Biosc 0815 1st Edition Lecture 15 Outline of Last Lecture I. Different Traits:a. Dihybrid cross.II. Law of independent assortmentIII. Product Law of ProbabilityIV. Human Genetic PatternsV. Patterns of Inheritancea. Autosomal Recessiveb. Autosomal DominantVI. Reading Pedigree ChartsOutline of Current Lecture I. Mendel’s DiscoveriesII. Genetic outcomes that depart from Mendel’s Lawsa. Lethal Allelic Combinationsb. Multiple Allelesc. Incomplete Dominanced. Epistasise. Pleiotropic effectsf. LinkageIII. Mitochondrial GenesIV. Codominance vs Incomplete DominanceCurrent Lecture- Mendel’s discoverieso Unfortunately many traits are not so straightforward and have more than one or two variations. Some have multiple parts of the gene that can combine.These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.- Genetic outcomes that depart from mendel’s lawso Lethal allelic combinations: Some alleles are so disruptive that embryonic development is stopped. Miscarriage or spontaneous abortion occurs.  Some allow for survival but result in serious illnesses such as tay-sachs.  Another example is achrondroplasia (dwarfism). Dominant homozygous isnot possible. These limited outcomes give the appearance of violating mendel’s laws. Because you would only see the surviving ratio.o Multiple alleles: Example: blood type.  Codominants. A and B show codominance when both are present and both are expressed. Blood can be IA IB or i. both A and B can be present, orboth can be missing. o Incomplete dominance: It appears like blending. In a heterozygous phenotype, you get a result between two traits. If you cross a red or white flower, you might get a pink flower. Ex: Cw and Cr Punnet Square.o Epistasis: One gene makes a product that interferes with the expression of another gene.  Example: red hair. B = brown b=blond r=red- The red hair will mask the brown or blonde hair gene. Combinations are BBrr, Bbrr, and bbrr. One of the genes will mask the effect of the presence of the other genes. - Maybe A mutation on one gene prevents the protein from working. Another example:- Black and brown furred mice were crossed and some offspring were white in about a 9:3:4 ratio. This is close to mendel’s results in a dihybrid cross. The scientists realized there must be another trait influencing the outcome. B=black b=brown C=color c=no color. If the mouse had cc with any other combination, the mice were white. (recessive epistasis) A departure from Mendel’s classical dihybrid cross. There weren’t four different outcomes. o Pleiotropic effects: One allele has more than one effect. Example: fruitfly has one allele that reduces wing size, changes egg …….. Example 2: porphyria veriegata is a disease in the Englihs royal family. Changes on enzyme that effects the organs of the individual. - Missing enzyme allowed a protein to accumulate in organs and resulted in changed behavior.o Linkage: Goes against mendel’s law of independent assortment where genes were unrelated If genes are close together on the same chromosome they are often inherited together. There should only be two possible outcomes, the dominant combination and the recessive combination.  Ex: fly. Gray body is associated with long wings(GgLl), and a black body with short wings (ggll). This is a test cross. Most have either one or the other but some flies are grey and some are black with long wings.  Linkage is disrupted by the crossing over during Prophase 1 of meiosis. This produces recombinant offspring. If the genes are further apart there is more crossing over. The closer together they are the more rarely they separate.  This can help us figure out the position of genes on the chromosomes.- The percent of recombinants indicates the distance between genes on the chromosome. o These all show that Mendel’s work has many other factors. These can change theratios. - Mitochondrial genes:o These organelles have their own DNA separate from nuclear DNA. This DNA has 37 genes. This mitochondria comes from the mother. o Mitochondria divide and replicate DNA. There is no meiosis. There may be more than one chromosome in each mitochondria. o Some mitochondria contain errors. A mother passes on this mutation to all offspring. o There is a theory that the mitochondria was its own bacteria that was taken up by a larger cell and they benefited from this symbiosis so it became part of the cell but it kept its own DNA.o IT can only be from the mother. The mitochondria is important to study because it is being investigated whether we can replace the mitochondria from an egg without a mitochondrial disease with that from a normal egg while still keeping the egg’s DNA from the mother with the disease. - Codominance and incomplete dominance:o Red and white flower: In codominance you would get red and white spots. In incomplete dominance you would get a blending.-Terms To Know:Pleiotropy: when a single gene locus affects more than one traitMultiple alleles: when a single gene locus has more than two possible allelesIncomplete Dominance: whe the phenotype of heterozygotes is intermediate between the homozygotesCodominance: when the phenotype of heterozygotes shows some aspects of both homozygotesEpistasis: when alleles at one gene locus can mask the expression of alleles at another gene locusGenetic Heterogenity: when different genes produce the same phenotype.When a genotype is incompletely penetrant some individuals with the genotype do not have the phenotype. Expressivity: the extent to which a phenotype is expressedPhenocopy: an environmentally caused condition whose symptoms are similar to those of a known inherited disorderA lethal allele may result in a phenotypic class that does not survive long enough to