BEYOND MENDEL…. OBJ discuss the characteristics and cause of some of the following genetic diseases and conditions

Objectives SWBAT describe the experiments of Gregor Medel, which led to the development of modern genetics SWBAT define and apply the following genetic terms: homozygous, heterozygous, alleles, genotypes, phenotypes, probability, monohybrid/dihybrid, dominance/recessive, codominance, incomplete dominance, multiple alleles, polygenic traits, sex-linked traits, test cross, pedigree SWBAT list and explain Mendel’s laws of inheritance, noting the exceptions to the laws SWBAT complete punnett squares to determine genotypic and phenotypic ratios SWBAT discuss the characteristics and cause of some of the following genetic diseases and conditions: color blindness, hemophilia, male-pattern baldness, sickle cell anemia, albinism, cystic fibrosis, tay-sachs diease, huntingtin’s disease, dwarfism SWBAT act as a genetic counselor to determine the probability of a couple passing a genetic condition to offspring SWBAT analyze and address a bioethical issue regarding genetic engineering.

When Dominant and Recessive is too simple…real life Not all genes are dominant/recessive Many traits are controlled by +2 alleles, +1 gene

Beyond Mendel Incomplete Dominance Codominance Multiple Alleles Polygenic Traits Sex Linked Traits Genetics and the Environment

Beyond Mendel Incomplete Dominance Codominance Multiple Alleles Polygenic Traits Sex Linked Traits Genetics and the Environment

Incomplete Dominance One allele is not completely dominant over another The heterozygous phenotype= mix between the two homozygous phenotypes Example: a cross between a red flowered plant (RR) and a white flowered plant (WW) produces a pink flowered plant (RW)

Incomplete Dominance

Beyond Mendel Incomplete Dominance Codominance Multiple Alleles Polygenic Traits Sex Linked Traits Genetics and the Environment

Codominance Both phenotypes contribute to the phenotype of the offspring Two different proteins are produced, and both are detected Chicken Example: White feathers = dominant Black feathers = dominant offspring = checkered chickens

More Codominance Sickle Cell Anemia

Beyond Mendel Incomplete Dominance Codominance Multiple Alleles Polygenic Traits Sex Linked Traits Genetics and the Environment

Multiple Alleles Many genes have more than two alleles This means that more than two alleles exist in the general population Example: blood type Type A (I A I A ) Type B (I B I B ) Type AB (I A I B ) Type O (ii)

Blood Typing

Beyond Mendel Incomplete Dominance Codominance Multiple Alleles Polygenic Traits Sex Linked Traits Genetics and the Environment

Polygenic Traits Many genes control these traits Results in a wide range of phenotypes Example: skin color in humans is controlled by more than four different genes

Beyond Mendel Incomplete Dominance Codominance Multiple Alleles Polygenic Traits Sex Linked Traits Genetics and the Environment

Sex-Linked Traits Genes found on the X or Y chromosome are called sex- linked Most of these genes are found on the X chromosome human Y chromosome is much smaller/carries only a few genes

Color-Blindness The X chromosome carries 3 human genes for color vision In males, a defective version of any of these will cause color-blindness Red-green color-blindness (1/10 American males and 1 out of 100 females) Males have only one X chromosome, the X alleles are expressed in the males, even if they are recessive

What about the girls? In order for an X chromosome gene to be expressed in females, she must receive two copies of the defective allele (one on each X chromosome) Since this trait is carried on the X chromosome, it will be passed from father to daughter, and may appear again in her sons

Hemophilia… Sex-linked trait passed on the X chromosome Affects gene that helps control blood clotting A recessive allele in either of the two genes required causes hemophilia in the individual

Hemophilia… affects 1 in 10,000 males Small cuts can be lethal Can be treated by injections of normal clotting proteins

Beyond Mendel Incomplete Dominance Codominance Multiple Alleles Polygenic Traits Sex Linked Traits Genetics and the Environment

Genetics and Environment Genes + Environment = trait Example: the height of a sunflower is determined by: the genes it receive sunlight, amount of water, and climate The genes - development plan actual plan is determined by the environment

Human Traits Inherited the same way that Mendel discovered Tricky= biologists must identify a trait determined by a single gene (must also ensure that the trait is inherited and not environmentally influenced) Then study how the gene is passed from one generation to the next

LINKAGE AND GENE MAPS

Gene Linkage Certain genes linked together (located on same chromosome) Chromosomes assort independently, not genes

Applying Mendel’s Principles Thomas Morgan decided to apply Mendel’s principle of genetics Does this apply to animals too? Fruit fly it is small, can be kept in the lab reproduces quickly (1 pair can create 100 offspring)