Karyotypes and Chromosomal Mutations

Look at the karyotype diagram showing human chromosomes arranged by size and number. Which type of mutation is most directly detectable using a karyotype?

• nondisjunction causing extra chromosomes

• point mutation in a single gene

• small gene duplication within DNA

• frameshift within a gene sequence

Answer explanation

A karyotype can easily detect nondisjunction, which results in an abnormal number of chromosomes, such as trisomy. In contrast, point mutations, small duplications, and frameshifts are too small to be seen in a karyotype.

A technician compares two karyotypes. Karyotype A shows 46 chromosomes, including XX. Karyotype B shows 47 chromosomes with XXY. Which statement best explains the difference?

• A has a point mutation in SRY

• B has a gene deletion on X only

• A has a frameshift in meiotic genes

• B has nondisjunction of sex chromosomes

Answer explanation

Karyotype B has 47 chromosomes, indicating an extra chromosome due to nondisjunction during meiosis, leading to XXY. Karyotype A is normal with 46 chromosomes (XX), showing no such error.

Robert and his wife are ready to start a family, but they are concerned about having a child inherit a disease. This disease is an autosomal recessive disorder that requires both parents to contribute a recessive allele in order for the child to express the disorder. If both Robert and his wife are heterozygous for this trait, what is the probability that their child will have the disease?

• 75%

• 50%

• 25%

• 100%

Answer explanation

Since both Robert and his wife are heterozygous (Aa), the Punnett square shows a 1 in 4 chance (25%) for their child to inherit the recessive alleles (aa) and express the autosomal recessive disorder.

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Which description supports the claim that mutations in gametes could cause an increase in genetic diversity in a population?

• A brain cell has a missense mutation that allows it to function more effectively.

• UV rays create thymine dimers that negatively affect a skin cell’s function.

• A drug creates a mutation in a liver cell. The mutated cell multiplies.

• A deletion during meiosis results in a new version of an allele.

Answer explanation

A deletion during meiosis can create a new allele, introducing genetic variation. This supports the claim that mutations in gametes increase genetic diversity, unlike the other options which do not involve gametes.

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Which statement best explains how recombination increases genetic diversity during meiosis?

• It swaps alleles between paired homologous chromosomes.

• It raises the chance of gamete fertilization overall.

• It changes chromosome numbers in gametes produced.

• It rearranges the sequence order within single chromosomes.

Answer explanation

Recombination increases genetic diversity by swapping alleles between paired homologous chromosomes during meiosis, leading to new allele combinations in gametes.

Scientists engineer salmon to reach adult size faster than wild salmon. What primary environmental risk arises if these salmon escape into the ocean?

• They would reproduce less than normal wild populations.

• They would fail to grow well outside controlled facilities.

• They would eat slightly more than typical wild salmon.

• They could spread inserted genes into wild populations.

Answer explanation

The primary risk is that engineered salmon could interbreed with wild populations, spreading inserted genes and potentially disrupting local ecosystems and genetic diversity.

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A crop is modified to resist an herbicide. Propose one evidence-based management plan that reduces ecological harm if some plants or genes spread beyond fields. Explain why your plan helps.

Answer explanation

Implementing buffer zones around fields can help contain gene spread. This plan reduces ecological harm by limiting the interaction between modified crops and wild relatives, preserving biodiversity and preventing unintended herbicide resistance.

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In the bar chart titled "Wirelettuce Height Distribution," offspring heights range from 7 to 17 dm with most plants around 11–13 dm. Which statement best explains why offspring from the same parents show this spread in heights?

• Environmental factors like light and soil vary among plots

• Dominant alleles always produce a single uniform height

• All offspring inherited identical height alleles from both parents

• Somatic mutations in the parents were passed to the offspring

Answer explanation

The variation in offspring heights is best explained by environmental factors like light and soil, which can differ among plots, affecting growth. This leads to a range of heights rather than uniformity.

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A scientist argues that traits are influenced by interactions between genes and the environment. Based on common mechanisms, which example directly supports her claim?

• Recessive alleles being masked by dominant alleles in crosses

• A carrier not showing symptoms of an autosomal disorder

• Mitosis producing identical daughter cells in liver tissue

• UV radiation causing thymine dimers in DNA of skin cells

Answer explanation

UV radiation causing thymine dimers in DNA of skin cells illustrates how environmental factors can directly affect genetic material, supporting the scientist's claim about gene-environment interactions.

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Use evidence from the wirelettuce height distribution to propose and justify two plausible causes for the observed variation in height among the offspring. Your explanation should distinguish between genetic and environmental influences and comment on whether somatic or germline mutations could contribute.

Answer explanation

Variation in wirelettuce height may stem from genetic factors, such as inherited traits, and environmental influences like soil quality or water availability. Germline mutations could affect height, while somatic mutations are less likely to impact offspring.

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