1

Let there be

PEAS ON EARTH!

math.uit.no

Unit 5 Notes: Genetics

• 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

Pollen transferred from white flower to stigma of purple flower

anthersremoved

all purple flowers result

• Bred pea plants

– cross-pollinate true breeding parents

– raised seed & then observed traits

– allowed offspring to self-pollinate& observed next generation

?

self-pollinate

When bred to themselves will always produce

organisms with same phenotype.

EX. White bred to white always produces white; purple bred to purple

always produces purple.

When a flower pollinates itself. No new genes are

introduced.

Mendel’s workMendel collected data for 7 pea traits

Each of these

traits is

represented by a

specific allele on

a specific

chromosome.

Allele = genes

that determine a

specific trait.

Flower color

Seed color

Seed shape

Pod color

Pod shape

Flower location

Plant size

2nd

generation

3:175%purple-flower peas

25%white-flower peas

Parents

100%1st

generation(hybrids)

100%purple-flower peas

Xtrue-breeding

purple-flower peastrue-breeding

white-flower peas

self-pollinate

• 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

allele producing

functional protein

mutant allele

malfunctioning

protein

What did Mendel’s findings mean?

2

• 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 & genotypeF1

PX

purple white

all purple

Genotype vs. phenotype Environment effect on genes

• 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

Coat color in arctic

fox influenced by

heat sensitive alleles

Phenotype is a result of both genetics and environment.

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www.cats-central.com

Cold Environment

Warm Environment

Siamese cats that grow

up in a cold

environment are

darker…

…than those that grow

up in a warmer

environment.

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.

Effect of genes

• Genes come in different versions - alleles

– brown vs. blue eyes

– brown vs. blonde hair

– Alleles = different forms of a gene

3

Homozygous dominant = AA

Homozygous recessive = aa

Heterozygous = Aa

Tt

Bb

WwYy

rr

RR

Aa

AB

Ss

bb EeBB

aaXY

Genes affect how you look…

X

BBbb

Bb Bb Bb Bb

Where did the blue eyes go??

X

Bbbb

Bb Bb bb bb

Why did the blue eyes stay??

X

BbBb

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

• People who have one recessive allele and one dominant allele are called CARRIERS (they carry the recessive allele, but do not express the trait)

• Carriers can pass on allele to offspring

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

gene

allele

4

Traits are inherited as separate units• 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

1 from Mom

1 from Dad

homologous chromosomes

Making gametes

BB = brown eyes

bb = blues eyes

Bb = 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 eyes

bb = blues eyes

Bb = brown eyes

2 of the same alleles

Homozygous

2 different

Heterozygous

BB

B

B

bb

b

b

Bb

B

b

homozygous dominant

homozygous recessive

Punnett squaresBb (carrier) x Bb (carrier)

male / sperm

fem

ale

/ e

gg

s

X

BB

Bb bb

BbB

b

B b

Punnett square practice.

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

eye

color

(brown)

eye

color

(brown)

eye

color

(blue)

eye

color

(brown)

vs.

BB

B

B

Bb

B

b

How were these

brown eyes made?

5

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

PX

purple white

all purple

Punnett squares

Pp x Pp

P pmale / sperm

P

p

fem

ale

/ e

gg

s

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

Using Punnett Squares

Bb x Bbmale / sperm

fem

ale

/ e

gg

s

X

BB

Bb bb

BbB

b

B b

A Punnett Square is a diagram used to identify possible combinations resulting from a mating.

This married

couple is

considering

having their first

baby.

The man is

heterozygous for

a disease. The

woman is also

heterozygous for

the disease.

The couple comes to you for counseling. They want

you to know the chances they will have a healthy baby.

You know that the disease they carry is a recessive

trait and that both parents are heterozygous.

RR Rr rrWhich of the above genotypes will you need to use?

Man x Woman

Rr RrRrR r

RR

r

r

RR rR

Rr rr?

6

Man x Woman

Rr RrR r

R

r

RR rR

Rr rr

Genotype %RR =Rr =rr =

25%50%25%

Phenotype %Healthy =Carrier =Diseased =

25%50%25%

The chance that the

couple will have a baby

that has the disease is

25%.Let’s Practice!

Not-so-bad Traits determined by Simple Inheritance

• Tongue rolling (dominant form)

• Widow’s peak (dominant form)

• Hitchhiker’s thumb (dominant form)

• Freckles (dominant form)

• Taste PTC (dominant form)

• Cleft chin (dominant form)

• Dimples (dominant form)

No major consequences for these inherited conditions!

