Unit 9: The Molecular Basis of Heredity Flashcards
What are completely dominant alleles?
Give the same phenotype and fitness in the heterozygote and homozygote. Ex. The fitness of BB = Bb.
What determines dominance of one allele over another?
It’s determined by the protein product of
that allele.
Ex. The protein produced by the dominant allele might have a functional effect that results in a visible trait, while the recessive allele may either produce a non functional protein or no protein at all.
The overall _________ is the consequence
of the activities of the _______ _______ of
the alleles of the gene.
The overall phenotype is the consequence
of the activities of the protein products of
the alleles of the gene.
What is haplosufficient?
The dominant wild-type allele is haplosufficient, meaning that one copy of it is enough for normal function in heterozygotes.
Given that A wild-type allele (A+) produces an active enzyme (50 units), and a mutant allele (A- )
produces little or no active enzyme (5 units), how many enzyme units will an A+A+, A+A-, A-A- individuals produce? Will they be wild type or mutant?
- 40 or more units of enzyme activity will produce a wild-type phenotype; thus A+A+
(100 units) or A+A- (50 units) individuals are
wild-type. - A-A- individuals (10 units) have the mutant
phenotype; thus, the mutant allel.e is
recessive
An allele (T1) produces an active enzyme (10 units), and a mutant allele (T2) produces less active enzyme (2 units). 18 or more units of enzyme activity will produce a wild-type phenotype. Is the T2 mutation dominant or recessive?
T^1T^2 (12 units) and T^2T^2 (4 units) individuals have a mutant phenotype
because neither produces enough enzyme. Thus, only T^1T^1 (20 units) individuals will be wild-type and this mutation is DOMINANT!
What is haploinsufficient?
The wild-type allele is haploinsufficient, meaning that one copy of it is not enough for normal function.
What is incomplete dominance?
When heterozygous individuals display
intermediate phenotypes between either homozygous type.
What allele designations are used for incomplete dominance?
Allele designations such as A^1A^2 or B^1B^2 are used instead of Aa or Bb.
What is codominance?
Detectable expression of both alleles in the
heterozygotes, and both alleles are fully expressed.
What is an example of a gene that shows both complete and incomplete dominance?
ABO Blood Group System
In the ABO blood system, which alleles are completely dominant and codominant?
The I^A and I^B alleles are completely dominant over the i allele but codominant to each other.
The two blood group antigens (____ and ____) are ____ with the lipid portion anchored in the _ ________ _______ ________.
The two blood group antigens (Type A and Type B) are glycolipids with the lipid portion anchored in the red blood cell membrane.
The blood group antigens are based on the _ ____, which is then modified by the addition of an extra ____ of ____ or ____ or no extra ____ molecules added (_).
The blood group antigens are based on the H antigen, which is then modified by the addition of an extra sugar of type A or type B or no extra sugar molecule added (O).
What is the Bombay phenotype?
The Bombay phenotype (or hh genotype) is a rare genetic condition in which individuals do not produce the H antigen at all (used to produce Type A or Type B blood type). The lack of the H antigen results in them being blood type O.
Considering the genotype I^AI^B Hh x I^AI^B Hh, what is the probability of producing a blood type O child?
25%
Some single-gene mutations are so detrimental that they cause…
death in the organism.
________ _______ ________typically have ___ frequencies in populations due to intense selection against ___________.
Recessive lethal alleles typically have low
frequencies in populations due to intense selection against homozygotes.
What is the wild-type color of fur in mice? What is the combination of the pigment?
In mice, wild-type coat color is agouti (A), produced by a combination of yellow and black pigments along each hair.
What is the mutant allele of agouti (A) in mice? What phenotype does it result in?
The mutant allele of agouti, A^Y, is dominant and causes yellow pigment to be deposited along the entire hair, resulting in a yellow coat.
Because an A^Y homozygote genotype is lethal…
yellow mice are heterozygous.
What is the phenotypic F1 ratio of an Agouti AA x Yellow AA^Y cross of two mice?
1/2 AA Agouti, 1/2 AA^Y Yellow
What is the phenotypic F1 ratio of a Yellow AA^Y x Yellow AA^Y cross of two mice?
1/3 AA Agouti, 2/3 AA^Y Yellow
What is an example of a dominant lethal allele?
A prominent example is Huntington disease
(HD), a fatal neurodegenerative disorder that does not usually show symptoms until the late thirties or early forties.
What is delayed age of onset?
The abnormalities they produce are not evident until after the affected individual has reached reproductive age.
What are sex-limited traits?
The traits involved are called sex-limited traits; both sexes carry the genes for such traits, but they are expressed in just one sex.
In sex-limited traits, The biological sex of an organism can influence gene expression due to…
differing hormone profiles.
What is an example of a sex-limited trait?
Cock-feathered males (hh) have have long, pointed, and colorful feathers, while hen-feathered male (HH or Hh) have regular tails.
What are three reasons why harmful dominant alleles exist in a population?
- Delayed Age of Onset
- Sex-limited traits
- Incomplete penetrance
What is penetrant?
