Edexcel IGCSE Biology 3.23 Monohybrid inheritance
Practise using genetic diagrams to show parent genotypes, gametes, offspring genotypes and phenotype ratios in single-gene crosses.
- Syllabus
- First assessment 2019
- Course
- Biology 4BI1
Exam points
- draw genetic diagrams with parent genotypes, gametes, offspring genotypes and phenotype ratios
- use a test cross with a homozygous recessive individual to infer an unknown genotype
- distinguish homozygous and heterozygous genotypes from dominant and recessive phenotypes
3.23 Monohybrid inheritance question 1
[Maximum number: 4]
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.
A male and female rat from these offspring are then mated together in a second cross.
Some of the offspring of this second cross have agouti coloured fur and some have black coloured fur.
Draw a genetic diagram to show this second cross. Include the genotypes of the parents, the gametes they produce, and the genotypes and the phenotypes of the offspring.
allow from
Punnett
square
An answer that makes reference to two the following:
- parent genotypes Aa and Aa
- parent gametes A or a A or a
- offspring genotypes AA Aa aa
- offspring phenotypes labelled or ratio 3: 1
allow other letters allow A and b
eg
ECF max 2 for mp 2
gametes
and mp 3 genotypes of offspring
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