Podcast
Questions and Answers
What is the primary use of pedigree analysis?
What is the primary use of pedigree analysis?
- To identify new mutations in a population.
- To determine the exact DNA sequence of an individual.
- To analyze the inheritance of genetic traits in humans. (correct)
- To perform test crosses in humans.
In pedigree symbols, what does a shaded circle typically represent?
In pedigree symbols, what does a shaded circle typically represent?
- An affected male.
- An affected female (correct)
- A carrier female.
- An unaffected female.
What is the significance of Roman numerals in a pedigree chart?
What is the significance of Roman numerals in a pedigree chart?
- They denote the birth order of siblings.
- They symbolize different alleles of a gene.
- They represent different generations. (correct)
- They indicate the number of individuals in a generation.
Why are test crosses not feasible in human genetic studies?
Why are test crosses not feasible in human genetic studies?
What is the key difference between autosomal and sex-linked traits?
What is the key difference between autosomal and sex-linked traits?
Which of the following is a characteristic of a pedigree for an autosomal dominant trait?
Which of the following is a characteristic of a pedigree for an autosomal dominant trait?
If a pedigree shows that only males are affected by a certain trait, what type of inheritance is most likely?
If a pedigree shows that only males are affected by a certain trait, what type of inheritance is most likely?
What does a half-filled circle or square typically represent in a pedigree?
What does a half-filled circle or square typically represent in a pedigree?
In pedigree analysis, what does 'consanguineous mating' refer to?
In pedigree analysis, what does 'consanguineous mating' refer to?
What is a key characteristic of autosomal recessive inheritance as observed in a pedigree?
What is a key characteristic of autosomal recessive inheritance as observed in a pedigree?
Why is it more challenging to definitively determine inheritance patterns from human pedigrees compared to controlled breeding experiments?
Why is it more challenging to definitively determine inheritance patterns from human pedigrees compared to controlled breeding experiments?
If a disease is caused by a recessive allele and both parents are carriers, what is the probability that their child will have the disease?
If a disease is caused by a recessive allele and both parents are carriers, what is the probability that their child will have the disease?
How many pairs of autosomes do humans have?
How many pairs of autosomes do humans have?
Which of the following human genetic disorders is caused by a single gene mutation?
Which of the following human genetic disorders is caused by a single gene mutation?
Which of the following statements best describes the genetic basis of albinism?
Which of the following statements best describes the genetic basis of albinism?
Sickle-cell disease offers protection against which other disease?
Sickle-cell disease offers protection against which other disease?
What is the direct cause of the symptoms associated with Huntington's disease?
What is the direct cause of the symptoms associated with Huntington's disease?
For a trait to be considered Y-linked, which of the following must be true?
For a trait to be considered Y-linked, which of the following must be true?
If a trait is X-linked recessive, who is most likely to express the trait?
If a trait is X-linked recessive, who is most likely to express the trait?
Considering autosomal dominant inheritance, if one parent is heterozygous for a disease-causing allele and the other is homozygous recessive, what is the chance that their child will inherit the disease?
Considering autosomal dominant inheritance, if one parent is heterozygous for a disease-causing allele and the other is homozygous recessive, what is the chance that their child will inherit the disease?
What accounts for most human traits not following simple Mendelian inheritance patterns?
What accounts for most human traits not following simple Mendelian inheritance patterns?
What is the role of the HBB gene?
What is the role of the HBB gene?
In the context of sickle cell anemia, how does the mutation in the HBB gene affect hemoglobin?
In the context of sickle cell anemia, how does the mutation in the HBB gene affect hemoglobin?
How does a mutation affect the function of the resulting protein in Huntington's Disease?
How does a mutation affect the function of the resulting protein in Huntington's Disease?
What is meant by the statement that dominance can be condition-dependent, using sickle cell anemia as an example?
What is meant by the statement that dominance can be condition-dependent, using sickle cell anemia as an example?
In pedigree analysis, what key factor distinguishes traits determined by single genes from traits influenced by multiple genes?
In pedigree analysis, what key factor distinguishes traits determined by single genes from traits influenced by multiple genes?
Suppose two parents, both heterozygous for albinism (an autosomal recessive trait), have four children. What is the probability that exactly two of their four children will be affected by albinism?
