Chapter 5. Extensions of Mendelian Inheritance

Question 1

Simple Mendelian inheritance describes the inheritance patterns that obey

Answer 1

1. The Law of Segregation
2. The Law of Independent Assortment

Question 2

Simple Mendelian

Answer 2

Inheritance: Follows strict dominant/ recessive relationship
Molecular: Dominant allele encodes a functional protein, 50% to produce a dominant trait

Question 3

X-linked

Answer 3

Inheritance: inheritance genes located on X chromosome. Males have one x while females have 2.
Molecular: Males always express the copy they carry.

Question 4

Incomplete Penetrance

Answer 4

Inheritance: When a dominant phenotype is not expressed even though an individual carries a dominant allele.
Molecular: A dominant gene may be present but not expressed due to environmental factors or other genes

Question 5

Incomplete Dominance

Answer 5

Inheritance: Occurs when the heterozygote has a phenotype that is intermediate between either corresponding homozygote.
Molecular: 50% of functional protein is not enough to produce the same trait as a homozygote with 100% of the same protein.

Question 6

Overdominance

Answer 6

Inheritance: When a heterozygote has a trait that confers a greater level of reproductive success than either homozygote has.
Molecular: 3 main ways:
1. cells may have increased resistance to infection by microorganisms.
2. may produce more forms of protein dimers with enhanced function.
3. may produce proteins that function under a wider range of conditions.

Question 7

Codominance

Answer 7

Inheritance: When a heterozygote expresses both alleles simultaneously without forming an intermediate phenotype.
Molecular: The codominant alleles encode proteins that function slightly differently from each other, and the function of protein in heterozygotes affects the phenotype uniquely

Question 8

Sex-influenced inheritance

Answer 8

inheritance: effect of sex on the phenotype of the individual.
molecular: sex hormones may regulate the molecular expression of genes. This regulation can influence the phenotypic effects of alleles.

Question 9

Sex-limited inheritance

Answer 9

Inheritance: trait occurs in only one of the two sexes.
Molecular: sex hormones may regulate the molecular expression of genes. Sex hormones that are primarily produces in only one sex are essintial for an individual to display a particular phenotypye.

Question 10

Lethal Alleles

Answer 10

Inheritance: has the potential to cause death to an organism
Molecular: most commonly loss-of-function alleles that encode proteins that are necessary for survival.

Question 11

2 reasons to understand Mendelian inheritance

Answer 11

1. Predict the outcome of crosses
2. how the molecular expression of genes can account for an individual’s phenotype

Question 12

Wild-type allele

Answer 12

most prevalent version of a gene in wild populations

Question 13

genetic polymorphism

Answer 13

more than one common allele that is considered wild-type

Question 14

mutant allele

Answer 14

a less common version of a gene

Question 15

How is one wild-type copy sufficient to provide full function?

Answer 15

1. 50% of normal levels of protein are good enough.
2. the one wild-type copy is unregulated in expression.

Question 16

Dominant mutant alleles are….

Answer 16

less common in natural populations,

Question 17

3 types of dominant mutant alleles

Answer 17

1. Gain-of-function
2. Dominant-negative
3. Haploinsufficiency

Question 18

Gain-of-function

Answer 18

• gene gains new or abnormal function
• may be overexpressed, producing higher levels of the protein

Question 19

Dominant-negative

Answer 19

mutant protein acts to antagonize the normal protein

Question 20

Haploinsufficiency

Answer 20

the mutant is a loss-of-function allele, and one wild-type copy is not enough to provide a function

Question 21

What can explain incomplete penetrance and variable expressivity?

Answer 21

1. environment
2. modifier genes

Question 22

Incomplete Dominance

Answer 22

heterozygote exhibits a phenotype that is intermediate between the phenotypes of the two homozygotes.

Question 23

Overdominance

Answer 23

a heterozygote has greater reproductive success than either homozygote.

Question 24

3 explanations for overdominance at the molecular/cellular level

Answer 24

1. Disease resistance
2. Subunit composition of proteins
3. differences in protein function

Question 25

Codominance

Answer 25

Many genes have multiple alleles (3 or more)

Question 26

Sex-Influenced Traits

Answer 26

an allele is dominant in one sex but recessive in the other

Question 27

Sex-Limited Traits

Answer 27

traits that occur in only one of the two sexes

Question 28

Lethal Alleles

Answer 28

has the potential to cause the death of an organism

Question 29

essential genes

Answer 29

required for survival

Question 30

Nonessential genes

Answer 30

not required for survival

Question 31

Pleiotropy

Answer 31

multiple effects of a single gene on the phenotype of an organism

Question 32

Gene interactions

Answer 32

occur when two or more different genes influence the outcome of a single trait

Question 33

Epistasis

Answer 33

an inheritance pattern in which the alleles of one gene mask the phenotypic effects of the alleles of a different gene

Question 34

Complementation

Answer 34

a phenomenon in which two different patterns that express the same or similar recessive phenotypes produce offspring with a wild-type phenotype.

Question 35

Gene modification

Answer 35

a phenomenon in which an allele of one gene modifies the phenotypic outcome of the alleles of a different gene

Question 36

Gene redundancy

Answer 36

a phenomenon in which the loss of function in a single gene has no phenotypic effect, but the loss of function of two genes has an effect. Functionally if only one of the two genes is necessary for a normal phenotype; the genes are functionally redundant.

Question 37

Complementation

Answer 37

Each recessive allele (c and p) is complemented by a wild-type allele (C and P). This phenomenon indicates that the recessive alleles are in different genes.

Question 38

Epistasis

Answer 38

when a gene can mask the phenotypic effects of another gene

Question 39

Gene modification

Answer 39

allele of one gene modifies the phenotypic outcome of a different gene

Question 40

Gene redundancy

Answer 40

loss of function alleles may have no effect on phenotype