Term
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Definition
| An organism's observable characteristics or traits: such as its morphology, development, biochemical or physiological properties, behavior, and products of behavior (such as a bird's nest). Phenotypes result from the expression of an organism's genes as well as the influence of environmental factors and the interactions between the two. |
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Term
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Definition
| The genetic makeup of a cell, an organism, or an individual (i.e. the specific allele makeup of the individual) usually with reference to a specific character under consideration. It is generally accepted that inherited genotype, transmitted epigenetic factors, and non-hereditary environmental variation contribute to the phenotype of an individual. |
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Term
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Definition
The manner in which a particular genetic trait or disorder is passed from one generation to the next. MOIs to know include:
1) Autosomal dominant
2) Autosomal recessive
3) X-linked dominant
4) X-linked recessive
5) Codominant
6) Mitochondrial
7) Y-linked
8) Sex limited |
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Term
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Definition
| Genetic diseases which result from mutations in just one gene i.e. severe mutations in just one gene are sufficient to result in the expression of the disease. |
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Term
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Definition
| Genetic diseases which require mutations in multiple genes at the same time and which are often more sensitive to changes in the environment. |
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Term
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Definition
| The result of problems at the chromosomal level (e.g. deletions, translocations, etc.). |
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Term
| What percentage of alleles do first degree relatives share? |
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Definition
| For the most part, first degree relatives share half their autosomal alleles in common with each other, (though this will depend on their gender when considering X-linked genes and mitochondrial genes). This means that the “risk” is typically halved by each connection between individuals in a pedigree because of “independent assortment” in meiosis. |
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Term
| What is the chance that an allele at an autosomal gene is 'shared by descent' between a grandparent and grandchild? |
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Definition
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Term
| Assume your father is known to carry an autosomal recessive mutation. What are the chances his sister (your aunt) also carries this autosomal recessive mutation? |
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Definition
| 1/2. For the most part, first degree relatives share half their autosomal alleles in common with each other. |
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Term
| How are autosomal recessive mutations inherited? |
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Definition
| One allele is inherited from their mother and one from their father. Typically both parents will be unaffected “silent” carriers of a recessive mutation |
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Term
| If two parents carry an autosomal recessive allele, where did these mutations come from? |
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Definition
| Ignoring the small chance that they are the result of random mutations, then they were inherited from two of the four grandparents (i.e. one of the father’s parents and one of the mother’s parents (and so on back into their ancestry i.e. 2 of the 8 great grandparents etc.). |
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Term
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Definition
| Method used to predict offspring when the parental genotypes are known. Punnett squares help conceptualize the recurrence risk of genetic diseases in families who have already had an affected child or are otherwise known to be carriers. They also help predict recessive carrier risks in relatives of affected patients. |
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Term
| T or F: It is usually phenotypically evident whether an individual carries one copy of a recessive mutation? |
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Definition
| False. Mostly it is impossible to tell based on phenotype alone. It is thought we all carry some recessive mutations, but fortunately usually at different genes than our spouses. |
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Term
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Definition
| A mimic of a phenotype that is usually determined by a specific genotype, produced instead by the interaction of some environmental factor with a different genotype. |
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Term
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Definition
| A situation when the same phenotype (genetic disease) can result from mutations at different genes. |
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Term
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Definition
| The typical phenomenon of different mutations occurring at the same gene. |
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Term
| Do locus heterogeneity and allelic heterogeneity always appear exclusively? |
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Definition
| No, these can both occur simultaneously. For example, retinitis pigmentosa can result from many mutations (allelic heterogeneity) at many different genes (locus heterogeneity). |
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Term
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Definition
| The variation in phenotype that can occur in patients with mutations in a specific gene this could include variation in expression (mild versus severe) of a disease, the presence or absence of any phenotypic effect (i.e. disease penetrance) or even different diseases e.g. Hirschsprung disease and Multiple endocrine neoplasia type II result from mutations in the same gene (RET). |
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Term
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Definition
| Describes variability in the severity of the disease. (For example, mild versus severe.) |
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Term
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Definition
| The presence or absence of any phenotypic effect. Penetrance only considers whether individuals express the trait or not. Expressivity considers the degree of expression of the given train. |
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Term
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Definition
| An allele that expresses its phenotypic effect even when heterozygous with a recessive allele. For example, if A is dominant over a, then AA and Aa have the same phenotype. |
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Term
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Definition
| An allele whose phenotypic effect is not expressed in a heterozygote (e.g. Xx). The phenotype is only expressed when the paired allele is identical (e.g. xx). |
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Term
