Chapter 4 - Extension of Mendelian Inheritance Flashcards
Mendelian inheritance describes inheritance patterns that obey these two laws
Law of segregation and law of independent assortment
Simple Mendelian inheritance involves these two assumptions
A single gene has two different alleles and the alleles display a simple dominant/recessive relationship
This term is commonly applied to the inheritance of alleles that obey Mendel’s laws and follow a strict dominant/recessive relationship
Simple Mendelian
In this type of inheritance pattern, 50% of a protein, produced by a single copy of the dominant allele in a heterozygote, is sufficient to produce a dominant trait
Simple Mendelian
This inheritance pattern occurs when a dominant phenotype is not expressed even though an individual carries a dominant allele
Incomplete penetrance
What are two reasons why a dominant allele may have incomplete penetrance?
Environmental influence or other genes that encode counteracting proteins
This inheritance pattern occurs when the heterozygote has a phenotype that is intermediate between either corresponding homozygote
Incomplete dominance
In this inheritance pattern, 50% of a protein produced by a single copy of the functional allele in a heterozygote is not sufficient to produce the same trait as in a homozygote making 100% of that protein
Incomplete dominance
This inheritance pattern occurs when the heterozygote has a trait that confers a greater level of reproductive success than either homozygote
Overdominance
What are three common ways that heterozygotes may gain benefits from overdominance?
- Their cells may have increased resistance to infection by microorganisms; 2. They may produce more forms of protein dimers with enhanced function; 3. They may produce proteins that function under a wider range of conditions
This inheritance pattern occurs when the heterozygote expresses both alleles simultaneously without forming an intermediate phenotype
Codominance
In this inheritance pattern, alleles encode proteins that function slightly differently from each other and the function of each protein in the heterozygote affects the phenotype uniquely
Codominance
This inheritance pattern involves genes that are located on the X chromosome
X-linked inheritance
This inheritance pattern refers to the effect of sex on the phenotype of the individual, where some alleles are recessive in one sex and dominant in the other
Sex-influenced inheritance
In this inheritance pattern, sex hormones may regulate the molecular expression of genes, influencing the phenotypic effects of alleles
Sex-influenced inheritance
This is an allele that has the potential of causing the death of an organism
Lethal allele
Lethal alleles are most commonly this type of allele that may be due to a mutation in a nonessential gene that changes a protein so that it functions with abnormal/detrimental consequences
Loss-of-function allele
These alleles are prevalent in a population
Wild-type alleles
This can produce more than one wild-type allele in large populations
Genetic polymorphism
These altered and often defective alleles tend to be rare in natural populations
Mutant alleles
Are mutant alleles often inherited in a dominant or recessive fashion?
Recessive
These are usually caused by mutant alleles preventing production of a fully functional protein
Genetic diseases
This recessive genetic disease is characterized by the inability to metabolize phenylalanine
Phenylketonuria
Phenylketonuria is caused by lack of production of this protein
Phenylalanine hydroxylase
Albinism is caused by lack of production of this protein
Tyrosinase
This genetic disease is a defect in lipid metabolism and leads to paralysis, blindness and death
Tay-Sachs disease
Tay-Sachs disease is caused by lack of production of this protein
Hexosaminidase A
This genetic disease is a defect in lipid metabolism that causes muscle weakness in infancy, early blindness and progressive mental and motor deterioration
Sandhoff disease
Sandhoff disease is caused by lack of production of this protein
Hexosaminidase B
This genetic disease is characterized by the inability to regulate ion balance across epithelial cells and leads to production of thick mucus, chronic lung infections, poor weight gain and organ malfunctions
Cystic fibrosis
Cystic fibrosis is caused by lack of production of this protein
Chloride transporter
This genetic disease is characterized by an inability to metabolize purines, leading to self-mutilation behavior, poor motor skills, mental impairment and kidney failure
Lesch-Nyhan syndrome
Lesch-Nyhan syndrome is caused by lack of production of this protein
Hypoxanthine-guanine phosphoribosyl transferase
This type of dominant mutation encodes a protein with a new or abnormal function
Gain-of-function
This type of dominant mutation encodes a protein that acts antagonistically to the normal protein
Dominant-negative
In this type of dominant mutation, the mutant is loss-of-function and the heterozygote does not make enough product to give the wild-type phenotype
Haploinsufficiency
This is the degree to which a trait is expressed
Expressivity
Environment
This is another term for overdominance
Heterozygote advantage
This autosomal recessive disorder in which affected individuals produce an abnormal form of hemoglobin is an example of overdominance/heterozygote advantage
Sickle-cell disease
What are two effects of red blood cells forming a sickle shape under conditions of low oxygen tension?