Suppose two parents, both heterozygous for albinism (an autosomal recessive trait), have four children. What is the probability that exactly two of their four children will be affected by albinism?
A man with Huntington's disease (autosomal dominant) marries a woman whose father had Huntington's but she does not have the disease. What is the probability their first child will develop Huntington's?
A man with Huntington's disease (autosomal dominant) marries a woman whose father had Huntington's but she does not have the disease. What is the probability their first child will develop Huntington's?
If a mother is a carrier for an X-linked recessive trait and the father does not have the trait, what is the probability that their daughter will be a carrier and their son will have the trait?
If a mother is a carrier for an X-linked recessive trait and the father does not have the trait, what is the probability that their daughter will be a carrier and their son will have the trait?
Two parents, both with normal pigmentation, have a child with albinism. What are the genotypes of the parents?
Two parents, both with normal pigmentation, have a child with albinism. What are the genotypes of the parents?
In a family where the mother has an X-linked dominant disorder and the father is unaffected, what percentage of their daughters will inherit the disorder?
In a family where the mother has an X-linked dominant disorder and the father is unaffected, what percentage of their daughters will inherit the disorder?
In a certain pedigree, a disease appears in every generation, and affected fathers always pass the trait to all their sons but never to their daughters. What is the most likely mode of inheritance?
In a certain pedigree, a disease appears in every generation, and affected fathers always pass the trait to all their sons but never to their daughters. What is the most likely mode of inheritance?
If a trait is autosomal recessive and appears in both males and females with equal frequency, what does this indicate about the location of the gene responsible for the trait?
If a trait is autosomal recessive and appears in both males and females with equal frequency, what does this indicate about the location of the gene responsible for the trait?
An unaffected couple has two children with a rare genetic disease. What is the chance their next child also will have the disease? Assume full penetrance.
An unaffected couple has two children with a rare genetic disease. What is the chance their next child also will have the disease? Assume full penetrance.
A researcher discovers a new genetic disease. Preliminary pedigree analysis shows nearly all affected individuals are male, and the son of an affected father will sometimes display the trait. How is this trait inherited?
A researcher discovers a new genetic disease. Preliminary pedigree analysis shows nearly all affected individuals are male, and the son of an affected father will sometimes display the trait. How is this trait inherited?
In a maternity ward mix-up, two sets of parents are unsure which child belongs to them. Family 1 consists of parents where the mother is blood type A and the father is blood type B. Family 2 consists of parents where both the mother and father are blood type O. Child A is determined to be blood type O, while Child B is blood type AB. Which child belongs to which family?
In a maternity ward mix-up, two sets of parents are unsure which child belongs to them. Family 1 consists of parents where the mother is blood type A and the father is blood type B. Family 2 consists of parents where both the mother and father are blood type O. Child A is determined to be blood type O, while Child B is blood type AB. Which child belongs to which family?
Flashcards
Pedigree Analysis
Pedigree Analysis
A diagram of a family's genetic history used to study inheritance patterns in humans.
Pedigree Symbols
Pedigree Symbols
Squares represent males, circles represent females.
Affected vs. Unaffected (Pedigree)
Affected vs. Unaffected (Pedigree)
Filled symbols indicate affected individuals, while empty indicate unaffected.
Mating (Pedigree)
Mating (Pedigree)
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Consanguineous Mating
Consanguineous Mating
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Generations (Pedigree)
Generations (Pedigree)
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Individuals (Pedigree)
Individuals (Pedigree)
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Complex Traits
Complex Traits
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Albinism
Albinism
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Sickle-Cell Disease
Sickle-Cell Disease
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Huntington's Disease
Huntington's Disease
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Autosomal Trait
Autosomal Trait
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Sex-Linked Trait
Sex-Linked Trait
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Study Notes
- Lesson objectives include being able to look at a pedigree and determine inheritance patterns and individual genotypes, also differentiating between automsomal and sex-linked traits.
- Test crosses can determine inheritance patterns.
