Chapter 10: Patterns of Inheritance

1
Chapter 10 Patterns of Inheritance

• By Miss Dreher

2

• Genotype the genetic makeup of an individual
  (PP or Pp or pp)
• Phenotype the physical appearance or observable
  trait, such as flower color. (purple or white)

Genotype Phenotype
bb Blue eyes (recessive)
BB Brown eyes (dominant)
Bb Brown eyes (dominant)
3
(No Transcript)
4
The Blending Hypothesis of Inheritance

• blending hypothesis explained how offspring
  inherit traits of both parents.
• Ex.
• red-flowers X yellow-flowersorange-flowers
• red yellow paint orange paint.
• orange-flowers X orange-flowers orange
  flowers

5
There are Exceptions to Blending

• red-flowered parents sometimes produced
  yellow-flowered offspring.
• So, the blending hypothesis was eventually
  discarded because it could not explain how traits
  that disappear in one generation can reappear in
  later ones.

6
Terms

• Trait variation in character (appearance)
• flower color, fur length, eye shape, eye color..
• Genetics the study of heredity
• Gregor Mendel- father of Genetics
• cross-fertilization one flowers pollen/sperm
  fertilizes the eggs in a flower of a different
  plant

7
The Experiments of Gregor Mendel

• The modern science of genetics was founded by an
  Austrian monk named Gregor Mendel.
• Mendel was in charge of the monastery garden,
  where he was able to do the work that changed
  biology forever.
• Mendel carried out his work with ordinary garden
  peas, partly because peas are small and easy to
  grow. A single pea plant can produce hundreds of
  offspring.

8
Mendels Laws stated simply

• 1.) There are at least 2 forms of each factor
  or gene.
• 2.) Factors for a particular trait occur in
  pairs. (TT Tall tt short Tt Tall)
• 3.) Dominant factors hide recessive ones.
• 4.) Factors separate/segregate randomly
  during meiosis? egg or sperm.

9
The Role of Fertilization

• Male part of each flower makes pollen, which
  contains sperm
• Female portion of each flower produces
  reproductive cells called eggs.

10
(No Transcript)
11
(No Transcript)
12

13
True-breeding homozygous

• A true-breeding plant produces offspring
  identical in appearance to itself generation
  after generation. (PP or pp)
• Ex. PP or
  pp
• Purple-flowered (PP) ?self fertilized ?
  offspring purple
• Mendel crossed 2 true-breeding plants both with
  2 distinct and contrasting traits purple(PP) X
  white (pp).

14
(No Transcript)
15
10-2 Mendel discovered that inheritance follows
rules of chance.

• P generation Tall x Short
• TT x
  tt
• F1 generation 100 Tt
• Tt hybrid or
  heterozygous
• F2 generation 1 TT 2 Tt 1 tt
• 1 homozygous Tall 2 Heterozygous
  1homozygous short

16
(No Transcript)
17
(No Transcript)
18
THINK ABOUT IT

• Nothing in life is certain.
• If a parent carries two different alleles for a
  certain gene, we cant be sure which of those
  alleles will be inherited by one of the parents
  offspring.
• However, even if we cant predict the exact
  future, we can do something almost as usefulwe
  can figure out the odds.

19
Probability and Punnett Squares

• Punnett Square type of diagram that shows all
  possible outcomes of a genetic cross
• You can use a Punnett square to predict
  probabilities of particular outcomes if you know
  the genetic makeup of both parents.

20
(No Transcript)
21
(No Transcript)
22
(No Transcript)
23
Practice Problem 1

• Predict the fur color of the offspring of a brown
  heterozygous hamsters and a white homozygous
  hamster. Brown is dominant. White is recessive.
• Use any letter you like.

24
Practice Problem 1
B b
Bb bb
Bb bb
b b
25
Practice Problem 2

• Predict the offspring of 2 white homozygous cows.
  Black is dominant over white.
• Use any letter you like.

26
Practice Problem 2
b b
bb bb
bb bb
b b
27
Practice Problem 3

• Predict the offspring of 2 Grey Heterozygous
  rats. Gray is dominant over white, which is
  recessive.
• Use any letter you like.

28
Practice Problem 3
G g
GG Gg
Gg gg
G g
29
Practice Problem 4

• Predict the pea shape of the offspring of one
  Heterozygous Round Pea plant and one homozygous
  wrinkled pea plant. Round is dominant over
  wrinkled.
• Use any letter you like.

30
Practice Problem 4
R r
Rr rr
Rr rr
r r
31
Practice Problem 5you dont have to write this
one down

• What are the chances of having a boy or a girl?
• How would you solve this one?

32
Practice Problem 5
X Y
XX XY
XX XY
X X
33
The Testcross

• Dominant Phenotype purple flowers.
• What is the Genotype? PP or Pp
  ?
• Testcross A testcross breeds an individual of
  unknown genotype (PP or Pp), but dominant
  phenotype, with a homozygous recessive
  individualwhite-flowered plant (pp).
• The appearance of the offspring resulting from
  the testcross will reveal the genotype of the
  mystery plant.