An organism is penetrant for a trait when the phenotype is consistent with the genotype.
What is nonpenetrant?
An organism that does not produce the phenotype generally associated with the
genotype is nonpenetrant.
What is fully penetrant?
When the genotype is always expressed in the phenotype, the trait is fully penetrant.
What is incomplete penetrance?
Traits that are nonpenetrant in some individuals are said to display incomplete
penetrance.
What is Polydactyly? What type of penetrance does it have?
Polydactyly is an autosomal dominant condition in which affected individuals have
more than five fingers and toes.
In populations, the number of alleles is theoretically _________ and some _____ have many _____.
In populations, the number of alleles is theoretically unlimited and some genes have many alleles.
What is an allelic series?
In order of dominance among the alleles may form a sequential series referred to as an allelic series.
What is the C-Gene for mammalian coat color?
The C gene is responsible for coat color in mammals like cats, rabbits, and mice.
What enzyme does the C gene produce? What is this enzyme responsible for?
It produces an enzyme, tyrosinase, which is active in the production of melanin.
What are the four
alleles of the C gene?
c^ch, c^h, and c, and C
What does the c^ch allele produce in the c-gene system for mammalian coat color?
c^ch produces a “dilute” phenotype called chinchilla. (Greyish color)
What does the c^h allele produce in the c-gene system for mammalian coat color?
c^h produces a phenotype called Himalayan with little pigment on the body but full color on the extremities. (Black and white)
What does the c allele produce in the c-gene system for mammalian coat color?
c is a fully recessive null (nonfunctional) allele and produces an albino
phenotype in cc homozygotes.
What does the C allele produce in the c-gene system for mammalian coat color?
Full color (tan color)
What is the dominance relationships in the allelic series of the c-gene?
- The C allele is dominant over all the others
- c^ch allele is partially dominant over c^h
- All the alleles are dominant over the c allele
What will F1 look like for CC Full Color x c^chc^ch Chinchilla?
100% Full color
What will F1 look like for c^chc Chinchilla x c^hc Himalayan?
1/2 chinchilla, 1/4 himalayan, 1/4 albino. 2:1:1 phenotypic ratio.
What will F1 look like for c^chc Chinchilla x c^hc Himalayan?
1/2 chinchilla, 1/4 himalayan, 1/4 albino. 2:1:1 phenotypic ratio.
Different patterns of ________ ________ result from different ways ___ _______ interact in ________.
Different patterns of epistatic interactions result from different ways gene products interact in pathways.
Where is the expected 9:3:3:1 ratio seen?
The expected 9:3:3:1 ratio is seen in the
absence of epistasis: when the genes do not interact to change the expression of one another.
How are budgerigar parakeets an example of a 9:3:3:1 ratio?
- When pure-breeding blue budgies (BByy)
are crossed to pure-breeding yellow
budgies (bbYY), the F1 all have wild-type
green feathers (BbYy). - When the F1 are interbred, the F2 are:
* 9/16 wild type, green feathers (BbYy)
* 3/16 blue feathers (Bbyy)
* 3/16 yellow feathers (bbYy)
* 1/16 white feathers (bbyy)
This is a 9:3:3:1 ratio.
What is complementary gene interaction? What type of ratio does it have?
Complementary gene interaction is a type of gene interaction where two different genes work together to create a specific trait. It has a 9:7 ratio.
In complementary gene interaction, in order for a specific trait to appear…
both genes must have at least one dominant allele. If either of the genes is homozygous recessive (both alleles are recessive), the trait will not appear.
When genes work in tandem to produce a single produce, the process called ___________ _____ _________.
complementary gene interaction
What is the 9 and the 7 representative of in a 9:7 ratio of complementary gene interaction?
- The 9 represents individuals that show the trait (because both genes have at least one dominant allele).
- The 7 represents individuals that do not show the trait (because at least one gene has two recessive alleles, which masks the trait).
What is the ratio of the F1 generation when you cross AaBb x AaBb where the alleles of A and B produce colored flowers and a and b produce no pigmented flowers?
9:7
What is recessive epistasis?
In recessive epistasis, homozygosity for the recessive allele at one locus will mask the phenotypic expression of the alleles at a second locus, giving a 9:3:4 ratio.
What is the ratio of the F1 generation when you cross two mice BbCc x BbCc where CC or Cc creates normal color development with BB and Bb as black agouti and bb as brown agouti while cc produce albino mice?
9:3:4 recessive epistasis ratio.
What is the ratio of the F2 generation when you cross two dogs BbEe Black x BbEe black where BB and Bb is black fur, bb is brown fur, and ee is yellow fur?
9:3:4 9/16 black, 3/16 brown, 4/16 yellow
A number of all-black cats are crossed and they produced the following types of
progeny: 9/16 black; 3/16 grey; and 4/16 white. Out of the choices below, what is
the most likely genotype of the white kittens?
A. AaBB
B. AaBb
C. AABb
D. aaBb
D. aaBb Since it’s a recessive epistasis interaction.
