Genes, Cell Division & Heredity — Chapter Practice, Grade 7

Five focused units, a three-session investigation, chapter review, and chapter quiz.

Problem 1

Is a gene normally a whole chromosome?
Answer and explanation

No. A gene is a region of genetic material; a chromosome contains many regions and other DNA.

Problem 2

Why is “DNA letters directly become an eye color” incomplete?
Answer and explanation

Genetic information affects cellular products and processes; traits emerge through those processes and often involve several influences.

Problem 3

Can a capital letter alone prove dominance in a real organism?
Answer and explanation

No. Dominance describes an observed relationship between allele effects in a specified model, not a property of typography.

Problem 4

Why are complex traits poorly represented by one letter pair?
Answer and explanation

Several genetic and environmental contributions can interact; the one-pair model omits them.

Problem 5

Illustrative draft places a chromosome inside one gene and says every body cell with the same DNA performs the same task. Repair the nested relationship and explain cell specialization without inventing separate inherited genomes for every cell type.
Answer and explanation

Gene regions are parts of chromosome DNA, not containers for whole chromosomes. Cells with broadly similar genetic information can use different portions and develop different structures and roles. The model does not show every gene, product, or interaction, so a shared genome does not imply identical activity in all cells.

Place gene regions along chromosome DNA.

Connect information use with functional products.

Distinguish shared information from identical activity.

Response criteria

  • Explain the relevant biological process accurately.
  • Use the supplied evidence and show calculation steps with units where needed.
  • Connect a labeled model or mechanism with the claim.
  • State an assumption, evidence limitation, or useful next observation.

Problem 6

A fictional trait has alleles labeled P and p, but no relationship is supplied. Can its appearance be inferred from Pp alone?
Answer and explanation

No. The genotype letters identify versions under the model, but the genotype-phenotype relationship must be specified or supported by evidence.

Response criteria

  • Explain the relevant biological process accurately.
  • Use the supplied evidence and show calculation steps with units where needed.
  • Connect a labeled model or mechanism with the claim.
  • State an assumption, evidence limitation, or useful next observation.

Problem 7

Which relationship is correct?
  1. A gene contains every chromosome
  2. A chromosome contains DNA with many gene regions
  3. DNA is an organ
  4. Alleles are whole species
Answer and explanation

A chromosome contains DNA with many gene regions

Gene regions occur within genetic material organized into chromosomes.

Problem 8

How can two cells with similar DNA have different functions?
Answer and explanation

They can use different parts of the information and develop different structures and cellular activities.

Problem 9

Why is copying needed before the modeled division?
Answer and explanation

It provides corresponding genetic information for the daughter nuclei rather than merely splitting the original information into incomplete portions.

Problem 10

Does DNA replication mean each daughter must have eight chromosomes in a four-chromosome model?
Answer and explanation

No. Proper separation gives each daughter the original four-chromosome set; copying DNA is not permanent doubling of each daughter’s set.

Problem 11

Why is mitosis not automatically gamete formation?
Answer and explanation

Mitosis normally preserves the studied chromosome set; meiosis reduces the set in the sexual reproduction model.

Problem 12

Can a stable cell count coexist with division?
Answer and explanation

Yes. Division can replace cells that are lost, giving no net change in total count.

Problem 13

Illustrative cell starts with six chromosomes. DNA is copied, corresponding copies separate normally, and the cell forms two daughters. State each daughter’s chromosome count and distinguish DNA copying from permanent doubling of the chromosome set.
Answer and explanation

Each daughter receives six chromosomes in the stipulated normal model. Replication supplied DNA copies so both receive the set; it does not leave each daughter with twelve chromosomes. The result depends on normal distribution and does not describe every real division error or specialized cell.

Begin with the six-chromosome set.

Represent each as copied before separation.

Distribute one corresponding copy to each daughter.

Response criteria

  • Explain the relevant biological process accurately.
  • Use the supplied evidence and show calculation steps with units where needed.
  • Connect a labeled model or mechanism with the claim.
  • State an assumption, evidence limitation, or useful next observation.

