Analyse the following four pedigrees.
Which row in the table correctly identifies the pedigree with the type of inheritance?
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Analyse the following four pedigrees.
Which row in the table correctly identifies the pedigree with the type of inheritance?
Consider Pedigree 1:
→ Both parents affected, daughter unaffected (received recessive alleles from each parent).
→ Trait autosomal dominant (eliminate
Consider Pedigree 3:
→ Father affected, mother unaffected, all daughters affected, all sons unaffected. Trait sex linked with all daughters inheriting one dominant allele (from father) and one recessive (from mother).
Huntington's disease is an autosomal dominant genetic disease.
Using the pedigree, justify the genotype of individual
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→ Let
→ As individual
→ However individual
→ Let
→ As individual
→ However individual
A non-infectious disease was observed in a mother and her four sons who live with her. She has no daughters. The father of these children does not have the disease and does not live with them. The woman's parents and her two sisters who live overseas do not have the disease.
A geneticist suspects that the disease is inherited.
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a.
b. Evidence disease is recessive and not sex-linked:
→ Generation 1 parents do not have the disease but it is present in their daughter, meaning it must be recessive.
→ If the disease was sex-linked, the same daughter who has the disease must have a father with the disease, however this is not the case.
a.
b. Evidence disease is recessive and not sex-linked:
→ Generation 1 parents do not have the disease but it is present in their daughter, meaning it must be recessive.
→ If the disease was sex-linked, the same daughter who has the disease must have a father with the disease, however this is not the case.
A student completed a genetics exercise by preparing a Punnett square.
What were the likely genotypes of these parents?
→ Genotype ratio
What is the probability of producing a tall pea plant when a heterozygous tall pea plant is crossed with a homozygous short pea plant?
→ Half the gametes produced by the heterozygous pea will have the T allele and the other half the t.
→ The homozygous short produces only t that are dominated by the T.
The pedigree shows the inheritance of a characteristic.
What pattern of inheritance is shown?
→ Characteristic is not dominant (recessive) or sex-linked.
The following pedigree shows the inheritance of a disorder.
Which row of the table shows the genotypes of individuals 1 and 2 ?
By Elimination
→ Both individuals do not have the disorder but have children which do and therefore the condition must be recessive. This means the individuals must be unaffected (have dominant allele) and be heterozygous if it is autosomal. (Eliminate B and D).
→ If the disease is sex-linked, then the genotype of individual 1 when crossed with any female genotype will never have any female children with the disease, which therefore means it cannot be sex-linked. (Eliminate C).
In a certain plant species, individual plants have either yellow, red or orange flowers.
Two plants, each with a different flower colour, were crossed in a breeding experiment like those carried out by Mendel. The F2 results were: 6 red, 11 orange and 5 yellow flowered plants.
What were the genotypes of the original parent plants?
→ The original parents were both homozygous because the F2 parents were both heterozygous.
Experiments were conducted to obtain data on the traits 'seed shape' in plants and 'feather colour' in chickens. In each case, the original parents were pure breeding and produced the first generation (F1). The frequency data diagrams below relate to the second generation offspring (F2), produced when the F1 generations were bred together.
Explain the phenotypic ratios of the F2 generation in both the plant and chicken breeding experiments. Include Punnett squares and a key to support your answer. (5 marks)
→ Graph A shows a 3:1 phenotypic ratio. This is typical of a dominant/recessive allele phenotypic ratio of two heterozygous parents.
→ The Punnet square below supports this argument, where R refers to the dominant seed shape (e.g. round) and r is the recessive allele, producing another seed shape (e.g. wrinkled). The offspring have a 3:1 ratio of dominant : recessive seed shape.
Key: R = Round r = wrinkled
→ Graph B shows a 1:2:1 phenotypic ratio. Because both parents are heterozygous, this ratio is typical of a co-dominant or incomplete dominant trait.
→ If B is an allele referring to black colour feathers and W is the allele for white colour feathers then both parents will be BW, which is either grey colour feathers (co-dominance) or both black and white feathers (incomplete dominance). A cross between these genotypes will produce a phenotypic ratio of the same seen in the graph.
Key: B = Black Feathers W= White Feathers
→ Graph A shows a 3:1 phenotypic ratio. This is typical of a dominant/recessive allele phenotypic ratio of two heterozygous parents.
→ The Punnet square below supports this argument, where R refers to the dominant seed shape (e.g. round) and r is the recessive allele, producing another seed shape (e.g. wrinkled). The offspring have a 3:1 ratio of dominant : recessive seed shape.
