1. End result 1n or 2n?

2. Daughter cells Distinct or identical?

3. Chiasmata?Yes or no?

Meiosis Mitosis

4. # of divisions

5. PurposeGrowth or germ cells?

QUIZ Name___________________

1. End result 1n or 2n?

1n 2n

2. Daughter cells Distinct or identical?

identicaldistinct

3. Chiasmata?Yes or no?

Meiosis Mitosis

NoYes

4. # of divisions 2 1

5. PurposeGrowth or germ cells?

GrowthGerm cells

QUIZ Name___________________

Observable Patterns of Inheritance

Chapter 10

•Attached or detached earlobes depends on a single _____

•A gene has two molecular forms (______)

•Inherit one form each _______•Dominant allele specifies detached earlobes

Earlobe Variation

• You inherited one allele for this gene from each parent

• _______ allele specifies detached earlobes

• __________ allele specifies attached lobes

Early Ideas About Heredity

• _______________ theory-– Genetic material mixes much like

yellow and blue paint makes ____

Problem:

– Would expect variation to ________

– Yet variation in traits _______

How are traits transmitted?

Gregor Mendel• Strong background in plant breeding and

mathematics- __________• Using pea plants, found indirect but

observable evidence of how parents transmit ____to offspring

The Garden Pea Plant

•Self-pollinating

•______________ (different alleles not normally introduced)

•Can be experimentally _-___________

What is a gene?• Units of information about specific ____

• Passed from _________ to offspring

• Each has a specific location (_____) on a chromosome

What is an allele?•Different ________________ of a gene

•Arise by _____________

•Dominant allele ___________ a recessive allele that is paired with it

Vocabulary• _____________ - An organism with two _______

alleles for a character (e.g. AA or aa)

• ___________- An organism with two ____________ alleles for a character (e.g. Aa)

• ________ - A description of an organism’s ______

• ________ - A description of its ______________

•Example- For flower color in peas, both PP and Pp plants have the same phenotype (purple) but different genotypes (homozygous and heterozygous).

_________________

P1 x P2_________________

F1_________________

Mendel cross-pollinated peas

F1 x F1

F2

The F2 generation revealed two principles of heredity:1._____________________

2._______________________

Mendel’s Monohybrid Cross Results

787 tall 277 dwarf

651 long stem

207 at tip

705 purple 224 white

152 yellow428 green

299 wrinkled882 inflated

6,022 yellow 2,001 green

5,474 round 1,850 wrinkled

F2 plants showed dominant-to-recessive ratio that averaged 3:1

Mendel’s Law of Segregation

1. An individual inherits a unit of information (_______) about a trait from each parent

2. During gamete formation, the alleles _________ from each other

• A ________________ predicts the results of a genetic cross between individuals of known genotype.

PP x pp

All Pp

Purple

Purple

White

F1

Pp x Pp

F2Predicts 75% purple: 25% white

Or 3:1 ratio

Call the dominant allele “P”Call the recessive allele “p”

1. Law of segregation

p

P p

P

Dihybrid Cross • Experimental cross between individuals

that are homozygous for different versions of two traits

AABB aabbx

AaBb

AB AB ab ab

TRUE-BREEDING PARENTS:

GAMETES:

F1 HYBRID OFFSPRING:

purple flowers, tall

white flowers,dwarf

All purple-flowered, tall

Phenotypic Ratios in F2

Four Phenotypes:– Tall, purple-flowered (9/16)

– Tall, white-flowered (3/16)

– Dwarf, purple-flowered (3/16)

– Dwarf, white-flowered (1/16)

AaBb X AaBb

9:3:3:1 is magic ratio in dihybrid cross

Explanation of Mendel’s Dihybrid Results

If the two traits are coded for by genes on separate chromosomes, sixteen gamete combinations are possible

aB

AB

AB

abAb

Ab

aB

ab

1/4

1/4

1/4

1/4

1/4 1/4 1/4 1/4

AaBb aabbAabb aaBb

AABB AABb AaBB AaBb

AABb AAbb AaBb Aabb

AaBb aaBB aaBbAaBB

1/161/161/161/16

1/161/161/161/16

1/161/161/161/16

1/16 1/16 1/16 1/16

Metaphase I

Metaphase II:

