Transcript Heredity Notes

Heredity Notes
Chapter 10
Heredity & Genetics
Heredity: passing of traits from parent to
offspring
Genetics: STUDY of heredity
– Gregor Mendel: “Father of Genetics”
Austrian monk who was first to trace a trait
passing through generations.
He was first to use probability in plant science.
Mendel’s work was forgotten for many years, but
when more scientists came across his work in
their research and came to the same
conclusions, he became known as the father of
genetics.
Traits
Characteristics of an organism
– Hair color, flower color, seed shape, etc.
– Controlled by genes (sections of chromosomes)
Each chromosome will have a gene for each trait. (A few
exceptions.) Because chromosomes are in pairs, genes
for traits are in pairs. The type of genes an organism has
for a trait is called the genotype.
To make the physical appearance, genes work together.
The physical appearance that results is called the
phenotype.
See the traits studied by Mendel on p. 368-371
Alleles
Different forms a gene can have for a trait.
For example, the trait plant height has two
alleles: tall and short.
Look on pg. 371: What do you think the
alleles are for the trait seed shape?
round and wrinkled
Letters are used to represent the alleles
Purebred: same alleles for a trait
Hybrid: different alleles from each parent
(hybrid= mix or combination)
Complete Dominance
Complete dominance: one form of a gene can
completely “cover up” the other form
– Form that is seen = dominant
– Form not seen = recessive
– Example: In pea plants, purple flower color is completely
dominant over white, so when both alleles are present, the
flower color will be purple.
Representing alleles in complete dominance:
– ONE LETTER is used to represent both forms of a trait
Dominant form determines letter
Dominant form uses the capital letter
Seed Shape, R=Round (round is dominant)
Plant Height, T=Tall (tall is dominant)
Recessive form gets the same letter, but lowercase
Seed Shape, r=wrinkled (round is dominant)
Plant Height, t=short (tall is dominant)
Now you try…
Trait
Alleles
Representation
Shape of
Seeds
round
R
r
wrinkled
green
Color of
Pods
yellow
Position of
Flowers
Side of stem
tips of stem
G
g
S
s
 All traits have complete dominance.
 Use Table 1 on page 371 to help you.
Now try this…
Flower colors: purple, white
(Purple has complete dominance over white.)
Flower
Identify color
the trait.
Purple
Identifyand
the white
alleles.
Purple=P
andallele
white=p
How is each
represented?
Combining Alleles
Because chromosomes are in pairs, organisms will
have pairs of alleles.
When there are two different alleles, there are three
ways those alleles can combine.
– Two dominant alleles
– Two recessive alleles
– One dominant and one recessive
For example, the two alleles for flower color are
purple (P) and white (p). The possible
combinations are:
– PP, pp, and Pp (always write the capital letter first)
 What are the possible ways that the alleles for
seed shape can combine? (R=round, r=wrinkled)
– RR, rr, Rr
Let’s try this…
Seed colors: yellow, green
(Yellow has complete dominance over green.)
Identify
the trait.
Seed
color
Identifyand
the green
alleles.
Yellow
How is each
represented?
Yellow=Y,
green=y
What
YY, yy,are
Yythe possible ways
alleles can combine?
Incomplete Dominance
One allele doesn’t completely cover another, so
both forms of the gene show at the same time.
– Example: In snapdragons, red and white flower color
share incomplete dominance, so when both alleles are
present, the flower color will be pink.
Representing alleles in incomplete dominance
– Each allele uses its own letter, and they are all capital
Remember, when there are two different
alleles, there are three ways those alleles can
combine.
Now you try…
Trait
Alleles
Flower
color
red
R
white
W
brown
B
W
Fur color
white
Representation
 All traits have incomplete dominance.
Now you try…
Coat colors: black, white
(Black and white share incomplete dominance.)
Identify
the trait.
Coat
color
Identify
thewhite
alleles.
Black
and
How is each
Black=B
and represented?
white=W
What
are BW
the possible ways
BB, WW,
alleles can combine?
Genotype & Phenotype
Genotype: genetic make-up an organism has
for a particular trait
– THINK: type of gene=genotype
– Represented with a pair of letters because
genes for traits are in pairs. (TT, Tt, tt, etc.)
Phenotype: physical appearance resulting
from the forms of the genes an organism has
– THINK: physical appearance=phenotype (tall,
short, etc.)
