How is this possible? Before we knew anything about DNA, there was only the examination of traits. The grandfather of this was… 3/22/2016 4 Genetics 101 Mendel’s experiment Mendel looked at 7 characteristics of pea plants, each had 1 alternate form that did not “blend” when crossbred 3/22/2016 6 Mendel’s experiment: P = parental Generations are F1= results of PxP F2= results of F1 x F1 named What were Mendel’s conclusions? 3/22/2016 7 Mendel’s experiment: P = parental Generations are F1= results of PxP F2= results of F1 x F1 named What were Mendel’s conclusions? PRINCIPLE OF DOMINANCE 3/22/2016 8 Essential Genetics Vocab homozygous – 2 identical alleles for a trait, ex. DD, dd heterozygous – 2 different alleles for a trait, carrier, ex. Dd phenotype – organism’s expressed traits, ex. color, height genotype – organism’s genetic makeup, letters, ex. PP, Pp 3/22/2016 9 If an offspring received one of these traits from a parent, did they always get the other? 3/22/2016 10 Conclusion: Principle of Independent Assortment 3/22/2016 11 Independent assortment The principle of independent assortment states that genes for different traits can segregate independently during the formation of gametes ◦ Some genes are inherited together (linked) What is an example? Independent assortment Worked for Mendel’s 7 traits in peas, but not always the case. ◦ Some genes are inherited together (linked) What is an example? How is this possible that genes get often passed on together? Independent assortment Worked for Mendel’s 7 traits in peas, but not always the case. ◦ Some genes are inherited together (linked) What is an example? How is this possible that genes get often passed on together? How can two genes on the same chromosome still separate? Independent assortment The principle of independent assortment states that genes for different traits can segregate independently during the formation of gametes ◦ Some genes are inherited together (linked) What is an example? How can two genes on the same chromosome still separate? Crossing-over during tetrad formation ◦ The farther apart genes are on a chromosome, the more likely that they will be able to separate during meiosis. So… if you have two genes, in typical (somatic) cells, do your gametes have both, too? 3/22/2016 16 So… Principle of Segregation When do alleles segregate? 3/22/2016 17 So… When do alleles segregate? Anaphase I 3/22/2016 18 Punnett square used to predict the results 3/22/2016 19 So now we can go back and apply Mendel’s ideas to the knowledge of DNA and chromosomes Chromosome sets You have 23 pairs of identical chromosomes, 1 from each parent ◦ 22 autosomes & 1 sex chromosome (see karyotype to right) Other organisms have different amounts Examples: ◦ Chicken: 49 pairs ◦ Mosquito: 3 pairs ◦ Lettuce: 9 pairs Each chromosome is composed of a super long strand of DNA, and each section of the chromosome codes for a specific gene you have about 20,000 genes 98% of your DNA does not code for genes, but is “empty space” Chromosomes and sex cells (a.k.a. gametes) Your sex cells (sperm and eggs) only contain 1 set of chromosomes, totaling 23 (HAPLOID or N) , as opposed to body cells containing 46 (DIPLOID or 2N) ◦ Non-sex cells are called somatic cells Which parent determines gender? Traits A trait is a physical expression of a gene (hair color, height, etc.), and your phenotype is your physical characteristics Your genetic make-up is your genotype Genes come in different versions called alleles ◦ e.g. eyes come in brown, blue, green, hazel Some traits are polygenic, meaning their expression is controlled by more than one gene ◦ Like blood type Gene Expression You have 2 of each of your 20,000 genes, 1 from mom and 1 from dad. but ◦ Some genes are dominant and some recessive, ◦ alleles can also be codominate, where both alleles show in the phenotype (ex. black and white cows) or ◦ incompletely dominant , where one allele is not completely dominant over another (ex. gray kittens from black and white parents) See section 11-2 What’s happening here? What’s happening here? Incomplete dominance What’s happening here? What’s happening here? codominance A better example of a codominant trait Punnett squares show probablity of traits being passed down to offspring. •Since one allele is from each parent, the Punnett Square shows all of the possible options that two gene combinations can make •This is just like the drop your genes activity, only all options are show Carrying alleles Heterozygous: 2 different alleles for a given trait (Bb) Homozygous: 2 identical alleles for a given trait (can be homozygous dominant or recessive, i.e. BB or bb) Predicting offspring traits with Punnett squares Predicting offspring traits with Punnett squares What would the pups look like? Predicting offspring traits with Punnett squares You can also look at 2 traits in the same Punnett square Pedigree charts show how traits are passed within families Human Genome Project The human genome is made up of 3 billion base pairs, totaling about 6 feet in each cell. (There are about 30 trillion cells in your body, which means that all your DNA could stretch to the sun and back 300 times) For more info: See chapter 11 & 14 in your text