Basic GeneticBios.docx

18 Pages
Unlock Document

Anatomy & Cell Biology
ANAT 212
Jason Young

Basic Genetics – BIOL202 Lecture 1 - Introduction - Primary goal of biologists: o Functional aspects of life (how do things move, how does a plant recognize its own pollen) - Cell biologists, biochemists: o Break down organisms, look at their components o Approach the biological function based on the components - Geneticists o Searches for mutations (either in natural populations, or induced in a population) o Check to see function, and how is it disrupted by mutation o Go about this through modification of genes - Genetic approach (genetic dissection) o Taking apart the genes  look at normal function gene  look at mutation gene  find potential differences and see if they can be fixed - Molecular Biology o Genetic tools allow us to understand and read the genetic code o Biochemists can now read genes and see what the components contained o Geneticists could use tools to manipulate material to see mutations Forward Genetics - Classical approach - Look for natural mutations - Do crosses between differing species and phenotypes (which differ in a certain characteristic) o Between a wild type and normal type - Note different ratios, genetic controls (how many genes control this) - Through these techniques, the presence of genes can be inferred by the progeny generation - Observe different molecular and developmental differences for different genotypes - Which leads to identifying the DNA sequence - Forward from the different forms and mutations down to the DNA sequence Reverse Genetics - Start out with a manipulation to the genetic code o Induce a mutation with a chemical compound in a certain part of the genome o Mess with the mRNA o Inactivate the protein, with a chemical - Makes usually very subtle effects on the phenotype, sometimes drastic - Works backward starting from the DNA message back up to the phenotype A Century of Genetics (1900-2000) - Mendel’s Laws helped establish the science of genetics - Spent a lot of time in the first 25 years of the 20 century in discovering that phenotypes resided in the genes, and the genes were found in the chromosomes - Next 25: the chemical basis of inheritance with DNA experiments - Next 25 years spent trying to figure out how the code is read o How it is replicated, how it is transmitted - Final 25 years spent sequencing all sorts of organisms - 2000: human genome was published Cost of DNA Sequencing has plummeted - Cost has tumbled at a ridiculous rate - Ability to sequence millions (billions) of bases of the genome for a very cheap cost SNPs – HapMap Project - Haplotype map of human genome o Haplotype: combination of alleles at adjacent locations (loci) on the chromosome that are transmitted together o SNP – Single-nucleotide-polymorphisms o Haplotype is also a set of SNPs on a single chromosome of a pair that are statistically associated - Goal: look for common patterns of human DNA sequence - This will allow researchers to find major genes that affect certain aspects of health, disease and responses to different drugs and environments Summary of Genetics Lecture 2 – Single Gene Inheritance Case study on Gastric cancer - Relevant conclusion: knowledge of equal segregation of a gene mutation in the body, which would lead to high risk of gastric cancer Gregor Mendel’s work - Use of Garden Peas o Used because they make many progeny per generation o Have very short generation time o Easily discernible traits - Pure Breeding Line: self-fertilize the parent and the progeny are identical to the parent - In his F1 generation with the pure green and pure yellow peas o If he was expecting blending, he would have expected a color around yellow-green, not pure yellow Mendel’s Explanation - Y/Y crosses with y/y - In the F1 generation, the progeny becomes Y/y - Mendel’s first law: equal segregation - PUNNET SQUARE FOR THE F2 GENERATION o Anything that carries Y will be a yellow pea, the y/y homozygous pea will be green - In order to test his explanation, and make sure that it was valid, he had to test the model o The model was derived because it fit the data very well o Since the model makes predictions, you test if the model can make verifiable predictions o Some tests of the model:  Cross F2 with yellow and get all yellow peas  Cross the F2 yellow peas with greens  Sometimes you’ll get yellow still, sometimes you’ll get 1:1  1/3 of the time you will get the results Terms - Mutant: something bearing a mutation - Wild-type: - Pure breeding line: line that when selfed yields the