| What conditions determine whether an allele is dominant or recessive? |
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Definition
| If there is sufficient gene product from a single normal (wild type) allele in a recessive MOI then it will be recessive, but not in a disease with a dominant MOI. |
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Term
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Definition
| A situation in which both alleles are equally stong and both alleles are visible in the hybrid genotype-- the heterozygotes can be distinguished from the homozygotes. An example of codominance is found in chickens. When white chickens are crossed with black chickens, the result is not a grey chicken, but a chicken with both black and white feathers. |
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Term
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Definition
| The phenotype of the typical form of a species as it occurs in nature. |
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Term
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Definition
| The phenotype resulting from mutation, contrasts with normal/wild type. |
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Term
| Male-to-male transmission of a disease suggests which MOI? |
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Definition
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Term
| What are the odds that the unaffected offspring of two carrier parents of an autosomal recessive disease is also a carrier? What are the odds that the couple's future children will be carriers? Affected? |
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Definition
Unaffected child: 2/3
Future children carriers: 2/4
Future children affected: 1/4 |
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Term
| Which sex is preferentially affected by x-linked recessive disorders? |
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Definition
| Males, because they only inherit one X chromosome from their parents. The pedigree will often appear as though the disease has jumped generations via asymptomatic females. |
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Term
| What can be said about the female offspring of a male affected with an X-linked mutation? |
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Definition
| They will be carriers since they inherit their father's only X chromosome. |
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Term
| What pattern is generally seen by X-linked dominant disorders? |
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Definition
| On average, twice as many females are affected compared to males, although they are usually more severe or even lethal in males. Affected males have normal sons and affected daughters. Most affected females will be heterozygous so half the offspring of affected females will be affected. |
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Term
| Why are there no known Y linked genetic disorders? |
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Definition
| Most Y linked mutations result in infertility which is not passed on. |
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Term
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Definition
| Two or more clearly different phenotypes exist in the same population of a species. Polymorphism exists when the frequency of an allele increases to over 1%. |
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Term
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Definition
| Describes a situation where the frequency of an allele remains at a frequency of less than 1%. |
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Term
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Definition
| An example of phenotypic heterogeneity in which the diversity of different tissues involved is difficult to explain and results from the use of the same gene product in multiple tissues and periods of development. This occurs when a single gene influences multiple phenotypic traits. Consequently, a mutation in a pleiotropic gene may have an effect on some or all traits simultaneously. |
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Term
| What's the difference between a germline mutation and a somatic mutation? |
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Definition
| A germline mutation is a permanent change in the DNA that can be inherited through transmission via a gamete, whereas an acquired (somatic) mutation is in the soma and so is not transmitted to the next generation. |
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Term
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Definition
| Occurs as a result of a mutation event that results in a second population of cells differentiated from the original cells only by the new mutation. If the mutation occurs in the germline of an individual it can give rise to more than one child with the same mutation even if the mutation is absent from a different parental tissue such as the peripheral blood. Thus testing DNA isolated from blood may not accurately reveal the genotype of a patient’s gametes. |
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Term
| Gene–environment interaction |
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Definition
| The phenotypic effect of interactions between genes and the environment. |
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Term
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Definition
| The phenomenon where the effects of one gene are modified by one or several other genes, which are sometimes called modifier genes. The gene whose phenotype is expressed is called epistatic, while the phenotype altered or suppressed is called hypostatic. |
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Term
| Heterozygous advantage (heterosis) |
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Definition
| The improved or increased function of any biological quality in a hybrid offspring. It is the occurrence of a genetically superior offspring from mixing the genes of its parents. |
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Term
| What is the most likely mode of inheritance? |
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Definition
[image]
Autosomal recessive. It's unlikely dominant since neither parent is affected, and it's unlikely X-linked because the affected individual is female. |
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Term
| What is the most likely mode of inheritance? |
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Definition
[image]
Autosomal recessive is still likely, but since affected is male, you can't rule out X-linked. |
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Term
| What is the most likely mode of inheritance? |
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Definition
[image]
Autosomal dominant. |
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Term
| What is the most likely mode of inheritance? |
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Definition
[image]
Mitochondrial inheritance (because mitochondrial DNA is inherited from the mother and all the offspring are affected). Alternatively it could be autosomal dominant and very bad luck. |
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Term
| What is the mode of inheritance for hemophilia A? |
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Definition
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Term
| What is the mode of inheritance for cystic fibrosis? |
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Definition