Traits with Complete Dominance
Trait
Plant Height
Alleles: tall, short
Flower Color
Alleles: purple,
white
Seed Shape
Alleles: round,
wrinkled
Genotype
Phenotype
TT
Tt
tt
PP
Pp
pp
tall
tall
short
rr
RR
Rr
purple
purple
white
wrinkled
round
round
Traits with Incomplete Dominance
Trait
Flower Color
Alleles: red, white
Fur Color
Alleles: black,
white
Genotype
Phenotype
RR
RW
WW
red
pink
BB
BW
WW
white
black
gray
white
Think about it…
How can two organisms
with different genotypes
have the same phenotype?
Genotype
Phenotype
TT
Tt
tt
tall
tall
short
Homozygous & Heterozygous
Genotypes are represented with letters.
Those letters can be matched or
unmatched.
Homozygous: a genotype with alleles
that are the same.
–TT, tt, PP, pp, RR, rr
Heterozygous: a genotype with alleles
that are are different.
–Tt, Pp, Rr, RW
Now you try…
How is each genotype represented?
TT 1. Homozygous tall
Tt 2. Heterozygous tall
tt 3. Short
PP 4. Homozygous purple
Rr 5. Heterozygous round
rr 6. Wrinkled
Punnett Squares
Used to show all possible combinations of
Performand
the cross.
alleles
predict probability of possible
Analyze
results.
Look
You
can
at
the
alsoparent
bring
allele
each two genotypes.
outcomes
of
crossing
4top
out of 4
– Howdown
many
areof
tall?
letter
above
and left
from
the
each
T
T
tt
–
Short?
0 out
of 4 left.
blank
and
over
in
the
from
square.
the
The
alleles from one
– Homozygous? 0 out of 4
Write
both
alleles,
putting
parent
are
written
onof 4
– Heterozygous? 4 out
the
first.
t
the capital
top of letters
the square.
This represents
Alleles
the
other
Mendel’sfor
first
experiment.
parent are written on
the side of the square.
t
T
T
Punnett Squares
Let’s try another one. This time let’s
Perform the cross.
show
Mendel’s
second
(Capital
letters should
be experiment.
written before lower case.)
Tt
Tt
Analyze
results.
The alleles
from one
out of 4
– How many
tall? 3
parent
are are
written
on
– Short? 1 out of 4
the top of the square. T
– Homozygous? 2 out of 4
Alleles
for the other
– Heterozygous?
2 out of 4
parent are written on t
This led to many more
the
side of the
square.
experiments
by Mendel.
T
t
Punnett Squares
Remember, a Punnett square shows probability.
Results can be expressed as ratios, fractions, or
percents. (We will use fractions & percents.)
RATIO
FRACTION
PERCENT
(purple to white)
1:3
¼ purple
25% purple
2:2
½ purple
50% purple
3:1
¾ purple
75% purple
Punnett Squares
Try crossing a heterozygous
tall plant with a short plant.
Identify the genotypes for
each parent.
Tt
Tt
tt
Tt
tt
tt
– ½up
or 50%
Set
and perform the cross.
– ½ or 50%
Analyze
the results:
–
–
–
–
(Alleles: tall, short)
½
or 50%
What
are the chances of tall?
½
or 50%
Short?
– Homozygous?
– Heterozygous?
Punnett Squares
Now cross homozygous round
with heterozygous round.
Identify the genotypes for
each parent.
RR
(Alleles: round, wrinkled)
RR
RR
Rr
Rr
Rr
Set
up and perform the cross.
– 100%
– 0%
Analyze
the results:
–½
or 50%
What
are the chances of round?
–½
or 50%
Wrinkled?
– Homozygous?
– Heterozygous?
Punnett Squares
Cross green seeds with
heterozygous yellow.
Identify the genotypes for
each parent.
yy
(Alleles: yellow, green)
Yy
Yy
yy
yy
Yy
Set
– ½up
or and
50% perform the cross.
– ½ or 50%
Analyze
the results:
–½
or 50%
What
are the chances of Yellow?
–½
or 50%
Green?
– Homozygous?
– Heterozygous?
Incomplete Dominance
No allele completely dominates over
another, so both alleles represented with
CAPITAL LETTERS. (Letters are usually
written in alphabetical order.)
Flower color:
– 2 alleles: Red (R), White (W)
– Since both forms can show simultaneously, the
heterozygous genotype (RW) would have a pink
phenotype.
Incomplete Dominance
Let’s cross a red snapdragon
with a white snapdragon.
Identify the genotypes for
each parent.
RR
RW
RW
RW
RW
WW
Set
up and perform the cross.
– 0%
– 0%
Analyze
the results:
–
–
–
(Alleles: red, white)
100%
What are the chances of red?
White?
Pink?
Incomplete Dominance
Now let’s cross a pink
snapdragon with another pink.
Identify the genotypes for
each parent.
