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    the pedigree on the right shows the inheritance pattern for an x-linked recessive disorder. how many individuals are carriers of the disease but are not affected?

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    Pedigrees review (article)

    Key terms

    Term Meaning

    Pedigree Chart that shows the presence or absence of a trait within a family across generations

    Genotype The genetic makeup of an organism (ex: TT)

    Phenotype The physical characteristics of an organism (ex: tall)

    Dominant allele Allele that is phenotypically expressed over another allele

    Recessive allele Allele that is only expressed in absence of a dominant allele

    Autosomal trait Trait that is located on an autosome (non-sex chromosome)

    Sex-linked trait Trait that is located on one of the two sex chromosomes

    Homozygous Having two identical alleles for a particular gene

    Heterozygous Having two different alleles for a particular gene

    Pedigrees

    Pedigrees are used to analyze the pattern of inheritance of a particular trait throughout a family. Pedigrees show the presence or absence of a trait as it relates to the relationship among parents, offspring, and siblings.

    Reading a pedigree

    Common pedigree symbols and identifiers

    Common pedigree symbols.

    Pedigrees represent family members and relationships using standardized symbols.

    By analyzing a pedigree, we can determine genotypes, identify phenotypes, and predict how a trait will be passed on in the future. The information from a pedigree makes it possible to determine how certain alleles are inherited: whether they are dominant, recessive, autosomal, or sex-linked.

    To start reading a pedigree:

    Determine whether the trait is dominant or recessive. If the trait is dominant, one of the parents must have the trait. Dominant traits will not skip a generation. If the trait is recessive, neither parent is required to have the trait since they can be heterozygous.Determine if the chart shows an autosomal or sex-linked (usually X-linked) trait. For example, in X-linked recessive traits, males are much more commonly affected than females. In autosomal traits, both males and females are equally likely to be affected (usually in equal proportions).

    Example: Autosomal dominant trait

    Pedigree showing the inheritance of freckles across three generations.

    The diagram shows the inheritance of freckles in a family. The allele for freckles (F) is dominant to the allele for no freckles (f).

    At the top of the pedigree is a grandmother (individual I-2) who has freckles. Two of her three children have the trait (individuals II-3 and II-5) and three of her grandchildren have the trait (individuals III-3, III-4, and III-5).

    [What is the genotype of individual I-2?]

    Example: X-linked recessive trait

    Pedigree showing the inheritance of colorblindness across four generations.

    The diagram shows the inheritance of colorblindness in a family. Colorblindness is a recessive and X-linked trait

    (\text{X}^{b}) (X b )

    left parenthesis, start text, X, end text, start superscript, b, end superscript, right parenthesis

    . The allele for normal vision is dominant and is represented by

    \text{X}^{B} X B

    start text, X, end text, start superscript, B, end superscript

    .

    In generation I, neither parent has the trait, but one of their children (II-3) is colorblind. Because there are unaffected parents that have affected offspring, it can be assumed that the trait is recessive. In addition, the trait appears to affect males more than females (in this case, exclusively males are affected), suggesting that the trait may be X-linked.

    [What is the genotype of individual III-2?]

    Common mistakes and misconceptions

    The presence of many affected individuals in a family does not always mean that the trait is dominant. The terms dominant and recessive refer to the way that a trait is expressed, not by how often it shows up in a family. In fact, although it is uncommon, a trait may be recessive but still show up in all generations of a pedigree.You may not always be able to determine the genotype of an individual based on a pedigree. Sometimes an individual can either be homozygous dominant or heterozygous for a trait. Often, we can use the relationships between an individual and their parents, siblings, and offspring to determine genotypes. However, not all carriers are always explicitly indicated in a pedigree, and it may not be possible to determine based on the information provided.

    Source : www.khanacademy.org

    What are the different ways a genetic condition can be inherited?: MedlinePlus Genetics

    Conditions caused by genetic variants (mutations) are usually passed down to the next generation in certain ways. Learn more about these patterns.

    What are the different ways a genetic condition can be inherited?

    Some genetic conditions are caused by variants (also known as mutations) in a single gene. These conditions are usually inherited in one of several patterns, depending on the gene involved:

    Patterns of inheritance

    Inheritance pattern Description Examples Autosomal dominant

    One altered copy of the gene in each cell is sufficient for a person to be affected by an autosomal dominant disorder. In some cases, an affected person inherits the condition from an affected parent. In others, the condition may result from a new variant in the gene and occur in people with no history of the disorder in their family.

