AQA · GCSE · Biology
Course version: 8461 · Version from Sept 2018
Students should be able to explain the terms: • gamete • chromosome • gene…
Full specification wording
Genetic inheritance: Students should be able to explain the terms: • gamete • chromosome • gene • allele • dominant • recessive • homozygous • heterozygous • genotype • phenotype.
These ten terms form the vocabulary of inheritance.
Checked against the AQA 8461 specification (opens in a new tab) on .
- Point 1 of 11
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
These ten terms form the vocabulary of inheritance. A gamete is a sex cell, such as a sperm or egg, with a haploid number of chromosomes. A chromosome is a long DNA molecule carrying many genes. A gene is a section of DNA that codes for a protein or characteristic. An allele is a different form of the same gene. A dominant allele is expressed even when only one copy is present, while a recessive allele is expressed only when two copies are present. Homozygous means two identical alleles for a gene; heterozygous means two different alleles. Genotype is the alleles present; phenotype is the observable characteristic.
For example: A mouse with genotype Bb is heterozygous and may have black fur if B is dominant.
What earns the marks
- Gamete: a sex cell with a haploid chromosome number, such as sperm or egg.
- Chromosome: a structure of DNA that carries many genes; gene: a DNA section coding for a protein or characteristic.
- Allele: a different form of the same gene; dominant alleles are expressed when one copy is present, recessive alleles only when two copies are present.
- Homozygous: two identical alleles for a gene; heterozygous: two different alleles for a gene.
- Genotype: the alleles an organism carries; phenotype: the observable characteristics resulting from genotype and environment.
Common mistakes and how to put them right
Confusing gene and allele.
Put it right by saying a gene is a section of DNA and an allele is a version of that gene.
Using dominant to mean common or stronger.
Put it right by defining dominant as the allele expressed when one copy is present.
Treating genotype and phenotype as the same.
Put it right by stating genotype is the allele combination and phenotype is the observable characteristic.
Exam tips
- Learn each term with a short example, such as Bb for heterozygous.
- When defining a term, include the key idea in one precise sentence rather than a long story.
- Use genetic diagrams to show how genotype leads to phenotype and to practise the vocabulary.
Try the lesson
The start of the Genetic inheritance: Students should be able to explain the terms: • gamete • chromosome • gene • allele • dominant • recessive • homozygous • heterozygous • genotype • phenotype. lesson, made from checked teaching notes for this specification point.
Have a go first
In human reproduction, a sperm cell fuses with an egg cell. What is the biological term used to describe these types of reproductive cells?
Listen
These ten terms form the vocabulary of inheritance. A gamete is a sex cell, such as a sperm or egg, with a haploid number of chromosomes. A chromosome is a long DNA molecule carrying many genes. A gene is a section of DNA that codes for a protein or characteristic. An allele is a different form of the same gene. A dominant allele is expressed even when only one copy is present, while a recessive allele is expressed only when two copies are present. Homozygous means two identical alleles for a gene; heterozygous means two different alleles. Genotype is the alleles present; phenotype is the observable characteristic. For example, a mouse with genotype Bb is heterozygous and may have black fur if B is dominant. A strong answer earns marks for these points. Gamete: a sex cell with a haploid chromosome number, such as sperm or egg. Chromosome: a structure of DNA that carries many genes; gene: a DNA section coding for a protein or characteristic. Allele: a different form of the same gene; dominant alleles are expressed when one copy is present, recessive alleles only when two copies are present. Homozygous: two identical alleles for a gene; heterozygous: two different alleles for a gene. A common slip: Confusing gene and allele. Instead, saying a gene is a section of DNA and an allele is a version of that gene. Exam tip: Learn each term with a short example, such as Bb for heterozygous.
See it
Key words
Say what each word means before you turn the card.
Gamete
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Chromosome
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Gene
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Allele
Try answering aloud or in your head before turning the card.
See every definition
- Gamete
- A sex cell, such as a sperm or egg, with a haploid number of chromosomes.
- Chromosome
- A long DNA molecule carrying many genes.
- Gene
- A section of DNA that codes for a protein or characteristic.
- Allele
- A different form of the same gene.
Label the diagram
Some boxes have lost their names. Pick the right name for each number.
1Box 1
2Box 2
3Box 3
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Test your understanding of Genetic inheritance: Students should be able to explain the terms: • gamete • chromosome • gene • allele • dominant • recessive • homozygous • heterozygous • genotype • phenotype.
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