Regents Biology 2007-2008 Genetics & The Work of Mendel.

Regents Biology 2007-2008

Genetics&

The Work of Mendel

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Modern genetics began in the mid-1800s in an abbey garden, where a monk named Gregor Mendel documented inheritance in peas used good experimental design used mathematical analysis

collected data & counted them excellent example of scientific

method

Gregor Mendel

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Pollen transferred from white flower to stigma of purple flower

all purple flowers result

Mendel’s work

?

self-pollinate

Bred pea plants cross-pollinate

true breeding parents raised seed & then

observed traits allowed offspring

to self-pollinate & observed next generation

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Mendel collected data for 7 pea traits

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2nd

generation

3:175%purple-flower peas

25%white-flower peas

Looking closer at Mendel’s work

Parents

100%1st

generation(hybrids)

100%purple-flower peas

Xtrue-breedingpurple-flower peas

true-breeding white-flower peas

self-pollinate

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What did Mendel’s findings mean? Some traits mask others

purple & white flower colors are separate traits that do not blend purple x white ≠ light purple purple masked white

dominant allele functional protein

affects characteristic masks other alleles

recessive allele no noticeable effect allele makes a

non-functioning protein

homologouschromosomes

I’ll speak for both of us!

allele producingfunctional protein

mutant allele malfunctioning

protein

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Genotype vs. phenotype Difference between how an organism

“looks” & its genetics phenotype

description of an organism’s trait genotype

description of an organism’s genetic makeup

Explain Mendel’s results using…dominant & recessive …phenotype & genotype F1

P X

purple white

all purple

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Making crosses Can represent alleles as letters

flower color alleles P or p true-breeding purple-flower peas PP true-breeding white-flower peas pp

PP x pp

PpF1

P X

purple white

all purple

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Punnett squaresPp x Pp

P pmale / sperm

P

p

fem

ale

/ eg

gs

PP

75%

25%

3:1

25%

50%

25%

1:2:1

%genotype

%phenotype

PP Pp

Pp pp pp

Pp

Pp

1st

generation(hybrids)

Aaaaah,phenotype & genotypecan have different

ratios

Regents Biology 2007-2008

Any Questions??

Regents Biology 2007-2008

Beyond Mendel’s Lawsof Inheritance

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Extending Mendelian genetics Mendel worked with a simple system

peas are genetically simple most traits are controlled by single gene each gene has only 2 version

1 completely dominant (A) 1 recessive (a)

But its usually not that simple!

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Incomplete dominance Hybrids have “in-between” appearance

RR = red flowers rr = white flowers Rr = pink flowers

make 50% less color

RR Rr rr

RR

WW

RW

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Incomplete dominancetrue-breeding

red flowerstrue-breeding white flowers

XP

100%

100% pink flowers1st

generation(hybrids)

self-pollinate

25%white

2nd

generation

25%red 1:2:1

50%pink

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Incomplete dominance

R Wmale / sperm

R

Wfem

ale

/ eg

gs RR

RW WW

RW

25%

1:2:1

25%

50%

25%

1:2:1

%genotype

%phenotype

RR

RW

RW

WW

25%

50%

RW x RW

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Codominance Equal dominance

human ABO blood groups 3 version

A, B, i A & B alleles are codominant both A & B alleles are

dominant over i allele the genes code for different

sugars on the surface of red blood cells “name tag” of red blood cell

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Genetics of Blood type

pheno-type

genotypeantigenon RBC

antibodiesin blood

donationstatus

A A A or A itype A antigens

on surface of RBC

anti-B antibodies __

B BB or B itype B antigens

on surface of RBC

anti-A antibodies __

AB ABboth type A &

type B antigens on surface

of RBC

no antibodiesuniversal recipient

O i ino antigens on surface

of RBC

anti-A & anti-B antibodies

universal donor

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Blood donation

clotting clotting

clotting clotting

clotting clotting clotting

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One gene: many effects The genes that we have covered so far

affect only one trait But most genes are affect many traits

1 gene affects more than 1 trait dwarfism (achondroplasia) gigantism (acromegaly)

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Acromegaly: André the Giant

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Aa x aa

Inheritance pattern of Achondroplasia

a a

A

a

A a

A

a

Aa x Aa

Aa

aa aa

Aa

50% dwarf:50% normal or 1:1

AA

aa

Aa

67% dwarf:33% normal or 2:1

Aa

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Many genes: one trait Polygenic inheritance

additive effects of many genes humans

skin color height weight eye color intelligence behaviors

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Human skin color AaBbCc x AaBbCc

can produce a wide range of shades

most children = intermediate skin color

some can be very light & very dark

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AlbinismJohnny & Edgar Winter

albinoAfricans

melanin = universal brown color

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OCA1 albino Bianca Knowlton

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Coat color in other animals 2 genes: E,e and B,b

color (E) or no color (e) how dark color will be: black (B) or brown (b)

E–B–E–bbeeB–eebb

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Phenotype is controlled by both environment & genes

Color of Hydrangea flowers is influenced by soil pH

Human skin color is influenced by both genetics & environmental conditions

Environment effect on genes

Coat color in arctic fox influenced by heat sensitive alleles

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Genetics of sex Women & men are very different, but just a

few genes create that difference

In mammals = 2 sex chromosomes X & Y 2 X chromosomes = female: XX X & Y chromosome = male: XY

X Y

X X

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Sex chromosomes

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Sex-linked traits Sex chromosomes have other genes on

them, too especially the X chromosome hemophilia in humans

blood doesn’t clot Duchenne muscular dystrophy in

humans loss of muscle control

red-green color blindness see green & red as shades of grey X Y

X X

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Sex-linked traits

XH Ymale / sperm

XH

Xhfe

mal

e / e

gg

s XHXH

XHXh

XHY

XhYXHXh

XH

Xh

XHY

Y

XH

XHXH XHY

XHXh XhY

sex-linked recessive

2 normal parents,but mother is carrier

HH HhxXHY XHXh

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Dominant ≠ most common allele

Polydactylydominant allele

Because an allele is dominant does not mean… it is better, or it is more common

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Polydactyly

recessive allele far more common than dominant only 1 individual out of 500

has more than 5 fingers/toes so 499 out of 500 people are

homozygous recessive (aa)

the allele for >5 fingers/toes is DOMINANT & the allele for 5 digits is recessive

individuals are born with extra fingers or toes

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Hound Dog Taylor

Regents Biology 2007-2008

Any Questions?