Mendel’s law of dominance states that ____.
Correct answer A. in a heterozygote one allele masks the expression of the other
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MDCAT Biology MCQs
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Alternative forms of the same gene found at the same locus on homologous chromosomes are called ____.
Correct answer A. alleles
A test cross is made between an individual showing the dominant phenotype and ____.
Correct answer D. a homozygous recessive individual
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In a dihybrid cross between two plants heterozygous for both genes (AaBb × AaBb), the expected phenotypic ratio is ____.
Correct answer B. 9 : 3 : 3 : 1
A dihybrid test cross AaBb × aabb with unlinked genes produces offspring in the ratio ____.
Correct answer D. 1 : 1 : 1 : 1
In the cross AaBb × AaBb, what fraction of the offspring is expected to be aabb?
Correct answer A. 1/16
In the F₂ of a dihybrid cross (AaBb × AaBb), what fraction of offspring is homozygous for both genes?
Correct answer B. 1/4
How many different genotypes appear in the F₂ of a dihybrid cross between two AaBb plants?
Correct answer C. 9
How many genetically different gametes can a plant of genotype AaBbCc produce if the genes are unlinked?
Correct answer C. 8
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When AaBbCc is self-fertilised (genes unlinked, complete dominance), what fraction of offspring show all three dominant traits?
Correct answer B. 27/64
Two parents are both heterozygous (Aa) for a recessive condition. What is the probability that their first child is affected (aa)?
Correct answer A. 1/4
Two heterozygous tall pea plants (Tt × Tt) produce three offspring. What is the probability that all three are tall?
Correct answer D. 27/64
Two carriers (Aa × Aa) of a recessive trait have two children. What is the probability that at least one child is aa?
Correct answer B. 7/16
In the cross AaBb × aaBb (genes unlinked), what fraction of offspring is expected to be aabb?
Correct answer D. 1/8
The Michaelis constant (Km) of an enzyme is the substrate concentration at which the reaction rate is ____.
Correct answer C. half of the maximum rate
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A competitive inhibitor reduces enzyme activity by ____.
Correct answer B. resembling the substrate and occupying the active site
The effect of a competitive inhibitor can be reduced by ____.
Correct answer A. increasing the substrate concentration
Malonate inhibits succinate dehydrogenase because it ____.
Correct answer D. resembles succinate and competes for the active site
A non-competitive inhibitor acts by ____.
Correct answer C. binding at a site other than the active site and altering its shape
Which statement is true of non-competitive inhibition?
Correct answer A. Adding more substrate does not restore the maximum rate