Chapter 14 Part II Chromosomes and Genes Incomplete dominance, codominance, multiple alleles, epistasis, polygenic inheritance, the chromosomal theory of inheritance, sex chromosomes, linked genes, and chromosomal mutations are covered in this chapter.

12-1 Mendelism and the Genotype Incomplete Dominance and Codominance Incomplete Dominance: offspring show traits intermediate between 2 parental phenotypes. Red x white = pink One allele only partially dominant to partner

Codominance: pattern of inheritance in which both alleles of a gene are expressed Ex: A person with AB blood

12-1 Mendelism and the Genotype Genes that interact More than one pair of genes may interact to produce the phenotype

Epistasis Epistasis: absence of expected phenotype as a result of masking expression of one gene pair by the expression of another gene pair. Homozygous recessive masks effect of dominant allele at another locus. Ex: albino animals (aa) for melanin production prevent expression of hair and eye color

D. Pleiotropy

D. Pleiotropy

Multiple Allele There may be more than 2 alleles for one locus, but each individual inherits only two alleles Ex: Blood Type ABO gives 4 possible phenotypes: A, B, AB, O

Polygenic Inheritance Polygenic Inheritance: occurs when a trait is controlled by several diff. Allelic pairs at diff. loci Ex: Seed color and skin color

12-1 Mendelism and the Genotype Environment and Phenotype Both temperature and environment affect phenotype ex: plants like primrose and animals like Siamese cats and Himalayan rabbits

12-2 Mendelism and Chromosomes Chromosomal Theory of Inheritance Both chromo’s and alleles are paired in diploid cells Chromo’s and alleles of each pair separate during meiosis so gametes have 1/2. Chromo’s and alleles separate individually; gametes contain all combinations. Fertilization restores diploid chromo # and pairs alleles.

Sex Chromosomes Autosomes - non-sex chromo’s that are the same # and kind in between sexes Sex Chromosomes determine if the individual is male or female Males produce X-containing or Y-containing gametes, males determine sex X-linked Gene is any gene located on X chromosome

12-2 Mendelism and Chromosomes Sex-Linked Problems X-linked alleles are designed as superscript to X chromosome Heterozygous females are carriers; they do not show the trait but can pass it on. Males are never carriers but express the one allele on the X chromosome One form of color-blindness is X-linked

12-3 Chromosomal Mutations Changes in Chromo # Monosomy: indiv. only has one particular type of chromosome Trisomy Nondisjunction: failure Polyploidy: offspring end up with more than two complete sets of chromo’s.

Changes in Chromosomal Structure Environmental Factors Inversion Translocation Deletion Duplication