Chapter 5

Question 1

Discontinuous variation

Answer 1

Phenotypes that fall into two or more distinct,
non-overlapping categories (Ex. pea plants are either dwarf or tall)

Question 2

Continuous variation

Answer 2

Phenotypes that are distributed from one extreme to another in an overlapping or continuous fashion (Ex. tobacco plant height varies from dwarf to tall, including many intermediate heights)

Question 3

Monogenic traits

Answer 3

Controlled by a single gene

Question 4

Complex multifactorial trait

Answer 4

Controlled by more than one gene, as well as environmental influences (ex. Human height) Normally creates many different classes of phenotypes, creating a continuous distribution

Question 5

Complex polygenic traits

Answer 5

Controlled by more than one gene. Normally has multiple very distinct phenotypes

Question 6

Relationship between genes and phenotypic classes

Answer 6

The greater the number of genes controlling a trait, the greater the number of phenotypic classes

More genes = more variance

Question 7

Additive effects/alleles

Answer 7

Each dominant allele adds onto the next one, making the trait “stronger” or more pronounced

Question 8

what is phenotypic variation derived from?

Answer 8

Genetic variance and environmental variance

Heritability = 1 (genetics factors contribute greatly to phenotypic variation)

Heritability = 0 (environmental factors contribute greatly to phenotypic variation and has very little genetic contribution)

Question 9

Dizygotic vs monozygotic twins

Answer 9

DZ twins (2 different eggs) have a correlation coefficient of 0.5 or roughly 50% of their genes are shared, like normal siblings

MZ twins (1 egg) are identical and have a correlation coefficient of 1.0.

Question 10

Concordant vs discordant trait

Answer 10

Concordant trait- both twins have the trait

Discordant trait- only one twin has the trait

Question 11

For a polygenic trait, how do you find the number of phenotypic classes?

Answer 11

2n+1 = number of phenotypic classes, with n = # of genes

Ex. You will have 7 phenotypic classes for 3 genes

Question 12

How to find the number of extreme phenotypes?

Answer 12

Extreme phenotype = all recessive or all dominant

Ex. If there are 2 genes involved for height, use the formula 1/4^n to find how many of each would be the extremes. In this case, 1/4^2 is 1/16 so 1/16 would be extremely short and 1/16 would be extremely tall

Question 13

What is often true about genetic diseases like diabetes and cancer?

Answer 13

They are often complex traits that result from an interaction of many genes with the environment