Chromosomes, genes and DNA: keep the levels distinct
הוצג| English | משמעות |
|---|---|
| chromosome/ˈkrəʊməsəʊm/ | כרומוזום |
| gene/dʒiːn/ | גן |
What would explain this observation?
- A chromosome 染色体 is not one gene 基因. A single chromosome carries many genes along its DNA molecule, and body cells normally contain chromosomes in pairs.
Build the model
- The nucleus contains chromosomes made of DNA molecules.
- A gene is a section of DNA, and each chromosome carries a large number of genes.
- Chromosome pairs contain corresponding types of genetic information; they are not two halves joined merely because the cell is large.
- chromosome: A DNA-containing structure carrying many genes.
- gene: A section of DNA associated with genetic information.
Which statement distinguishes a gene from a chromosome?
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
A chromosome is one long DNA molecule carrying many genes; a gene is one section of that DNA coding for a product. So a chromosome contains many genes - never the reverse.
Match each technical term to its precise meaning.
רמת קושי 2/5 · 140 מטבעות + בונוס קטן בהשלמה הראשונה היום
Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- Keep three levels separate: DNA is the chemical genetic material, a chromosome is an organized DNA-containing structure, and a gene is a section of DNA.
- A replicated chromosome has copied genetic material ready for division.
- Replication and the later distribution into daughter cells have different effects.
In the lab: Use a labelled chromosome model and a short DNA segment. Identify the chromosome pair and mark several gene positions on each model rather than labelling an entire chromosome as a single gene. For counting exercises, state whether chromosomes are being counted in a body cell, a gamete or a daughter cell.
Which two habits make the investigation or model in this case more defensible?
רמת קושי 2/5 · 140 מטבעות + בונוס קטן בהשלמה הראשונה היום
Stating the conditions and assumptions lets others repeat the work exactly, and recording the supporting evidence lets them check the conclusion. Hiding disagreeing results removes the evidence that could challenge a wrong conclusion, and one measurement can never establish a wider claim.
Work from known quantities
- Known: a model body cell has 12 chromosomes, organized as six pairs.
- The number of pairs is 12/2=6.
- After mitosis, each daughter cell normally has the same chromosome number, 12, rather than six.
- The halving associated with gamete production belongs to meiosis, studied separately.
Your turn: A model body cell has 18 chromosomes in pairs. How many pairs are present?
A model body cell has 18 chromosomes in pairs. How many pairs are present?
רמת קושי 2/5 · 140 מטבעות + בונוס קטן בהשלמה הראשונה היום
The result is 9 pairs. Known: 18 chromosomes organized in pairs. Number of pairs = 18/2 = 9 pairs. Body cells carry pairs; gametes, made by meiosis, carry one chromosome from each pair.
Check the conclusion and its limits
- DNA, gene and chromosome are not interchangeable terms.
- A chromosome count alone does not tell how many genes an organism has.
- Copying DNA before mitosis is not the same as permanently doubling the chromosome number of each daughter cell.
Not true: Every chromosome contains only one gene. A typical chromosome carries hundreds or thousands of genes along its DNA. One gene is only a small section of one chromosome.
- The nucleus contains chromosomes made of DNA molecules.
- Keep three levels separate: DNA is the chemical genetic material, a chromosome is an organized DNA-containing structure, and a gene is a section of DNA.
- Watch for: DNA, gene and chromosome are not interchangeable terms.
A typical chromosome carries hundreds or thousands of genes along its DNA.
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
True. A typical chromosome carries hundreds or thousands of genes along its DNA. One gene is only a small section of one chromosome.
A DNA-containing structure carrying many genes: write the technical term.
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
chromosome means A DNA-containing structure carrying many genes.