answer 11

16 black rabbits

Question 12

You are given two true-breeding groups of rabbits. The first group has floppy ears and white fur. The second group has straight ears and black fur. When you perform a cross of these two groups, your F1 rabbits all have floppy ears and gray fur. If each of these traits was determined by a single gene and underwent independent assortment, you would predict that 75% of your F2 generation rabbits have _____ ears and _____ of your rabbits have black fur.

Answer 12

floppy; 25%

Question 13

For a trait such as flower color in snapdragons that is determined by two alleles with incomplete dominance, the offspring of true-breeding parents show an intermediate phenotype. This is also what would be expected of blending inheritance. The difference is that:

Answer 13

The trait with blending inheritance will lose variation over time.

Question 14

Transmission Genetics

Answer 14

The discipline that deals with the manner in which genetic material is passed from generation to generation.

Question 15

Trait

Answer 15

A characteristic of an individual.

Question 16

Blending Inheritance

Answer 16

The now-discredited model in which heredity factors transmitted by the parents become intermingled in the offspring instead of retaining their individual genetic identities.

Question 17

Hybridization

Answer 17

Interbreeding between two different varieties or species.

Question 18

True Breeding

Answer 18

Describes a trait whose physical appearance in each successive generation is identical to that in the previous one.

Question 19

P1 Generation

Answer 19

The parental generation in a series of crosses.

Question 20

F1 Generation

Answer 20

The first filial, or offspring, generation.

Question 21

Reciprocal Cross

Answer 21

A cross in which the female and male parents are interchanged.

Question 22

Dominant

Answer 22

Describes an allele or trait that is expressed in heterozygotes. Only one dominant allele is needed to express the phenotype.

Question 23

Recessive

Answer 23

Describes an allele or trait that is only expressed in homozygotes, and not expressed in heterozygotes. Two recessive alleles are needed to express the phenotype.

Question 24

Allele

Answer 24

The different forms of a gene, corresponding to different DNA sequences in each different form.

Question 25

Genotype

Answer 25

The genetic makeup of a cell or organism; the particular combination of alleles present in an individual.

Question 26

Phenotype

Answer 26

The expression of a physical, behavioral, or biochemical trait; an individual’s observable phenotypes include height, weight, eye color, and so forth.

Question 27

Homozygous

Answer 27

Describes an individual who inherits an allele of the same type from each parent, or a genotype in which both alleles for a given gene are of the same type.

Question 28

Gamete

Answer 28

A reproductive haploid cell; gametes fuse in pairs to form a diploid zygote. In many species, there are two types of gametes: eggs in females, sperm in males.

Question 29

Segregate

Answer 29

Separate; applies to chromosomes or members of a gene pair moving into different gametes.

Question 30

Principle of Segregation

Answer 30

The principle by which half the gametes receive one allele of a gene and half receive the other allele.

Question 31

Zygote

Answer 31

The diploid cell formed by the fusion of two gametes.

Question 32

Heterozygote

Answer 32

Describes an individual who inherits different types of alleles from the parents, or genotypes in which the two alleles for a given gene are different.

Question 33

Punnett Square

Answer 33

A worksheet in the form of a checkerboard used to predict the consequences of a random union of gametes.

Question 34

Testcross

Answer 34

Any cross of an unknown genotype with a homozygous recessive genotype.

Question 35

Incomplete Dominance

Answer 35

Inheritance in which the phenotype of the heterozygous genotype is intermediate between those of homozygous genotypes.

Question 36

Probability

Answer 36

Among a very large number of observations, the expected proportion of observations that are of a specified type.

Question 37

Addition Rule

Answer 37

The principle that the probability of either of two mutually exclusive outcomes occurring is given by the sum of their individual probabilities.

Question 38

Multiplication Rule

Answer 38

The principle that the probability of two independent events occurring together is the product of their respective probabilities.

Question 39

Principle of Independent Assortment

Answer 39

The principle that segregation of one set of alleles of a gene pair is independent of the segregation of another set of alleles of a different gene pair.

Question 40

Epistasis

Answer 40

Interaction between genes that modifies the phenotypic expression of genotypes.

Question 41

Pedigree

Answer 41

A diagram of family history that summarizes the record of the ancestor–descendent relationships among individuals.

Question 42

Multiple Alleles

Answer 42

Two or more different alleles of the same gene, occurring in a population of organisms.

Question 43

Incomplete Penetrance

Answer 43

The phenomenon in which some individuals with a genotype corresponding to a trait do not show the phenotype, either because of environmental effects or because of interactions with other genes.

Question 44

Variable Expressivity

Answer 44

The phenomenon in which a particular phenotype is expressed with a different degree of severity in different individuals.

Question 45

Genetic Test

Answer 45

A method of identifying the genotype of an individual.