Unit 2: Beyond Mendelian Genetics Flashcards
Lethal Allele Combinations
A genotype (allele combination) that causes death is, by strict definition _____.
Death from genetic disease can occur at any stage of development or life.
Lethal
Lethal Allele Combinations
Tay-Sachs disease is lethal by age ____ or ___
3 or 4
Lethal Allele Combinations
Huntington
disease may not be lethal until ________.
late middle age
Lethal Allele Combinations
In a population and evolutionary sense, a lethal genotype has a more specific meaning—it causes death before the individual can reproduce, which prevents passage
of mutations to the next generation
BASAHIN LANG
An example of a lethal genotype in humans is ______________ dwarfism, which has
the distinct phenotype of a long trunk, short limbs, and a large head bearing a flatvface. It is an autosomal dominant trait, but is most often the result of a spontaneousv(new) mutation.
achondroplastic dwarfism
Different Dominance Relationships
■ type of relationship between alleles, with a
heterozygote phenotype intermediate
between the two homozygote phenotypes
Incomplete Dominance
When F1 generation (all pink flowers) is self
pollinated, the F2 generation is 1:2:1
red, pink, white
___________ in which a threshold level is necessary for health illustrate both complete and incomplete dominance.
Enzyme deficiencies
_________ (FH) is an example of incomplete dominance that can be observed in carriers on both the molecular and whole-body levels
Familial hypercholesterolemia
A person with two disease-causing alleles does not have receptors on liver cells that take up the ___________ (LDL) form of cholesterol from the bloodstream, so it builds up.
Ex. The phenotypes parallel the number of receptors—individuals with two mutant alleles die
in childhood of heart attacks
low-density lipoprotein
A person with one disease-causing allele has half the ______ number of receptors.
those with one mutant allele may suffer heart attacks in
young adulthood,
normal
Someone with two wild type alleles has the ______ number of receptors
those with two wild type alleles do not develop this inherited form of
heart disease.
normal
Different alleles that are both expressed in a heterozygote are codominant.
The ABO blood group system is based on the
expression of codominant alleles.
Co-dominance
Codominant traits
Genotype: AA and AO
Phenotype: ______
A
Codominant traits
Genotype: BB and BO
Phenotype: ______
B
Codominant traits
Genotype: AB
Phenotype: ______
AB
Codominant traits
Genotype: OO
Phenotype: ______
O
Blood type: A
Antigen: A
Genotype:_________
A / A / Ai
Blood type: AB
Antigen: AB
Genotype:_________
B / B / Bi
Blood type: AB (rare)
Antigen: A and B
Genotype:_________
A / B
Blood type: O
Antigen: neither
Genotype:_________
ii
Mendel’s laws can appear not to operate when one gene masks or otherwise affects the phenotype of another
It refers to interaction between different genes, not
between the alleles of the same gene.
Epistasis
Epistasis
A gene that affects
expression of another is called a ________.
modifier gene
A familiar epistatic interaction is
____, in which one gene blocks the action of genes that confer color.
______ is seen in many species.
In epistasis, the blocked gene is expressed (transcribed into RNA normally, but the protein product of the modifier gene inactivates it removes a structure needed for it to contribute to the phenotype, or otherwise counteracts its effects.
albinism
A blood type called the __________ phenotype also illustrates epistasis.
It results from an interaction between a gene called H and the I gene tha confers ABO blood type. The H gene controls the placement of a molecul to which antigens A and B attach on red blood cell surfaces.
Bombay
WHen was Bombay first discovered?
It is present in 0.004% population
Can receive blood only from Bombay blood group people
1952
Bombay was named by whom?
Dr. Bhande and others
Pleiotropy
A single-gene disease with many symptoms, or a gene that controls several functions or has more than one effect, is termed
__________.
Such conditions can be difficult to trace through
families because people with different subsets of symptoms may appear to have different diseases.
pleiotropic
Pleiotropy
The most common form of this autosomal
dominant condition is a defect in an elastic connective tissue protein called
fibrillin.
The protein is abundant in the lens of the eye, in the aorta (the largest artery in the body, leading from the heart), and in bones of the limbs, fingers, and ribs.
The symptoms are lens dislocation, long limbs, spindly fingers, and a caved-in chest. The most serious symptom is a weakening in the aorta, which can suddenly burst. If the weakening is detected early, a synthetic graft can replace the section of artery wall and save the person’s life.
Marfan syndrome
Mutations in different genes that produce the same
phenotype lie behind ___________
It can occur when genes encode enzymes or other proteins that are part of the same biochemical pathway, or when proteins affect the same body part
genetic heterogeneity
genetic heterogeneity
Consider ____________, in which abnormal collagen causes
fragile bones.
Before a second causative gene was discovered, some
parents of children who were brought to the hospital with frequent fractures and who did not have a mutation in the one known gene were accused of child abuse. Today eight genetically distinct forms of the disease are recognized.
osteogenesis imperfecta
Phenocopies
An environmentally caused trait that appears to be inherited is a _________.
Such a trait can either produce symptoms that resemble those of a known single-gene disease or mimic inheritance patterns by affecting certain relatives.
For example, the limb birth defect caused by the drug thalidomide **is a phenocopy of the rare inherited illness phocomelia. **
phenocopy
Physicians recognized the environmental disaster when they began seeing many children born with what looked like phocomelia. A birth defect caused by exposure to a widely used teratogen was more likely than a sudden increase in incidence of a rare inherited disease.
Regulate organ development
a. Homeotic
b. Homeobox
c. Hox Genes
a
Code for transcription factors
a. Homeotic
b. Homeobox
c. Hox Genes
b
Determine the identifies of each body segement.
a. Homeotic
b. Homeobox
c. Hox Genes
c
Homeobox genes in humans:
Vitamin __ can affect homeobox genes
Vitamin A
Homeobox genes in humans:
Drug ________ affected 1 or more homeobox genes
Thalidomide
Homebox genes in humans
The most dramatic examples of homology are in the ______ genes, as well.
Hox genes
Drug that was meanr as a sleeping aid but prescribed to pregnant women to treat anxiety and nausea
- Caused serious birth abnormalities for hundreds of children
- This sdrug led to stricter tests to determine a drug’’s impact on a fetus
Thalidomide
On Phenotypic Expression - Penetrance and Expressivity
refers to the percentage of individuals who have a particular genotype who have the associated phenotype.
An allele combination that produces a phenotype in everyone who inherits it is completely penetrant.
Huntington disease is nearly completely penetrant.
Almost all people who inherit the mutant allele will
develop symptoms if they live long enough. Complete ______ is rare.
Penetrance
On Phenotypic Expression - Penetrance and Expressivity
refers to variability in severity of a phenotype, or the **extent to which
the gene is expressed.
Expressivity
This refers to the inheritance of a trait
*governed by more than one genes. Generally, *three or more genes govern the inheritance of _________ traits. Multipl independent genes have an additive or similar effect on a single quantitative trait.
Ex. Human Height, Weight, Skin color
Polygenic traits
This is another example of polygenic disorder with multiple genes located on different chromosomes contributing to it susceptibility. Analysis of the genetic factors is further
complicated by the fact that numerous environmental factors interact with genes to produce the disorder.
Type 2 diabetes
