Unit 6 - Genetics Introduction

1. Unit 6 - Genetics Introduction You look the way you do because of the genes your parents passed on to you at fertilization (the joining of the sperm and the egg). The transfer of genes from parents to offspring gives you your unique strand of DNA which every cell in your body uses to function. The scientificstudy of heredity is called genetics. http://www.exploringautism.org/genetics/images/overview.jpg

2. The unique combination of your parents geneswhich they passed on to you is what makes you look, and to a certain extent, act the way you do. Heredity is the passing of traits from parents to offspring. You might have blue eyes, even though both of your parents have brown eyes. How does this happen? The specifics behind the scientific study of heredity, or genetics, will be discussed in this chapter. Introduction to Heredity http://news.bbc.co.uk/media/images/38149000/jpg/_38149935_cartoon_family300.jpg

3. Gregor Mendel: The Father of Genetics • An Austrian monk named Gregor Mendel performed experiments during the 1800s to understand the process of traits. • Traits are the specific characteristics of an organism (blue eyes, brown hair, etc). • Mendel used pea plants from his garden to study. • He noticed that sometimes the “parent” pea plants did not match the characteristics in “children.” http://mac122.icu.ac.jp/gen-ed/mendel-gifs/18-mendel-cartoon.JPG

4. Mendel’s Experiments • Mendel studied the plants and found variations, or differences. • EX Purple or white flowers, tall or short plants, and even round versus wrinkled peas. • He crossed (or pollinated) plants with different traits and observed the results. http://www.micro.utexas.edu/courses/levin/bio304/genetics/mendel.gif

5. Mendel’s Results • He found thatpurple flowers, round peas, and tall plants were the MOST common. (called the F1 generation or first generation). • In the second cross, the F2 generation, Mendel observeddifferences (white flowers, wrinkled peas, short plants). • He concluded that some traits only appear under certain conditions. http://www.groundscience.com/solutionsnewsletter/solutions15/pea.jpg

6. Alleles • We now know that genes are responsible for coding for a specific trait (EX blue eyes, brown hair). • Genes are sequences of DNA that codes for a protein and determines a trait (EX the protein for blue eyes). • Every part of you, from your height to the color of your skin, is related to your genes. • The different forms of a gene are known asalleles. • White flowers versus purple flowersare thesame trait but different alleles. http://biology.clc.uc.edu/graphics/bio105/all%20cats.jpg

7. Multiple Alleles • Shades of hair color represent the multiple alleles of for possible combinations. http://www.indiana.edu/~oso/lessons/Genetics/figs/HairColor/browns.jpg

8. http://trc.ucdavis.edu/biosci10v/bis10v/week4/dihybridf1.gif

9. Dominant & Recessive • The stronger trait that will always appear is the dominant trait(shown with a capital letter). • But what happened to the white flowers? • The wrinkled peas? • The trait that did not appear, sometimes called the hidden trait, is called recessive(shown with a lowercase letter). http://www.emc.maricopa.edu/faculty/farabee/biobk/mendel'str-1.gif

10. Incomplete dominance • We now know that there are also instances of Incomplete dominance, where there is none that is dominant or recessive but a blending of both alleles. • An example of co dominance would be roses. A white crossed with a red to produce a pink. http://www.gwu.edu/~darwin/BiSc150/One/rose.GIF

11. Co dominance • Codominance occurs when two different alleles for a trait both show up in the phenotype(physical appearance) • Examples • Blood type – Type AB • Roan Cattle

12. Multiple Alleles • Notall genes have just two alleles for the trait, but some can have many alleles to choose from and are said to have multiple alleles. • Hair color, eye color, and blood types are all examples of human traits where multiple alleles are involved, not just the standard two often used in punnett squares. http://ghs.gresham.k12.or.us/science/ps/sci/soph/genetics/notes/bloodtype.htm

13. Polygenic Traits • Not every trait is controlled by a single gene. Traits that are controlled by two or more genes are said to be polygenic traits, which means “having many genes”. • Human stature (or height) is controlled by multiple genes. http://www.algebralab.org/img/49ab8f77-f675-423a-b8af-d46874987ab3.gif

14. Homozygous: RR or rr • These letters that we “GET” from our parents code for traits. • EX the flower color trait (R or r). • An organism can be homozygous dominant or homozygous recessive if they have two identical alleles for a trait (Sketch it!). • Homozygous dominant (RR) = Red • Homozygous recessive (rr) = White. • The recessive allele can ONLY be seen if it is in a homozygous pair (remember it is normally HIDDEN). http://discover.edventures.com/images/termlib/h/homozygous/support.gif

15. Heterozygous: Rr • An organism with a mixed allele pair is heterozygous, (Rr) has the opportunity of having offspring with both traits. • If two heterozygous organisms cross, you can have offspring that exhibit (or show) the recessive trait. http://discover.edventures.com/images/termlib/h/heterozygous/support.gif

16. Sketch it! http://www.plant.uoguelph.ca/research/biotech/haploid/homo.gif

17. Scientists have now developed a system using symbol combinations to study heredity. A Punnett square is a chart used to predict and compare the genetic combinations that will result from a cross. A capital letterrepresents the dominant trait while a lowercase letteris the recessive trait. A plant that IS always tall would be TTwhile a plant that is short would be tt. The Punnett Square http://www.tea.state.tx.us/student.assessment/resources/online/2002/eoc/biology/p23no34.gif