RW
RR
RW
RW
WW
RW
Set
and perform the cross.
– ¼up
or 25%
– ¼ or 25%
Analyze
the results:
–
–
–
(Alleles: red, white)
½
or 50%
What
are the chances of red?
White?
Pink?
Incomplete Dominance
Finally, we’ll cross a black
mouse with grey mouse.
Identify the genotypes for
each parent.
BB
BB
BB
BW
BW
BW
Set
and perform the cross.
– ½up
or 50%
– 0%
Analyze
the results:
–
–
–
(Alleles: black, white)
½
or 50%
What
are the chances of black?
White?
Grey?
Codominance
When both alleles for a gene are
expressed equally, codominance occurs.
– Example: a white rooster and black hen cross
to form offspring that have feathers that are
black and white (look spotted)
Codominance
We represent codominance by using the
capital letter F for the trait feathers and a
superscript B or W to tell you the color.
– FB – feather black
– FW – feather white
Codominance
Now let’s cross a white
rooster with a black hen.
Identify the genotypes for
each parent.
W
W
F
F
B
F
(Alleles: feather black,
feathers white)
FBFW FBFW
FB
0/4and
or 0%
Set– up
perform the cross.
– 0/4 orthe
0%results:
Analyze
– 4/4are
or 100%
– What
the chances of black
feathers?
– White feathers?
– Black & White feathers
FBFW FBFW
Codominance
Now let’s cross a black and
white rooster with a black hen.
Identify the genotypes for
each parent.
FB
FW FB FB
2/4and
or 50%
Set– up
perform the cross.
– 0/4 orthe
0%results:
Analyze
– 2/4are
or 50%
– What
the chances of black
feathers?
– White feathers?
– Black & White feathers
(Alleles: feather black &
white, feathers black)
FBFB FBFW
FBFB FBFW
Codominance
Now let’s cross a black and white
rooster with a black and white hen.
Identify the genotypes for each
parent.
FB
FW FB FW
1/4and
or 25%
Set– up
perform the cross.
– 1/4 orthe
25%
Analyze
results:
– 2/4are
or 50%
– What
the chances of black
feathers?
– White feathers?
– Black & White feathers
(Alleles: feather black &
white, feathers black)
FBFB FBFW
FBFW FWFW
Multiple Alleles
Traits can be controlled by more than two alleles.
This results in more possible phenotypes.
There are multiple alleles for human blood type.
3 alleles: A, B, O
Complete the list of possible combinations.
– AA, AB, AO, BB, BO, OO
O is recessive to A and B
A and B can show simultaneously (at same time)
This results in 4 possible phenotypes:
A, B, AB, and O blood types
Genotype(s)
Phenotype
AA, AO
Type A
BB, BO
Type B
AB
Type AB
OO
Type O
Predicting Blood Type
Try crossing a type AB with
type O.
Identify the genotypes for
each parent.
AB
(Alleles: A, B, O)
AO
BO
AO
BO
OO
Set
and perform the cross.
– ½up
or 50%
– ½ or 50%
Analyze
the results:
– 0%
What are the chances of type A?
– 0%
Type B?
– Type AB?
– Type O?
Predicting Blood Type
Now cross genotype AO with
genotype BO.
Identify the PHENOTYPES for
each parent.
AO
AB
BO
AO
OO
BO
Set
and perform the cross.
– ¼up
or 25%
– ¼ or 25%
Analyze
the results:
–¼
or 25%
What
are the chances of type A?
–¼
or 25%
Type
B?
– Type AB?
– Type O?
Working Backwards
You can use a Punnett square to help answer
questions by working backwards. Try this:
If a parent has type A blood, could he have
offspring with type O blood? Explain.
In the square, you will need
the genotype for type O blood.
This means that offspring
O
A
B
?
would have to get one O
allele from each parent.
Now think of the possible
O
alleles to complete the
second parent’s genotype.
O
A
B
?
O
OO
Polygenic Inheritance
Traits can be produced by the
combination of many genes—they
act together to produce a trait.
–Produces wide variety of phenotypes
Human hair color, eye color, skin color,
height
Milk production in cows
Wheat grain color
Mutations &
Genetic Disorders
A mutation is any permanent change in the DNA of
a cell’s gene or chromosome. This can result in a
change in the way a trait is expressed.
– Can be caused by outside factors like X-rays, sunlight, and
some chemicals.
– Can also result from an error in DNA replication (copying).
Not all mutations are harmful; they can even be
helpful. Mutations allow variety within species.
Mutations can be passed to offspring only if
mutation is copied to a sperm cell or egg cell.
