Lecture 3

Question 1

What are complete dominance and complete recessiveness?

Answer 1

Extremes of a range

Question 2

What is incomplete dominance?

Answer 2

BB, Bb and bb all differ phenotypically; Bb is intermediate between homozygous phenotypes

Example: flower colour (red - RR + white - rr = pink - Rr)

Question 3

What is codominance?

Answer 3

BB, Bb and bb all differ phenotypically, but Bb exhibits phenotypes of both homozygotes

Example: flower colour (red - RR + white - rr = red and white - Rr)

Question 4

What happens in a population?

Answer 4

Multiple alleles may exist.

Question 5

How many alleles exist in an individual (haploid)?

Answer 5

Two Alleles

Question 6

What is an example of multiple alleles?

Answer 6

Fur Coloration in Cats

C: full colour

Cb: burmese

Cs: siamese

c: white. blue eyes

Question 7

What is a Dominance series or allelic series?

Answer 7

For fur colouration, C > Cb = Cs > c > Ca

Where > indicates the dominance and = indicates incomplete dominance or codominance

Question 8

What does an allelic series describe?

Answer 8

The dominance hierarchy of multiple alleles.

Question 9

What is a null allele?

Answer 9

Nonfunctional

Question 10

What is a hypomorphic allele?

Answer 10

Has partial function

Question 11

What is ABO blood phenotype an example of?

Answer 11

Codominance

Question 12

For blood types, what does Gene I encode?

Answer 12

Transferase enzyme

Question 13

What are the three alleles for blood type?

Answer 13

IA, IB and I

Question 14

What does IA encode?

Answer 14

A Transferase which adds Acetylgalactosamine

Question 15

What does IA encode?

Answer 15

A Transferase which adds Galactose

Question 16

What does i encode?

Answer 16

A Non-Functional Transferase (amorphic allele)

Question 17

Type A Genotype

Answer 17

IAIA or IAi

Question 18

Type B Genotype

Answer 18

IBIB or IBi

Question 19

Type O Blood

Answer 19

ii

Question 20

What is Type AB Blood

Answer 20

IAIB

• It is not a new phenotype, but rather an example of codominance that has both galactose and acetylgalactosamine
• In this case two different transferases are made

Question 21

What is a Wildtype Allele?

Answer 21

A functional enzyme or other protein is produced (normal version of the gene)

Question 22

What is a Loss of Function Allele?

Answer 22

An enzyme or other protein is no longer being produced, is produced at lower levels or in non-functional.

Question 23

What type of allele is dominant?

Answer 23

The wild type allele is often dominant over loss of function allele.

Question 24

What is Haplosufficiency?

Answer 24

Half as much protein is synthesized yet this is often sufficient enough to achieve this wild type phenotype (half of two genes is enough to be ok)

Question 25

What can dominant alleles be?

Answer 25

A gain of function mutation, in which the mutant allele produces a protein that has increased detrimental function

Example: Huntingtons Disease Is a Dominant recessive disease, where it never skips a generation.

Question 26

How can dominant alleles also be loss of function alleles?

Answer 26

In a heterozygote, half as much protein is synthesized and this is not sufficient for a normal phenotype therefore haploinsufficent.

Question 27

What is an example of haploinsufficent?

Answer 27

Tailess cats (Manx), one copy causes the cat to have no tail..

Question 28

What is a recessive lethal allele?

Answer 28

It will cause death only if homozygous (need two copies of it)

Example: if a mice receives two big YY, it will die - but if it is heterozygous Yy, it will survive and be yellow - if yy white

Therefore the effect of the allele on colour is dominant.

Question 29

What ratio does a recessive lethal allele produce?

Answer 29

2 yellow: 1 non-yellow

Question 30

What is an example of a recessive lethal allele with cats?

Answer 30

Manx Cats

mm = normal tail

Mm = no tail (phenotypically)

MM - lethal (cat dies)

Question 31

Why is it considered to be Dominant Recessive for Lethal Alles?

Answer 31

As the allele is dominant but considered recessive as you need two copies of it for the cat to do

Question 32

What is Dominant Lethal Genes

Answer 32

Only need one copy of it of the allele for it to be lethal (can be expressed in both heterozygote and homozygote)

Example:
Bb lethal, BB lethal, bb not lethal (one copy of big B will kill the creature)

Question 33

What happens to individuals who are homozygote for Tay Sachs?

Answer 33

Often die before the age of 3

tsts = lethal, TSTS not lethal, TSts = not lethal

Question 34

What does a Wild-Type allele produce?

Answer 34

A functional protein

Question 35

What does a recessive amorphic loss of function allele produce?

Answer 35

A non-functional polypeptide (severe mutant)

Question 36

What does a recessive hylomorphic loss-of-function allele produce?

Answer 36

A partially functional polypeptide.

Question 37

What does a Dominant-negative allele produce?

Answer 37

A polypeptide that interferes with the wild-type polypeptide (severe mutant)

Question 38

If you have one allele that is wild type and the other allele is recessive, what will be the phenotype?

Answer 38

Wild-Type as you only need one good allele - if the other allele was dominant then it would be a mutant.