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Chapter 10:. Patterns of Inheritance. Thinking Time!!!!!!!!!. Why is it, in some cases, that two brown-eyed parents have all brown-eyed children, and in other cases two brown-eyed parents have some brown-eyed children and some blue-eyed children?

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chapter 10

Chapter 10:

Patterns of Inheritance

thinking time
Thinking Time!!!!!!!!!
  • Why is it, in some cases, that two brown-eyed parents have all brown-eyed children, and in other cases two brown-eyed parents have some brown-eyed children and some blue-eyed children?
  • What do you think would be the result of a cross between a red flower and a white flower?
slide4
1. The Blending Hypothesis:
  • Predicts that offspring appearances will be blends of the phenotypes of their parents.

2. The Particulate Hypothesis (Mendel):

  • One copy of each factor is inherited from each parent.
  • The factors remain intact and do not physically blend together.

+

red

white

all pink

+

+

red

white

red

white

genetic vocabulary
Genetic Vocabulary:
  • Trait:Variation of a particular character.
    • Ex: eye color is a character,
  • Hybrids:The offspring of 2 different true-breeding species.
  • Monohybrid cross:a pairing in which the parents differ in only one (mono) character.
    • Ex: Flower color

traits

while

+

mule

slide6
P generation:Parent plants

F1 generation:The hybrid offspring

F2 generation:When F1 plants self-fertilize or fertilize each other, their offspring makes up the F2 generation.

terms need to know
Terms need to know:
  • Allele: The different forms of genes.
    • Organisms have two alleles for each trait, one from each parent.
  • Dominant: appear to hide other traits.
    • capital letters
  • Recessive: can be hidden in one generation and then appear in the next.
    • lower-caser letters
  • Phenotype - the way an organisms’ genes express themselves (physical type, description)
    • either short, tall, purple, white, & etc
  • Genotype - the gene type of an organism (genes, letters)
    • TT, Tt, tt

ABCDEFGH

abcdefgh

homozygous vs heterozygous
Homozygous vs. Heterozygous

In pea plants,

  • Homozygous - 2 alleles are the same.
    • homozygous dominant
      • 2 dominant genes : PP
    • homozygous recessive
      • 2 recessive genes : pp
  • Heterozygous – 2 alleles are different.
    • 1 dominant gene and 1 recessive gene: Pp.

is dominant over

gregor mendel
Gregor Mendel
  • Often called the "Father of Genetics”
  • Performed many experiments with plants, mostly garden peas.
  • His 1st step: identify true-breeding plant.
  • 2nd step: He crossed true-breeding plants that had two distinct traits.

?

mendel s first experiment
Mendel’s First Experiment:

¾of plants are purple

¼ of plants are white

mendel s results
Mendel’s Results:
  • He examined the inheritance patterns of 7 different pea-plant characters.
  • For each character, one of the two parent traits disappeared in the F1, but reappeared in ¼ of the F2 generation.
the testcross
The Testcross:
  • It is not possible to predict the genotype of an organism with a dominant phenotype.
  • It could be homozygous dominant PP or heterozygous Pp.
  • A test cross can determine the identity of the unknown allele.
writing genotypes from phenotypes
Writing Genotypes from phenotypes:

For Height:

tall (T) is dominant and short (t) is recessive.

  • 1. homozygous dominant for height
    • Answer: TT
  • 2. heterozygous for height
    • Answer: Tt
  • 3. homozygous tall
    • Answer: TT
  • 4. recessive for height
    • Answer: tt
  • 5. heterozygous tall
    • Answer: Tt
writing phenotypes from genotypes
Writing phenotypes from genotypes:

For Height:

tall (T) is dominant and short (t) is recessive.

For Flower color:

red (R) is dominant and white (r) is recessive.

  • 6. TT
    • Answer: homozygous dominant, tall
  • 7. tt
    • Answer: homozygous recessive, short
  • 8. Tt
    • Answer: heterozygous, tall
  • 9. Rr
    • Answer: heterozygous, red
  • 10. rr
    • Answer: homozygous recessive, white
activity time

Activity Time:

The Coin Activity

slide17
When tossing one penny, what is the probability of getting one head?
  • When tossing one penny, what is the probability of getting one tail?
slide20

Punnett Squares

  • It shows the possible outcomes for the Phenotypes of the individual.  
slide21

Predicting Genotypes & Phenotypes

  • In pea plants,
  • Cross: homozygous tall X homozygous short

is dominant over

Tall

Short

slide22

Step 1:

  • Write down the genotypes of each parent
    • ABCDEFGH  dominant traits
    • abcdefgh  recessive traits
  • Homozygous tall:
  • Homozygous short:

TT

tt

slide23

Step 2:

  • Draw a Punnett square
  • Write the gametes of one parent across the top and the other parent along the side

T

T

t

t

slide24

Step 3:

  • Fill in each box of the Punnett square
    • Capital letter  goes 1st

T

T

t

T

t

T

t

t

T

t

T

t

slide25

Step 4:

  • List the possible genotypes and phenotypes of the offspring.
  • Possible genotypes:
  • Possible phenotypes:

Tt

Tall

slide26

Results

Parent 1:

T

T

Parent 2:

t

T

t

T

t

t

T

t

T

t

slide27

Results

  • Each of the offspring has a ____ /4 or _____% chance of showing ______ genotype.
  • Since T (tall) is dominant over t (short). Therefore, each of the offspring has a ____/4 or _____% chance of being __________.