- Red blood cell lifespan shortens, causing anemia; 2. Odd-shaped cells clump, forming capillary blockages
What is the advantage of individuals that are heterozygous for sickle-cell disease?
Malaria resistance
This protozoan causes malaria
Plasmodium
This type of mosquito is host for one part of the Plasmodium life cycle
Anopheles mosquito
The red blood cells of sickle-cell heterozygotes are likely to do this when infected by Plasmodium
Rupture, preventing propagation of the parasite
At the molecular level, overdominance is due to two alleles that do this to produce a favorable phenotype in the heterozygote
Produce slightly different proteins
What are three possible explanations for overdominance at the molecular/cellular level?
- Disease resistance; 2. Homodimer formation; 3. Variation in functional activity
These are proteins composed of two subunits encoded by the same type of gene, but the alleles of that gene can be different
Homodimers
Individuals with heterozygote advantage may produce two of these that function over a wider range of conditions
Enzymes
These proteins may have better functional activity in individuals with heterozygote advantage
Homodimers
This is determined by the antigen present on the surface of red blood cells
Blood type
These are substances that are recognized by antibodies produced by the immune system
Antigens
On the surface of red blood cells, this is composed of three sugars
Carbohydrate tree
This enzyme can add a fourth sugar to the carbohydrate tree on red blood cells
Glycosyl transferase
These are genes found on one of the two types of sex chromosomes, but not both
Sex-linked genes
Males are more likely to be affected by these sex-linked genes
X-linked genes
This is another name for Y-linked genes
Holandric genes
Are Y-linked genes common in humans?
No
This type of inheritance refers to the very few genes found on both X and Y chromosomes
Pseudoautosomal inheritance
Does sex-influenced mean the same thing as sex-linked?
No
In this type of inheritance, traits occur in only one of the two sexes
Sex-limited inheritance
Are sex-influenced traits autosomal?
Yes
It is estimated that this portion of all genes is essential for survival
1/3
Can a lethal allele produce ratios that seemingly deviate from Mendelian ratios?
Yes
Does the effect of a lethal allele always exert at the same time during organism development?
No
This disease caused by a lethal allele is characterized by progressive degeneration of the nervous system, dementia and early death
Huntington disease
What is the usual age of onset of Huntington disease?
30-50
This type of lethal allele may kill an organism only when certain environmental conditions prevail
Conditional lethal allele
These conditional lethal alleles are typically caused by mutations that alter structure of the protein at the nonpermissive temperature
Temperature-sensitive lethal alleles
This type of allele kills some individuals in a population, but not all of them
Semilethal alleles
This is when genes have multiple effects on the phenotype of an organism
Pleiotropy
What are three types of pleiotropy?
- Gene product affects cell function in multiple ways; 2. Gene may be expressed in different cell types; 3. Gene may be expressed at different stages of developement
Do most genes have pleiotropy?
Yes
This genetic disease affecting ionic balance is an example of a mutation causing multiple effects due to pleiotropy
Cystic fibrosis
These occur when two or more different genes influence the outcome of a single trait
Gene interactions
This is an inheritance pattern in which the alleles of one gene mask the phenotypic effects of the alleles of a different gene
Epistasis
This is a phenomenon in which two parents that express the same or similar recessive phenotypes produce offspring with a wild-type phenotype
Complementation
This is a phenomenon in which an allele of one gene modifies the phenotypic outcome of the alleles of a different gene
Gene modifier effect
This is a pattern in which the loss of function in a single gene has no phenotypic effect, but the loss of function of two genes has an effect
Gene redundancy
These often arise because two (or more) different proteins participate in a common cellular function
Epistatic interactions
This is a technique to directly generate loss-of-function alleles to understand the effects of a gene on structure or function of the organism
Gene knockout
These are gene copies that are similar but not identical due to the accumulation of random changes during evolution
Paralogs
If one gene is missing, may a paralog carry out the missing function?
Yes
This scientist investigated gene redundancy in Shepherd’s purse seed capsule shape
George Shull
