Biology 102 Patterns of Inheritance (cont.)

Lecture outline Inheritance of multiple traits Inheritance of multiple traits Same chromosome (linkage) Same chromosome (linkage) Sex chromosomes Sex chromosomes Overview Overview Sex linkage Sex linkage Incomplete dominance Incomplete dominance Codominance Codominance Other variations Other variations Sickle cell anemia example Sickle cell anemia example Pedigrees Pedigrees

Crosses with two traits If genes are on different chromosomes, they sort independently If genes are on different chromosomes, they sort independently

Genes on the same chromosome tend to be inherited together They are on the same chromosome. Considered to be “linked”. They are on the same chromosome. Considered to be “linked”.

Recombination creates new combination of “linked” alleles The farther away two genes are on a chromosome from each other, the more likely they will be exchanged during crossing over The farther away two genes are on a chromosome from each other, the more likely they will be exchanged during crossing over The closer together two genes are on a chromosome, the more likely they will travel together The closer together two genes are on a chromosome, the more likely they will travel together

Sex chromosomes Differ in appearance Differ in appearance Only small parts are homologous (carrying same genes) Only small parts are homologous (carrying same genes) Sex-linked genes Sex-linked genes Found only on one of the sex chromosomes Found only on one of the sex chromosomes Only 20 genes on Y Only 20 genes on Y Related to male characteristics Related to male characteristics 1500 genes on X 1500 genes on X Related to a variety of traits (few are gender-related) Related to a variety of traits (few are gender-related)

Sex determination Male determines the gender in mammals Male determines the gender in mammals How so? How so? Birds are the opposite Birds are the opposite Females XY, Males XX Females XY, Males XX

Sex-linked inheritance: Eye color in fruit flies

Incomplete dominance Snapdragon example Snapdragon example Heterozygote is intermediate between the two homozygotes Heterozygote is intermediate between the two homozygotes R codes for enzyme catalyzing production of red pigment R codes for enzyme catalyzing production of red pigment R’ codes for non-functional enzyme R’ codes for non-functional enzyme Amount of enzyme determines amount of pigment Amount of enzyme determines amount of pigment

Human eye color: Polygenic, incomplete dominance

Codominance Both phenotypes expressed fully. Both phenotypes expressed fully. Example: Human blood groups Example: Human blood groups These genes code for enzymes that stick sugars to cell-surface glycoproteins These genes code for enzymes that stick sugars to cell-surface glycoproteins Alleles A and B code for addition of distinct sugars Alleles A and B code for addition of distinct sugars O does not code for a sugar O does not code for a sugar Make antibodies to sugars not present on own cells Make antibodies to sugars not present on own cells

10% 10% 40% 40% 46% 46% 4% 4% B or AB B or AB A or AB A or AB O,AB, A,B (universal) O,AB, A,B (universal) AB AB B or O B or O A or O A or O O AB, A, B, O (universal) AB, A, B, O (universal) A B Both Both Neither Neither BB or BO BB or BO AA or AO AA or AO OO OO AB AB O B A Freq Freq Donates Donates Re- ceives Re- ceives Anti- bodies Anti- bodies RBCs RBCs Genotype Genotype Type Type Human Blood Types

Other variations Environmental influences Environmental influences Expression of gene for black pigment in Himalayan rabbit depends upon temperature Expression of gene for black pigment in Himalayan rabbit depends upon temperature Most traits affected by both genes and environment Most traits affected by both genes and environment Pleitropy Pleitropy Multiple effects of a single gene Multiple effects of a single gene Example: Sickle cell anemia Example: Sickle cell anemia Also great example from single error in a single nucleotide to whole organism effect Also great example from single error in a single nucleotide to whole organism effect

Some human genetic diseases Sickle-cell anemia: A case of incomplete dominance Sickle-cell anemia: A case of incomplete dominance Go from gene to whole organism effects Go from gene to whole organism effects

Sickle cell anemia: From amino acid substitution to whole body effects… A A single nucleotide is substituted in 18 th position of B-chain of Hb molecule (6 th amino acid) GUG instead of GAG Altered primary protein structure Valine instead of Glutamic acid Altered tertiary structure Altered quaternary protein structure Chains don’t fit together correctly

Sickle cell anemia: From amino acid substitution to whole body effects… Hemoglobin molecules stick together Red blood cell shape is altered

Sickle cell anemia (cont.) Whole body effects (symptoms of sickle cell anemia)

Investigating human genetic disorders Pedigrees: Use to figure out how trait is inherited (dominant, recessive, sex-linked) Pedigrees: Use to figure out how trait is inherited (dominant, recessive, sex-linked)