1 / 34

Fundamentals of Genetics

Fundamentals of Genetics. Regular Biology. Fundamentals of Genetics. Genetics The field of biology that deals with the study of heredity. ( the transmission of traits from the parents to the offspring ). Gregor Mendel. Gregor Mendel

chava
Download Presentation

Fundamentals of Genetics

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Fundamentals of Genetics Regular Biology

  2. Fundamentals of Genetics • Genetics • The field of biology that deals with the study of heredity. ( the transmission of traits from the parents to the offspring )

  3. Gregor Mendel • Gregor Mendel • The father of modern genetics • A monk in the 1850’s • worked with pea plants

  4. Gregor Mendel (1822-1884)

  5. Why Peas? • Easy to raise • Short life span • He could control reproduction • Large # of offspring • Characteristics easy to identify

  6. His Experiments • P1 (parental generation) • Pure tall X Pure short •  All TALL ( F1 ) • F1 (first filial generation) • F1 X F1 •  ¾ tall (787 tall), ¼ short (277 short)

  7. Mendel’s conclusions • Law of Dominance One factor (gene/allele) of a pair may mask the effect of the other, preventing it from having an effect (being shown) • Law of Segregation A pair of factors (genes) are separated during meiosis so that only one from each pair passed on to the offspring.

  8. Genetic crosses • Alleles (genes) are designated by the FIRST letter of the adjective of the dominant trait. ex: tall is dominant over short T = tall t = short Phenotype physical appearance of the trait. ex: tall, short

  9. …Genetic crosses • Genotype • The genes (letters) that an organism has in it’s cells that determine the trait. • -2 genes (letters) for each trait • -1 from Dad • -1 from Mom

  10. Genotype • Homozygous (pure) • when both letters are the same • ex: TT, tt • Heterozygous (hybrid) • when letters are different • always write the big letter first • ex: Tt , Xx , Bb

  11. Monohybrid cross ( involves 1 trait) R = red fur (dominate) r = white fur (recessive) Rr X Rr 1 red pure, 2 red hybrid, 1 white pure Punnett SquareShows probability/likelihood of offspring

  12. How do you write it ? • Genotypic ratio • RR : Rr : rr -- 1 : 2 : 1 G • This is in the genes • Phenotypic ratio • Dominate/recessive --3 : 1 P • This is what we see

  13. Remember………………. • Dominate = CAPITAL letter (goes first) • Recessive = small letter (comes second) • Homozygous (pure) all dominant or recessive • ex: RR rr • Heterozygous (hybrid) 1 dominant, 1 recessive • ex: Rr • Punnett Sq. Mom on side, Dad on top side • Cross (of 2 heterozygous) = Rr x Rr • Cross of homozygous Dominant vs. Resessive • RR x rr

  14. Pedigrees -Used to show relationships w/in families -Shaded individuals have a different phenotype than unshaded

  15. Pedigree

  16. Pedigree male = = female Mating

  17. Steps in solving pedigree problems • Figure out which trait is dominant/recessive • Fill out all recessive genotypes in pedigree as “nn” • Fill out all dominant genotypes “N__” • (See blackboard)

  18. Varying types of dominance • Complete dominance –one allele is completely dominant over the other • RR = Red • Rr = Red • rr= white

  19. 2. Incomplete dominance • Blending between “dominant” and “recessive” alleles, resulting in a 3rd possible phenotype which is between the other 2 phenotypes • RR = Red • Rr = pink • rr = white *** 3 phenotypes & 3 genotypes…genotypic and phenotypic ratios are the same (3 “options”) Ex: 1:2:1 (G & P)

  20. 3. Codominance • Both alleles are expressed in heterozygous offspring… • NO Blending…NO Recessive Alleles • Ex: Horse Coat Color • R = Red, W = White • RR = red, WW = White, • RW = Roan (both red and white hairs present) http://www.mustangs4us.com/Horse%20Colors/roan.htm

  21. More on Codominance… • ***3 phenotypes and 3 genotypes • What does this mean in regards to the ratios? • Same genotypic and phenotypic ratios • You MUST label these ratios…can’t just write the #’s, must include letters in order to “label” • Ex: 1 RR: 2 RW: 1 WW (G and P)

  22. Dihybrid Crosses • Crosses involving 2 traits in parents & offspring • Genotypes consist of 4 letters, 2 genes for each trait • Mendel’s 3rd Law/ Law of Independent Assortment • The inheritance of genes for one trait (ex: hair color) is not affected by the inheritance of genes for another trait (ex: eye color) • ***only true if genes are on different Chr’s***

  23. Making a dihybrid punnet square • cross: TtRr x ttrr • (1234) (1234) • Use the FOIL (1-3, 1-4, 2-3, 2-4) • 2 letters on sides of P. square, 4 letters inside each box…keep the same letters together • See Blackboard for example

  24. Order for Phenotypic Ratio • Both dom: 1stdom/2ndrec: 1strec/2nddom: Both rec • TTRR :T__rr:ttR__ :ttrr • should add up to 16 • What do you do to get F2 generation? • Cross two F1 individuals

  25. Sex-Linked Traits • Traits controlled by genes carried on X Chr • Males XY, Females XX • Males have only 1 X sex chr so they have only one gene for those traits (makes it EASIER for males to inherit sex-linked recessive traits) • B/c males = have just 1 of the recessive gene, the recessive trait will be expressed • females must have both recessive XX’s (like what we previously learned)

  26. …Sex linked traits • Males inherit recessive sex-linked traits from their mother • EX: Colorblindness is a recessive sex-linked trait • A female can be: • XNXN = homozygous for normal vision • XNXn = carrier of colorblindness gene (hetero) • XnXn = colorblindness

  27. …Sex Linked Traits • A male can be: • XNY = normal vision • XnY = colorblind • ***males cannot be carrier of recessive sex-linked traits***

  28. Phenotypic ratio for Sex-linked traits • Dom Females: Rec. Females: Dom Males: Rec Males • XNX? : XnXn : XNY : XnY

  29. Blood Type • Multiple alleles – trait controlled by more than 2 alleles (such as blood type) • Blood type is controlled by 3 alleles: IA IB i • I = antigen on surface of blood • Antigen = Proteins capable of stimulating specific responses in one’s immune system • Antibody = produced by the body to fight off foreign substances • i = no antigen

  30. …Blood Type • IA and IB are codominant over i (i = recessive) • 4 blood types (phenotypes) possible: A, B, AB, O • (actually 8 possible b/c of A+, A- …due to another antigen called Rh factor on the surface of some red blood cells…we will NOT consider this in our crosses) • The letters A and B refer to the 2 types of antigens found on the surface of red blood cells • AB = both antigens present A = A antigen present • O = neither antigen present B = B antigen present

  31. 6 Genotypes possible for blood type: • IAIA, IAi = A • IBIB, IBi = B • IAIB = AB Universal Recipient, can receive from anyone • ii = 0 Universal Donor, can give blood to anyone

  32. Why is knowing about blood type antigens important? • Critical for blood transfusions… • If a person with Type B blood (has B antigens) donates to Type A blood. • Type B = donor, Type A = recipient • The person with Type A will produce antibodies to fight off the B antigen. • These antibodies bind to the B antigens and cause that person’s blood cells to clump together…the recipient could die.

  33. Phenotypic Ratios for Blood Type • A : B : AB : O

More Related