Monohybrid Inheritance

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9 Terms

1
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State Mendel’s law of segregation.

‘The characteristics of an organism are determined by factors which occur in pairs.


Only one member of a pair of factors can be represented in a single gamete'.

2
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What is monohybrid inheritance?

The inheritance of a single gene.

3
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What is the phenotypic ratio of the offspring of 2 heterozygous individuals?

3 dominant, 1 recessive.

4
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Describe how you would carry out a monohybrid cross.

  1. Find the phenotypes of the parents and whether they are homo/heterozygous.

  1. Choose suitable letters for the alleles e.g. T for tall, t for short.

  1. Represent the parental genotypes with the appropriate pairs of letters

  1. State the gametes produced by each parent. Circle the gametes and label them clearly.

  1. Use a matrix, called a Punnett square, to show the results of the random crossing of the gametes.

  1. State the phenotype of each different genotype and indicate the numbers of each type.

<ol><li><p>Find the phenotypes of the parents and whether they are homo/heterozygous.</p></li></ol><p></p><ol start="2"><li><p>Choose suitable letters for the alleles e.g. T for tall, t for short.</p></li></ol><p></p><ol start="3"><li><p><span>Represent the parental genotypes with the appropriate pairs of letters</span></p></li></ol><p></p><ol start="4"><li><p>State the gametes produced by each parent. Circle the gametes and label them clearly.</p></li></ol><p></p><ol start="5"><li><p>Use a matrix, called a Punnett square, to show the results of the random crossing of the gametes.</p></li></ol><p></p><ol start="6"><li><p>State the phenotype of each different genotype and indicate the numbers of each type.</p></li></ol><p></p>
5
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Why is a back cross / test cross useful?

Used to determine whether an individual is homozygous or heterozygous for a dominant characteristic.

6
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How is a back cross carried out?

Cross the individual with the unknown dominant phenotype and a known recessive genotype.

7
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What is co-dominance?

When both alleles in the heterozygote are expressed individually.

8
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Give an example of co-dominance.

Human ABO blood group system- the I gene has 3 alleles, IA, IB and IO.

  • Homozygous parents who have the genotype IAIA have the A antigen on their red blood cells and are blood group A.

  • Homozygous parents who have the genotype IBIB have the B antigen on their red blood cells and are blood group B.

  • Their offspring has the genotype IAIB. Both alleles are expressed; they both have A and B antigens on their red blood cells so are blood group AB.

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What is incomplete dominance?

When the phenotype of the heterozygote is intermediate between the 2 parental phenotypes.

E.g. red flowered carnations crossed with white flowered carnations have an F1 of pink flowers. Neither the alleles for red petals nor white petals is completely dominant.