Just like any other trait, genetic disorders can be
passed down. Some disorders, like cystic fibrosis,
are caused by recessive genes.
Sex Determination
One pair of
chromosomes
determine sex (XX in
females, XY in males)
Females always
contribute an X egg
Males can contribute an
X-containing sperm or a
Y-containing sperm
X
X
X
Y
Sex-Linked Disorders
Caused by alleles inherited on sex
chromosomes
Color-blindness: a recessive allele
on the X chromosome
XC
– Females that have the gene on one chromosome
are not colorblind. The normal allele is dominant
over the colorblindness allele. They are “carriers.”
– Females have two X chromosomes, so they are
colorblind only when trait is on both chromosomes.
– Males have only one X, so they are colorblind when
the trait is on that chromosome
Genotype(s)
Phenotype
XX , XY
Normal Vision
XXC
Carrier
XCXC, XCY
Colorblind
Predicting Colorblindness
Predict the result of crossing a
normal female with a colorblind
male.
Identify the genotypes.
XX
XC Y
Set up and perform the cross.
0%
Analyze the results:
XXC XXC
XY
– What are the chances of a child who
They will be carriers.
is colorblind?
– What will be special about daughters
these parents might have?
XY
Predicting Colorblindness
Now try crossing a carrier
female with a male who has
normal vision.
Identify the genotypes.
X XC
XX
XXC
XY
XCY
XY
Set up and perform the cross.
25%
Analyze the results:
– What are the chances of a child who
0%
is colorblind?
– What are the chances of a daughter
who is colorblind?
50%
– What are the chances of a child who
Genetics in Humans
Some situations do not provide the opportunity to
perform controlled crosses, such as when studying
human genetics. In these situations, we have to
analyze existing populations.
Scientists have devised an approach called pedigree
analysis to study the inheritance of genes in humans.
Pedigree analysis is also useful when studying a
population when data from several generations is
limited or when studying species with a long
generation time.
Pedigrees
A pedigree is visual tool for following a trait
through generations of a family; it is similar to a
family tree.
Common Pedigree Symbols
 Use the pedigree to help you complete the following.
Why are some shapes filled in and others not?
Why are some of the females carriers while others are
not?
Why is a pedigree useful?
Creating a Pedigree
 Using the symbols, create a pedigree that
represents your family, including your
parents and your siblings. (If you’re up for
a challenge, try including your parents’
siblings and your grandparents.)
Selective Breeding
Breeders of animals and plants are looking to produce
organisms that will possess desirable characteristics.
- high crop yields
- high growth rate
- resistance to disease
- many other characteristics
To accomplish this, the organisms with desirable
characteristics are chosen for breeding.
Over time, the desirable characteristics become more
common in the population.
This intentional breeding for certain traits (or
combinations of traits) over others is called selective
breeding or artificial selection.
How does selective
breeding work?
Examples of Selective Breeding
Wheat has been selectively bred for
higher yields, shorter stems to reduce
wind damage and greater resistance
to diseases.
Turkeys with the desired
characteristics (large breast muscles)
are bred, passing along their genes
to their offspring.
Bananas have been selectively bred
to be sweet and seedless.
Examples of Selective Breeding
Selecting for different traits
over hundreds of years of
breeding has caused
different dog breeds to have
distinctive characteristics
although all the different
breeds belong to the same
species.
Top row- Alaskan Malamute,
Basset Hound, Llasa Apsa;
Middle row- Beagle puppy, Shar
Pei, Chow
Bottom row- Pekinese, Tibetan
Terrier, Pug.)
Examples of Selective Breeding
English shorthorn cattle,
which provided for good
beef, but lacked heat
resistance, were crossed
with Brahman cattle from
India, which were highly
resistant to heat and
humidity. This produced the
Santa Gertrudis breed of
cattle, which has both of
these characteristics.
English Shorthorn:
Good beef, no heat
resistance
Brahman:
Poor beef, good
heat resistance.
Santa Gartrudis:
Good beef, good
heat resistance.
Advances in Genetics
Genetic Engineering: Biological or chemical methods
can be used to change an organism’s genes. This
only works because there is one language of life:
DNA from one organism will work in others.
– Recombinant DNA methods insert useful segments of DNA
into the DNA of another organism.
First used insert DNA into bacteria that caused them to make insulin.
Genetically modified (GM) plants: Flavr Savr Tomato, antifreeze
potatoes
There is significant controversy surrounding the use of genetic
modification. The possible benefits are limitless, but no one can
predict possible consequences.
Gene therapy can be used to treat diseases, including
hereditary diseases. A normal allele is placed into a
virus and the virus acts to replace defective hereditary
material.