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 anthers removed 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 work Mendel 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 2 nd generation 3:1 75% purple-flower peas 25% white-flower peas Parents 100% 1 st generation (hybrids) 100% purple-flower peas X true-breeding purple-flower peas true-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 homologous chromosomes allele producing functional protein mutant allele malfunctioning protein What did Mendel’s findings mean?
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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.
www.safeandsoundlostandfound.org
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
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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static.howstuffworks.comwww.vetnetwork.net
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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static.howstuffworks.comwww.vetnetwork.net
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
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