18. The Punnett Square Cross • In the Punnett square here, you can visualize the genes the parents are passing to offspring. • Each square of the box represents one offspring(or child). • Each parent donates one allele. • The dominant (stronger) allele will always go first, and will always be seen in the organism. • Sketch it! http://www.world-builders.org/lessons/less/les4/casino/casinogifs/pun2.gif

19. If you look at the punnett square, the top organism is considered the male while the organism on the side is the female. One allele (or letter) from each parent moves into each square. Remember if the organism has identical alleles (SS or ss) it is said to be homozygous. An organism that has two different alleles for a trait it is considered heterozygous (or Ss). Studying the Cross http://www.emc.maricopa.edu/faculty/farabee/biobk/mono2.gif http://www.phschool.com/atschool/science_images/human_punnett_square.jpg

20. Genotype & Phenotype • The genetic makeup and inherited combination of alleles is known as the offspring’s genotype, or “the letters that you GET.” • EX “Tt” or “tt” • The physical characteristic and the appearance shown in the organism (purple flowers, blue eyes, etc) is called the phenotype. • The phenotype is the “PROOF” of the allele that is there and is what you “SEE”. • EX “Tall plant” or “short plant”

21. Genotype & Phenotype(the Right, the Left) http://bio1151.nicerweb.com/doc/class/bio1151/Locked/media/ch14/14_06PhenotypeVsGenotype_L.jpg

22. So what? How does this apply to me? • How do genes and traits apply to me? • Send a representative to the front to pick up the packets for your group. • The “Inventory my traits survey” will show you some REAL dominant/recessive genes in humans. http://www.abpischools.org.uk/resources/genome/en-images/dominantrecessivealles.gif

23. Where are those genes? • Okay, so we understand that each parent gives half of their genes to each child, but where are those genes located? • The genes that make you tall or can make you have curly hair are located within the chromosomes made of DNA in the nucleus of every cell of your body. • Modern science allows us to view all chromosomes in a karyotype where they arranged in pairs, one chromosome from the mother and one from the father. http://www.genomenewsnetwork.org/gnn_images/whats_a_genome/karyotype.gif

24. Mendel began studying genetics in the 1820s, but science has advanced and we know can that DNA carries genes in our chromosomes. In 1911, the first gene map was produced that showed the gene locations on the chromosomes of a fruit fly. The shaded areas represent a gene that controls a specific trait(s). Gene maps are now widely used in understanding genetic mutations, sickness, and the human genome project. Gene Maps http://ccr.coriell.org/nigms/genes/17gene.gif

25. Fruit Flies • Fruit flies (as shown here) are used to study genes and genetic relationships because they have a small number of chromosomes and can reproduce quickly. http://www-tc.pbs.org/wgbh/nova/allfours/images/gene-fruitfly-l.jpg

26. Sex Cells • Sperm and egg cells, known as sex cells (gametes),contain all the genetic material needed to build an organism • EX a cat, the zebra at the zoo, or even a little brother or sister! • A sperm is the male sex cell while an egg is the female sex cell. • Sex cells are haploid and have half the number of chromosomes in a normal cell (diploid). • Half of the genes in an organism are from the mother, the other half from the father. http://www.dorlingkindersley-uk.co.uk/static/clipart/uk/dk/exp_humanbody/exp_human098.jpg

27. Humans have 46 chromosomes total in the body; 44 of them are called autosomes. Two of the 46 chromosomes in humans are known as sex chromosomes because they determine an individual's sex. Females most often have two copies of a large X chromosomes (XX) Males most often have one X and one small Y chromosome (XY). XX & XY http://www.web-books.com/MoBio/Free/images/Ch1C4.gif

28. Genes that are located on the X or Y chromosomes are called sex-linked genes. Many sex-linked genes are found on the X chromosome(which contains more than 100 genetic disorders). Colorblindness and hemophilia are just two examples of genes relating to the X chromosome. The human Y chromosome (in males) is much smaller than the X and only contains a few genes. Sex-Linked Genes http://anthro.palomar.edu/biobasis/images/sex_cells.gif

29. Pedigree • Modern geneticists study the family history of persons using a pedigree chart. • A pedigree shows the relationships within a family and can track the appearance of a genetic disease or disorder. • Boxes represent males; circles represent females. • A pedigree always has a key. http://www.mcw.edu/cellbio/colorvision/images/pedigree.jpg

30. My Family Pedigree • Choose one trait from your family to study. • Eye color • Hair type (straight/curly) • Earlobes (attached/unattached) • Right handed/left handed. • Create a key. • Create a pedigree for your parents and your siblings. • Extra credit! Include your grandparents!!!!

31. Conclusion: Genetics and the Future • Genetics and DNA technology improves daily in the scientific community. • The entire human DNA strand is mapped, every gene identified; scientist are currently discovering which genes control which functions. • Predict what you think our knowledge of our DNA will have on the future? http://www.mcg.edu/news/2001NewsRel/images/poduslo1.jpg