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Title: Heredity Notes


1
Heredity Notes
  • Chapter 10

2
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.

3
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

4
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)

6
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.
7
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

8
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

9
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

10
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.

11
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.
12
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

13
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.)

14
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
15
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
16
Think about it
  • ?How can two organisms with different genotypes
    have the same phenotype?

Genotype Phenotype
TT tall
Tt tall
tt short
17
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

18
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
19
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
20
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
21
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



13
¼ purple
25 purple
22
½ purple
50 purple
31
¾ purple
75 purple
22
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?

23
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?

24
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?

25
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.

26
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?

27
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?

28
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?

29
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)

30
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

31
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

32
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

33
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

34
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

35
Genotype(s) Phenotype
Type A
BB, BO
AB
Type O
AA
, AO
Type B
Type AB
OO
36
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?

37
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?

38
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
39
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

40
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.

41
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
42
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
43
Genotype(s) Phenotype

XXC
XCXC, XCY
XX
, XY
Normal Vision
Carrier
Colorblind
44
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.
45
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
46
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.

47
Pedigrees
  • A pedigree is visual tool for following a trait
    through generations of a family it is similar to
    a family tree.

48
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.)

51
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.

52
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.

54
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.)
55
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.
56
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.
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