chapter 5 chromosomes and inheritance: opening...

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© 2017 Pearson Education, Inc.

Chapter 5 Chromosomes and Inheritance:

• 5.1 Cell division

• 5.2 What is DNA?

• 5.3 Cell cycle

• 5.4 Mitosis

• 5.5 Cytokinesis

• 5.6 Gametes

• 5.7 Meiosis

• 5.8 Mitosis vs. meiosis

• 5.9 Genetic variation

• 5.10 Meiosis mistakes

• 5.11 Mendelian genetics

• 5.12 Punnett square

• 5.13 Independent assortment

• 5.14 Pedigrees

• 5.15 Complex inheritance

• 5.16 Linked genes

• 5.17 Sex-linked genes

• 5.18 Clones


5.1 Opening Questions: Cell birth and death

• Is your body making any new cells right

now? What kind?

• Are certain types of cells replaced

faster? What might be examples?

• Are certain types of cells never replaced

or slowly replaced? What might be

examples?

Between 50 and 70 billion of your

cells die each day?

Chapter Table of Contents


5.1 All living organisms consist of cells.

• A fundamental concept in

biology is the cell theory,

which states:

1. All life is cellular.

2. All cells arise from

preexisting cells.

Some living organisms

have just one cell, but

others have trillions.

Chapter Table of Contents © 2017 Pearson Education, Inc.

5.1 Cell division is the formation of new

cells from preexisting cells.

Cell division provides for:

1. Growth

2. Repair

3. Reproduction

Organisms can use cell

division to reproduce

sexually or asexually.



5.1 Sexual reproduction takes two parents.

• Two parents produce

genetically unique

offspring.

• Gametes (egg and

sperm cells) are

formed via cell

division from adult

cells in the gonads

(testes and ovaries).


5.1 Life cycle in sexual reproduction:


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5.1 Asexual reproduction only needs one

parent.

• One parent produces

genetically identical

offspring.

• There is no sperm or

egg involved.


5.1 Sexual vs. asexual reproduction

Complete the comparison table:

Sexual Asexual

Number of parents needed?

Gametes involved? (yes/no)

Fertilization? (yes/no)

Number of chromosome sets

Offspring genetically unique?

(yes/no)



5.1 Sexual vs. asexual reproduction

Sexual Asexual

Number of parents needed 2 1

Gametes? (yes/no) YES NO

Fertilization? (yes/no) YES NO

Number of chromosome sets 2 1

Offspring genetically unique?

(yes/no)YES NO


5.2 Opening Questions: What is DNA?

• What type of information is stored in DNA?

• How different is your DNA from the person

sitting next to you?



• What type of information is stored in DNA?

• How different is your DNA from the person

sitting next to you?

5.2 Opening Questions: What is DNA?


5.2 DNA and genes:

• All life on Earth uses DNA

as the genetic material.

• The nucleus of every

eukaryotic cell contains long

strands of DNA called

chromosomes.

• Each chromosome contains

genetic information in

genes.


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5.2 DNA and genes:

• A gene is a length of DNA

that codes for the proteins

that make up our bodies.

Genes are the unit

of inheritance.


450x11,000x550,000x

5.2 A closer look at the chromosome

• Inside the nucleus,

the chromosomal

DNA is wound

around proteins;

together they form

chromatin.

Most of the time

chromosomes are

unraveled as loose

chromatin.



5.2 Chromosome number: Every human

body cell has 46 chromosomes.

How many

chromosomes

did you inherit

from your

mother?


At cell division,

chromosomes

1. Become tightly

packed

2. Duplicate

Pairs of duplicated chromosomes

are called sister chromatids.

5.2 Chromosomes at cell division have

unique properties.



5.2 Chromosomes duplicate prior to

division.

• Sister chromatids

(duplicated

chromosome pair)

are joined at the

centromere.

Formation of sister

chromatids means the

cell is preparing to divide.


5.3 Opening Questions: What is the normal

cycle for a cell division?

• Name at least three examples of a time

when a cell (animal, plant, or fungi)

would need to go through cell division.


Did YOUR cells undergo any cell division

today? Explain.

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5.3 Cells have regular cycles of growth and

division.

• Healthy cells only start dividing if there is a

need for replication.

• Unhealthy cells may undergo unregulated

cell division.

• Cancer begins when a cell divides when it

should not.


Why is cancer so difficult to treat?


5.3 Cells have regular cycles of growth and

division.

• The cell cycle is an ordered sequence of

events in the “lifetime” of a cell.

