Albinism Punnett Square

GENETICS SUPPLEMENT HOW DO GENES INFLUENCE OUR CHARACTERISTICS? 1. A gene is a segment of a DNA molecule that gives the instructions for making a protein. Different versions of the same gene are called alleles, and different alleles give the instructions for making different versions of a protein. The different versions of a protein can result in different characteristics, as illustrated in this table. GENOTYPE AA or Aa aa  PROTEIN  PHENOTYPE (Characteristics)  Enough normal enzyme to make melanin in skin and hair  Normal skin and hair color  Defective enzyme for melanin production  Very pale skin and hair color (albino) 2. Circle the genotypes in the table that are homozygous. Explain how the two different homozygous genotypes result in different phenotypes.  PROTEIN  PHENOTYPE (Characteristics) AA or Aa  Enough normal enzyme to make melanin in skin and hair  Normal skin and hair color aa  Defective enzyme for melanin production  Very pale skin and hair color (albino) GENOTYPE The different genotypes code for different proteins: • AA: normal enzyme • aa: defective enzyme 3. What are the two different genotypes for the albinism gene that result in the same phenotype? Explain how two people with different genotypes can have the same phenotype.  PROTEIN  PHENOTYPE (Characteristics) AA or Aa  Enough normal enzyme to make melanin in skin and hair  Normal skin and hair color aa  Defective enzyme for melanin production  Very pale skin and hair color (albino) GENOTYPE AA and Aa result in the same phenotype. Aa produces enough of the normal enzyme and, therefore, the dominant phenotype masks the recessive phenotype. HOW DOES A BABY INHERIT GENES FROM HIS OR HER MOTHER AND FATHER? meiosis fertilization mitosis 4. 5. In this Punnett square, circle each symbol which represents the genetic makeup of a gamete produced by the heterozygous mother or father. Use a * to indicate the genotype of each zygote. A a A a AA Aa Aa aa 6. The genotypes of the zygotes in the Punnett square represent the possible genotypes of the children of this couple. Explain why each child will have the same genotype as the zygote that he or she developed from. Mitosis  DNA is copied into each new cell as the child develops from a zygote (single cell) into a multicellular child 7. For the Aa mother in this Punnett square, what fraction of her eggs have an a allele? What fraction of the Aa father’s sperm have an a allele? What fraction of this couple’s children would you expect to be aa? A a A a AA Aa Aa aa 8a. Complete this Punnett square for two parents who are homozygous AA. A A A A AA AA AA AA 8b. Complete this Punnett square for two parents who are homozygous aa. a a a a aa aa aa aa 8c. Complete this Punnett square for a mother who is heterozygous Aa and a father who is homozygous aa. A a a a Aa Aa aa aa A A N A N A a N N N O AA Aa Aa aa a N N O A A a a a N N O O N AA AA N N AA AA a O a aa aa O O aa aa A N a O a N Aa Aa O O aa aa 10. Explain why two albino parents won’t have any children with normal skin and hair color, but two parents with normal skin and hair color could have an albino child. aa X aa Aa X Aa Can only pass on recessive alleles Each can pass on one recessive allele 11. Albino children are rare in the general population. Based on this observation, what is the most common genotype for parents? Explain your reasoning. AA If Aa, albino children would not be as rare. Few “a” in the gene pool.