Chromosomal Inheritance: Evidence that DNA is Genetic Material

Chromosomal Inheritance Evidence that DNA is Genetic Material: Material given to each cell was not necessarily the same but the DNA given to both through mitosis was the exact same Miescher (isolate and identify nucleic acids) and Roux (showed that material in the nucleus was genetic information) showed individually that genetic material had both nucleic acids and protein within the nucleus, however, Hershey-Chase (1952) showed that genetic information is passed on through nucleic acid (as shown by the bacteriophage experiment, where they radioactively labeled sulfur, but when the cell made more bacteriophages, the protein coat no longer had this radio-labeled sulfur; in the second part they radio-labeled the phosphorus in DNA and showed that this did pass onto the new generation of bacteriophages) In 1953 Watson and Crick found out that the structure of DNA is a double stranded helix with a sugar phosphate backbone with nitrogenous bases running in the middle Sex Linked Traits: Autosomal chromosomes are the 22 pairs of chromosomes not including the sex chromosomes (XX is homologous while XY is NOT) The homologous pairs each have the same genes on them, just different version of them (known as alleles) The male determines the gender of the offspring since they decide if they will give an X or a Y chromosome The X and Y chromosome DO code for some other things than just sex related characteristics Color blindness (red-green specifically) and hemophilia (inability of the blood to clot properly, several versions though) are both the result of mutations on the X chromosome but are recessive mutations (women can mask it with a normal dominant but men will ALWAYS show the phenotype) Genetic Recombination: We count chromosomes by the number of centromeres present During Prophase I, homologous pairs of chromosomes come together to form a unit known as a tetrad (since it has 4 chromatids) and the process of them pairing up with each other is known as synapsis Crossing over (Genetic Recombination) occurs when the homologous pairs of chromosomes swap genetic information between their respective chiasmata) The process of genetic recombination allows for the production of 4 unique gametes as opposed to 2 unique gametes pairs Gene Mapping: Genetic recombination occurs between the two inside chromatids (it can happen within one chromosome but they’re identical so it doesn’t really matter) The further apart two genes are, the more likely they are to be separated from one another and the closer two genes are to each other, the less likely they are to be separated from one another Centimorgan is the unit of measurement to measure distance on a chromosome (m.u.) If two genes are 1 m.u. apart, then 1 out of every 100 trials, they will be separated Extranuclear Inheritance: Two organelles that have their own DNA: 1. Mitochondria: have about 37 genes in it and most of them code for things important for mitochondrial processes 2. Chloroplasts: found in plant cells (algae) and are the site of photosynthesis (which occurs within the thylakoids) The egg cell has its own mitochondria, meaning that it is passed down from mother to offspring, the father contributes no mitochondria (chloroplasts in plants also exhibit this same phenomenon, maternal inheritance in MAJORITY but not all cases) Maternal Inheritance: occurs only from maternal line/egg cell and is contrary to Mendelian Genetics Extranuclear Inheritance: any genetic information passed on from structures that do not originate from the nucleus Endosymbiotic Theory: states that at some point, mitochondria/chloroplasts (that were proks) about 1.5 billions years ago joined in with a eukaryotic cell to become an organelle in order to benefit both parties (euk gives the organelle a nice place to live with plenty of nutrients and the organelle then gives ATP/Glucose with mitochondria/chloroplast respectively) Extra Notes: Penetrance: measures the fraction of people with the genotype who express the corresponding phenotype Expressivity: measures the range of expression of a certain genotype (constant expressivity means that the genotype is expressed exactly the same way each time and variable expressivity means that everyone with the TALL gene is above average height) Single, double, or triple refers to how many crossover events occurred while the # of strands has to do with how many strands were involved in the crossover event