Monohybrid cross

Monohybrid cross Practical 1

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.

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

Aim • To carry out a simulation of a monohybrid cross

Method • 1 The following cross is carried out: • 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 P True Breeding True breeding x Round seeds Wrinkled seeds F1

Results

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

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

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

Results - group

Results - class

Interpretation • 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 RR Rr Rr rr Expected phenotype ratio 3 round: 1 wrinkled

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

The Backcross

May have the genotype RR or Rr Further cross • Round seeds from the F2 _______________________ • To find out which a ______________ was carried out 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 ____________

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.

Interpretation • What was the genotype of the cross A parent? • Give a reason for your answer RR 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

Monohybrid cross