parent - Phenotype: appearance - Genotype: genetic makeup at the gene level - Gene/Locus (place in genome where gene is found) - Allele: Y or y - Monohybrid cross: take something with a single interesting trait and take a cross between two pure parents - Homozygote: 2 copies of allele - Heterozygote: 1 copy of allele Chromosomes - Could be dyed, found in nucleus - When meiosis was analyzed, its behaviour was found to be similar to Mendel’s work o Each gamete produces y and Y o Duplicates into yy and YY o YY and yy come together during meiosis  After first cell division, they end up into different strands  Then they separate into y, y, Y, Y  They segregate at meiosis 1  Recombine into a zygote Lecture 3 – Behaviour of Chromosomes and Genes The behaviour of chromosomes during meiosis - 2 different alleles leading to segregation - People weren’t willing to accept that chromosomes were the bearers of these factors Discovery of sex chromosomes - Sex chromosomes (X Y) - Thomas Hunt Morgan and fruit fly genetics o Benefits of working with fruit fly:  Short generation time  Easy to find  Very simple to grow on a very simple medium  Feed them yeast  Only 4 pairs of chromosomes in the fruit fly o First person to establish large genetics program using fruit flies - He discovered Red-eyed and white-eyed Drosophila Drosophila - 2 X will give female, 1 X or XY will give male - Did a cross in which the female was a pure-breeding red and male was pure-breeding white o In F1, he got all red eyes, as expected o In F2, he expected the 3:1 ratio based on Mendelian genetics  75% red males/females  25% white males/females o What he observed was that the only flies that had white eyes were male  Still got his 3:1 ratio  50% female red  25% male red  25% male white - Biggest assumption: that it was not sex-based - Postulated that red female was homozygous for wild-type o Male had a X and Y factor o On the X factor was the mutation for white eyes  The Y was a very small chromosome so it would be too small to carry the gene - The 3:1 ratio was there, and the male has chromosomal potential for white and red - Made the connection between chromosomes in determining gender, and in determining a phenotype Calvin Bridges - Discovered in the second cross an exceptional result: white females and red males - What he proposed was that something was going wrong in meiosis sometimes o The egg ends up with 2 X and the other egg is missing the X - Non-disjunction of meiosis - The ones without an X never survive, so you don’t see them o Normally you won’t see the ones with 3 X either - What you end up with is red-eyed male and white-eyed female - Morgan was the first North American to win the Nobel Prize for this work Autosomes and sex chromosomes - There’s a gene that determines gender on the Y chromosome - The Y chromosome is tiny compared to the X - There is a small region of homology between the two (pseudo-autosomal) o Where you find similarity between the two - Functional reason for this: o So that they can pair up during meiosis o Very few Y-linked inheritance genes because Y has so few genes Mendelian genetics in humans - Many genetic polymorphisms o Difference in a single gene that controls traits - Brachydactyly (dominant) o Extra digit - Albanism (recessive) - Widow’s peak (dominant) - Sickle cell anemia (partially recessive) - Many traits in human population that are not particularly rare o Important to keep in mind whether or not some of these are rare or common Pedigree charts - Double line joining together two people  incest - Generations are numbered by roman numerals o Individuals numbered 1,2,3,4,5 Cystic fibrosis chart - Basis of cystic fibrosis is autosomal recessive - Parents gen. 3 are heterozygous - Traits could not have entered the family line, it’s more likely that it has been passed down so you can assume that gen 2 #2 and 4 are most likely the carriers Marfan Syndrome - Skeletal aberration - Dominant because it appears in every generation - Not sex-linked because it is not present in any one gender o We expect males to more often show the mutation because of the double-likelihood of a mutation being present on the X chromosome Pedigree analysis - Some traits (PTC tasting) can be recessive because both parents are non-expressing but their children express the gene - Some not rare entering the pedigree in many places Sex-linkage diseases - Most likely assignment for the diagram on the right o Knowing that it is rar
More Less

Related notes for ANAT 212

Log In


Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.