Mendel’s Laws of Heredity Section 10.1 p. 253 - 262 Chapter 10 Mendel and Meiosis.
Gregor Mendel - nosborne.com · Beyond Mendel’s Laws of Inheritance Extending Mendelian genetics...
Transcript of Gregor Mendel - nosborne.com · Beyond Mendel’s Laws of Inheritance Extending Mendelian genetics...
1
Let there be
PEAS ON EARTH!
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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?
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• 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
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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
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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?
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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
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?
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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
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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
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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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aaawebmaster.com
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
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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
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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
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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!