Ciera Ventura L12 Patterns of Inheritance II Guided Reading Qs Chapter 9 11 9 16 Reading Objectives Explain and apply the terms complete dominance co dominance incomplete dominance and multiple alleles pleiotrophy polygenic variation autosomes and sex chromosomes Determine the types of gametes that form through independent assortment in a dihybrid and link this to metaphase I of meiosis Module 9 11 Compare contrast the terms complete dominance incomplete dominance and co dominance and give example of each Complete dominance is a type of inheritance in which the phenotypes of the heterozygote and dominant homozygote are indistinguishable Purple pea plants PP or Pp while white pea plants pp Incomplete dominance is a type of inheritance in which the phenotype of a heterozygote Aa is intermediate between the phenotypes of the two types of homozygotes AA and aa Red snap dragons and white snap dragons pink snap dragons 1 2 1 ratio Co dominance is a type of inheritance pattern in which a heterozygote expresses the distinct trait of both alleles AB blood Module 9 12 Mendel focused on traits that had two alleles A or a in which one was dominant and the other was recessive Yet many genes may have multiple alleles What is an example in your book of a gene that has multiple alleles ABO blood group How many alleles are there in this system 3 How many different genotypes are possible with these alleles What are they 6 genotypes IAIA IAi IBIB IBi IAIB ii Module 9 13 When one gene influences two or more characters we call this pleiotrophy Many of the genetic disorders we will learn about have multiple symptoms or traits This is because whatever protein is defective usually does not function in only a single cell type or tissue All the parts of the body affected by a disorder indicate the cells that require this protein normally As an example of pleiotrophy sickle cell disease has many symptoms and does what to Red blood cell shape Curved shape of a sickle with jagged edges Red blood cell count Lowered and can cause anemia and weakness Blood flow Reduced resulting in periodic fever severe pain and damage to various organs Kidneys Kidney failure Module 9 14 Whereas pleiotophy describes the multiple traits resulting from a single gene a polygenic many gene trait describes how multiple genes result in a single trait What is an example of a polygeneic trait Height diseases such as diabetes heart disease and cancer Polygenic inheritance can be recognized how Many different phenotypes for one trait Skin color eye color Height is another polygenic trait yet one s height can also be influenced from the environment how Nutrition Module 9 15 Are human traits more heavily influenced by genes or the environment Human traits are influenced by both genes and the environment Module 9 16 Figure 9 16 is really important in showing how meiosis is linked to inheritance Pretend you have to give a short presentation to a group of students explaining this figure What would you say We start in the cell of a member of the F1 generation whose genotype is heterozygous for both traits RrYy The two chromosomes with seed shape alleles R and r are homologous chromosomes and so are the two with seed color alleles Y and y In metaphase I when the duplicated chromosomes are arranged down the center of the cell there are different alignments into which they can be arranged Theses alignments determine which allele dominant or recessive are passed on together in the gametes In this case the first alignment results in two gametes with both dominant alleles Y and R and two gametes with both recessive alleles r only In the second alignment the result is two gametes with the recessive allele for seed shape and the dominant allele for seed color as well as two gametes with the dominant allele for seed shape and the recessive allele for seed color Have been using the questions at the end of each chapter to test your knowledge You might want to do this now or when you come back to review this chapter later
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