34
(No Transcript)
35
Mendel's Principle of Independent Assortment

• dihybrid crosscrossing organisms differing in
  two characters
• Round/Yellow seed (RRYY)?only produces RY
  gametes
• wrinkled/ green seed (rryy)? only produces ry
  gametes.
• Only outcome
• RY x ry (RrYy) Round/
  Yellow

36
(No Transcript)
37
RrYy x RrYy 9331

• F1 generation hybrid peas (RrYy)
• (Rr) x (Yy) use FOIL to determine
  possible gametes
• F- RY
• O- Ry
• I- rY
• L- ry
• RrYy x RrYy ? always produces a 9331
  ratio
• 9 Round/ Yellow 3 Round/ Green 3
  wrinkled/ Yellow 1 wrinkled/green

38
(No Transcript)
39
Figure out the Gametes

40
(No Transcript)
41
Solution
42
Mendels principle of independent assortment

• Principle of independent assortment during
  gamete formation a particular allele (R or r)
  will be paired with either Y or y.
• 4 gametes possible for genotype RrYy RY, Ry, rY
  , ry
• 2 gametes possible for genotype RRYy RY or Ry
  only
• The alleles for each gene are sorted into the
  gametes independently of one another.
• There are some exceptions

43
THINK ABOUT IT

• Mendels principles offer a set of rules with
  which to predict various patterns of inheritance.
• There are exceptions to every rule, and
  exceptions to the exceptions.
• What happens if one allele is not completely
  dominant over another? What if a gene has several
  alleles?

44
10.3 Intermediate Inheritance or Incomplete
dominance

• Four oclock flowersA red flower crossed with a
  white flower makes a PINK flower
• RED Flower x WHITE Flower ? PINK Flower
• What color is
• Dominant?

45
Incomplete Dominance

• A cross between two four oclock plants shows a
  common exception to Mendels principles.
• The F1 generation produced by a cross between
  red-flowered (RR) and white-flowered (WW) plants
  consists of pink-colored flowers (RW), as shown.

46
There are many variations of inheritance
patterns

• Intermediate inheritance or Incomplete dominance
  neither
• allele is dominant.
• Heterozygous individuals CBCW Blue chickens
• (C color B black W white)
• P CBCB X CWCW
• F1 CBCW
• F2 1 CBCB 2 CBCW 1 CWCW
• (typical121 ratio)

47
(No Transcript)
48
Multiple Alleles Codominance

• Human Blood types (phenotypes) A, B, AB, or O
• Both type A and B are dominant
• Type AB -example of codominance
• 3 possible alleles A, B, O (multiple
  alleles)
• 6 possible Genotypes
• Type A AA or AO Type AB(universal
  acceptor)
• Type B BB or BO Type OO
  (universal donor)
• A and B carbohydrates found on the surface of a
  RBC.
• Both A and B are dominant!!!!
• Type O -neither carbohydrate.
• Type AB -both carbohydrates.

49
(No Transcript)
50
Polygenic Inheritance

• Polygenic inheritance two or more genes affect a
  single character.
• Examples Height and skin color.
• Height and skin have a large range of phenotypes.
  
• The more genes that affect each character, the
  greater the range of phenotypes.
• Hypothetical Example
• 3 tall alleles A,B, C 3 short
  alleles X, Y, Z
• AABBCC very tall
• AABBCZ tall
• AXBYCZ average height
• XXYYZZ very short

51
Importance of Environment

• Phenotype depends on 2 things
• 1.) genes
• 2.) environment
• Example Siamese cat- fur color/ temperature
• Face, ears, paws, tail are cooler ? darker color
  than the rest of the body.
• Example in humans Nutrition influences height,
  exercise affects build, sun exposure darkens
  skin..
• Twins sepearaed _at_ birth

52
Himalayan RabbitsHimalayan rabbits are
native to the Himalayan Mountains, where a great
deal of snow falls annually. These rabbits have
white fur over most of their bodies, with black
fur on the ears,noses, feet and tails. This color
pattern results from temperature differences in
different parts of the rabbits bodies. Areas
where the body temperature is below 33C the fur
grows in black.To demonstrate this color change,
a scientist shaved a small area of fur on the
backs of adult Himalayan rabbits. Ice packs were
kept on the shaved areas long enough for the
rabbits fur to begin growing back. When the ice
packs were removed, the fur growing beneath them
was black.

53

• Suppose the same scientist wanted a Himalayan
  rabbit with white feet. Which procedure would
  most likely generate these results?
• A. place ice packs on the rabbits feet
• B. place the rabbit outside on a sunny day
• C. place the rabbit outside when it is snowing
• D. place the rabbit in a cage with a heated floor

54
10-5 Sex-linked traits have unique inheritance
patterns

• Sex chromosomes (X and Y) determine the sex of
  an individual.
• Egg cells contain X chromosome
• Sperm cells contain either X or Y chromosomes.
• Which determines the sex of a baby-sperm or egg?
• XX-female XY-male
• Sex-linked gene any gene that is located on the
  sex chromosome (23rd pair).
• Most sex-linked genes are found on the X
  chromosome.

55
(No Transcript)
56
(No Transcript)
57
Thomas Morgan Hunt- FRUIT FLY experiment?
Sex-linked traits

• White eyes?rare/ recessive Red eyes?
  dominant
• P- red eyed fly X white eyed fly
• F1- 100 red eyed flies
• F2- 31 red white eyed flies
• twist- none of the flies with white eyes was
  female.
• Eye color ?linked to the sex of the fly.
• Gene involved in eye color ?found on the sex
  chromosome
• males only have 1 X chromosome? they are more
  likely to inherit white eyes
• White XrY or XrXr (rare) Red XRXR, XRXr, XRY

58
(No Transcript)
59
Sex-Linked Disorders

• Red-green color blindness
• http//www.toledo-bend.com/colorblind/Ishihara.htm
  l
• Hemophilia- blood fails to clot normally.
• Recessive sex-linked traits are more common in
  men than in woman.
• Male get the sex-linked allele from his mother
  (XrY).
• A female has to receive this allele from both
  parents to have the disorder (XrXr)