Extensions and Modifications of Basic Principles

Question 1

What is incomplete dominance?

Answer 1

-BB, Bb and bb all differ phenotypically, Bb is intermediate between homozygous phenotypes
ex: flower colour (red,
white, pink-new phenotype)
-the phenotype of the heterozygote falls between the phenotypes of the two homozygotes

Question 2

What does codominance mean?

Answer 2

-BB, Bb and bb all differ phenotypically but Bb exhibits phenotypes of both homozygotes
ex:blood type
-alleles are equal to the phenotypes

Question 3

What is the P generation for incomplete dominance?

Answer 3

-two true breeding gametes are crossed
-one with two dominant alleles (PP-purple)
-one with two recessive alleles (pp-white)

Question 4

What is the F1generation for incomplete dominance?

Answer 4

-mixture of alleles occurs and two heterozygous gametes are produced
-Pp (violet)

Question 5

What is the F2 generation for incomplete dominance?

Answer 5

-two heterozygous gametes with mixed phenotype
-one homozygous dominant
gamete
-one homozygous recessive
gamete
-1:2:1 ratio

Question 6

What happens when multiple alleles exist for a gene at a particular locus?

Answer 6

-some genes have many alleles some common some rare (form mutants of wild type gene)
-some are associated with certain breeds or variety of plants and animals
-wild type gene is the most common type in nature

Question 7

What does population mean?

Answer 7

Multiple alleles may exist

Question 8

What does individual/diploid mean?

Answer 8

-only two alleles coexist in each cell

Question 9

What does > and = indicate in an allelic series?

Answer 9

-> dominance
-= incomplete dominance or codominance
-start of series is dominant over all alleles end is the most recessive allele

Question 10

What is an allelic series?

Answer 10

-describes the dominance hierarchy of multiple alleles
-null=nonfunctional
-Hypomorphic=partial function

Question 11

What does each allele signifiy in codominance of the ABO blood phenotype?

Answer 11

-gene I encodes transferase enzyme
-three alleles Ia Ib i
-A and Ab = over 90% of population
-B and O are more rare as they are determined by recessive alleles

Question 12

What does Ia encode and transfer?

Answer 12

transferase, which transfers acetyl galactosamine
-phenotype is the protein inside the gene

Question 13

What does Ib encode and transfer?

Answer 13

-transferase which adds galactose
-galactose has red blood cells

Question 14

What does i encode and transfer?

Answer 14

-non-functional transferase
-transfers nothing to red blood cells

Question 15

What are the possible genotypes for type A blood?

Answer 15

-IAIA or IAi
-i allele is frequent even though it is recessive therefore it is not technically rare

Question 16

What are the possible genotypes for type B blood?

Answer 16

IBIB or IBi

Question 17

What are is possible genotypes for type O blood?

Answer 17

ii

Question 18

What is the genotype for AB blood?

Answer 18

-IAIB
-red blood cells have both a & b at the surface
-contain both acetylgalactosamine and galactose
-is an example of codominance as both alleles are fully expressed in the heterozygote

Question 19

What is the wildtype allele?

Answer 19

-a functional enzyme or other protein is produced
-refers to the normal version of that gene or the most common in the wildtype

Question 20

What is the loss of function allele?

Answer 20

-an enzyme or other protein is no longer being produces is produced at lower levels or is nonfunctional
-sometimes losing one copy affects the genotype
-some can function on one good copy

Question 21

What is haplosufficiency?

Answer 21

-when wildtype alleles are dominant over the loss of function
-half as much protein is synthesized yet it is sufficient to achieve the wildtype phenotype
-still phenotypically normal but only half (haplo) is sufficient

Question 22

What is a gain of function mutation?

Answer 22

-the mutant allele produces a protein that has increased (detrimental) function
It does not matter if you have one normal copy you are still affected
-dominant alleles isn’t normal and recessive allele isn’t mutation
Ex: Huntington’s disease

Question 23

What does haploinsufficient mean?

Answer 23

-one loss of function allele causes a phenotype (dominant allele)
-in the heterozygote half as much protein is synthesized and this is not sufficient for a normal phenotype
ex: Tailless cats (Manx)
-has normal allele (tail) one copy of no tail allele and it takes over

Question 24

What is recessive lethal alleles?

Answer 24

-essential genes when mutated lead to a lethal phenotype (embryos die)
-only expressed in the homozygote
-individuals homozygous for a Tay Sachs allele often die before the age of 3
tsts lethal, TSts not lethal, TSTS not lethal
Ex: Manx cats are tailless

Question 25

What are dominant lethal alleles?

Answer 25

-can be expressed in both the heterozygote and the homozygote
-has to be rare
-Huntington disease can be considered Bb lethal, BB lethal bb not lethal
-typically comes after reproduction and becomes lethal later in time

Question 26

What is the severe mutant phenotype?

Answer 26

-recessive amorphic loss of function allele does not produce a functional polypeptide (cannot do its job)
-1/2 functioning
-1/2 not functioning

Question 27

What is the mild mutant phenotype?

Answer 27

-recessive hypomorphic loss-of-function allele produces a partially functional polypeptide (protein is misshapen slightly)
-1/2 functioning
-1/2 not functioning

Question 28

What is a dominant severe mutant phenotype?

Answer 28

-dominant-negative allele produces a polypeptide that interferes with the wild-type polypeptide (single copy carries phenotype)
-the negative touches the normal protein and cant perform its job