Key: R = Round r = wrinkled
→ Graph B shows a 1:2:1 phenotypic ratio. Because both parents are heterozygous, this ratio is typical of a co-dominant or incomplete dominant trait.
→ If B is an allele referring to black colour feathers and W is the allele for white colour feathers then both parents will be BW, which is either grey colour feathers (co-dominance) or both black and white feathers (incomplete dominance). A cross between these genotypes will produce a phenotypic ratio of the same seen in the graph.
Key: B = Black Feathers W= White Feathers
Huntington's disease is an autosomal dominant condition caused by a mutation of a gene on chromosome 4. It causes nerve cells to break down.
Stargardt disease is an autosomal recessive condition caused by a mutation of a different gene on chromosome 4 . It causes damage to the retina.
A patient is heterozygous for both Huntington's (Hh) and Stargardt disease (Rr). His father's extended family has numerous cases of both of these diseases. His mother does not have either disease and is homozygous for both genes.
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The pedigree shows the inheritance of a genetic disorder.
Which row of the table correctly identifies the two possible types of inheritance for this disorder?
By Elimination:
→ If the trait is autosomal recessive, then it would be impossible to not be affected if both parents are affected (aa x aa).
→ This is not the case for the first individual in generation 3 (eliminate C and D).
→ If the trait is sex-linked recessive, then anytime an affected female has male children, they must be affected, as the recessive allele from the mother must couple with the Y chromosome.
→ This is not the case for the first individual in generation 3 (eliminate B).
Which of the following is always true of a mutation that produces a dominant allele?
→ If a mutation occurs in a dominant allele, this mutation will be expressed in the individual (or in the offspring if it occurs in germline cells).
In a plant species, red flower colour (R) is dominant over white flower colour (r).
Two plants of known genotype for flower colour were crossed. A punnet square was used to determine the proportion of genotypes expected in the offspring. Part of the punnet square is shown.
Which statement is true for the parents in this cross?
→ Parent 1 must be homozygous dominant (RR), making it red.
→ Parent 2 must be heterozygous (Rr), also making it red.
An inherited characteristic in a family is mapped in the pedigree shown.
Inheritance of this characteristic is
By Elimination:
→ The characteristic can be unaffected in the parents but apparent in the offspring.
→ Therefore must be recessive (eliminate C and D).
→ The father in generation 2 is unaffected
→ Therefore it cannot be sex-linked (eliminate B).
One of the genes involved in determining the colour of a species of fish has two alleles: yellow and orange.
The diagram shows a pedigree chart for the inheritance of colour in the fish.
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a. → Parents are both orange (exhibiting dominant allele).
→ Some offspring are yellow, indicating that the yellow allele is present in the parents but not expressed.
→ Therefore yellow allele must be recessive.
b. If sex-linked Inheritance:
→
→ A cross between these individuals will result in all male offspring being yellow (
Autosomal Inheritance
→ If the inheritance it autosomal, then
→ A cross between Aa and aa would result in 50% yellow and 50% orange fish, and a cross between AA and aa will result in all orange fish.
→ Both crosses will have orange fish offspring, but sex does not have any influence on inheritance.
Therefore, to determine the inheritance:
→ The absence of orange, male fish would be indicative of a sex-linked inheritance style.
→ The appearance of orange, male fish would confirm the inheritance is autosomal.
a. → Parents are both orange (exhibiting dominant allele).
→ Some offspring are yellow, indicating that the yellow allele is present in the parents but not expressed.
→ Therefore yellow allele must be recessive.
b. If sex-linked Inheritance:
→
→ A cross between these individuals will result in all male offspring being yellow (
Autosomal Inheritance
→ If the inheritance it autosomal, then
→ A cross between Aa and aa would result in 50% yellow and 50% orange fish, and a cross between AA and aa will result in all orange fish.
→ Both crosses will have orange fish offspring, but sex does not have any influence on inheritance.
Therefore, to determine the inheritance:
→ The absence of orange, male fish would be indicative of a sex-linked inheritance style.
→ The appearance of orange, male fish would confirm the inheritance is autosomal.
In a population of rabbits, black fur colour is dominant over white fur. A black rabbit, whose mother has white fur, mates with a white rabbit.
Predict the phenotypic ratio for the offspring of this cross. Show your working. (3 marks)
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Black : White = 1 : 1
Black : White = 1 : 1