Fundamentals of Genetics

Fundamentals of Fundamentals of GeneticsGenetics

Regular BiologyRegular Biology

Fundamentals of Fundamentals of GeneticsGenetics

•Genetics Genetics • The field of biology that deals The field of biology that deals

with the study of heredity.with the study of heredity.

( the transmission of traits ( the transmission of traits from the from the

parents to the offspring )parents to the offspring )

Gregor MendelGregor Mendel

• Gregor MendelGregor Mendel• The father of modern geneticsThe father of modern genetics

• A monk in the 1850’sA monk in the 1850’s

• worked with pea plantsworked with pea plants

Gregor Mendel (1822-Gregor Mendel (1822-1884)1884)

Why Peas?Why Peas?

• Easy to raiseEasy to raise• Short life spanShort life span• He could control reproductionHe could control reproduction• Large # of offspringLarge # of offspring• Characteristics easy to identifyCharacteristics easy to identify

His ExperimentsHis Experiments

• P1 (parental generation)P1 (parental generation)• Pure tall X Pure shortPure tall X Pure short• All TALL ( F1 )All TALL ( F1 )

• F1 (first filial generation)F1 (first filial generation)• F1 X F1F1 X F1• ¾ tall (787 tall), ¼ short ¾ tall (787 tall), ¼ short

(277 short)(277 short)•

Mendel’s conclusionsMendel’s conclusions

• Law of DominanceLaw of Dominance One factor (gene/allele) of a pair may One factor (gene/allele) of a pair may

mask the effect of the other, preventing mask the effect of the other, preventing it from having an effect (being shown)it from having an effect (being shown)

• Law of SegregationLaw of Segregation A pair of factors (genes) are A pair of factors (genes) are

separated during meiosis so that only separated during meiosis so that only one from each pair passed on to the one from each pair passed on to the offspring.offspring.

Genetic crossesGenetic crosses

• Alleles (genes) are designated by the Alleles (genes) are designated by the FIRST letter of the adjective of the FIRST letter of the adjective of the dominant trait.dominant trait.

ex: tall is dominant over shortex: tall is dominant over short

T = tall t = shortT = tall t = short

PhenotypePhenotype physical appearance of physical appearance of the trait.the trait.

ex: tall, shortex: tall, short

……Genetic crossesGenetic crosses

• GenotypeGenotype• The genes (letters) that an The genes (letters) that an

organism has in organism has in

it’s cells that determine the trait.it’s cells that determine the trait.• -2 genes (letters) for each -2 genes (letters) for each

traittrait• -1 from Dad-1 from Dad• -1 from Mom-1 from Mom

GenotypeGenotype

• HomozygousHomozygous (pure) (pure)• when both letters are the samewhen both letters are the same• ex: TT, ttex: TT, tt

• HeterozygousHeterozygous (hybrid) (hybrid)• when letters are differentwhen letters are different• always write the big letter firstalways write the big letter first• ex: Tt , Xx , Bbex: Tt , Xx , Bb

Punnett SquarePunnett Square Shows probability/likelihood of Shows probability/likelihood of

offspringoffspring

• Monohybrid cross Monohybrid cross ( involves 1 trait) ( involves 1 trait)

• R = red fur R = red fur (dominate)(dominate)

• r = white fur r = white fur (recessive)(recessive)

• Rr X Rr Rr X Rr • 1 red pure, 2 red 1 red pure, 2 red

hybrid, 1 white purehybrid, 1 white pure

How do you write it ?How do you write it ?

• Genotypic ratioGenotypic ratio– RR : Rr : rr RR : Rr : rr

-- 1 : 2 : 1 G-- 1 : 2 : 1 G– This is in the genesThis is in the genes

• Phenotypic ratioPhenotypic ratio– Dominate/recessiveDominate/recessive

--3 : 1 P--3 : 1 P• This is what we This is what we

seesee

Remember……………….Remember……………….• Dominate = CAPITAL letter (goes first)Dominate = CAPITAL letter (goes first)• Recessive = small letter (comes second)Recessive = small letter (comes second)• Homozygous (pure) all dominant or Homozygous (pure) all dominant or

recessiverecessive• ex: RR rrex: RR rr• Heterozygous (hybrid) 1 dominant, 1 Heterozygous (hybrid) 1 dominant, 1

recessiverecessive• ex: Rrex: Rr• Punnett Sq. Mom on side, Dad on top side Punnett Sq. Mom on side, Dad on top side • Cross (of 2 heterozygous) = Rr x RrCross (of 2 heterozygous) = Rr x Rr• Cross of homozygous Dominant vs. Cross of homozygous Dominant vs.

