Chapter 4 Gen Flashcards
Wild-type alleles
Prevalent alleles in a population
Polymorphism
More than one wild-type allele may occur in large populations, a phenomenon
Mutant alleles
Alleles that have been altered by a mutation
Incomplete Dominance
heterozygote exhibits a phenotype that is intermediate between the corresponding homozygotes
Codominance
both alleles are expressed in a heterozygous individual
Incomplete Dominance Example
If a red and white flower mix and makes a pink flower
Codominance example
In an AB blood type both the antigens for A and B are expressed
Incomplete Dominance for Mendel round peas
On a surface level the Round Peas showed the traits for the dominant allele, either homozygote or heterozygote
BUT
In a closer look, we could see that the heterozygotes were actually less starchy than the homozygotes making it incomplete
Over-Dominance
-phenomenon where a heterozygote has greater reproductive success compared to both of the corresponding homozygotes (heterozygote advantage)
over-dominance in respect to sickle cell
HbAHbS individuals (heterozygotes) have an “advantage”:
* over HbSHbS, because they do not suffer from sickle cell
disease
* over HbAHbA, because they are more resistant to malaria
Describe various mechanisms that might make a heterozygote more fit than
either homozygote. Given an example be able to identify over-dominance.
A blood Type
Antigen: A
Antibody:B
B blood type
Antigen: b
Antibody: A
AB Blood Type
Antigen: A and B
Antibody: Neither A nor B
O Blood Type
Antigen: Neither A nor B
Antibody: Both A and B
What is the molecular basis for the production of the A and B antigens, and
what happens if an individual possesses only the i allele.
Given a case of disputed paternity, ascertain if a particular blood group for
the parents is theoretically possible.
What is a complete H antigen? What happens to a person who has the
Bombay blood group (hh, homozygous recessive)? Which of the three
antigens does he normally produce A, B, H? Which of the antibodies does he
naturally produce Anti-A, Anti-B, anti-H? When tested using standard tests
that usually test for A and B antigens only but not the H antigen, individuals
with Bombay blood group (hh) show up as O blood group. Therefore, if they
receive transfusion from an O individual explain why it would be dangerous.
Lethal allele
allele that may lead to the death of an organism
essential gene
recessive lethal allele
dominant lethal allele
Why do recessive lethal alleles such as in the case of Manx cats, give a ratio of
2:1 (phenotype: normal) for a second trait (eg defective spine and tail) that
the allele may be associated when heterozygotes are crossed to one another?
(the first trait is lethality). For this second trait the allele behaves in a
dominant manner
Dominant homozygotes die an embryonic death so they are left out of the ratio of offspring.
conditional lethal alleles
lethal allele that may be the death of an organism if all the conditions are met
example of conditional lethal allele
G6PD deficiency results from a deficiency of an enzyme that is especially important for protecting red blood cells from harmful oxidizing agents. People with G6PD deficiency can live healthy lives but can die from severe destruction of red blood cells after eating fava beans. Fava beans have multiple oxidizing agents that can endanger the red blood cells in these patients.
semi-lethal alleles
lethal allele that does not kill every single organism that has this allele
Be able to explain the dominant lethal nature of the Huntington allele (Look
at the dominant allele in heterozygote and does it lead to death due to the
neurodegenerative disease). In this case of heterozygote, the individual is
able to be born and enter adulthood, however thereafter he or she begins to
develop neurodegeneration that is 100% fatal by 65 years and therefore it is
categorized as a lethal allele). What is the nature of the mutation carried in
the disease allele and what is the consequence on the Huntingtin protein?
Be able to explain how this lethal mutation continues to be maintained in the
human population
pleitropy
expression of one gene at different stages of development
expression of one gene that affects cell function in more than one way
expression of one gene in different cell types
gene interaction
pattern where allelic variants of two different genes affect a single trait
complementation
epistasis
epistasis example
For summer squash, the dominant allele for one gene leads to yellow color while the recessive allele for this gene leads to green color. When the genotype of a second gene is either homozygous dominant or heterozygous, neither color is produced and the squash is white.
gene modifier effect
gene redundancy
Which ratio is modified due to gene interaction between the alleles of two
genes lying on two non-homologous chromosomes?
Do epistasis and other observations of gene interactions results suggest the
violation of Mendel’s laws of segregation and independent assortment?
Justify your answer
sex-limited inheritance
occurs in only one of the two sexes
sex-influenced inheritance
-autosomal
-Traits where an allele is dominant in one sex but recessive in
the opposite sex
* Sex influence is a phenomenon of heterozygotes
sex-influenced inheritance example
Scurs (hornlike growth) in cattle
* Caused by an autosomal gene
* Allele Sc is dominant in males, but recessive in females
scur example
The growth of scurs, small horn-like growths on the faces of cattle, is inherited with the sex-influenced alleles Sc and sc. The trait is dominant in males and recessive in females. Suppose a male with no scurs is mated to a female with scurs. What is the pattern expected for their offspring?
sex-linked inheritance
found on one of the two types of
sex chromosomes, but not both
