Variation and the Monohybrid Cross

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Variation and the Monohybrid Cross

Higher Biology

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Significance of meiosis

Allele: different forms of the same gene

‘Meiosis provides the opportunity for new combinations of the existing alleles of genes to arise”

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Independent assortment of chromosomes

Homologous pairs line up at equator during first meiotic division

Final position of any one pair is random relative to any other

Second meiotic division brings about independent assortment of chromosomes

This may lead to new phenotypes in the next generation

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Crossing over and separation of linked genes

Chromosome is aligned with its homologous partner during first meiotic division

Portions of chromatid exchanged at points called chiasmata

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Chiasmata

Chromatids become broken

Broken end of one joins with that of another

Alleles of linked genes can become separated

Formation of new allele combinations

Formation of new phenotypes

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Importance of Variation

Helps species adapt to a changing environment

‘Survival of the fittest’ then occurs as a result of natural selection

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Monohybrid Cross

Cross between true-breeding parents with different alleles of the same gene

Genotype: the alleles the individual possesses of a particular gene

Phenotype: physical appearance of an individual

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Mendel’s First Law

The principle of segregation

alleles of a gene exist in pairs

when gametes form

members of each pair pass into different gametes

each gamete contains only one allele of each gene

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Incomplete dominance