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Term
| What is the mode of inheritance for alpha-1-antitrypsin deficiency? |
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Definition
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Term
| What is the mode of inheritance for Duchenne muscular dystrophy (DMD)? |
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Definition
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Term
| What is the mode of inheritance for Tay Sachs? |
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Definition
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Term
| What is the mode of inheritance for sickle cell disease? |
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Definition
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Term
| What is the mode of inheritance for fragile X syndrome? |
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Definition
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Term
| What is the mode of inheritance for Huntington disease? |
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Definition
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Term
| What is the mode of inheritance for myotonic dystrophy? |
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Definition
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Term
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Definition
| The Law of Segregation states that every individual possesses a pair of genes for any particular trait and that each parent passes a randomly selected copy of only one of these to its offspring. The offspring then receives its own pair of genes for that trait. Whichever of the two genes in the offspring is dominant determines how the offspring expresses that trait (e.g. the color of a plant, the color of an animal's fur, the color of a person's eyes). |
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Term
| Under what conditions will a disease have a dominant mode of inheritance? |
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Definition
| If product from a heterozygote is not enough to cross threshold, then mutation is dominant. |
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Term
| Under what conditions will a disease have a recessive mode of inheritance? |
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Definition
If product from a heterozygote is enough to cross
threshold, then disease is recessive. |
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Term
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Definition
Gene is located on one of the 22 pairs of
autosomal chromosomes. |
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Term
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Definition
| Genes, or traits determined by genes located on the X chromosome. |
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Term
| What are the criteria for a disease to be autosomal dominant? |
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Definition
1) Most affected individuals will be heterozygous
2) Expressed in every generation; but more likely to
have reduced Penetrance compared to a recessive.
3) Half offspring of an affected individual are
affected (i.e. recurrence risk of 50%)
4) Affected individuals usually have affected parents
5) Normal individuals usually don’t have affected offspring (except for reduced penetrance)
6) Male to male transmission indicates trait probably not X-linked |
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Term
| If a woman is affected with an autosomal dominant disease, what are the odds that her offspring will also be affected? |
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Definition
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Term
| What are the criteria for a disease to be autosomal recessive? |
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Definition
1) Expect both parents of affected individuals to be carriers
2) Affected individuals usually have asymptomatic parents
3) May appear as a sporadic
4) Often more severe than dominant disorders
5) If rare, parents more likely to be consanguinous
6) Recurrence risk 1 in 4
7) Affecteds have two mutations i.e. are homozygous or compound heterozygotes |
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Term
| What are some of the characteristics of X-linked recessive inheritance? |
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Definition
1) Usually males affected (hemizygous)
*(unless an affected male marries a carrier female, or extreme X- inactivation)
2) All daughters of affected males are carriers
3) Half the sons of carrier females are affected
4) No male to male transmission (since
pass on their y)
5) Many more affected males than females, mostly males more severe than females (occasionally extreme X inactivation results in mildly affected females)
6) In “genetic lethal” disorders a significant proportion of cases will be due to new mutations |
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Term
| What are some of the characteristics of X-linked dominant inheritance? |
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Definition
1) Rare
2) Affected males have normal sons and
affected daughters
3) Twice as many affected females as males in population
4) Most affected females will be heterozygous so half the offspring of affected females will be affected
5) Usually more severe or even lethal in males |
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Term
| What is the linkely mode of inheritance? |
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Definition
[image]
Likely X-linked dominant. Rare. Twice as many females as males affected. Males transmit to all their daughters, affected mothers to half their offspring (irrespective of their sex). |
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Term
| What are some of the characteristics of Y-linked inheritance? |
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Definition
1) Apart from male infertility, no known Y linked diseases
2) Only males would be affected, all sons affected.
3) Affected males would have an affected father and all their sons would be affected and no affected daughters
4) Only about 78 protein-coding genes on the Y. |
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Term
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Definition
| A single organism that is composed of two or more different populations of genetically distinct cells that originated from different zygotes involved in sexual reproduction. This is different from a mosaic, where the different cells emerged from the same zygote. |
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Term
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Definition
| A combination of alleles at different loci on the chromosome that are transmitted together. A haplotype may be one locus, several loci, or an entire chromosome depending on the number of recombination events that have occurred between a given set of loci. |
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Term
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Definition
| A chromosome in a diploid organism is hemizygous when only one copy is present. The cell or organism is called a hemizygote. Hemizygosity is observed when one copy of a gene is deleted, or in the heterogametic sex when a gene is located on a sex chromosome. For organisms in which the male is heterogametic, such as humans, almost all X-linked genes are hemizygous in males with normal chromosomes because they have only one X chromosome and few of the same genes are on the Y chromosome. |
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