4

100

Tt

4

100

tall

practice time
Practice Time:

Key: brown eyes (B) is dominant, blue eyes (b) is recessive

Homozygous dominant X Heterozygous

  • Genotypes: BB & Bb

is dominant over

Questions:

  • Phenotype of offspring?
  • Genotype of offspring?
  • Phenotypic ratio:
  • Genotypic ratio:

B B

all brown

Bb

BB

BB

BB & Bb

4 brown: 0 blue

Bb

Bb

2 BB: 2Bb

slide29

Your Turn

In humans,

is dominant over

Questions:

  • Phenotype of offspring?
  • Genotype of offspring?
  • Phenotypic ratio:
  • Genotypic ratio:

brown & blue

BB, Bb & bb

1 BB: 2 Bb: 1 bb

3 Brown: 1 blue

heterozygous brown X heterozygous brown

dihybrid cross
Dihybrid Cross
  • In one dihybrid cross experiment, Mendel studied the inheritance of seed color and seed shape.

is dominant over

Yellow (Y)

green (y)

is dominant over

Round (R)

wrinkled (r)

dihybrid cross1
Dihybrid cross:
  • Mendel crossed true-breeding plants that had yellow, round seeds (YYRR) with true-breeding plants that has green, wrinkled seeds (yyrr).
  • The first parent could only produce RY gametes. The other could only produce ry gametes.
  • The union of these gametes results in RrYy.
dihybrid cross2
Dihybrid Cross:

Four classes of gametes (YR, Yr, yR, and yr) are produced in equal amounts.

  • Which results in 16 equally probable ways in which the alleles can combine in the F2 generation.
  • Phenotypic ratio - 9:3:3:1
intermediate inheritance
Intermediate Inheritance:
  • In Mendel’s pea crosses, the F1 offspring always looked like the dominant homozygous parent.
    • Because the recessive phenotype required two recessive alleles.
    • But, for some characters of organisms, neither allele is dominant  intermediate inheritance.

YY  yellow

Yy  yellow

yy  green

Dominant

intermediate inheritance1
Intermediate Inheritance:
  • Heterozygous F1 generation hybrids do not show the phenotype of the dominant allele or the recessive allele but somewhere in between.
    • For example, in a particular breed of chickens called Andalusians, black and white offspring produce blue F1 hybrid offspring.
    • Because neither the black nor white is dominant, capital or lower case letters are not used.
    • Instead a C for color is paired with a superscript B for black or W for white.

CBCW

CWCW

CB CB

black

white

blue

c b c b
CB CB

X

CWCW

The predicted phenotypes in F2 are 1 black: 2 blue: 1 white

CBCW

CBCW

CBCW

CWCW

CB CB

multiple alleles
Multiple Alleles:
  • Codominant: both alleles are expressed
  • The gene for human blood type expresses four phenotypes:
    • A, B, AB or O.
  • The alleles IA and IB are codominant and the i allele is recessive to both.
slide37
The letters refer to two carbohydrates, designated A and B, which are found on the surface of red blood cells.
slide38
FYI:
  • Type O-negative blood does not have any antigens. It is called the "universal donor" type because it is compatible with any blood type.
  • Type AB-positive blood is called the "universal recipient" type because a person who has it can receive blood of any type.
polygenic inheritance
Polygenic inheritance
  • When a single phenotype results from the expression of two or more genes.
  • For instance, phenotypes like high blood pressure are not the result of a single "blood pressure" gene with many alleles.
  • The phenotype is an interaction between a person's weight,

cholesterol level, kidney function, smoking, and probably lots of

others too.

the importance of environment
The Importance of Environment
  • An individual’s phenotype depends on environment as well as genes.
  • In human, nutrition influences height, exercise affects build, and exposure to sunlight darkens skin.
  • The product of a genotype is generally not a single defined phenotype, but a range of possibilities influenced by the environment.
chromosome theory of inheritance
Chromosome Theory of Inheritance:
  • It states that:
    • Genes are located on chromosomes.
    • Homologous Chromosomes separate during meiosis so that alleles are segregated.
    • Chromosomes under go segregation and independent assortment during meiosis.
mendel s law of genetics
Mendel’s Law of Genetics:

1. Alleles are different forms of the same gene that segregate during gamete formation (Law of Segregation)

2. Alleles of different genes segregate independently (Law of independent assortment)

sex linked genes
Sex-linked Genes
  • Located on a sex chromosome
  • In humans, most sex-linked genes are found on the X chromosome, which is much larger than the Y chromosome.
  • Discovered by Thomas Hunt Morgan.
slide44

P:

Morgan mated a white-eyed male fly with a red-eyed female fly.

F1:

All the F1 offspring hadred eyes.

slide45
X

F1:

Then, he bred the F1 offspring together.

XRXrfemale

XRYmale

He got the classical 3:1 phenotypic ratio.However, none of the flies with white eyes were female.He concluded that the gene involved is only on the X chromosome.

F2: