Chapter 12

Question 1

Purple or White petals are determined but different _______.

Answer 1

Alleles

Question 2

What are all the possible gamete combinations between a Pp and pp cross?

Answer 2

Pp, pp

Question 3

Prior to Mendal, how did people think that inheritance worked?

Answer 3

The basis for ideas about heredity involved blending

Question 4

Define: True-breeding, self-crossing, progeny, hybrid, dihybrid

Answer 4

True-breeding -

Self-crossing -

Progeny - offspring

Hybrid - crossing two different lines or varieties

Dihybrid -

Question 5

What did the work of TA Knight demonstrate?

Question 6

Why did Mendel choose to work with Peas?

Answer 6

1. Other research showed that pea hybrids could be produced
2. Many pea varieties were available
3. Peas are small plants and easy to grow — quick generation time
4. Peas can self-fertilize or be cross-fertilized

Question 7

Outline the basic structure of Mendel’s experimental design.

Answer 7

Three stages:
1. Produce true-breeding lines for each trait he was studying
2. Cross-fertilize true-breeding strains having alternate forms of a trait
3. Allow the hybrid offspring to self-fertilize for several generations and count the number of offspring showing each form of the trait

Question 8

Mendel worked with 7 specific traits, why did he choose these traits?

Answer 8

• Easily observable
• Minimal variation
• “Either or” exclusive traits
• Existed in alternate forms (e.g., purple vs. white flower; wrinkled vs. smooth seed)

Question 9

In a monohybrid cross, what % of F1 have the dominant phenotype?

Answer 9

100%

Question 10

Why are true breeding lines always homozygous?

Question 11

CONCEPT QUESTION: How can different genotypes result in the same phenotype? Or why does the 1:2:1 genotype ratio appear as the 3:2 phenotype ratio?

Answer 11

The 1:2:1 genotypic ratio appears as the 3:1 phenotypic ratio because the genotype is homozygous dominant: 2heterozygous: homozygous recessive. Heterozygous genotype displays the dominant phenotype because it has one dominant allele and one recessive. The dominant allele takes priority in the phenotype. For that reason different genotypes can result in the same phenotype. Homozygous dominant and heterozygous genotype both appear as the dominant phenotype.

Different genotypes can produce the same phenotype due to dominant and recessive alleles. In a 1:2:1 genotype ratio (like AA, Aa, and aa), the dominant allele (A) masks the effect of the recessive allele (a) in heterozygous individuals (Aa). This results in a 3:1 phenotype ratio because both AA and Aa display the dominant trait, while only aa shows the recessive trait. So, three have the dominant phenotype, and one has the recessive.

Question 12

What does it mean for two alleles to segregate? When does this happen?

Question 13

What is the principle of segregation?

Answer 13

Two alleles for a gene segregate during gamete formation and are rejoined at random, one from each parent during fertilization

Question 14

CONCEPT QUESTION: Can individuals have more than two alleles for a gene? Why or why not?

Answer 14

No.

Question 15

Monohybrid cross

Answer 15

cross that follows a single trait with two variations

Question 16

First filial generation

Answer 16

offspring resulting from a cross between a parental generation (P)

Question 17

Dominant

Answer 17

An allele that is expressed when present in either the heterozygous or the homozygous condition

Question 18

Recessive

Answer 18

An allele that is expressed only when present in the homozygous condition, but is “hidden” by the expression of a dominant allele in the heterozygous condition

Question 19

Second filial generation (F2)

Answer 19

offspring resulting from a cross between members of first filial (F1) generation

Question 20

What is the monohybrid phenotyptic ratio?

Answer 20

3:1

Question 21

What is the monohybrid genotypic ratio?

Answer 21

1:2:1

Question 22

1:2:1 ratio

Answer 22

1/4 true-breeding dominant (homozygous dominant)

1/2 non-true breeding dominant (heterozygous)

1/4 true-breeding recessive (homozygous recessive)

Question 23

Alleles

Answer 23

different forms of a gene

Question 24

Genotype

Answer 24

total set of alleles an individual contains

Question 25

Phenotype

Answer 25

physical appearance of an individual

Question 26

Dihybrid cross

Answer 26

single genetic cross involving two different traits

Question 27

Principle of Independent Assortment

Answer 27

In a dihybrid cross, the alleles of each gene assort independently –> The segregation of different allele pairs is independent

Question 28

Testcross

Answer 28

unknown genotype is crossed with homozygous recessive genotype

Question 29

T or F: Dominant phenotype can only be heterozygous

Answer 29

F: Dominant phenotype can be either homozygous or heterozygous

Question 30

Polygenic inheritance

Answer 30

more than one gene can affect a single trait

Question 31

In polygenic inheritance, the phenotype has

Answer 31

continuous variation

Question 32

Continuous variation

Answer 32

Variation in a trait that occurs along a continuum

Question 33

Quantitative traits

Answer 33

A trait that is determined by the effects of more than one gene

Question 34

Quantitative traits are traits with a ________ distribution

Answer 34

Continuous

Question 35

What are examples of quantitative traits?

Answer 35

Height, weight, eye color in humans

Question 36

The more genes involved in determining a phenotype, the more …

Answer 36

Continuous variation there is

Question 37

Pleiotropy

Answer 37

A single gene can affect more than one trait

Allele has more than one effect on phenotype

Question 38

What are examples of diseases in human that are the result of pleiotropic alleles?

Answer 38

Sickle cell anemia

Cystic fibrosis

Question 39

Cystic fibrosis cause?

Answer 39

Mutation in a gene that encodes a chloride ion transmembrane channel

Question 40

Patients with cystic fibrosis exhibit the following symptoms:

Answer 40

Clogged blood vessels

Sticky mucus

Salty sweat

Liver and pancreas failure

Question 41

Incomplete dominance

Answer 41

two or more alleles of a gene do not display clear dominance

phenotype of heterozygote is intermediate between the two homozygotes

Question 42

Complete dominance

Answer 42

two or more alleles of a gene are each dominant to other alleles but not to each other

The phenotype of a heterozygote for codominant alleles exhibits characteristics of each of the homozygous forms