Heredity Notes

1
Heredity Notes

• Chapter 10

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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.
• Mendels 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.

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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

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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?
• Letters are used to represent the alleles
• Purebred same alleles for a trait
• Hybrid different alleles from each parent
  (hybrid mix or combination)

round and wrinkled
5
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, RRound (round is dominant)
• Plant Height, TTall (tall is dominant)
• Recessive form gets the same letter, but
  lowercase
• Seed Shape, rwrinkled (round is dominant)
• Plant Height, tshort (tall is dominant)

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Now you try
Trait Alleles Representation
Shape of Seeds
Shape of Seeds
Color of Pods
Color of Pods
Position of Flowers
Position of Flowers
round
R
r
wrinkled
green
G
g
yellow
Side of stem
S
tips of stem
s
? All traits have complete dominance. ? Use Table
1 on page 371 to help you.
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Now try this

• Flower colors purple, white
• (Purple has complete dominance over white.)
• Identify the trait.
• Identify the alleles.
• How is each allele represented?

• Flower color
• Purple and white
• PurpleP and whitep

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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? (Rround, rwrinkled)
• RR, rr, Rr

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Lets try this

• Seed colors yellow, green
• (Yellow has complete dominance over green.)
• Identify the trait.
• Identify the alleles.
• How is each represented?
• What are the possible ways alleles can
  combine?

• Seed color
• Yellow and green
• YellowY, greeny
• YY, yy, Yy

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Incomplete Dominance

• One allele doesnt 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.

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Now you try
Trait Alleles Representation
Flower color red
Flower color white
Fur color brown
Fur color white
R
W
B
W
? All traits have incomplete dominance.
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Now you try

• Coat colors black, white
• (Black and white share incomplete dominance.)
• Identify the trait.
• Identify the alleles.
• How is each represented?
• What are the possible ways alleles can
  combine?

• Coat color
• Black and white
• BlackB and whiteW
• BB, WW, BW

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Genotype Phenotype

• Genotype genetic make-up an organism has for a
  particular trait
• THINK type of genegenotype
• 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 appearancephenotype (tall,
  short, etc.)

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Traits with Complete Dominance
Trait Genotype Phenotype
Plant Height Alleles tall, short TT
Plant Height Alleles tall, short Tt
Plant Height Alleles tall, short tt
Flower Color Alleles purple, white purple
Flower Color Alleles purple, white Pp
Flower Color Alleles purple, white white
Seed Shape Alleles round, wrinkled rr
Seed Shape Alleles round, wrinkled round
Seed Shape Alleles round, wrinkled
tall
tall
short
PP
purple
pp
wrinkled
RR
round
Rr
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Traits with Incomplete Dominance
Trait Genotype Phenotype
Flower Color Alleles red, white RR
Flower Color Alleles red, white RW
Flower Color Alleles red, white white
Fur Color Alleles black, white black
Fur Color Alleles black, white gray
Fur Color Alleles black, white WW
red
pink
WW
BB
BW
white
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Think about it

• ?How can two organisms with different genotypes
  have the same phenotype?

Genotype Phenotype
TT tall
Tt tall
tt short
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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

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Now you try

• How is each genotype represented?

1. Homozygous tall
2. Heterozygous tall
3. Short
4. Homozygous purple
5. Heterozygous round
6. Wrinkled

TT Tt tt PP Rr rr
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Punnett Squares
Used to show all possible combinations of alleles
and predict probability of possible outcomes of
crossing two genotypes.

• Perform the cross.
• Analyze results.
• How many are tall?
• Short?
• Homozygous?
• Heterozygous?
• This represents Mendels first experiment.

• Look at the parent allele above and left of each
  blank in the square.
• Write both alleles, putting the capital letters
  first.

• You can also bring each letter down from the top
  and over from the left.

4 out of 4
T
T
t
t
T
T
T
T
T
T
0 out of 4

• The alleles from one parent are written on the
  top of the square.
• Alleles for the other parent are written on the
  side of the square.

