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Monohybrid cross Practical 1

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**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.

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**Introduction round wrinkled**

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

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Aim To carry out a simulation of a monohybrid cross

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**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

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Results Round seeds Wrinkled seeds

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**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

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**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

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**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

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Results - group Round seeds Wrinkled seeds Numbers Ratio

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**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

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**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

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**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

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The Backcross

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**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 ____________

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**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

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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

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