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Chapter 4
General Genetics- Exam 1
| Question | Answer |
|---|---|
| What are Mendel's two laws? | The law of segregation and the law of independent assortment |
| What does simple Mendelian inheritance involve? | A single gene with two different alleles in a simple dominant/recessive relationship |
| What is incomplete dominance? | The phenotype of the heterozygote is intermediate between the phenotypes of the two homozygotes; it is also called partial dominance |
| What is the example of incomplete dominance given in the slides? | Flower color in four-o'clock plants |
| What is the phenotypic ratio for incomplete dominance? | A 1:2:1 phenotypic ratio rather than the 3:1 ratio seen in simple Mendelian inheritance |
| What is codominance? | The phenotype of the heterozygote is a mixture of the phenotypes of the homozygotes |
| What human blood group is used as an example of codominance? | The MN blood group |
| What is multiple allelism? | Having more than two alleles for the same gene |
| Why can multiple allelism only be studied in populations? | An individual can only have two alleles for any given gene |
| What is the example of multiple allelism in humans? | The ABO blood group system |
| What are the three ABO alleles? | IA, IB, and IO |
| What blood types result from the six ABO genotypes? | IAIA = A; IAIB = AB; IAIO = A; IBIB = B; IBIO = B; IOIO = O |
| What are two uses of the ABO blood group? | Establishing compatibility of blood transfusions and assessing the possibility of a parent-offspring relationship |
| What happens when incompatible ABO blood samples come together? | Agglutination occurs, meaning donor red blood cells clump in the recipient's bloodstream |
| What is the most important Rh antigen? | The D antigen |
| What do D and d represent in the Rh system? | D directs synthesis of the Rh antigen; d means the Rh antigen is absent |
| What Rh phenotypes result from DD, Dd, and dd? | DD = Rh+; Dd = Rh+; dd = Rh− |
| What are the A and B antigens chemically? | Sugar groups bound to lipids that protrude from the red blood cell membrane |
| What does glycosyl transferase do? | It adds terminal sugars to the H substance |
| What happens in type O individuals at the ABO biochemical level? | They cannot add either terminal sugar and therefore possess only the H substance |
| What is the Bombay phenotype? | A rare phenotype in which a person can be genetically type B, for example, but functionally type O because the ABO genotypes cannot be expressed |
| What gene controls the H antigen? | The H gene on chromosome 19 |
| What genotype produces the Bombay phenotype? | hh, a homozygous rare recessive mutation that prevents synthesis of the complete H substance |
| What are the four rabbit coat-color alleles? | C (full coat color), cch (chinchilla), ch (Himalayan), and c (albino) |
| What is the dominance hierarchy for rabbit coat color? | C > cch > ch > c |
| What is a lethal allele? | An allele that has the potential to cause the death of an organism |
| What is a recessive lethal allele? | A lethal allele in which the heterozygous state is tolerated |
| What is a dominant lethal allele? | A lethal allele in which the heterozygous state leads to death |
| Why did yellow × yellow mice produce a 2:1 ratio? | The homozygous yellow genotype is lethal, so those individuals die and are absent from the surviving offspring |
| What is an example of a dominant lethal allele in cats? | The Manx cat mutation, which dramatically shortens the tail and is lethal in the homozygous state |
| What are conditional lethal alleles? | Lethal alleles that kill an organism only when certain environmental conditions prevail |
| What are semilethal alleles? | Alleles that kill some individuals in a population, but not all of them |
| Why can a dominant lethal allele such as Huntington's disease persist? | The onset of disease can occur after reproductive age |
| What is pleiotropy? | A phenomenon in which one gene has multiple effects |
| Why can pleiotropy occur? | The gene product can affect cell function in more than one way, the gene may be expressed in different cell types, or it may be expressed at different stages of development |
| How does CFTR illustrate pleiotropy? | A CFTR mutation affects ionic balance and can produce multiple effects, including thick mucus in the lungs, salty sweat, and poor weight gain from digestive blockages |
| What causes sickle-cell anemia? | An autosomal recessive mutation in the gene for the β chain of hemoglobin |
| What are the two major hemoglobin alleles discussed? | HbA and HbS |
| What happens in HbSHbS individuals? | They have sickled blood cells; cells are destroyed by the liver, anemia can cause impaired growth and weakness, and abnormal cells can clump and block capillary circulation |
| What is overdominance? | The phenomenon in which a heterozygote is more vigorous than both corresponding homozygotes; also called heterozygote advantage |
| Why is the sickle-cell allele found at relatively high frequency in some malaria regions? | Heterozygous red blood cells are likely to rupture when infected by Plasmodium, which helps prevent propagation of the parasite |
| What are the three possible molecular/cellular explanations for overdominance? | Disease resistance, homodimer formation, and variation in functional activity |
| What is epistasis? | The masking or alteration of the expression of alleles of one gene by allelic combinations of another gene |
| What happens to the typical 9:3:3:1 dihybrid ratio with epistasis? | The phenotypic ratio is modified |
| What are the five frequently encountered types of gene interaction? | Recessive, dominant, complementation, duplicate gene action, and suppression |
| What is the phenotypic ratio for recessive epistasis in the mouse coat-color example? | 9:3:4 |
| What is the phenotypic ratio for dominant epistasis in summer squash? | 12:3:1 |
| What is the phenotypic ratio for complementation epistasis in pea flower color? | 9:7 |
| What is the phenotypic ratio for duplicate gene action in shepherd's purse fruit shape? | 15:1 |
| What is the phenotypic ratio for suppression in chicken feather color? | 13:3 |
| What do the slides say about Mendel's laws during epistasis? | The principles of equal segregation and random assortment are not violated |
| What does a phenotypic ratio expressed in sixteenths indicate? | Two gene pairs are controlling the observed phenotype |
| What is sex-limited inheritance? | Expression of a specific phenotype is absolutely limited to one sex, even though it is controlled by an autosomal gene |
| What is sex-influenced inheritance? | Expression of a specific phenotype is influenced by the sex of the individual |
| What is an example of sex-limited inheritance? | Tail and neck plumage in domestic fowl |
| What is an example of sex-influenced inheritance? | Scurs (hornlike growth) in cattle |
| How does the ScP allele behave in cattle? | ScP is dominant in males but recessive in females |
| What is an example of sex-influenced inheritance in humans? | Pattern baldness |
| How does the B allele for pattern baldness behave? | The slides state that B behaves as recessive in females and dominant in males |
| What other human trait is presented as sex-influenced? | Length of the index finger |
| How does the L allele for index-finger length behave? | The slides state that L behaves as recessive in females and dominant in males |
Created by:
KristenR2025