0 out of 4
4 out of 4
t
t
t
t
t
t
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Punnett Squares

• Lets try another one. This time lets show
  Mendels second experiment.

• Perform the cross. (Capital letters should be
  written before lower case.)
• Analyze results.
• How many are tall?
• Short?
• Homozygous?
• Heterozygous?
• This led to many more experiments by Mendel.

t
T
T
t
T
t
T
t
t
T

• The alleles from one parent are written on the
  top of the square.
• Alleles for the other parent are written on the
  side of the square.

3 out of 4
T
T
T
1 out of 4
2 out of 4
2 out of 4
t
t
t
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Punnett Squares

• Remember, a Punnett square shows probability.
• Results can be expressed as ratios, fractions, or
  percents. (We will use fractions percents.)

RATIO (purple to white) FRACTION PERCENT



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¼ purple
25 purple
22
½ purple
50 purple
31
¾ purple
75 purple
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Punnett Squares

• Try crossing a heterozygous tall plant with a
  short plant.
• Identify the genotypes for each parent.

(Alleles tall, short)
Tt
tt

• ½ or 50
• ½ or 50
• ½ or 50
• ½ or 50

t
T
t
t
Tt
tt

• Set up and perform the cross.
• Analyze the results
• What are the chances of tall?
• Short?
• Homozygous?
• Heterozygous?

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Punnett Squares

• Now cross homozygous round with heterozygous
  round.
• Identify the genotypes for each parent.

(Alleles round, wrinkled)
RR
RR

• 100
• 0
• ½ or 50
• ½ or 50

R
R
R
r
Rr
Rr

• Set up and perform the cross.
• Analyze the results
• What are the chances of round?
• Wrinkled?
• Homozygous?
• Heterozygous?

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Punnett Squares

• Cross green seeds with heterozygous yellow.
• Identify the genotypes for each parent.

(Alleles yellow, green)
Yy
Yy

• ½ or 50
• ½ or 50
• ½ or 50
• ½ or 50

y
y
Y
y
yy
yy

• Set up and perform the cross.
• Analyze the results
• What are the chances of Yellow?
• Green?
• Homozygous?
• Heterozygous?

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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.

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Incomplete Dominance

• Lets cross a red snapdragon with a white
  snapdragon.
• Identify the genotypes for each parent.

(Alleles red, white)
RW
RW

• 0
• 0
• 100

R
R
W
W
RW
RW

• Set up and perform the cross.
• Analyze the results
• What are the chances of red?
• White?
• Pink?

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Incomplete Dominance

• Now lets cross a pink snapdragon with another
  pink.
• Identify the genotypes for each parent.

(Alleles red, white)
RR
RW

• ¼ or 25
• ¼ or 25
• ½ or 50

W
R
R
W
RW
WW

• Set up and perform the cross.
• Analyze the results
• What are the chances of red?
• White?
• Pink?

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Incomplete Dominance

• Finally, well cross a black mouse with grey
  mouse.
• Identify the genotypes for each parent.

(Alleles black, white)
BB
BB

• ½ or 50
• 0
• ½ or 50

B
B
B
W
BW
BW

• Set up and perform the cross.
• Analyze the results
• What are the chances of black?
• White?
• Grey?

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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)

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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

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Codominance

• Now lets cross a white rooster with a black hen.
• Identify the genotypes for each parent.

(Alleles feather black, feathers white)
FBFW
FBFW

• 0/4 or 0
• 0/4 or 0
• 4/4 or 100

FW
FW
FB
FB
FBFW
FBFW

• Set up and perform the cross.
• Analyze the results
• What are the chances of black feathers?
• White feathers?
• Black White feathers

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Codominance

• Now lets cross a black and white rooster with a
  black hen.
• Identify the genotypes for each parent.