• There are two broad phases:

1. Interphase

90% of cell’s lifetime

Normal cell functions

2. Mitotic phase

Active cell division



Healthy cells

only enter the

mitotic phase

if duplication

is needed.

5.3 The cell cycle:


During interphase, the cell

• Performs its normal functions

• Grows

• Prepares for division by duplicating its

chromosomes

5.3 Most of a cell’s lifetime is spent in

interphase.

What are some normal

functions of cells?



5.3 Active cell division is the mitotic phase.

During the mitotic phase, the cell

• Undergoes active division (mitosis)

• Splits into two offspring cells

(cytokinesis)

The result of the mitotic

phase is two genetically

identical offspring cells.


5.4 Opening Questions: Mitosis puzzle

A B C D

The cells below are all undergoing the

process of cell division.

Think about what is happening in the cell

during division, and try putting them in

logical order from start to finish. Explain

your choices.


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5.4 Mitosis is active cell division.

Mitosis occurs in major stages.

• These stages help us think about how the

chromosomes are organized during mitosis.

• However, cell division proceeds seamlessly

through all the stages.


5.4 Interphase:

1. Early interphase

– Cell is carrying

out its normal

activities.

2. Chromosomes

duplicate

– Cell is preparing to

divide; generates

sister chromatids.



5.4 Stages of mitosis:

3. Chromosomes

condense

– Nuclear membrane

dissolves. Cell lays

down mitotic spindle.

4. Chromosomes align

– Sister chromatids

line up and attach

to mitotic spindle.


5.4 Stages of mitosis:

5. Chromosomes

split

– Sister chromatids

are pulled apart as

mitotic spindle

retracts.

6. Nucleus reforms

– Two duplicated

nuclei are formed.



5.5 Cytokinesis is the final step in cell

division.

• Cytokinesis is the

division of the

cytoplasm and is the

final step in the cell

cycle.

• The process of

cytokinesis is different

for plant and animal

cells.


5.5 Cytokinesis in animal cells:

• The parent animal cell is pinched into two,

leaving two independent offspring cells.


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5.5 Cytokinesis in plant cells:

• Plant cells divide by forming a cell plate

along the center line of the cell.


5.5 Review Questions:

• What side effects are related to chemotherapy

treatment for cancer?

• With your understanding of mitosis, can

you explain some of the side effects of

chemotherapy?

Many chemotherapy drugs are used to treat

cancer by killing cells undergoing mitosis.



5.6 Opening Questions: How do you get one

from two?

• Most of the cells in your

body are diploid; they

have two copies of each

chromosome.

If your cells are diploid, how

could you reproduce without

doubling the chromosome

number in your offspring?


5.6 Gametes are the answer!

• To prevent doubling

chromosome number

in offspring, sexually

reproducing organisms

need to make cells with a

single set of chromosomes.

• Gametes, or sex cells,

are haploid: They contain

only one copy of each

chromosome.



5.6 Male and female gametes:

• Male gametes are called sperm.

• Female gametes are called eggs.

How many

chromosomes

are there in a

human sperm

cell?


DEVELOPMENT

Through repeated

rounds of cell division, the

original zygote cell is duplicated,

eventually forming an embryo,

then a baby, and finally an adult.

ZYGOTE

The zygote, or fertilized egg,

is the original cell that was

formed by the fusion of sperm

and egg. The zygote contains

one haploid set of chromo-

somes from the father and

one haploid set of chromo-

somes from the mother that

together make a unique

diploid set of chromosomes.

During fertilization, the

gametes (male sperm

and female egg) fuse.

Each contributes a

haploid number of

chromosomes to produce

a diploid zygote.

GAMETE FORMATION

In the adult gonads (testes in

males and ovaries in females),

a special kind of cell division

produces gametes. The male

gamete is the sperm and the

female gamete is the egg. As

the only haploid cells in your

body, gametes can be used

to form the next generation.

5.6 The human life cycle:

ADULTS

Every somatic cell in

your body is diploid,

with one set of

chromosomes derived

from your mother and

one from your father.

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5.6 One pair of chromosomes makes you

male or female.

• The 46 chromosomes in your body are

organized as 23 homologous pairs.

• Of these, 22 pairs are autosomes.

• One pair is your sex chromosomes.

– Females are XX.

– Males are XY.


5.6 Karyotypes are photographic inventories

of chromosomes.

• Chromosomes are

organized in

homologous

pairs.

Can you tell if this a

male or a female?


5.7 Opening Questions: Why do we need to

produce sperm and eggs (gametes)?

• Explain why all sexually reproducing

organisms need both haploid and diploid

cells.

Remember:

Haploid cells have only one copy of each chromosome.