Problem 14

A tissue gains four cells by division and loses four in the same interval. What is its net change, and did division occur?
Answer and explanation

Net change is zero, but division occurred. Equal gains and losses can keep the total count stable.

Response criteria

  • Explain the relevant biological process accurately.
  • Use the supplied evidence and show calculation steps with units where needed.
  • Connect a labeled model or mechanism with the claim.
  • State an assumption, evidence limitation, or useful next observation.

Problem 15

What is the modeled chromosome set after normal mitosis?
  1. Half in every daughter
  2. The corresponding starting set in each daughter
  3. No DNA
  4. Double forever
Answer and explanation

The corresponding starting set in each daughter

Normal mitosis distributes corresponding sets after replication.

Problem 16

Five cells each divide once into two; none are lost. How many daughter cells result?
Answer and explanation

10 cells

5×2=10 daughter cells under the stipulated model.

Problem 17

Why is “any random half of the chromosomes” inadequate?
Answer and explanation

A functional gamete in this simplified normal model needs one representative of each type, not an arbitrary subset missing some types.

Problem 18

Why is one mitotic division not a sufficient meiosis model?
Answer and explanation

It normally preserves the paired set rather than producing the reduced gamete set through the studied two-division process.

Problem 19

Does reshuffling necessarily create a new allele sequence?
Answer and explanation

No. It can combine existing versions differently. A mutation changes genetic material; these are distinct processes.

Problem 20

Why is reduction relevant before gamete fusion?
Answer and explanation

It permits the paired set to be restored rather than repeatedly doubling the set across generations in this model.

Problem 21

Illustrative species has eight chromosomes in a diploid body cell, arranged in four pairs. Normal gametes form and two fuse. Find gamete and zygote counts and explain how different gametes can carry different combinations.
Answer and explanation

Each modeled gamete has four chromosomes; fusion yields a zygote with eight. Different pair distributions and exchanges can produce varied combinations despite equal counts. Equal chromosome count does not imply identical allele versions. The conclusion assumes the stipulated normal diploid life cycle, not every organism’s reproductive arrangement.

Divide the paired set into one per pair: four.

Combine two gamete sets: four plus four equals eight.

Connect distributions with varied inherited combinations.

Response criteria

  • Explain the relevant biological process accurately.
  • Use the supplied evidence and show calculation steps with units where needed.
  • Connect a labeled model or mechanism with the claim.
  • State an assumption, evidence limitation, or useful next observation.

Problem 22

A diagram gives an eight-chromosome species eight in each gamete and sixteen in the zygote. What missing process should be examined?
Answer and explanation

The diagram omitted chromosome-set reduction during meiosis in the stated diploid model. Normal gametes should have four and the zygote eight.

Response criteria

  • Explain the relevant biological process accurately.
  • Use the supplied evidence and show calculation steps with units where needed.
  • Connect a labeled model or mechanism with the claim.
  • State an assumption, evidence limitation, or useful next observation.

Problem 23

Which set belongs to a normal gamete of the fictional six-chromosome diploid species?
  1. Six paired chromosomes
  2. Three, one from each pair
  3. Twelve
  4. No genetic material
Answer and explanation

Three, one from each pair

Reduction gives three chromosomes, one representative of each modeled pair.

Problem 24

A fictional diploid species has ten chromosomes. How many are in a normal gamete?
Answer and explanation

5 chromosomes

Ten arranged in five pairs yields one per pair: five.

Problem 25

What can an Aa parent contribute at the studied region?
Answer and explanation

Either A or a, one version per gamete in the stipulated model.

Problem 26

Why are Aa and aA not separate phenotype categories by letter order?
Answer and explanation

They contain the same two allele versions; the written order does not create a different genotype category in this model.

Problem 27

Does dominance make an Aa parent transmit A more than half the time in this model?
Answer and explanation

No. Dominance concerns phenotype expression, while the supplied gamete probabilities remain one half A and one half a.

Problem 28

Must four offspring contain exactly one aa individual?
Answer and explanation

No. One quarter is a probability for each event, not a fixed allocation in every group of four.

