Chapter 14: mendel and the gene idea

Question 1

Describe the difference between a character and a trait. Give an example

Answer 1

A character is a heritable feature that varies among individuals, like flower color

The variant for a character is a trait, such as a purple or white flower

Question 2

What is true breeding?

Answer 2

two parents are homozygous for every trait and produce offspring that are the same phenotype

aaxAA=Aa, all same phenotype

Question 3

When Mendel crossed the F1 generation of hybrids, what did the F2 generation look like?

Answer 3

a 3:1 ratio of purple to white plants

Question 4

How did Mendel’s breeding of the plants refute blending theory?

Answer 4

blending theory would produce lighter purple plants, and the white plants would not have reappeared in the F2 generation

Question 5

How many alleles will an organism inherit from its parent, according to Mendel?

Answer 5

two

Question 6

What is the law of segregation?

Answer 6

the two alleles for a heritable character separate, or segregate, during gamete formation and end up in different gametes

Question 7

What are the four points of Mendel’s model?

Answer 7

1. alternative versions of genes account for variations in inherited characters (some white, some purple)
2. an organism inherits two alleles from each parent
3. If the two alleles differ, the dominant trait will be expressed
4. law of segregation, the two alleles for a heritable character separate during gamete formation and end up in different gametes

Question 8

An ___ will help synthesize a dominant allele pigment, leading to its expression

Answer 8

enzyme

Question 9

Why is a trait dominant?

Answer 9

The enzyme is made that will synthesize the dominant allele

Question 10

What does a testcross determine?

Answer 10

whether the genotype is heterozygous or homozygous

Question 11

You perform a testcross between a dominant phenotype and a recessive phenotype and receive a 1/2 offspring dominant and 1/2 offspring recessive. What is the genotype of the dominant parent?

Answer 11

The genotype is heterozygous

Question 12

What is the law of independent assortment?

Answer 12

Crossing two true-breeding parents differing in two characters produces dihybrids which are heterozygous

a dihybrid cross can determine whether two characters are transmitted to offspring together or separately (think about redheads being allergic to anesthesia. these traits are transmitted together)

Question 13

What is the multiplication rule?

Answer 13

the probability that two or more INDEPENDENT events will occur together is the product of their individual probabilities

Question 14

What is the probability that flipping a coin twice will land on heads both times?

Answer 14

25%
50%x50%=25%

Question 15

What is the addition rule?

Answer 15

the probability that any one of two or more mutually exclusive events will occur is calculated by adding together their individual probabilities

Question 16

You cross a red rose with a white rose and the F1 generation results in 100% pink, while the F2 generation 50% pink, 25% red, and 25% white. this is an example of

Answer 16

incomplete dominance

Question 17

Why does incomplete dominance still not support the blending hypothesis?

Answer 17

Because in the F2 generation, dominant and recessive phenotypes are still expressed, while the blending hypothesis would indicate that the mix is present in all generations

Question 18

Blood type is an example of what kind of dominance

Answer 18

codominance

Question 19

What is pleiotropy?

Answer 19

When the expression of a single gene has multiple effects on phenotypes

Question 20

what is epistasis?

Answer 20

the expression of a gene is modified by the expression of one or more other genes

Question 21

What is polygenic inheritance?

Answer 21

multiple genes independently affect a single trait, ex. skin color

Question 22

What is a testcross?

Answer 22

breeding of a recessive homozygote with a dominate phenotype (but unknown genotype)

Question 23

You perform an experiment with a yellow puffle (a recessive trait) and a purple puffle ( a dominant trait) to determine the purple puffle’s genotype. This is an example of-

Answer 23

a testcross

Question 24

A true-bred offspring is

Answer 24

homozygous for a trait

Question 25

What does a 3:1 offspring ratio tell us?

Answer 25

It confirms the law of segregation because the alleles for each character segregate during meiosis and end up in different daughter cells

Question 26

A dihybrid cross can determine whether two characters are

Answer 26

transmitted to offspring together or independently

Question 27

You cross a blue eyed puffle with a yellow eyed puffle and the F1 generation has green eyes. This is an example of what kind of degree of dominance?

Answer 27

Incomplete.

Question 28

Explain why incomplete dominance is not “blending”

Answer 28

the traits will appear again in F2. Additionally, the heterozygote is only expressing 50% of the encoded protein, rather than both at the same time

Question 29

The offspring phenotype must be _____ for codominance to occur

Answer 29

heterozygous

Question 30

14.3.1 Incomplete dominance and epistasis are both terms that
define genetic relationships. What is the most basic distinction between these terms?

Answer 30

Incomplete dominance describes the relationship between two alleles of a
single gene, whereas epistasis relates to the genetic relationship between two
genes (and the respective alleles of each).