Remember Chromosomes occur in pairs homologous pairs the
Remember: Chromosomes occur in pairs. (homologous pairs) the different alleles of a gene occupy the same positions on each chromosome
So far each gene we have discussed has been made of two possible alleles. Ex. B = blue b= yellow R = red r = white
However, it is possible to have several different allele possibilities for one gene. Multiple alleles is when there are more than two allele possibilities for a gene.
In traits with multiple alleles, each individual can carry any two of the several possible alleles. Ex. BLOOD TYPE The gene for blood type has 3 possible alleles. A, B, or O
In this case both A and B are dominant to O (recessive). A and B are codominant (both expressed) So. . . there are four human blood types AA, AO A blood type BB , BO B blood type AB blood type or OO O blood type
Practice Problems: 1. A mother is AB and a father is O. Draw the punnett square. A B O O What is the probability their offspring will have A type blood? Can they have an offspring with O blood?
2. A mother is AO and a father is BB. Draw the punnett square. What is the probability their offspring will have B type blood? Can they have an offspring with O blood?
3. If a child has AB blood which of the following could NOT be the parents? a) OO, AB b) AO, BB c) BB, AA d) AO, BO
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