Diploid cells have two copies of each chromosome.


5.7 Meiosis is the production of gametes.

• Gametes (sperm and egg) are formed by a special type of cell division, meiosis.

• Cells produced from meiosis are haploid.

• Like mitosis, meiosis occurs in stages.


5.7 Meiosis occurs in stages.

• Meiosis (like mitosis) starts with chromosome duplication before division.

• In meiosis, there are then two rounds of cell division.

• The result of meiosis is four haploid offspring cells, all with one-half the number of chromosomes.


5.7 Meiosis interphase:

Remember that

chromosomes

come in

homologous

(matched)

pairs.

• In meiosis interphase, chromosomes

duplicate.

• After interphase, cells that are producing

gametes undergo two rounds of division

called meiosis I and meiosis II.

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5.7 Meiosis I:

1. Homologous

chromosome

pairs line up.

2. Homologous

pairs separate.

3. Cytokinesis

Note that in meiosis I it is the homologous

pairs that line up and separate.


5.7 Stages of meiosis II:

4. Chromosomes

condense and

line up.

5. Chromosomes

separate.

6. Cytokinesis II

At the end of meiosis II

there are four haploid

offspring cells.



5.8 Opening Questions: Meiosis vs. mitosis

Meiosis Mitosis

Where does it occur?

When is it needed?

How many/type offspring cells?

(haploid/diploid)

How many rounds of cell

divisions?

Complete the comparison table below:


5.8 Mitosis and meiosis compared

Meiosis Mitosis

Where does it occur? Ovaries/

testes

All body

cells

When is it needed? Puberty Lifetime

How many/type offspring cells?

(haploid/diploid)

4 haploid 2 diploid

How many rounds of cell

divisions?2 1



5.8 Study aids:

• Come up with some study aids to help you

remember when the body needs to use

meiosis versus mitosis.


5.9 Opening Questions: How unique are

you?

• What is the probability that there is

another human on the planet that looks

like you and shares the same DNA

sequences?


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5.9 Opening Questions: How unique are

you?

• What is the probability that there is

another human on the planet that looks

like you and shares the exact same DNA

as you?

Unless you have an identical twin, you

are genetically different from any human

that has ever lived!


5.9 Sexual reproduction leads to variation.

Three major processes mean variation is the

norm for sexual reproduction:

1. Independent assortment

2. Random fertilization

3. Crossing over



5.9 Independent assortment of

chromosomes leads to variation.

• Chromosomes

line up by

homologous pairs

during meiosis I.

• Maternal and paternal

chromosomes are shuffled

randomly.

Independent assortment:

223 = 8 million possible

arrangements of chromosomes!

Chromosomes

are shuffled


5.9 Random fertilization by sperm and egg

leads to variation.

• The probability that

any one sperm will

fertilize any

particular egg is

extremely small.

Random fertilization:

8 million x 8 million =

64 trillion possible

arrangements of

chromosomes. Chromosomes

are shuffledChapter Table of Contents


5.9 Crossing over during meiosis leads to

variation.

• Chromosomes can

“swap” genetic material,

creating new, unique

combinations.

• Crossing over occurs

when homologous

chromosomes line up

during meiosis I.

Crossing over creates new hybrid chromosomes,

which increases gene variation.


5.10 Opening Questions: What if meiosis

goes wrong?

• Jason and Laura are pregnant with their

third child. Since they are both over 35,

they opt to have an amniocentesis test.

The doctor comes back to them with a

karyotype that shows 47 chromosomes.

Imagine you are Jason and Laura’s

genetic counselor. How would you

explain the results?


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5.10 Meiosis can have mishaps!

• Nondisjunction is when

chromosomes fail to

separate properly.

• Resulting gametes will

have too few or too many

chromosomes.

Zygotes with an abnormal chromosome number

will usually not develop or will have abnormalities.

Fertilization


5.10 Normal meiosis vs. nondisjunction



5.10 Examples of nondisjunction:

• Trisomy 21 is a

condition in which

a person receives

three copies of

chromosome 21.

• The resulting

condition is called

Down syndrome.



• Sex chromosome

nondisjunction can

also occur.

• Each combination

of extra or missing

sex chromosomes

produces its own

syndromes.




Turner syndrome is the sole

known case where having

only 45 chromosomes is not

fatal in humans.


5.11 Opening Questions: Did you inherit

your good looks?

• Why do children resemble their parents?

• Why do families resemble each other?

• Is there anything you can’t inherit from

your parents?


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5.11 Our understanding of genetics starts

with Mendel.

• Heredity is the transmission

of traits from one generation

to the next.

