Lesson 17: Patterns of Inheritance

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www.microscopy-uk.org.uk/mag/imgjul06/Image14.jpg www.purplemoon.com/Stickers/peas-earth.jpg

Roots: Di = 2mono = 1Homo = sameHetero = differentHemo = blood

Gregor Mendel

• 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

http://joefelso.files.wordpress.com/2007/04/mendel2.jpg

Pollen transferred from white flower to stigma of purple flower

anthersremoved

all purple flowers result

Mendel’s work

• Bred pea plants– cross-pollinate

true breeding parents– raised seed & then

observed traits– allowed offspring

to self-pollinate & observed next generation

?

self-pollinate

Mendel collected data for 7 pea traits

Each trait is represented by a specific allele on a specific chromosome.

Allele = genes that determine a specific trait.

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/150

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del/7

trai

ts.jp

g

2nd

generation

3:175%purple-flower peas

25%white-flower peas

Parents

100%1st

generation(hybrids)

100%purple-flower peas

Xtrue-breedingpurple-flower peas

true-breeding white-flower peas

self-pollinate

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

homologouschromosomeshomologous

chromosomes

allele producingfunctional protein

mutant allele malfunctioning

protein

mygenetic.wordpress.com

Genotype vs. phenotype

• Difference between how an organism “looks” & its genetics– phenotype

• Form of the trait that gets expressed“what you see”

– genotype • An organism’s actual alleles

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

P X

purple white

all purple

Inheritance of genes• On the chromosomes passed from Mom &

Dad to offspring are genes– may be same information– may be different information

eye color(blue or brown?)

eye color(blue or brown?)

Remember how Meiosis separates the alleles into sex cells?

This separation is called the Law of Segregation.

palaeos.com

Effect of genes

• Genes come in different versions– brown vs. blue eyes– brown vs. blonde hair– Alleles = different forms of a gene

Homozygous = same

Heterozygous = different

Homozygous = same

Heterozygous = differentHomozygous dominant = AAHomozygous recessive = aaHeterozygous = Aa

TtTt

BbBb

WwWwYyYy

rrrr

RRRR

AaAa

ABAB

SsSs

bbbb EeEeBBBB

aaaaXYXY

Genes affect how you look…

XBBbb

Bb Bb Bb Bb

Where did the blue eyes go??

XBbbb

Bb Bb bb bb

Why did the blue eyes stay??

XBbBb

BB or Bb BB or Bb BB or Bb bb

Where did the blue eyes come from??

• Genes come in “versions”– brown vs. blue eye color– Alleles (different forms of a gene)

• Alleles are inherited separately from each parent– brown & blue eye colors are separate & do

not blend • either have brown or blue eyes, not a blend

• Some alleles mask others– brown eye color masked blue

How does this work?

eye color(brown?)

hair color

hair color

eye color

(blue?)

• Paired chromosomes have same kind of genes– but may be different alleles

Traits are inherited as separate units

1 from Mom

1 from Dad

• For each trait, an organism inherits 2 copies of a gene, 1 from each parent– a diploid organism inherits

1 set of chromosomes from each parent• diploid = 2 sets (copies) of chromosomes

homologous chromosomes

Making gametesBB = brown eyesbb = blues eyesBb = brown eyes

BB

bb

Bb

brown is dominant over blue

blue is recessive to brown

Remember meiosis!

B

B

b

b

B

b

Dominant = can mask others

Recessive = can be hidden by others

How do we say it?

