1. Monohybrid cross
Practical 1

2. Learning objectives: By the end of the lesson you should be able to:
Solve problems in relation to monohybrid crosses from the P generation to the F2 generation using dominant and recessive alleles.
To predict ratios of offspring genotype in monohybrid crosses.
State the reasons for differences between observed and predicted figures in monohybrid crosses.

3. Introduction round wrinkled
The shape of pea seeds can be either ______________ or _________________________
wrinkled

4. Aim
To carry out a simulation of a monohybrid cross

5. Method P x 1 The following cross is carried out:
True Breeding
True breeding x
Round seeds
Wrinkled seeds F1
2 collect a dish of seeds from the F1 generation
3 Count the numbers of round and wrinkled seeds and enter your results in the table

6. Results
Round seeds
Wrinkled seeds

7. Interpretation Round seeds Dominant allele Recessive allele
The results show that all of the F1 generation have __________________________
Round seeds
Dominant allele
This shows that round is the _______________
This shows that wrinkled is the __________________________________
Recessive allele

8. Symbols Diagram of cross Round = dominant = R Wrinkled – recessive = r
P phenotype Genotype F1 phenotype genotype
Round seed x wrinkled seed
RR X rr
All round Rr

9. 4 Members of the F1 are crossed together to form the F2 generation
Collect a dish of seeds from the F2 generation
Count the numbers of each type of seed and enter them in the table

10. Results - group
Round seeds
Wrinkled seeds
Numbers
Ratio

11. Results - class Group 1 2 3 4 6 8 10 Total Ratio Round seeds
Wrinkled seeds 1 13 7 2 18 3 15 5 4 11 9 16 6 17 8 10
Total
131 49
Ratio

12. Interpretation R r RR Rr Rr rr Expected phenotype ratio 3 round:
When two of the F1 generation are crossed together some of the F2 are round and some are wrinkled.
This can be explained by looking at the diagram of the cross
F1 phenotype round seed x round seed Genotype Rr x Rr F2
Male/Female R r RR Rr Rr rr
Expected phenotype ratio
3 round:
1 wrinkled

13. Evaluation The class results
Does this match more closely with the group or the class results?
The class results
Evaluation
Why do the class results more closely match with the expected ratio?
Large numbers are used making the experiment more reliable

14. The Backcross

15. Round seeds from the F2 _______________________
May have the genotype RR or Rr
To find out which a ______________ was carried out
Further cross
crossed with wrinkled seeds
They were ____________________________ as the _____________________________________
genotype of these is known
The results of the cross will allow you to tell if the round seed was __________________________
homozygous or heterozygous
backcross
This is known as a ____________

16. Cross Round seeds Wrinkled seeds A B
7 Collect two dishes of seeds from cross A and cross B
Collect the numbers of each type of seed from in each and enter your results in the table.
Cross
Round seeds
Wrinkled seeds A B

17. Interpretation
What was the genotype of the cross A parent? RR
Give a reason for your answer
All of the offspring were round so all inherited the R allele from the round parent
What was the genotype of the cross B parent? Rr
Give a reason for your answer
Some of the offspring were wrinkled so must have inherited the r allele from the round parent