• Genetics is the study of

heredity.

• Gregor Mendel was the first

to deduce the basic

principles of inheritance.


5.11 Character and traits are inherited.

• Human eye color is a

character, or an inherited

feature that varies among

individuals.

• Each possible variation of

a character is a trait.



5.11 Alleles are the individual units of

inheritance.

• Traits derive from genes.

• Alternate forms of a particular gene are

called alleles.

Matched set of

chromosomes,

one derived

from the father

(blue) and one

derived from the

mother (red)


5.11 Genotype vs. phenotype

• An organism’s phenotype is its physical traits.

• An organism’s genotype is its underlying genetic makeup, the alleles it is carrying.



5.11 Dominant vs. recessive alleles

• An individual who is

heterozygous has two

different alleles.

• Only one allele will

usually determine an

organism’s appearance.

In pea plants, purple (P) is

the dominant trait for flower

color. White (p) is the

recessive trait.


5.12 Opening Questions: Can we predict the

inheritance patterns of genes?

• For some people the chemical PTC

(phenylthiocarbamide) tastes very bitter;

yet for others, it is tasteless. Scientists

report that the ability to taste PTC shows a

general pattern of dominant inheritance

(T and t).

What is the genotype of a non-taster?

Could a non-taster’s parents be tasters?


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5.12 A Punnett square can be used to

predict the results of a genetic cross.

• In a genetic cross, two parents

(P generation) are crossed to

produce offspring (F1 generation).

A Punnett square

can be used to

predict the offspring

that will result from a

genetic cross.


×


5.12 Punnett squares are predictions.

• Punnett squares are named after a British

geneticist named Reginald Punnett.

• A Punnett square allows you to predict the

genotype and phenotype of the offspring.

• The simplest Punnett

square follows one

character in a

monohybrid cross.



5.12 Punnett square: Monohybrid cross


5.12 Alleles separate during meiosis.

• The law of segregation states that the

two alleles for a character separate during

gamete formation.



5.12 We can use a test cross to determine

an individual’s genotype.

×

For the test cross above, predict offspring

ratios for each possible genotype.

Is the genotype

of this black LabBB or Bb? To find

out, mate it with

a chocolate Lab.Chocolate Labwith genotype bb


5.12 Test cross results if black dog is BB:


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5.12 Test cross results if black dog is Bb:


5.13 Opening Questions: Can we look at

more than one trait?

• In Labrador retrievers, breeders need to

keep track of traits for coat color (black is

dominant to chocolate) and hearing

(normal is dominant to deafness).

If you want all chocolate

coats, how would you

avoid breeding deaf

puppies?



5.13 Alleles separate independently during

gamete formation.

• The law of independent assortment

states that the inheritance of one character

has no effect on the inheritance of

another.


5.13 Traits for coat color and hearing are an

example of independent assortment.


Genotype: BbDd

Phenotype: black

coat, hearing


5.13 Independent assortment can be

observed during a dihybrid cross.

MALEPhenotype:

black coat

hearing

Genotype:

BbDd

×

What are the possible allele

combinations for the gametes?

• A dihybrid cross is one in which two

separate characters are studied.

FEMALEPhenotype:

black coat

hearing

Genotype:

BbDd


5.13 Dihybrid cross:


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5.14 Opening Questions: Can

understanding inheritance help us

understand disease?

• Katie and Dave are healthy adults, but

both have a sibling with cystic fibrosis, a

life-threatening autosomal recessive

genetic disorder. Genetic tests reveal they

are both heterozygous.

Imagine you are a genetic counselor and

explain to them their probability of having a

child with cystic fibrosis. Show your work.


5.14 Some human genetic characters are

controlled by one gene.

• For example, the freckled phenotype is

dominant to the non-freckled phenotype.



5.14 Many human genetic disorders are

recessive.

• A carrier is a

heterozygous

individual.

• Carriers do not

have the disease,

but they can pass it

on to offspring.


These three children must have received one a recessive

allele from their affected mother, but they don’t have

the trait. So they must be carriers themselves.

5.14 Pedigrees can be used to track genetic

traits in a family.


Because they produced a daughter

with the trait but don’t have it themselves,

both grandparents must be carriers.

Grandma and

grandpa had two

daughters, one of

whom married and

had four kids.

This daughter

does not have

the trait, but we

cannot tell if

she is Aa or AA.

This daughter has

the trait and

therefore must be

aa, having inherited

the recessive allele

from each parent.

Because this man

has a daughter with

the trait but does

not have the trait

himself, he must be

a carrier.

