Transcript
What is the chance of a child having a disease if both parents are heterozygous for the recessive gene for that disease?
100%
50%
25%
10%
What is the chance of a child having a disease if both parents are heterozygous for the recessive gene for that disease?
25%
Using a Punnett square to evaluate the problem, there is a 25% chance that the offspring will have the disease, a 50% chance that the offspring will carry one copy of the defective gene, and a 25% chance that an offspring will not carry the recessive trait at all.
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True or False? Genotype and phenotype always match.
True
False
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True or False? Genotype and phenotype always match.
False
A person’s genotype may be “hiding” a gene that is recessive, but not expressing it because the person is heterozygous for the gene. This can go on for generations until another recessive gene is contributed.
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True or False? A person with blood type AB has a dominant A and a dominant B gene.
True
False
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True or False? A person with blood type AB has a dominant A and a dominant B gene.
True
Both genes are dominant. This phenotype is called codominant, with both genes expressed independently of each other.
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True or False? A person with blood type O could have a child that is blood type AB.
True
False
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True or False? A person with blood type O could have a child that is blood type AB.
False
A child with blood type AB would have to inherit the A allele from one parent and the B allele from the other parent. A parent with blood type O has neither an A nor a B allele.
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True or False? A person with one copy of the sickle-cell gene has the disease.
True
False
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True or False? A person with one copy of the sickle-cell gene has the disease.
False
The sickle-cell gene is recessive; therefore, two copies are needed for it to be expressed. This person is heterozygous and is said to have sickle-cell trait and usually is asymptomatic. This person can pass the gene on, with 50% of offspring receiving it.
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True or False? Hemophilia is strictly a male disease.
True
False
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True or False? Hemophilia is strictly a male disease.
False
If a woman inherits an X chromosome with the gene for hemophilia from both parents, it is possible for her to have a “sex-linked” disease such as hemophilia. Although rare, this can occur.
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True or False? Males determine the sex of their offspring.
True
False
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True or False? Males determine the sex of their offspring.
True
The presence of the Y chromosome causes a male to develop. Its absence results in a female, so it is the father who determines the sex of any offspring. Generally 50% of sperm carry an X chromosome and 50% carry a Y chromosome.
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Traits that are determined by more than one gene, such as eye color, height, and skin color are referred to as _____.
dominant
polygenic
recessive
trisomic
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Traits that are determined by more than one gene, such as eye color, height, and skin color are referred to as _____.
polygenic
Polygenic traits are determined by more than one gene, and the resulting phenotypes are usually distributed in the population as a continuous range of values.
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Which of the following can result in trisomies such as Down syndrome (Trisomy 21) or Klinefelter syndrome (XXY)?
Independent assortment
Segregation
Nondisjunction
Linked genes
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Which of the following can result in trisomies such as Down syndrome (Trisomy 21) or Klinefelter syndrome (XXY)?
Nondisjunction
During meiosis I, homologous chromosomes separate from one another. During meiosis II, sister chromatids separate. Nondisjunction refers to the failure of either separation of homologous chromosomes or sister chromatids. This results in daughter cells that have either an extra chromosome or a missing chromosome. Fertilization of a gamete that already has an extra chromosome will result in a trisomy.
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