Transcript Genetics

blackwellpublishing.com
Lesson 17:
Patterns of
Inheritance
Roots:
Di = 2
mono = 1
Homo = same
Hetero = different
Hemo = blood
www.purplemoon.com/Stickers/peas-earth.jpg
www.microscopy-uk.org.uk/mag/imgjul06/Image14.jpg
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
Mendel’s work
Pollen transferred from white
flower to stigma of purple flower
• Bred pea plants
– cross-pollinate
true breeding parents
– raised seed & then
observed traits
– allowed offspring
to self-pollinate
& observed next
generation
anthers
removed
all purple flowers result
self-pollinate
?
Each trait is
represented by a
specific allele on
a specific
chromosome.
Allele = genes
that determine a
specific trait.
http://www.bio.miami.edu/~cmallery/150/mendel/7traits.jpg
Mendel collected data for 7 pea traits
Parents
1st
true-breeding
true-breeding
purple-flower peas X white-flower peas
100%
purple-flower peas
generation
(hybrids)
100%
self-pollinate
2nd
generation
75%
purple-flower peas
25%
white-flower peas
3:1
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
allele producing
functional protein
mutant allele
malfunctioning
protein
– dominant allele
• functional protein
– affects characteristic
• masks other alleles
– recessive allele
• no noticeable effect
• allele makes a
non-functioning protein
homologous
chromosomes
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
X
P
Explain Mendel’s results using
…dominant & recessive
…phenotype & genotype
purple
white
F1
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?
palaeos.com
This separation is called the
Law of Segregation.
Effect of genes
• Genes come in different versions
– brown vs. blue eyes
– brown vs. blonde hair
– Alleles = different forms of a gene
Homozygous dominant = AA
Homozygous recessive = aa
Heterozygous = Aa
rr
Ww
bb
Tt
aa
Ss
XY
Aa
Yy
BB
RR
Ee
AB
Bb
Genes affect how you look…
X
bb
Bb
BB
Bb
Bb
Where did the blue eyes go??
Bb
X
bb
Bb
Bb
Bb
bb
Why did the blue eyes stay??
bb
X
Bb
BB or Bb BB or Bb BB or Bb
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?
• Paired chromosomes have same kind of
genes
– but may be different alleles
eye
color
(blue?)
hair
color
eye
color
(brown?)
hair
color
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
homologous chromosomes
1 from Dad
Making gametes
BB = brown eyes
bb = blues eyes
Bb = brown eyes
B
BB
B
b
Dominant = can mask others
bb
b
 brown is dominant over blue
 blue is recessive to brown
Recessive = can be hidden
by others
Remember meiosis!
B
Bb
b
How do we say it?
2 of the same alleles
Homozygous
B
BB
B
BB = brown eyes
bb = blues eyes
homozygous dominant
homozygous recessive
2 different
Heterozygous
Bb = brown eyes
b
bb
b
B
Bb
b
Punnett squares
Bb x Bb
male / sperm
female / eggs
X
B
b
BB
Bb
Bb
bb
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
http://designora.com/wp-content/uploads/2009/11/32-brown-eyes.jpg
Genetics vs.
appearance
How were these brown eyes made?
eye
color
(brown)
eye
color
(brown)
eye
color
(brown)
eye
color
(blue)
vs.
B
BB
B
Bb
B
b
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
X
P
purple
white
F1
all purple
Pp
Punnett squares
Pp x Pp
1st
Aaaaah,
phenotype & genotype
can have different
ratios
generation
(hybrids)
%
genotype
male / sperm
female / eggs
P
p
PP
25%
75%
Pp
P
PP
%
phenotype
50%
Pp
Pp
p
Pp
pp
pp
25% 25%
1:2:1
3:1
http://crittergeek.com/wp-content/uploads/2006/11/calico.jpg
http://pixdaus.com/pics/12072579159eXGQHR.jpg
Beyond Mendel’s Laws
of Inheritance
p://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
mac122.icu.ac.jp
• 1 completely dominant (A)
• 1 recessive (a)
• But its usually not that simple!
