6.11 Mendel and our understanding of genetics
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What organism did Mendel use in his experiments?
Mark scheme
pea plants
Model answer
Pea plants.
Mendel crossed tall pea plants with dwarf pea plants. All the offspring were tall.
Explain this result using the terms dominant and recessive.
Mark scheme
- the tall allele / factor is dominant (1)
- the dwarf allele is recessive, so it is hidden when one tall allele is present (1)
Model answer
The allele for tall is dominant, and the allele for dwarf is recessive. Each offspring had one tall allele, so they were all tall.
When Mendel crossed the tall offspring with each other, what ratio did he get?
Mark scheme
3 tall : 1 dwarf
Model answer
3 tall : 1 dwarf.
Give two reasons why Mendel's work was not accepted in his lifetime.
Mark scheme
Any two from:
- chromosomes / genes / DNA not yet discovered (1)
- he was a monk / not a known scientist (1)
- published in an obscure journal / few people read it (1)
- others did not understand his mathematics (1)
Model answer
Genes and chromosomes had not been discovered, so his ideas could not be explained, and he published in a little-read journal.
Describe how later discoveries helped scientists accept Mendel's ideas.
Mark scheme
- chromosomes observed / behaved like his units (1)
- genes identified on chromosomes / DNA structure discovered (1953) (1)
Model answer
Scientists observed chromosomes and saw they behaved like Mendel's units, so the units were named genes; later, the structure of DNA was discovered.
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