Problem 29

Illustrative cross: Aa×aa; A is completely dominant and gametes have equal modeled probabilities. List possible genotypes, calculate recessive phenotype probability, and explain why four offspring need not split exactly two and two.
Answer and explanation

The expected genotype probabilities are 50% Aa and 50% aa; the recessive phenotype probability is 50%. Four independent offspring need not contain exactly two of each. These predictions depend on the fictional single-region model and supplied dominance rule; they are not general predictions for complex human traits.

Aa contributes A or a; aa contributes a.

Combinations are Aa and aa with equal probabilities.

Apply the stipulated phenotype rule and separate probability from count.

Response criteria

  • Explain the relevant biological process accurately.
  • Use the supplied evidence and show calculation steps with units where needed.
  • Connect a labeled model or mechanism with the claim.
  • State an assumption, evidence limitation, or useful next observation.

Problem 30

In an Aa×Aa model, a sample of four has no aa offspring. Does that alone prove the probability model wrong?
Answer and explanation

No. Small independent samples can differ from expected ratios. Examine more evidence and the assumptions before choosing between sampling variation and a different model.

Response criteria

  • Explain the relevant biological process accurately.
  • Use the supplied evidence and show calculation steps with units where needed.
  • Connect a labeled model or mechanism with the claim.
  • State an assumption, evidence limitation, or useful next observation.

Problem 31

Which genotype is heterozygous at the fictional region?
  1. AA
  2. aa
  3. Aa
  4. A alone as a full diploid genotype
Answer and explanation

Aa

Aa contains two different versions at the studied region.

Problem 32

In the stipulated Aa×Aa complete-dominance model, what percent of offspring events are expected to be aa?
Answer and explanation

25 %

One of four equally probable combinations is aa: 1/4×100=25%.

Problem 33

Does a height difference prove a genetic difference?
Answer and explanation

No. Resources and other environmental conditions can also affect height.

Problem 34

Why is “a seedling mutated because it wanted more light” incorrect?
Answer and explanation

It gives intention to mutation. Changes arise through biological processes; their consequences depend on conditions.

Problem 35

Does every body-cell mutation pass to offspring?
Answer and explanation

No. Transmission depends on contribution to reproductive genetic material, not simply occurrence anywhere in a body.

Problem 36

Is learning the same skill from a parent proof of a new inherited allele?
Answer and explanation

No. Teaching and experience can transmit a skill through learning; that is not evidence of a specific genetic change.

Problem 37

Illustrative identical-genotype seedlings: one group receives adequate light and averages 8 cm; another receives low light and averages 5 cm. No sequence change is recorded. Explain the supported environmental comparison and correct a claim that every shorter plant must have acquired a heritable mutation.
Answer and explanation

The supplied record supports an environmental growth comparison, with a 3 cm mean difference under the stated light conditions. It does not document a sequence change or heritable mutation. Actual causal interpretation still depends on the fairness of the comparison and variation. A trait difference alone cannot establish mutation or transmission to offspring.

Calculate the observed 3 cm mean difference.

Use the stated equal-genotype information.

Separate environmental response from undocumented mutation and transmission.

Response criteria

  • Explain the relevant biological process accurately.
  • Use the supplied evidence and show calculation steps with units where needed.
  • Connect a labeled model or mechanism with the claim.
  • State an assumption, evidence limitation, or useful next observation.

Problem 38

A mutation has no visible effect in one setting. Must it be impossible or meaningless?
Answer and explanation

No. Its effect may be small, depend on conditions, or not change the measured trait. A genetic change and a visible phenotype are different observations.

Response criteria

  • Explain the relevant biological process accurately.
  • Use the supplied evidence and show calculation steps with units where needed.
  • Connect a labeled model or mechanism with the claim.
  • State an assumption, evidence limitation, or useful next observation.

Problem 39

Which statement fits the model?
  1. All mutations help
  2. Mutations can have different effects depending on context
  3. Learning a skill proves an allele change
  4. Every body mutation enters gametes
Answer and explanation

Mutations can have different effects depending on context

Effects and transmission depend on the change and conditions.

Problem 40

Give one additional observation needed to claim a new variant was inherited.
Answer and explanation

Evidence of the genetic change in reproductive material or offspring, with a suitable comparison, is needed beyond one parent’s visible change.

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