(Alleles feather black white, feathers black)
FBFB
FBFW

• 2/4 or 50
• 0/4 or 0
• 2/4 or 50

FW
FB
FB
FB
FBFB
FBFW

• Set up and perform the cross.
• Analyze the results
• What are the chances of black feathers?
• White feathers?
• Black White feathers

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Codominance

• Now lets cross a black and white rooster with a
  black and white hen.
• Identify the genotypes for each parent.

(Alleles feather black white, feathers black)
FBFB
FBFW

• 1/4 or 25
• 1/4 or 25
• 2/4 or 50

FW
FB
FW
FB
FBFW
FWFW

• Set up and perform the cross.
• Analyze the results
• What are the chances of black feathers?
• White feathers?
• Black White feathers

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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

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Genotype(s) Phenotype
Type A
BB, BO
AB
Type O
AA
, AO
Type B
Type AB
OO
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Predicting Blood Type

• Try crossing a type AB with type O.
• Identify the genotypes for each parent.

(Alleles A, B, O)
AO
BO

• ½ or 50
• ½ or 50
• 0
• 0

B
A
O
O
AO
BO

• Set up and perform the cross.
• Analyze the results
• What are the chances of type A?
• Type B?
• Type AB?
• Type O?

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Predicting Blood Type

• Now cross genotype AO with genotype BO.
• Identify the PHENOTYPES for each parent.

AB
BO

• ¼ or 25
• ¼ or 25
• ¼ or 25
• ¼ or 25

O
A
B
O
AO
OO

• Set up and perform the cross.
• Analyze the results
• What are the chances of type A?
• Type B?
• Type AB?
• Type O?

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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.

O
A
O
B
?

• In the square, you will need the genotype for
  type O blood.
• This means that offspring would have to get one O
  allele from each parent.
• Now think of the possible alleles to complete the
  second parents genotype.

A
O
B
?

OO
O
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Polygenic Inheritance

• Traits can be produced by the combination of many
  genesthey 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

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Mutations Genetic Disorders

• A mutation is any permanent change in the DNA of
  a cells 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.

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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
Y
X
Y
Y
X
X
X
X
X
X
X
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Sex-Linked Disorders

• Caused by alleles inherited on sex chromosomes
• Color-blindness a recessive allele
  on the X chromosome
• 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

XC
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Genotype(s) Phenotype

XXC
XCXC, XCY
XX
, XY
Normal Vision
Carrier
Colorblind
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Predicting Colorblindness

• Predict the result of crossing a normal female
  with a colorblind male.
• Identify the genotypes.

XXC
XXC
X
X
XC
Y
XY
XY

• Set up and perform the cross.
• Analyze the results
• What are the chances of a child who is
  colorblind?
• What will be special about daughters these
  parents might have?

0
They will be carriers.
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Predicting Colorblindness

• Now try crossing a carrier female with a male who
  has normal vision.
• Identify the genotypes.

XX
XXC
XC
X
X
Y
XY
XCY

• Set up and perform the cross.
• Analyze the results
• What are the chances of a child who is
  colorblind?
• What are the chances of a daughter who is
  colorblind?
• What are the chances of a child who does not have
  the gene at all?

25
0
50
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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.

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Pedigrees

• A pedigree is visual tool for following a trait
  through generations of a family it is similar to
  a family tree.

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Common Pedigree Symbols
49

• ? 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?

50
Creating a Pedigree

• ? Using the symbols, create a pedigree that
  represents your family, including your parents
  and your siblings. (If youre up for a
  challenge, try including your parents siblings
  and your grandparents.)

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Selective Breeding

• Breeders of animals and plants are looking to
  produce organisms that will possess desirable
  characteristics.
• - high crop yields - resistance to disease
• - high growth rate - 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.

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How does selective breeding work?
53
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.

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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.)
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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.
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Advances in Genetics

• Genetic Engineering Biological or chemical
  methods can be used to change an organisms
  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.