Edexcel IGCSE Biology 3.20 Genetic Terminology Questions
A dominant allele can affect the phenotype in one copy; a recessive allele may be hidden in a heterozygote and appear only when homozygous.
- Syllabus
- First assessment 2019
- Course
- Biology 4BI1
Exam points
- Explain that a dominant allele can be expressed with one copy, while a recessive allele is expressed only when homozygous and can be hidden in a heterozygote.
- Use homozygous and heterozygous genotypes to infer possible phenotypes and explain why harmful recessive alleles can persist in a population.
Edexcel IGCSE Biology 3.20 Genetic Terminology Questions question 1
[Maximum number: 2]
Fur colour in rats is controlled by a gene with two alleles.
One allele codes for black fur colour. The other allele codes for agouti fur colour.
Several female rats with agouti coloured fur are mated with several male rats with black coloured fur.
All of the offspring have agouti coloured fur.
Explain which allele is dominant.
agouti
- all offspring are agouti / no offspring are black / as allele always expressed / shown / visible in all phenotype / expressed in heterozygous / black allele not expressed / /eq
ignore passed on as black allele also passed on
otherwise, all the black
parents
would need to be
heterozygous
and even then only 0.5
probability
that each is black / eq
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