This child has the trait, which is

how we know her father was a carrier

(she could not have inherited two

recessive alleles from her mother.)


5.15 Opening Questions: Can we always

count on Mendel’s laws?

• Farmers have long observed that crossing

cattle with red and white coats results in

offspring with a roan coat, which is a

mixture of interspersed red and white.

If coat color is a single gene with two

alleles (R and r), does the roan color make

sense according to Mendel’s laws?

If not, how would you explain it?


5.15 Genetic inheritance has complexities.

• Not all genes follow a

classic Mendelian

inheritance pattern.

• We often encounter

patterns that are

more complex.


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5.15 Sometimes both alleles are expressed.

• For some genes there is a

pattern of incomplete

dominance.

• Individuals that are

heterozygous will have a

phenotype intermediate in

appearance.

Remember: In classic Mendelian genetics,

heterozygous individuals have the appearance

(phenotype) of the dominant gene.


5.15 Flower color in snapdragons is a trait

with incomplete dominance.

• Heterozygous

individuals show an

intermediate trait.

Now use a Punnett

square to predict the

outcome of Rr× Rr

for snapdragons.



Only RR individuals

have a red phenotype.

5.15 A cross between two pink snapdragons

exemplifies incomplete dominance.


5.15 For most traits there are multiple

alleles.

• Classic Mendelian genetics only uses two

allele copies (such as R and r).

• Most genes actually have multiple alleles.

For most genes, how

many allele copies can

one person carry?



5.15 Blood types in humans are the result of

multiple alleles.

• Human blood types

are determined by a

gene with three

alleles: i, IA, IB.

• These three alleles

can be combined in

six ways.

Alleles for blood type are also codominant, which

means both are expressed.


5.15 Parents with different blood types

exemplify multiple alleles and codominance.


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5.15 Genes may have multiple effects.

• In some cases, one gene influences many

characters, a situation called pleiotropy.

• The sickle-cell mutation can cause many

physical changes.


5.15 Many phenotypic characters are the

result of many genes.

• Polygenic inheritance is the effect of

many genes on a single character.

• In humans, height and skin color are each

affected by several genes.



5.15 Many genes have both a genetic and

environmental component.

• Some traits are entirely genetic, some are

a mix of environment and genetics, and

some traits are just environmental.


5.16 Opening Questions: Hey, why didn’t my

dihybrid cross turn out as predicted?

• What is the offspring pattern you expect

with a traditional dihybrid cross?

– Such as BbDd x BbDd

– Coat color and hearing

in Labrador retrievers×

• What if instead you got a 3:1 ratio of

dominant to recessive traits? Explain.

So far, we have assumed that traits are on different

chromosomes. Will they still sort independently if

they are on the same chromosome?Chapter Table of Contents


5.16 Not all genes obey Mendel’s law of

independent assortment.

• Linked genes are

located close

together on the same

chromosome and

tend to be inherited

together.

Linked genes display

different offspring

ratios compared to

unlinked genes.


5.16 Crossing over is less likely to occur

for closely located genes.

• Crossing over produces new hybrid

recombinant chromosomes.

• Genes located very near each other have

little chance of a crossover.


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5.17 Opening Questions: What if traits are

carried on a sex chromosome?

• So far, we have assumed that traits are on

autosomes.

In humans, can a male get a genetic

disorder if the gene is carried just on the

X chromosome? Explain.

• But what if a gene is

carried on a sex

chromosome (X or Y)?


5.17 Sex-linked genes are those carried on

the sex chromosomes.

• Males have only one X, so sex-linked genes

display unusual inheritance patterns.



5.17 Hemophilia is an example of a

recessive mutation on the X chromosome.

• Can you explain why less than

1% of hemophiliacs are female?

In the last Russian

royal family, the son

had hemophilia, but

none of the daughters.


5.18 Opening Questions: Can science bring

back your cat?

• In 2004, a company called Genetic Savings

& Clone (for a fee of $50,000!) produced

the first commercially cloned pet, a cat

named “Little Nicky”.

• Would you clone your pet?

• How much would you pay?

• What are some other possible

uses of cloning?Chapter Table of Contents


5.18 Nuclear transfer can be used to

produce clones.

• Biologists can artificially manipulate cell

division to produce clones.

– Clones are genetically identical individuals

born of a single parent.


5.18 Cloning can be done through the

process of nuclear transplantation.


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5.18 Cloned embryos can be used to

produce a new individual.

• In reproductive cloning the embryo must

be transplanted into a surrogate.


5.18 Cloned embryos can be used to

produce stem cells.

• In therapeutic cloning, stem cells are

harvested from the cloned embryo.


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