Definitions Which word 1 The allele which influences
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Definitions: Which word? 1. The allele which influences the phenotype even in the presence of an alternative allele. 2. One of a number of alternative forms of a gene, at the same locus on homologous chromosomes. 3. The diploid condition in which the alleles at a given locus are different. 4. This individual receives the same alleles at a given locus. 5. The genetic constitution of an organism with respect to the alleles under consideration. 1 of 45 © Boardworks Ltd 2009
Answers • • • Dominant Allele Heterozygous Homozygote Genotype 2 of 45 © Boardworks Ltd 2009
Genetic Crosses – GCSE revision Monohybrid inheritance involves looking at the inheritance of only a single pair of alleles. Remember: - capital letter for dominant allele - lower case letter for recessive allele - organisms have pairs of alleles - gametes only have one allele each 3 of 45 © Boardworks Ltd 2009
Genetic crosses: a history One of the first people to study genetics was an Austrian monk called Gregor Mendel in the 1850 s and 1860 s. He experimented with thousands of pea plants and established the basic foundations of inheritance, such as dominant and recessive characteristics. Mendel had no knowledge of DNA or genes but he did identify that inheritance is particulate, i. e. it depends on the transfer of separate (discrete) factors from parents to offspring. 4 of 45 © Boardworks Ltd 2009
Genetic crosses: worked example 5 of 45 © Boardworks Ltd 2009
Example If eye colour is controlled by a pair of alleles: B = allele for brown eyes b = allele for blue eyes. What’s the genotype of… a blue eyed person a brown eyed person (2 possibilities!) the children of two heterozygous parents ? 6 of 45 © Boardworks Ltd 2009
Genetics Problems Information • Dimples are dominant over no dimples. • Unattached earlobes are dominant over attached. • Freckles are dominant over no freckles. • Short fingers are dominant over long. Questions: Draw genetic diagrams to explain your answers 1. Both a man and a woman are heterozygous for freckles. What are the chances that their children will have freckles? 2. A woman is homozygous dominant for short fingers. Will any of her children have long fingers? 3. Both Jane and her sister have attached earlobes, yet their parents’ earlobes are unattached. What are the genotypes of their parents? 4. A father has dimples, the mother does not have dimples, and all the children have dimples. Give the probable genotypes of all the family members.
