Unit 9: The Molecular Basis of Heredity Flashcards
(59 cards)
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.