    Huntington disease, Marfan syndrome

    Autosomal recessive

    In autosomal recessive inheritance, variants occur in both copies of the gene in each cell. The parents of an individual with an autosomal recessive condition each carry one copy of the altered gene, but they typically do not show signs and symptoms of the condition. Autosomal recessive disorders are typically not seen in every generation of an affected family.

    cystic fibrosis, sickle cell disease

    X-linked dominant

    X-linked dominant disorders are caused by variants in genes on the X chromosome. In males (who have only one X chromosome), a variant in the only copy of the gene in each cell causes the disorder. In females (who have two X chromosomes), a variant in one of the two copies of the gene in each cell is sufficient to cause the disorder. Females may experience less severe symptoms of the disorder than males. A characteristic of X-linked inheritance is that fathers cannot pass X-linked traits to their sons (no male-to-male transmission).

    fragile X syndrome X-linked recessive

    X-linked recessive disorders are also caused by variants in genes on the X chromosome. In males (who have only one X chromosome), one altered copy of the gene in each cell is sufficient to cause the condition. In females (who have two X chromosomes), a variant would have to occur in both copies of the gene to cause the disorder. Because it is unlikely that females will have two altered copies of this gene, males are affected by X-linked recessive disorders much more frequently than females. A characteristic of X-linked inheritance is that fathers cannot pass X-linked traits to their sons (no male-to-male transmission).

    hemophilia, Fabry disease

    X-linked

    Because the inheritance pattern of many X-linked disorders is not clearly dominant or recessive, some experts suggest that conditions be considered X-linked rather than X-linked dominant or X-linked recessive. X-linked disorders are caused by variants in genes on the X chromosome, one of the two sex chromosomes in each cell. In males (who have only one X chromosome), an alteration in the only copy of the gene in each cell is sufficient to cause the condition. In females (who have two X chromosomes), one altered copy of the gene usually leads to less severe health problems than those in affected males, or it may cause no signs or symptoms at all. A characteristic of X-linked inheritance is that fathers cannot pass X-linked traits to their sons (no male-to-male transmission).

    glucose-6-phosphate-dehydrogenase-deficiency, X-linked thrombocytopenia

    Y-linked

    A condition is considered Y-linked if the altered gene that causes the disorder is located on the Y chromosome, one of the two sex chromosomes in each of a male's cells. Because only males have a Y chromosome, in Y-linked inheritance, a variant can only be passed from father to son.

    Y chromosome infertility, some cases of Swyer syndrome

    Codominant

    In codominant inheritance, two different versions (alleles) of a gene are expressed, and each version makes a slightly different protein. Both alleles influence the genetic trait or determine the characteristics of the genetic condition.

    ABO blood group, alpha-1 antitrypsin deficiency

    Mitochondrial

    Mitochondrial inheritance, also known as maternal inheritance, applies to genes in mitochondrial DNA. Mitochondria, which are structures in each cell that convert molecules into energy, each contain a small amount of DNA. Because only egg cells contribute mitochondria to the developing embryo, only females can pass on mitochondrial variants to their children. Conditions resulting from variants in mitochondrial DNA can appear in every generation of a family and can affect both males and females, but fathers do not pass these disorders to their daughters or sons.

    Leber hereditary optic neuropathy (LHON)

    Many health conditions are caused by the combined effects of multiple genes (described as polygenic) or by interactions between genes and the environment. Such disorders usually do not follow the patterns of inheritance listed above. Examples of conditions caused by variants in multiple genes or gene/environment interactions include heart disease, type 2 diabetes, schizophrenia, and certain types of cancer. For more information, please see What are complex or multifactorial disorders?

    Disorders caused by changes in the number or structure of chromosomes also do not follow the straightforward patterns of inheritance listed above. To read about how chromosomal conditions occur, please see Are chromosomal disorders inherited?

    Other genetic factors sometimes influence how a disorder is inherited. For an example, please see What are genomic imprinting and uniparental disomy?

    Source : medlineplus.gov

    Genetics Quiz #6 Flashcards

    Study with Quizlet and memorize flashcards terms like Assuming that it is not a Y-linked trait, suggest the MOST likely mode of inheritance for the rare trait shown in the pedigree below, The pedigree below shows a rare autosomal recessive trait segregating. What is the probability of the first child of a marriage between III-3 and III-7 being affected?, If monozygotic and dizygotic twins have the same concordance value for a trait, which of the following is TRUE? and more.