BB = brown eyesbb = blues eyes

Bb = brown eyes

2 of the same allelesHomozygous

2 differentHeterozygous

BB

B

B

bb

b

b

Bb

B

b

homozygous dominanthomozygous recessive

Punnett squaresBb x Bb

male / sperm

fem

ale

/ eg

gs

X

BB

Bb bb

BbB

b

B b

Genetics vs. appearance

• There can be a difference between how an organism looks & its genetics– appearance or trait = phenotype

• brown eyes vs. blue eyes

– genetic makeup = genotype• BB, Bb, bb

2 people can have the same appearance but have different genetics: BB vs Bb

Genetics vs. appearance

vs.

eye color(brown)

eye color

(brown)

BB

B

B

eye color(blue)

eye color

(brown)

Bb

B

b

How were these brown eyes made?How were these brown eyes made?

http://designora.com/wp-content/uploads/2009/11/32-brown-eyes.jpg

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

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 & genotype

can have different ratios

Beyond Mendel’s Lawsof Inheritance

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http://www.drstandley.com/images/health%20topics/Acromegaly2.jpg http://staff.tuhsd.k12.az.us/gfoster/standard/3head.gif

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!

mac122.icu.ac.jp

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

http://www.mnstate.edu/www.margaretaflowers.com www.99andbarry.com

Incomplete dominance

true-breedingred flowers

true-breeding white flowers

XP

100%

100% pink flowers1st

generation(hybrids)

self-pollinate

25%white

2nd

generation

25%red 1:2:1

50%pink

Incomplete dominance

RW x RW

R Wmale / sperm

R

Wfem

ale

/ eg

gs

25%

1:2:1

25%

50%

25%

1:2:1

%genotype

%phenotype

RR

RW

RW

WW

25%

50%

Codominance• Equal dominance

– Chickens• A black-feathered chicken is crossed with a white-

feathered chicken.• All of the babies are white with black speckling.• Both white and black show up equally.

x =

www.self-sufficient-life.com /echotig8.files.wordpress.comwww.harvestofhistory.org

More Codominance…

x

www.smartpawsacademy.com

/z.about.com

Multiple Alleles• More than one allele to select from.

– Blood “types” can be A, B, AB, or O.– The alleles to make these types include A, B and i.– “i” is the recessive allele and A and B are both

dominant.– So to get…

• Type A you must have AA or Ai• Type B you must have BB or Bi• Type AB you must have AB• Type O you must have ii

BLOODBlood cells have antigens and antibodies.

Antigens are tiny receptors on the outside of the blood cell that matches the “type.”

Antibodies are what the cell doesn’t like (which is anything different from the “type.”)

Multiple Alleles

Multiple Alleles

Blood Types

A

A

A

Type A

B

BB

Type B

Type O

A

B

A

Type ABB

Antigens(none)

Anti-B Anti-

A

noneAnti-A and B

Multiple Alleles

Multiple Alleles

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

Multiple Alleles

Multiple Alleles

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

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

67% dwarf:33% normal or 2:1

Aa

library.thinkquest.org

Many genes : One trait

• Polygenic inheritance– additive effects of many genes– humans

• skin color• height• weight• eye color• intelligence• behaviors

Polygenic =

“many genes”Polygenic =

“many genes”

www.scientificamerican.com

Human skin color• AaBbCc x AaBbCc

– range of shades– most children =

intermediate skin color

– some can be very light & very dark

Polygenic =

“many genes”Polygenic =

“many genes”

Albinism Johnny & Edgar Winter

albinoAfricans

melanin = universal brown color

cnb.uam.es

xenophilius.files.wordpress.com

theglenblog.blogspot.com

www.heartlandhunters.com

Albinism is the absence of pigment.

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

Environment effect on genes• Phenotype is controlled by

both environment & genesCoat color in arctic fox influenced by heat sensitive alleles

www.saskschools.ca

s3.amazonaws.comColor of Hydrangea flowers is influenced by soil pH

/www.grahamrollason.co.uk/images.pictureshunt.com

Human skin color is influenced by both genetics & environmental conditions

wxyc.org

SEX and GENES

• 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

Sex chromosomes

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

XH Ymale / sperm

XH

Xhfe

mal

e / e

gg

s XHXH

XHXh

XHY

XhY

XHXh

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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Most Common AlleleDominant or Recessive • Because an allele is dominant

does not mean…– it is better, or– it is more common

Polydactylydominant allele

Either One!

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biocrawler.com thelastoutpost.com

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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