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Questions and Answers
In a scenario where four offspring are produced from a cross, what factor primarily determines whether the observed phenotypic ratio will precisely match the predicted 3:1 ratio?
In a scenario where four offspring are produced from a cross, what factor primarily determines whether the observed phenotypic ratio will precisely match the predicted 3:1 ratio?
- The presence of sex-linked traits.
- The dominance of one allele over another.
- The sample size of offspring observed; larger samples are more likely to reflect accurate ratios. (correct)
- The complete homozygosity of both parents.
What is the primary purpose of performing a test cross?
What is the primary purpose of performing a test cross?
- To identify if an organism expressing a dominant trait is homozygous or heterozygous for that trait. (correct)
- To create new mutations in an organism’s DNA.
- To determine the sex of an organism.
- To produce a large number of offspring quickly.
In a test cross, an organism showing a dominant phenotype is crossed with a homozygous recessive organism. If the offspring show a 1:1 phenotypic ratio of dominant to recessive traits, what does this indicate about the genotype of the parent with the dominant phenotype?
In a test cross, an organism showing a dominant phenotype is crossed with a homozygous recessive organism. If the offspring show a 1:1 phenotypic ratio of dominant to recessive traits, what does this indicate about the genotype of the parent with the dominant phenotype?
- The parent is homozygous dominant.
- The parent is heterozygous. (correct)
- The parent is homozygous recessive.
- The parent's genotype cannot be determined from this cross.
If a test cross results in all offspring displaying the dominant phenotype, what is the most likely genotype of the parent expressing the dominant phenotype?
If a test cross results in all offspring displaying the dominant phenotype, what is the most likely genotype of the parent expressing the dominant phenotype?
Why is the probability of a conceived child being male approximately 50%?
Why is the probability of a conceived child being male approximately 50%?
In human sex determination, what genotypes are possible in sperm cells and how do they influence the sex of the offspring?
In human sex determination, what genotypes are possible in sperm cells and how do they influence the sex of the offspring?
A healthy man and a woman who is a carrier for hemophilia have children. What is the probability that their son will have hemophilia?
A healthy man and a woman who is a carrier for hemophilia have children. What is the probability that their son will have hemophilia?
Given that the allele for healthy blood clotting is $X^H$ and the allele for hemophilia is $X^h$, what are the possible genotypes for a female who is a carrier of hemophilia?
Given that the allele for healthy blood clotting is $X^H$ and the allele for hemophilia is $X^h$, what are the possible genotypes for a female who is a carrier of hemophilia?
A woman is a carrier for hemophilia ($X^HX^h$) and her partner is healthy ($X^HY$). What is the probability that they will have a daughter who is also a carrier for hemophilia?
A woman is a carrier for hemophilia ($X^HX^h$) and her partner is healthy ($X^HY$). What is the probability that they will have a daughter who is also a carrier for hemophilia?
In a cross between a healthy man and a woman who is a carrier for hemophilia, what is the probability that their daughter will have hemophilia?
In a cross between a healthy man and a woman who is a carrier for hemophilia, what is the probability that their daughter will have hemophilia?
A hemophilic man has children with a homozygous healthy woman. What is the probability that their sons will be hemophilic?
A hemophilic man has children with a homozygous healthy woman. What is the probability that their sons will be hemophilic?
If a hemophilic man ($X^hY$) and a homozygous healthy woman ($X^HX^H$) have children, what is the genotype of their daughters?
If a hemophilic man ($X^hY$) and a homozygous healthy woman ($X^HX^H$) have children, what is the genotype of their daughters?
A colorblind woman has children with a man who has normal vision. Colorblindness is an X-linked recessive trait. What is the expected phenotype of their sons?
A colorblind woman has children with a man who has normal vision. Colorblindness is an X-linked recessive trait. What is the expected phenotype of their sons?
Suppose a man with normal vision has a daughter with colorblindness (X-linked recessive). What must be the genotype of the man's wife (the daughter's mother)?
Suppose a man with normal vision has a daughter with colorblindness (X-linked recessive). What must be the genotype of the man's wife (the daughter's mother)?
What is the overall phenotypic ratio of healthy to hemophilic offspring in a cross between a healthy man and a woman who is a carrier for hemophilia?
What is the overall phenotypic ratio of healthy to hemophilic offspring in a cross between a healthy man and a woman who is a carrier for hemophilia?
Flashcards
What is a test cross?
What is a test cross?