Gametes:

1/4 AB 1/4 ab 1/4 Ab 1/4 aB

A A A A

A A A A

AAAA

B B

B B

BB

B B

BBBB

a a a a

aa aa

aaaa

bb b b

bb b b

b b b b

OR

Law of independent assortment

•two “units” for the first trait were to be assorted into gametes ____________ of the two “units” for the other trait

Impact of Mendel’s Work

• Mendel presented his results in ____

• Paper received _______________

• Mendel discontinued his experiments in 1871

• Paper rediscovered in ______ and finally appreciated

Dominance Relations • _____________dominance

• ____________ dominance– Heterozygote phenotype is somewhere

___________that of two homozyotes

• _________________– Non-identical alleles specify two

______________ that are both expressed in ________________

1. ___________________ -one of every 2,500 whites of European descent.– One in 25 whites is a _______________– The normal allele codes for a membrane protein

that transports Cl- between cells and the environment.

– If these channels are defective or absent, there are abnormally high extracellular levels of chloride that causes the mucus coats of certain cells to become thicker and stickier than normal.

– This mucus build-up in the pancreas, lungs, digestive tract, and elsewhere favors bacterial infections.

– Without treatment, affected children die before five, but with treatment can live past their late 20’s.

Examples of recessive disorders

2. Tay-Sachs disease– Caused by a dysfunctional enzyme that fails to

break down specific brain lipids.

– Symptoms- seizures, blindness, and degeneration of motor and mental performance a few months after birth.

– Child dies after a few years.– Among Ashkenazic Jews (those from central

Europe) this disease occurs in one of 3,600 births, about 100 times greater than the incidence among non-Jews or Mediterranean (Sephardic) Jews.

Examples of recessive disorders

Flower Color in Snapdragons:

Pink-flowered plant X Pink-flowered plant

White-, pink-, and red-flowered plants in a 1:2:1 ratio

(heterozygote) (heterozygote)

Pink flowers have one normal and one ____________allele

__________________ Dominance

Genetics of ABO Blood Types: ______Alleles• Gene that controls ABO type codes for

enzyme that dictates structure of a glycolipid on blood cells

• Two alleles (IA and IB) are ________ when paired

• Third allele (i) is _________ to others

Codominance

• Type A - IAIA or Iai

• Type B - IBIB or IBi

• Type AB - IAIB

• Type O - ii

ABO and Transfusions• Recipient’s immune system will attack

blood cells that have an unfamiliar

glycolipid on surface

• Type __ is universal donor because it

has neither type A nor type B glycolipid

Pleitropy • Alleles at a ______ locus may have

effects on _______________ traits

• Classic example is the effects of the mutant allele at the _______________ that gives rise to sickle-cell anemia

•HbS homozygotes produce only the ___________hemoglobin; suffer from sickle-cell anemia

At low ___ levels, cells with only HbS hemoglobin “sickle” and stick together- clog __________-

•Eye disease, infection, heart disease

Fig. 10.12, p. 161

Albinism•________ production is completely blocked

•Homozygous recessive at the gene locus that codes for _____

Human Variation

• Some human traits occur as a few ________types– Attached or detached earlobes – Many genetic disorders

• Other traits show continuous variation– ________– Weight– Eye color

Describing Continuous Variation

Range of values for the trait

Nu

mb

er o

f in

div

idu

als

wit

hso

me

valu

e o

f th

e t

rait

(line of bell-shaped curve indicates continuous variation in population)

Range of values for the trait

Nu

mb

er o

f in

div

idu

als

wit

hso

me

valu

e o

f th

e t

rait

Temperature Effects on Phenotype

• Himalayan rabbits are Homozygous for an allele that specifies a heat-sensitive version of an enzyme in melanin-producing pathway

• Melanin is produced in cooler areas of body