Pedigree Analysis
- Pedigree analysis is specifically used for the study of human genetics
- Test crosses cannot be performed on humans
- A family tree is constructed to show a diagram of a family's genetic features, and can record matings along with genetic conditions
Pedigree Symbols Correspond To
- Males
- Females
- Mating
- Mating between genetic relatives
- Generations, designated with roman numerals
- Birth order, drawn left to right from first-born to last-born
- Individuals within a given generation, designated with arabic numbers
- Affected males or females
- Carriers
- Deceased males or females
- Sex is unknown
Difference between breeding experiments and pedigress
- Breeding experiments use inbreed lines of descendants, such as P, F1, F2 etc and introduce no new individuals
- Pedigrees add new individuals to each generation
Human Traits
- Many human traits run in families
- Most human traits do not show simple Mendelian inheritance
- Most traits are influced by more than one gene
- Confirmed single-gene traits in humans are rare
- Studying family genetic histories as pedigrees, gives insight as to how alleles are inherited
- Below are examples of monomorphic genes with mutant alleles.
Single-Gene Traits in Humans
- Albinism is related to a genotype of cc, includes a missing enzyme for melanin production, unpigmented skin, hair, and eyes
- Sickle cell presents with abnormal hemoglobin, causing sickle-shaped red blood cells and blocked circulation, but better resistance to malaria
- Huntington disease is related to an abnormal protein important for neurons, and progressive neurological damage
Albinism
- e.g. mm results in albino, M_ results in various shades, depending on the other genes
- Albino alleles can mask the effects of other genes, that would otherwise give traits of darker skin and hair
Sickle Cell Disease
- The mutant allele for the hemoglobin gene is recessive for disease
- Malaria parasites infect red blood cells, sickle cells are fragile and break down faster leading to parasite multiplication
HBBS
- Normal hemoglobin(HbAA) is formed from two a-globin and two ß-globin subunits.
- The HBB gene encodes ß-globin.
- Sickle cell anemia is caused by a single nucleotide mutation in the HBB gene.
- In SCD, an adenine to thymine substitution changes the 6th codon of the mature protein from a glutamine to a valine
- Sickle hemoglobin (HbSS) contains two a-globin and two ßS-globin.
- Upon deoxygenation, the presence of a hydrophobic valine residue in HbSS causes the molecules to polymerize, leading to stiffening of the RBC.
Condition-dependent Dominance
- Phenotypes at different levels of analysis, dominance relations at each level of analysis
- Red blood cells at sea level: normal HbBA HbBA, Carrier HbBA HbBpS, Disease HbBpS HbBpS
- Red blood cells concentration at sea level: normal, normal, lower
- B-globin polypeptide production: A protein, A & S protein, S protein
- Red blood cell shape at high altitudes: Normal, Sickled cells present, Severe sickling
- Red blood cell concentration at high altitudes: Normal, lower, very low; anemia
- Susceptibility to malaria: Normal susceptibility, Resistant, resistant
Recessive Trait Pedigree
- Recessive traits appear sporadically
- The appearance depends on mate being homo- or heterozygous for the respective allele
- Tracking can be performed through the generations
- At least 1 parent in generation 1 is heterozygous
- Not enough children to set the genotype of the other parent
- This pedigree assumes a rare allele because new individuals added to the family are unlikely to be carriers
Huntington Disease
- Huntington disease is usually inherited as a dominant trait
- Degenerates nerve cells in brain areas responsible for movement and thinking
- Rare condition that is inherited
- Has a 50% risk of being passed down to every offspring of someone with the disease
- Onset is between the ages of 30 and 50
- Is expected in half of siblings if a parent has the disease
- Can also some in a juvenile form
- It may be usually fatal (an example of a lethal allele), but normally after having the chance to reproduce
Gene Structure in Huntington Disease
- The basic structure of the HD gene's coding region includes a Triplet repeat region
- Each triplet encodes glutamine
- Some alleles in HD locus present with various triplet repeats resulting in normal or late-onset disease
Dominant Trait Pedigree
- Presents frequently in each generation
- There are no carriers
Autosomal VS. Sex-Linked Traits
- Autosomal traits – conferred by a gene residing on a chromosome that is involved in sex determination
- Human genome has 46 chromosomes - 22 pairs of autosomes and 1 pair of sex chromosomes (the X and Y chromosomes)
- Sex-linked traits are conferred by a gene residing on the X or Y chromosome
- Y-linked If it was Y-Linked only males would be affected, affected males would pass the trait to all male offspring
- If X-linked II's female offspring would all be affected, but males wouldn't
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