Chapter 4: Extensions of Mendelian Inheritance Flashcards
Incomplete dominance is an inheritance pattern in which the __ has an intermediate __
heterozygote; phenotype
Whether we consider an allele to be dominant of incompletely dominant may depend on how closely we examine the __
phenotype
Define overdominance
inheritance pattern in which the heterozygote has greater reproductive successes
T/F: Alleles cannot be codominant
False - AB blood type
Lethal alleles most commonly occur in __ genes
essential
Define pleiotropy
genes that exert multiple phenotypic effects
What two characteristics does Simple Mendelian inheritance involve?
a single gene with two different alleles
alleles display a simple dominant/recessive relationship
What two laws do Mendelian Inheritance obey?
Law of Segregation
Law of Independent Assortment
Define incomplete dominance
phenotype of a heterozygote is intermediate between that of the homozygotes
What is an example of incomplete dominance?
Flower color in four-o’ clock plants; red, pink, white
T/F: The 3:1 phenotypic ratio is observed in Incomplete dominance
False - becomes 1:2:1
Incomplete dominance is easier seen on a __ or __ level
cellular; microscopic
Define codominance
phenotype of the heterozygote is a mixture of the phenotypes of the homozygotes - both alleles are expressed
What is an example of codominance?
AB Blood Type - both A and B antigens are expressed
List the genotype, surface antigen, and serum antibodies for blood type O
Genotype: ii
Surface antigen: neither A or B
Serum antibodies: against A and B
List the genotype, surface antigen, and serum antibodies for blood type A
Genotype: I(A)I(A) or I(A)i
Surface antigen: A
Serum antibodies: against B
List the genotype, surface antigen, and serum antibodies for blood type B
Genotype: I(B)I(B) or I(B)i
Surface antigen: B
Serum antibodies: against A
List the genotype, surface antigen, and serum antibodies for blood type AB
Genotype: I(A)I(B)
Surface antigen: A or B
Serum antibodies: none
A and B are __ to O
dominant
Incompatible blood samples result in ?
agglutination
What is the code for Rh antigens?
D - directs synthesis of the Rh antigen
d - Rh antigen is absent
A and B antigens are __ groups that are bound to __ and protrude from the __ membrane
sugar; lipids; RBC
T/F: O cannot add any terminal sugar, and only possesses the H substance
True - why there’s no antigens
The B __ on the RBC reacts with the __ B body
antigen; anti
People with the Bombay phenotype are homozygous for a rare recessive mutation that prevents them from?
synthesizing the complete H substance resulting in no expression of A or B
Discuss the dominance hierarchy for coat color in rabits: full coat color, albino, chinchilla, and himalayan
C - full coat
c(ch) - chinchilla; partial defect in pigmentation
c(h) - himalayan; pigmentation only in certain areas
c - albino; no pigmentation
Define a lethal allele
one that has the potential to cause the death of an organism
Lethal alleles are usually inherited in a __ manner
recessive
How do lethal alleles typically result?
mutations in essential genes
If the heterozygous state of a lethal allele is tolerated, then the lethal allele is __
recessive
If the heterozygous state of a lethal allele leads to death, then the allele is __
dominant
Who first observed a lethal allele pattern in mice?
Lucien Cuenot
Who confirmed Cuenot’s observation of lethal alleles?
Castle and Little
T/F: Lethal alleles result in a Mendelian Inheritance Pattern
False - 2:1 ratio, homo recessive leads to death
Lethal alleles can also be __ and __
conditional - temperature
semilethal
Huntington disease is caused by a __ __ allele
dominant lethal
Discuss the phenotype based on the genotype for Huntington’s
Homozygous dominant
die in utero
Discuss the phenotype based on the genotype for Huntington’s
Heterozygous
develop normally; get disease later in live
Discuss the phenotype based on the genotype for Huntington’s
Homozygous recessive
phenotypically normal
Define pleiotropy
phenomenon in which a single gene affects a number of seemingly unrelated characters
What are three reasons pleiotropy occurs?
gene product can affect cell function in more than one way
gene may be expressed in different cell types
gene may be expressed at different stages of development
What is an example of pleiotropy?
sickle cell anemia
Sickle cell anemia is a __ __ disorder
autosomal recessive
What are the two alleles affected in Sickle Cell Anemia?
Hb(A)
Hb(S)
Sickle cell anemia results from a defect in the?
mutation in the gene for the beta chain of hemoglobin
What are the two major productions of sickle cell anemia?
sickled red blood cells are destroyed - causing anemia
odd-shaped cells clump - blocks in capillary circulation
Define overdominance
phenomenon in which a heterozygote is more vigorous than both of the corresponding homozygotes
What are three possible explanations for overdominance at the molecular/ cellular level?
Disease resistance
homodimer formation
variation in functional activity
What is an example of overdominance?
Sickle cell anemia + malaria
Discuss the overdominance pattern of sickle cell
Hb(A)Hb(A) - normal - dies to malaria
Hb(A)Hb(S) - sickle cell trait - protected from both
Hb(S)Hb(S) - sickle cell anemia - death from sickle cell anemia