    Genetics Quiz #6

    Assuming that it is not a Y-linked trait, suggest the MOST likely mode of inheritance for the rare trait shown in the pedigree below

    Click card to see definition πŸ‘†

    autosomal dominant

    Click again to see term πŸ‘†

    The pedigree below shows a rare autosomal recessive trait segregating. What is the probability of the first child of a marriage between III-3 and III-7 being affected?

    Click card to see definition πŸ‘†

    1/12

    Click again to see term πŸ‘†

    1/40 Created by Veronica_So-seing1

    Terms in this set (40)

    Assuming that it is not a Y-linked trait, suggest the MOST likely mode of inheritance for the rare trait shown in the pedigree below

    autosomal dominant

    The pedigree below shows a rare autosomal recessive trait segregating. What is the probability of the first child of a marriage between III-3 and III-7 being affected?

    1/12

    If monozygotic and dizygotic twins have the same concordance value for a trait, which of the following is TRUE?

    The trait is entirely due to environmental factors.

    In pedigree analysis, consanguinity refers to:

    mating between two closely related parents

    The pedigree below shows the segregation of an autosomal dominant trait. If IV-1 marries IV-5, what is the probability that their first child will be affected? Assume that the homozygous mutant genotype is viable and has the same phenotype as the heterozygote.

    3/4

    Which of the following is NOT a characteristic of X-linked recessive traits in humans?

    Affected daughters always have an affected mother.

    Which of the following statements is NOT true concerning newborn screening?

    It is particularly important to test for serious conditions where there is no treatment available.

    Which term refers to mating between closely related people?

    consanguinity

    If the pedigree below is for an autosomal recessive characteristic, which individuals are definitely heterozygous?

    I-1, I-2, II-4, II-5, III-1

    Which of the following is NOT normally used to study the inheritance of human traits or disorders?

    All of these are used in the study of human traits or disorders.

    The pedigree below shows the sex-linked recessive inheritance of Nance-Horan syndrome, a rare Mendelian disorder in which affected persons have cataracts and abnormally shaped teeth. What is the probability that the first child of IV-6 and V-3 would have Nance-Horan syndrome?

    1/8

    Which description of a Y-linked trait in humans is CORRECT?

    All the sons of an affected father will be affected with the trait.

    The pedigree below shows the segregation of an autosomal recessive trait in humans. Unless there is evidence to the contrary, assume that individuals who marry into the family do not carry the recessive allele. If IV-1 and IV-2 marry, what is the probability that their first child will have this trait?

    1/24

    What is the MOST likely mode of inheritance in the pedigree below?

    autosomal dominant

    Could the characteristic followed in the pedigree below be caused by an autosomal dominant disease? Why or why not?

    No, the offspring of I-1 and I-2 contradict an autosomal dominant inheritance.

    Which of the following is NOT correctly identified as an advantage is using amniocentesis?

    It can normally be done as early as the sixth week of pregnancy.

    If the phenotype followed in Pedigree 3 is X-linked recessive, then what is the genotype of II-2? Assume no new mutations and complete penetrance.

    heterozygous

    June has two brothers with Becker muscular dystrophy (BMD), an X-linked recessive condition that allows affected males to survive into adulthood. Her parents are phenotypically normal. She marries Sheldon who also has BMD. June and Sheldon have a daughter. What is the probability that this daughter will have BMD?

    1/4

    Which of the following is NOT a typical characteristic of human traits that follow an autosomal recessive inheritance pattern?

    All of the above are characteristic of autosomal recessive inheritance.

    The ability to roll the tongue is caused by a dominant allele. A woman is a roller, but one of her parents is not. What is the woman's genotype?

    heterozygous

    Two parents are phenotypically normal, but one of their four biological children has a typical autosomal recessive trait. The other three children are phenotypically normal. It is very likely that:

    the parents are both heterozygous for the trait

    What is the MOST likely mode of inheritance for the trait segregating in the pedigree below?

    autosomal recessive

    Assume that the concordance values for a particular disease are 63% for monozygotic twins and 36% for dizygotic twins. Which of the following are TRUE?

    Environmental factors are important in susceptibility to this disease, and genetic factors are important in susceptibility to this disease.

    A trait is caused by a rare recessive autosomal allele with full penetrance. Practically all individuals with the trait result from matings between normal individuals. What would be the expected concordance values for monozygotic and dizygotic twins?

    100% for monozygotic twins and 25% for dizygotic twins

    Heterozygote screening normally involves:

    testing adult members of a particular population to identify heterozygous carriers for a recessive disorder.

    Source : quizlet.com

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