Incomplete dominance
• Hybrids have “in-between” appearance
– RR = red flowers
– rr = white flowers
– Rr = pink flowers
• make 50% less color
www.margaretaflowers.com
RR
RR
WW
RW
http://www.mnstate.edu/
www.99andbarry.com
Rr
rr
Incomplete dominance
P
X
true-breeding
red flowers
true-breeding
white flowers
100% pink flowers
1st
100%
generation
(hybrids)
self-pollinate
25%
red
2nd
generation
50%
pink
25%
white
1:2:1
Incomplete dominance
RW x RW
male / sperm
female / eggs
R
R
W
W
%
genotype
RR
RW
%
phenotype
25% 25%
50% 50%
RW
WW
25% 25%
1:2:1
1:2:1
Codominance
• Equal dominance
– Chickens
• A black-feathered chicken is crossed with a whitefeathered 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.com
www.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
BLOOD
Blood cells
have
antigens
and
antibodies.
Antibodies are
what the cell
doesn’t like
(which is
anything different
from the “type.”)
Antigens
are tiny
receptors
on the
outside of
the blood
cell that
matches
the “type.”
Blood Types
A
B
Type A
Type B
A
Type AB
Antigens
(none)
Type O
Genetics of Blood type
phenogenotype
type
A
B
AB
O
antigen
on RBC
antibodies
in blood
donation
status
A A or A i
type A antigens
on surface
of RBC
anti-B antibodies
__
BB or B i
type B antigens
on surface
of RBC
anti-A antibodies
__
AB
both type A &
type B antigens
on surface
of RBC
no antibodies
universal
recipient
ii
no antigens
on surface
of RBC
anti-A & anti-B
antibodies
universal
donor
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)
www.lifeinthefastlane.ca
dymaxionweb.com
/mentalfloss.cachefly.net
Acromegaly: André the Giant
lat34.com
Inheritance pattern of Achondroplasia
Aa
x aa
Aa
a
a
A
Aa
Aa
A
a
aa
aa
a
x Aa
library.thinkquest.org
50% dwarf:50% normal or 1:1
A

a
AA
Aa
Aa
aa
67% dwarf:33% normal or 2:1
Many genes : One trait
• Polygenic inheritance
– additive effects of many genes
– humans
•
•
•
•
•
•
skin color
height
weight
eye color
intelligence
behaviors
www.scientificamerican.com
Human skin color
• AaBbCc x AaBbCc
– range of shades
– most children =
intermediate
skin color
– some can be
very light & very
dark
Albinism
Johnny & Edgar Winter
melanin = universal brown color
theglenblog.blogspot.com
cnb.uam.es
www.heartlandhunters.com
Albinism is the absence of
pigment.
albino
Africans
xenophilius.files.wordpress.com
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)
eebb
eeB–
E–bb
E–B–
Environment effect on genes
www.saskschools.ca
• Phenotype is controlled by
both environment & genes
Coat color in arctic
fox influenced by
heat sensitive alleles
/www.grahamrollason.co.uk
/images.pictureshunt.com
Color of Hydrangea
flowers is influenced
by soil pH
s3.amazonaws.com
wxyc.org
Human skin color
is influenced by
both genetics &
environmental
conditions
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
X
X
Y
– X & Y chromosome = male: XY
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
X
X
X
Y
• loss of muscle control
– red-green color blindness
• see green & red as shades of grey
HY
XHH
x
sex-linked recessive
H Xh
XHh
2 normal parents,
but mother is carrier
XH
male / sperm
XH Y
XH
Y
XH
XH XH
XH Y
Xh
XH Xh
XhY
XH
XH Xh
Xh
female / eggs
Y
library.thinkquest.org
Most Common Allele
Dominant Either
or One! Recessive
• Because an allele is dominant
does not mean…
– it is better, or
– it is more common
Polydactyly
dominant allele
accessexcellence.org
biocrawler.com
thelastoutpost.com
Polydactyly
individuals are born with
extra fingers or toes
the allele for >5 fingers/toes
is DOMINANT & the allele for
5 digits is recessive
stanford.wellsphere.com
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)
absurdintellectual.com
Hound Dog Taylor
http://www.last.fm/music/Hound%2BDog%2BTaylor%2B%2526%2Bthe%2BHouse%2BRockers
blogs.sun.com
mevio.com
www.mark-cole.co.uk
/aagallery.aadl.org