Genetics Lab

• Work with a lab partner at a station

• Check out each other’s traits

• Write answers on your own paper

• PTC and Control papers go in trash, not in sink (this will get you detention)

• Complete the lab on your OWN paper

Recessive Genetic Disorders

• Must inherit two faulty genes (one from mom, one from dad)

• Parents who do not express the trait, but pass it on are called CARRIERS (HETEROZYGOTES)

• Traits can be deadly

Recessive Genetic Disorders

• Cystic fibrosis

– Any of 1000 different mutations of one gene found on chromosome 7

– Buildup of chlorine produces thick mucus around organs and in lungs

– Weakened immune system

– Life expectancy: 35 years

– Found mostly in Caucasians

Recessive Genetic Disorders• Tay-Sachs

– Mutation of one gene on chromosome 15

– Lack of an enzyme

– Buildup of lipids on nervous tissue and in brain

– Symptoms vary, but include hearing loss and pain

– Nerve cells die

– Die young—most do not live past 4 years old

– European Jews

7

Recessive Genetic Disorders• Phenylketonuria

– Deletion of one gene on chromosome 12

– Protein buildup (phenylalanine)

– Kills nerve cells

– Tested for at birth

– Solution: diet restricting phenylalanine (found in diet foods)

– All demographics

Most Common Allele

Dominant or Recessive

• Because an allele is dominant does not mean…

– it is better, or

– it is more common

Polydactyly

dominant allele

Either One!

Dominant Genetic Disorders

• Only need one dominant allele for it to be expressed

• Most not lethal

– Polydactyly

• Chromosome 7

• Extra digits (fingers or toes)

• All demographics– 1/500 people have extra digits

Dominant Genetic Disorders

• Huntington’s Disease

– Additions to gene making it longer

– Chromosome 4

– Adult onset (30-50 years old)

Why is this bad?

– Brain dies

• Loss of muscle control, dementia, pain

HUNTINGTON’S DISEASE: dominantly inherited disease

Man x Woman

Rr rr

R r

r

r

Rr rr

Rr rr

A man has Huntington’s disease.

He does not know this because

Huntington’s doesn’t show

symptoms until later in life, after

children have been produced.His wife does not

have Huntington’s

and knows that it

has never been

diagnosed in her

family pedigree.

What are the

chances their first

born child will

have the disease?

Heterochromia

• Dominant autosomal

8

Dihybrid Crosses = mating of two individuals involving two traits.NOT A BIG DEAL. YOU HAVE OVER 30,000 GENES THAT CODE FOR PROTEINSEACH ONE HAS A GENOTYPE---THAT’S A LOT OF LETTERS

Heterozygous for both traits:

AaBb x AaBb

AB Ab aB ab

AB

Ab

aB

ab

A = tall

a = short

B = brown hair

b = blond hair

Tall/Brown

Tall/blond

Short/Brown

Short/blond

Testcrossunknown x aa

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R? rr

‘ello, my name is

Reginald.I am a

magnificent red canary.

I want to make ‘de beautiful red beebies like me.

But I do not know my genetics. How can I know if my beebies

will be red?

Hi there handsome! My name’s Gloria

and I’m a purely recessive white

gal.

Maybe I can help you with

a testcross!

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R? rr

‘Dees TESTCROSS…

What is it?

Hmm… I think this TESTCROSS is a good idea.

It’s when you cross an

unknown genotype with a

homozygous recessive.

If you get any homozygous recessive babies, you know you

carry the recessive gene!

TESTCROSS = a cross between any gene pair

and the homozygous recessive condition for

that trait.

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R? rr

‘Eeetworked!

Now I know that I carry

the rare white gene!

Congratulations handsome!

You’re a carrier!

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I’m the jailbird.

Rr rrThe twins

Rr and RrRr Rr

Later that year the babies were born…

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R?R

r

What would be the genotype needed to testcross a

heterozygous purple-flowering pea plant?

a. PP

b. Pp

c. ppAny Questions??

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Assignment:Punnett Square Practice Worksheet

9

2007-2008

Beyond Mendel’s Laws

of Inheritance

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 it’s usually not that simple!

Incomplete dominance

• Hybrids have “in-between” appearance

• BLENDING– RR = red flowers

– rr = white flowers

– Rr = pink flowers• make 50% less color

RR Rr rr

RRWW or R’R’

RW or RR’

Incomplete dominance

true-breedingred flowers

true-breeding white flowers

XP

100%

100% pink flowers

1st

generation(hybrids)

self-pollinate

25%white

2nd

generation

25%red 1:2:1

50%pink

Incomplete dominance

RW x RW

R Wmale / sperm

R

W

fem

ale

/ e

gg

s

25%

1:2:1

25%

50%

25%

1:2:1

%

genotype

%

phenotype

RR

RW

RW

WW

25%

50%

Incomplete Dominance Punnett Squares

1. Mate one white snapdragon with one red snapdragon.

2. Mate one pink snapdragon with one red snapdragon.

3. Mate one red snapdragon with another red snapdragon.

4. Mate two pink snapdragons.

5. Mate two white snapdragons.

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Codominance• Equal dominance

– Chickens

• A black-feathered chicken is crossed with a white-feathered chicken. (checkered chickens)

• All of the babies are white with black speckling.