ResessiveResessive• RR x rrRR x rr

PedigreesPedigrees

-Used to show relationships w/in -Used to show relationships w/in familiesfamilies

-Shaded individuals have a -Shaded individuals have a different phenotype than different phenotype than unshadedunshaded

PedigreePedigree

PedigreePedigree

male =

= female

Mating

Steps in solving pedigree Steps in solving pedigree problemsproblems

• Figure out which trait is Figure out which trait is dominant/recessivedominant/recessive

• Fill out all recessive genotypes in Fill out all recessive genotypes in pedigree as “nn”pedigree as “nn”

• Fill out all dominant genotypes “N__”Fill out all dominant genotypes “N__”• (See blackboard)(See blackboard)

Varying types of Varying types of dominancedominance

1.1. Complete dominanceComplete dominance –one allele is –one allele is completely dominant over the othercompletely dominant over the other

• RR = RedRR = Red• Rr = RedRr = Red• rr= whiterr= white

2. Incomplete 2. Incomplete dominancedominance

• BlendingBlending between “dominant” and “recessive” between “dominant” and “recessive” alleles, resulting in a 3alleles, resulting in a 3rdrd possible phenotype possible phenotype which is between the other 2 phenotypeswhich is between the other 2 phenotypes

• RR = RedRR = Red• Rr = pinkRr = pink• rr = whiterr = white

*** 3 phenotypes & 3 genotypes…genotypic and *** 3 phenotypes & 3 genotypes…genotypic and phenotypic ratios are the same (3 “options”)phenotypic ratios are the same (3 “options”)

Ex: 1:2:1 (G & P)Ex: 1:2:1 (G & P)

3. Codominance3. Codominance• Both alleles are expressed in Both alleles are expressed in

heterozygous offspring…heterozygous offspring…– NO Blending…NO Recessive AllelesNO Blending…NO Recessive Alleles

• Ex: Horse Coat ColorEx: Horse Coat Color• R = Red, W = WhiteR = Red, W = White• RR = red, WW = White, RR = red, WW = White, • RW = Roan (both red and white RW = Roan (both red and white

hairs present)hairs present)http://www.mustangs4us.com/Horse%20Colors/roan.htm

More on Codominance…More on Codominance…

• ***3 phenotypes and 3 genotypes***3 phenotypes and 3 genotypes• What does this mean in regards to the What does this mean in regards to the

ratios?ratios?• Same genotypic and phenotypic ratiosSame genotypic and phenotypic ratios• You MUST label these ratios…can’t You MUST label these ratios…can’t

just write the #’s, must include letters just write the #’s, must include letters in order to “label”in order to “label”

• Ex: 1 RR: 2 RW: 1 WW (G and P)Ex: 1 RR: 2 RW: 1 WW (G and P)

Dihybrid CrossesDihybrid Crosses• Crosses involving 2 traits in parents & offspringCrosses involving 2 traits in parents & offspring• Genotypes consist of 4 letters, 2 genes for each Genotypes consist of 4 letters, 2 genes for each

traittrait

• Mendel’s Mendel’s 33rdrd Law Law/ / Law of Independent Law of Independent AssortmentAssortment

• The inheritance of genes for one trait (ex: hair The inheritance of genes for one trait (ex: hair color) is not affected by the inheritance of genes color) is not affected by the inheritance of genes for another trait (ex: eye color)for another trait (ex: eye color)

• ***only true if genes are on different Chr’s******only true if genes are on different Chr’s***

Making a dihybrid Making a dihybrid punnet squarepunnet square

– cross: cross: TtRr x ttrrTtRr x ttrr

– (1234) (1234)(1234) (1234)

– Use the FOIL (1-3, 1-4, 2-3, 2-Use the FOIL (1-3, 1-4, 2-3, 2-4)4)

