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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
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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 • The father of modern genetics • A monk in the 1850’s • worked with pea plants
Why Peas? • Easy to raise • Short life span • He could control reproduction • Large # of offspring • Characteristics easy to identify
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)
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.
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
…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
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
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
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
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
Pedigrees -Used to show relationships w/in families -Shaded individuals have a different phenotype than unshaded
Pedigree male = = female Mating
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)
Varying types of dominance • Complete dominance –one allele is completely dominant over the other • RR = Red • Rr = Red • rr= white
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)
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
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)
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***
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
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
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)
…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
…Sex Linked Traits • A male can be: • XNY = normal vision • XnY = colorblind • ***males cannot be carrier of recessive sex-linked traits***
Phenotypic ratio for Sex-linked traits • Dom Females: Rec. Females: Dom Males: Rec Males • XNX? : XnXn : XNY : XnY
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
…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
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
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.
Phenotypic Ratios for Blood Type • A : B : AB : O