A cross to determine if an individual with a dominant phenotype is homozygous or heterozygous by crossing it with a homozygous recessive individual.
Test cross ratio (heterozygous)
Test cross ratio (heterozygous)
If the dominant phenotype individual is heterozygous, a 1:1 phenotypic ratio will be observed.
Test cross ratio (homozygous)
Test cross ratio (homozygous)
If the dominant phenotype individual is homozygous, all offspring will have the dominant phenotype.
Sex chromosome carried by Sperm
Sex chromosome carried by Sperm
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Sex chromosome carried by Egg
Sex chromosome carried by Egg
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Probability of male offspring
Probability of male offspring
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Human sex chromosomes
Human sex chromosomes
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What is X-linked Inheritance?
What is X-linked Inheritance?
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Hemophilia
Hemophilia
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What is $X^H$?
What is $X^H$?
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What is $X^h$?
What is $X^h$?
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Healthy man passing X
Healthy man passing X
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Healthy man passing Y
Healthy man passing Y
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Woman carrier daughters
Woman carrier daughters
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Woman carrier-hemophilic son
Woman carrier-hemophilic son
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Study Notes
- The more offspring produced from a single cross will result in the observed phenotypic ratio of the offspring matching the estimated phenotypic ratio.
- A large number of offspring should approach a phenotypic ratio of 3:1 in a cross between F1 offspring.
Test Cross
- Test Cross: A cross to determine if an individual with a dominant phenotype is homozygous or heterozygous for a trait.
- Performed by crossing the individual with the dominant phenotype with an individual known to be homozygous recessive for the trait.
- A phenotypic ratio of 1:1 is observed if the individual with the dominant phenotype is heterozygous.
- If the individual with the dominant phenotype is homozygous, all offspring will have the dominant phenotype.
Sex Determination Using Genetic Diagrams
- Genetic diagrams can be used to study sex inheritance.
- Normal eggs (female gametes) always carry one X chromosome (females have two X chromosomes and no Y chromosomes).
- The probability that an egg will carry an X chromosome is normally 1.
- Sperm (male gametes) can carry either a Y chromosome or an X chromosome.
- Approximately half of sperm produced by males carries a Y chromosome, and the other half carries an X chromosome.
- The probability that a sperm will contain an X chromosome is 0.5.
- The probability that a sperm will contain a Y chromosome is 0.5.
- The phenotypic ratio of males to females is 1:1, the probability of a zygote being male is 0.5 (50% chance) and the probability of a zygote being female is 0.5 (50% chance).
Genetic Diagrams for Sex-Linked Inheritance and Codominance
- Hemophilia is an X-linked trait
- The allele coding for a healthy clotting factor is XH.
- The altered allele causing hemophilia is Xh.
- In a cross between a healthy man (XHY) and a healthy woman carrier of hemophilia (XHXh):
- Probability that the man will pass an X chromosome with the healthy allele to his offspring is 0.5.
- Probability that the man will pass a Y chromosome to his offspring is 0.5.
- Probability that the woman carrier will pass a healthy allele to her offspring is 0.5.
- Probability that she will pass an altered allele to her offspring is 0.5.
- All female offspring from a healthy man and healthy carrier woman couple will be healthy, and none of the daughters will have hemophilia, but half will be carriers.
- The probability that this couple will have a healthy son (XHY genotype) is 1/2, or 0.5, and the probability that the son will have hemophilia (XhY genotype) is also 1/2, or 0.5.
- A son of a woman carrier and a healthy man has a 1/2 or 0.5 (50% chance) probability of being hemophilic.
- The phenotypic ratio of healthy to hemophilic males in this cross is 1:1.
- The phenotypic ratio of healthy to hemophilic offspring for all children (males and females) is 3:1.
- In a cross between a hemophilic man and a homozygous healthy woman:
- The probability that the healthy woman will pass on a healthy allele to her offspring is 1 (genotype XHXH).
- Probability that the hemophilic man will contribute an X chromosome carrying the altered hemophilic allele is 0.5.
- Probability that he will contribute a Y chromosome is 0.5.
- The probability that the couple's daughter will be a carrier with genotype of XHXh is 1.
- The probability that the couple will give birth to a healthy son with XHY genotype is 1.
- None of the children of a hemophilic father and a homozygous healthy woman will exhibit hemophilia.
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Description
Learn about how the number of offsprings in a single cross give the phenotypic ratio. Understand test crosses and sex determination using genetic diagrams. Also learn about dominant and recessive phenotypes.
