A farmer is breeding pea plants and observes that crossing two heterozygous tall plants (Tt × Tt) results in some short plants appearing in the next generation.
Which principle explains why some of the offspring are short?
Mendel’s law of segregation
Mendel’s law of independent assortment
Sex linkage
Gene linkage
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1 markScientists compared mitochondrial DNA from different species and find that it is composed of the same four nucleotide bases (A, T, C, G) as nuclear DNA.
What does this discovery suggest?
All cells contain DNA.
Mitochondria evolved independently of eukaryotic cells.
DNA in mitochondria is completely the same as nuclear DNA.
All modern organisms share a common ancestor that used DNA as its genetic material.
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1 markRed-green color blindness is an X-linked recessive trait. A carrier mother (XᴺXⁿ) and a normal-vision father (XᴺY) are expecting children.
What is the probability that their male offspring will be color-blind?
100 %
50 %
25 %
0 %
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1 markTay-Sachs disease is a genetic disorder caused by a mutation in the HEXA gene, resulting in a deficiency of the enzyme hexosaminidase A. It is possible for two healthy individuals to have a daughter with Tay-Sachs disease.
Which of the following best describes the inheritance of Tay-Sachs disease?
It is caused by a dominant allele on the X chromosome.
It is caused by a dominant allele on an autosomal chromosome.
It is caused by a recessive allele on an autosomal chromosome.
It is caused by a recessive allele on the Y chromosome.
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1 markIn Himalayan rabbits the gene responsible for fur pigmentation is active only in cooler parts of the body, such as the ears, feet, and nose.
Which of the following best explains the variation in fur color in Himalayan rabbits?
The gene for pigmentation is located on the sex chromosome.
Fur color in Himalayan rabbits shows phenotypic plasticity.
The gene for pigmentation is silenced.
The gene for pigmentation is randomly activated in some cells and not others.
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1 markIn a study researchers observed the inheritance of a single trait in the F2 generation of a pea plant cross. Table 1 shows the results collected from a cross between two parent plants with purple phenotypes.
Table 1
Phenotype | Number of plants |
|---|---|
Purple flowers | 92 |
White flowers | 32 |
Which of the following is the most likely conclusion from the inheritance pattern observed?
The trait is determined by codominant alleles.
The trait follows Mendel's laws of segregation.
The trait is determined by genes that are linked.
The trait is determined by polygenic inheritance.
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1 markIn a genetic study involving newts, researchers investigated two traits: tail length and skin color. They crossed a newt with a normal-length tail and green skin (heterozygous for both traits) with a newt with a short tail and white skin (homozygous recessive for both traits). Table 1 shows the phenotypes of 200 offspring produced in the cross.
Table 1
Phenotype | Males | Females |
|---|---|---|
Normal-length tail, green skin (TtGg) | 43 | 42 |
Normal-length tail, white skin (Ttgg) | 7 | 8 |
Short tail, green skin (ttGg) | 5 | 5 |
Short tail, white skin (ttgg) | 46 | 44 |
Which of the following conclusions can be drawn from these results?
The genes for tail length and skin color are located on different chromosomes and assort independently.
The genes for tail length and skin color exhibit incomplete dominance.
The genes for tail length and skin color are linked on the same chromosome and do not assort independently.
The genes for tail length and skin color are sex-linked and inherited through the X chromosome.
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1 markThe DNA in mitochondria and chloroplasts is separate from the nuclear DNA in eukaryotic cells.
Which of the following statements regarding the inheritance of traits determined by genes located in the chloroplasts and mitochondria is correct?
Chloroplasts and mitochondria are randomly assorted into gametes, meaning that traits determined by chloroplast and mitochondrial DNA follow Mendelian inheritance rules.
In animals, mitochondria are transmitted by both egg and sperm cells, meaning traits determined by mitochondrial DNA can be inherited from either parent.
In plants, mitochondria and chloroplasts are transmitted in the ovule and not in the pollen, meaning that mitochondria- and chloroplast-determined traits are maternally inherited.
In plants, mitochondrial DNA is transmitted via ovules, while chloroplast DNA is transmitted via pollen.
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1 markA geneticist analyzed a rare genetic disorder. Some features of the disorder include that:
it affects cellular respiration
individuals either have the disorder or they do not, i.e. there is no partial or mild form of the disorder
all affected individuals inherit the disorder from their mother, regardless of their father’s genotype
males and females are affected in equal numbers
Which of the following modes of inheritance is most likely to be responsible for this pattern?
Mitochondrial inheritance
Autosomal dominant inheritance
X-linked recessive inheritance
Polygenic inheritance
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The inheritance pattern of two separate genes was investigated in a double-heterozygous cross in domestic cats (Felis catus). A chi-squared test, carried out to assess the phenotypic ratios of the cross, resulted in a χ2 value of 7.96.
Table 1: Critical values for the chi-squared test
Degrees of freedom | P value | |||
0.1 | 0.05 | 0.01 | 0.001 | |
1 | 2.71 | 3.84 | 6.64 | 10.83 |
2 | 4.60 | 5.99 | 9.21 | 13.82 |
3 | 6.25 | 7.82 | 11.34 | 16.27 |
4 | 7.78 | 9.49 | 13.28 | 18.46 |
Which of the following rows in the table best describes a conclusion that can be drawn from this data?
| Probability that the difference between observed and expected results is due to chance | Could the two genes be linked? |
A | Low | Yes |
B | Low | No |
C | High | Yes |
D | High | No |
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1 markIn a breeding experiment a tall, round-seeded (homozygous dominant) pea plant was crossed with a short, wrinkled-seeded (homozygous recessive) pea plant. The F1 dihybrid plants were then used in a test cross. Note that a test cross here will cross the F1 offspring with a homozygous recessive individual.
If the genes for height and seed shape are always linked and no crossing-over occurs, what would be the predicted ratio in the F2 generation?
9 : 3 : 3 : 1
1 : 1 : 1 : 1
3 : 1
1 : 1
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