– 2 letters on sides of P. square, 2 letters on sides of P. square, 4 letters inside each box…4 letters inside each box…keep the same letters togetherkeep the same letters together

– See Blackboard for exampleSee Blackboard for example

Order for Phenotypic Order for Phenotypic RatioRatio

• Both dom Both dom :: 1 1stst dom/2 dom/2ndnd rec rec :: 1 1stst rec/2 rec/2ndnd dom dom :: Both Both recrec

• TTRR TTRR :: T__rr T__rr :: ttR__ ttR__ :: ttrr ttrr

• should add up to 16should add up to 16

• What do you do to get F2 generation?What do you do to get F2 generation?• Cross two F1 individualsCross two F1 individuals

Sex-Linked TraitsSex-Linked Traits• Traits controlled by genes carried on X ChrTraits controlled by genes carried on X Chr• Males XY, Females XXMales XY, Females XX• Males have only 1 X sex chr so they have Males have only 1 X sex chr so they have

only one gene for those traits (makes it only one gene for those traits (makes it EASIER for males to inherit sex-linked EASIER for males to inherit sex-linked recessive traits)recessive traits)

• B/c males = have just 1 of the recessive B/c males = have just 1 of the recessive gene, the recessive trait will be expressedgene, the recessive trait will be expressed

• females must have both recessive XX’s (like females must have both recessive XX’s (like what we previously learned)what we previously learned)

……Sex linked traitsSex linked traits

• Males inherit recessive sex-linked traits Males inherit recessive sex-linked traits from their motherfrom their mother

• EX: Colorblindness is a recessive sex-EX: Colorblindness is a recessive sex-linked traitlinked trait

• A female can be:A female can be: • XXNNXXN = homozygous for normal vision = homozygous for normal vision• XXNNXXnn = carrier of colorblindness gene = carrier of colorblindness gene

(hetero)(hetero)• XXnnXXnn = colorblindness = colorblindness

……Sex Linked TraitsSex Linked Traits

• A male can be: A male can be: • XXNNY = normal visionY = normal vision• XXnnY = colorblindY = colorblind• ***males ***males cannotcannot be carrier of be carrier of

recessive sex-linked traits***recessive sex-linked traits***

Phenotypic ratio for Sex-Phenotypic ratio for Sex-linked traitslinked traits

• Dom Females: Rec. Females: Dom Dom Females: Rec. Females: Dom Males: Rec MalesMales: Rec Males

• XXNNXX?? : X : XnnXXnn : X : XNNYY : X : XnnYY

Blood TypeBlood Type• Multiple alleles – trait controlled by more Multiple alleles – trait controlled by more

than 2 alleles (such as blood type)than 2 alleles (such as blood type)• Blood type is controlled by 3 alleles: IBlood type is controlled by 3 alleles: IAA

IIB B ii• I = antigen on surface of bloodI = antigen on surface of blood

– Antigen = Proteins capable of stimulating Antigen = Proteins capable of stimulating specific responses in one’s immune systemspecific responses in one’s immune system

– Antibody = produced by the body to fight off Antibody = produced by the body to fight off foreign substancesforeign substances

• i = no antigeni = no antigen

……Blood TypeBlood 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 6 Genotypes possible for blood type: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 Why is knowing about blood type antigens important?type antigens important?

• Critical for blood transfusions…Critical for blood transfusions…• If a person with Type B blood (If a person with Type B blood (has B has B

antigensantigens) ) donatesdonates to Type A blood. to Type A blood.• Type B = donor, Type A = recipientType B = donor, Type A = recipient• The person with Type A will produce The person with Type A will produce

antibodiesantibodies to fight off the B antigen. to fight off the B antigen. • These antibodies bind to the B antigens These antibodies bind to the B antigens

and cause that person’s blood cells to and cause that person’s blood cells to clump together…the recipient could die. clump together…the recipient could die.

Blood Blood TypesTypes

(phenotyp(phenotypes)es)

Genotype(Genotype(s)s)

AntibodieAntibodiess

TransfusiTransfusion from on from whom?whom?

AA Anti_______Anti_________

BB

ABAB

OO

Phenotypic Ratios for Phenotypic Ratios for Blood TypeBlood Type

• AA : : BB : : AB : AB : OO