• Both white and black show up equally.

x =

Codominance Punnett Squares

1. Mate a checkered rooster with a checkered hen.

2. Mate a checkered rooster with a white hen.

3. Mate a black rooster with a checkered hen.

4. Mate a black rooster with a white hen.

More Codominance…

x

Human Codominance Example• Sickle Cell Disease

– Alleles

• Normal red blood cell (HbA)

• Sickle red blood cell (HbS)– 1 in 12 African Americans carry allele

– If two HbS alleles are inherited (HbSHbS), a person will be fully affected by disease

• Aches, pains, fever, swelling

• Can be fatal

Sickle Cell Trait

• If only one HbS allele is inherited (HbAHbS), the person has sickle cell trait

– Produce both normal and sickle red blood cells

– Usually not affected by the symptoms

– IMMUNITY TO MALARIA

• Sickle cell allele originated in West Africa where malaria is common

• Malaria passed on by mosquitoes

• Plasmodium (malaria) cannot set up residence in sickle red blood cell

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Sickle Cell Punnett SquaresREMINDER: HbA (normal) HbS (sickle)

1) Heterozygous male and homozygous recessive female. Phenotypic ratio and genotypic ratio.

2) Homozygous recessive male and homozygous dominant female. Phenotypic ratio and genotypic ratio.

3) Homozygous dominant male and heterozygous female. Phenotypic ratio and genotypic ratio.

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 IA and IB are both dominant.

– So to get…

• Type A you must have IAIA or IAi

• Type B you must have IBIB or IBi

• Type AB you must have IAIB (CODOMINANCE)

• 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.”)

Blood Types

A

Type A

B

Type B

Type O

A

Type AB

Antigens(none)

Genetics of Blood type

pheno-

typegenotype

antigen

on RBC

antibodies

in blood

donation

status

A AA or A itype A antigens

on surface

of RBC

anti-B antibodiesReceive

A or O

B BB or B itype B antigens

on surface

of RBC

anti-A antibodiesReceive

B or O

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

Blood Typing Punnett Squares1. Heterozygous A dad with homozygous B

mom.

2. O dad with O mom.

3. Dad with AB and mom with homozygous A.

4. O dad with an AB mom.

5. Heterozygous B dad with O mom.

6. Heterozygous A dad with heterozygous A mom.

7. Heterozygous B dad with heterozygous A mom.

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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)

Acromegaly: André the Giant

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

Many genes : One trait

• Polygenic inheritance

– additive effects of many genes

– humans

• skin color

• height

• weight

• eye color

• intelligence

• behaviors

Human skin color

• AaBbCc x AaBbCc

– range of shades

– most children = intermediate skin color

– some can be very light & very dark

– BELL CURVE!!!

AlbinismJohnny & Edgar Winter

albino

Africans

melanin = universal brown color

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OCA1 albino Bianca Knowlton 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

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 only = XO (Turner’s Syndrome)

X Y

X X

Nondisjunction

Failure of chromosome pairs to separate properly during meiosis

Homologous chromosomes or sister chromatids

Autosomes or sex chromosomes

Can be diagnosed using a karyotype

Karyotype

Humans have 22 pairs of autosomes and 1 pair of sex chromosomes

14

Aneuploidy

Abnormal number of chromosomes within a cell

Can be more or less

MonosomyMissing one chromosome in a pair

Turner’s Syndrome• Females• Missing 2nd sex chromosome• XO genotype

• Short, broad chest, low set ears, sterile, amenorrhea (no period)

• Most spontaneous abort during pregnancy• 1/2500 births

Turner’s Syndrome Trisomy

Three copies of one chromosome in a set

Down’s syndrome, Patau syndrome, Klinefelter’s syndrome

Down’s Syndrome

● Trisomy 21● Low IQ, obese, slow

development, heart defects, poor eyesight

● Mother usually older● All demographics

equally affected● 1/700 children in US

Patau Syndrome

● Trisomy 13● Cleft lip, extra digits,

mental retardation, large triangular nose, central nervous system malformed

● Most children die within first year of life

● 1/5000 births

15

Klinefelter’s Syndrome

● All males● Extra X chromosome

(XXY)● Sterile, increased

breast tissue, increased risk of breast cancer

● Testosterone supplement

● 1/500 males

Another X-linked DisorderFragile X Syndrome● Caused by a nucleotide repeat on the X chromosome● Chromosome breaks very easily● Protruding ears, learning disabilities, poor speech, social

anxiety, short attention span, long face● Boys and men● All races

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 grayX Y

X X

XH Ymale / sperm

XH

Xhfe

male

/ 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

Sex-Linked Punnett Squares1. Father who has color-blindness with mother

who is a carrier.

2. Father who is not color-blind with mother who is color-blind.

3. Father who is not color-blind with mother who is a carrier.

4. Father who does not have hemophilia with a mother who is a carrier.

5. Father who has hemophilia with a mother is homozygous normal.

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Any Questions?

Pedigree = family record for one specific trait.

Sex-linked traits = genes for these traits are

carried on the sex chromosomes.

The gene for

Red-Green

colorblindness

is carried on

the X

chromosome.

Female must get two

(XX) X’s to have

colorblindness.

Male must get one

(XY) X to have

colorblindness.

Why are most sex-linked traits carried on the X chromosome?

Analyzing a Pedigree Interactivehttp://highered.mcgraw-hill.com/sites/0072485949/student_view0/chapter3/interactive_activity.html

Reading a Pedigree

= male carrier = female carrier

= male without trait

= male with trait

= female without trait

= female with trait

= two parents

= three children

I

II

Remember this?

Let’s Practice!