heredity and how traits change - christ the king school ckrs/faculty email and web pages/mrs....

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Mutations, Variation, and Natural Selection

Recall that mutations can lead to changes in traits. Therefore, mutations can produce differences among individuals. Slight differences in inherited traits among individuals in a population are called variations.

In 1976, scientists measured several traits in a population of medium ground finches on one of the Galápagos Islands. They discovered that the birds had variations in beak size. Most had smaller beaks, but all of the birds of this species preferred to eat small, soft seeds. The next year, it did not rain on the island. None of the plants reproduced, so no seeds formed. After all of the small, soft seeds had been eaten, many of the finches died. The few seeds left were fairly large and hard. The birds that survived were those that could crack and eat these larger seeds. These finches tended to be the birds with fairly large beaks.

In 1978, the scientists measured the beaks of the surviving birds’ offspring. They compared the average beak size of birds hatched in 1978 to that of birds hatched in 1976. In just two years, the average beak size of birds in the population had increased. How did this happen?

What do you think? Read the two statements below and decide whether you agree or disagree with them. Place an A in the Before column if you agree with the statement or a D if you disagree. After you’ve read this lesson, reread the statements to see if you have changed your mind.

Before Statement After

5. A population that lacks variation among its individuals might not be able to adapt to a changing environment.

6. Extinction occurs when the last individual of a species dies.

Key Concepts • How does natural selection

occur?• What is an adaptation?• Why do traits change over

time?

Building Vocabulary As you read, underline the words and phrases that you do not understand. When you finish reading, discuss these words and phrases with another student or your teacher.

Make a vertical three-tab book and use it to organize notes on the different types of adaptations.

Structural

Functional

Behavioral

Heredity and How Traits ChangeAdaptation and Evolution

Reading Essentials Heredity and How Traits Change 411

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Natural SelectionThe process by which individuals with variations that help them

survive in their environment live longer, compete better, and reproduce more than those individuals without these variations is called natural selection. For the finches, there was variation among individual birds for the trait of beak size. Some of the birds had small beaks, and some of them had larger beaks. When a change in the environment—a drought—occurred, the birds with larger beaks were better able to survive than birds with smaller beaks. The surviving individuals then passed on the favorable trait to their offspring. Over the two-year span of natural selection and reproduction, the average beak size of the birds in the population increased. The birds with larger beaks were naturally selected by environmental conditions and survived. Another example of natural selection in plants is shown in the figure below.

Key Concept Check1. Explain How does natural selection occur?

Visual Check2. Analyze What happened when individual sunflowers competed for limited resources?

Natural Selection: Sunflowers

1 Variation Individuals in a population differ from

one another. In this population, some sunflowers are

taller than others.

2 Inheritance Traits are inherited from parents. Tall

sunflowers produce tall sunflowers. Short sunflowers

produce short sunflowers.

3 Competition Due to limited resources, not all

offspring will survive. Individuals with a trait that

better suits the environment are more likely to

survive and reproduce. In this environment, short

sunflowers are more successful.

4 Natural Selection Over time, the average height of

the sunflower population is short if the short sunflowers

continue to reproduce successfully.

412 Heredity and How Traits Change Reading Essentials


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AdaptationsThe traits of surviving individuals, such as larger beaks or

shorter sunflowers, become more common as the survivors reproduce and pass the genes for their traits to their offspring. An adaptation is an inherited trait that increases an organism’s chance of surviving and reproducing in a particular environment. Adaptations can be structural, functional, or behavioral.

Structural AdaptationsA flying squirrel has a flap of skin between its forelegs

and hind legs. This flap of skin enables the squirrel to glide distances of up to 45 m. The behavior possibly is used to escape from predators. This flap of skin is an example of a structural adaptation. Structural adaptations involve physical characteristics, such as color or shape.

Another example of a structural adaptation occurs in many desert plants. Some types of cactus plants have spines. Spines are leaves that are reduced in size. The adaptation of smaller leaves helps reduce water loss in a dry environment.

Functional AdaptationsFunctional adaptations involve internal systems that

affect an organism’s physiology or biochemistry. For example, the alpine snowbell, a flower species, has adapted to survive in an environment with a short growing season.

In the high altitude of the mountains, where the alpine snowbell grows, light and temperature conditions for flowering are favorable for only a short period during the summer. The alpine snowbell produces flower buds at the end of the previous season. Over the winter, the buds remain dormant—alive, but not actively growing. In the spring, increased light triggers the plant to bloom even when it is still surrounded by snow. These adaptations enable the species to survive.

Behavioral AdaptationsMigration, and other behavioral adaptations, involve the

ways an organism behaves or acts. For example, caribou migrate south for the winter. Other animals, such as birds, whales, and butterflies, also migrate. Animal species that migrate to find adequate food and suitable temperatures survive and reproduce more successfully.

Key Concept Check5. Describe three types of adaptations.

Reading Check3. Identify How can a species benefit from an adaptation?

4. Hypothesize How might a monkey’s long tail be an example of a structural adaptation?



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Evolution of Populations—Why Traits Change

Once an inherited trait has become more frequent in a population, the population has adapted and evolved. Evolution is change over time. Evolution by natural selection is a way that populations change over time. When populations evolve, species can look and behave differently than their ancestors. This happens because the frequency of genetic traits changes over time. As the environment changes, different inherited traits might enable survival, and the population can evolve again.

A Modern Example of Change Over TimeBacteria can cause infections in your body, such as strep

throat or pneumonia. Sometimes a doctor might prescribe an antibiotic to help you fight an infection. Antibiotics are drugs that kill bacteria. Although antibiotics often kill bacteria effectively, variation exists within a population of bacteria. As shown in the figure below, some bacteria in a population might have a mutation that lets them survive when exposed to an antibiotic. When the surviving bacteria reproduce, that trait passes to their offspring. Soon, most individuals in the population survive when exposed to the antibiotic. Bacteria that survive when exposed to an antibiotic are called antibiotic-resistant. Antibiotic-resistant bacteria have caused deadly infections and are of great concern to scientists.

Visual Check7. Draw a circle around the dish with the largest number of resistant bacteria.

ACADEMIC VOCABULARYsurvive(verb) to remain alive

Key Concept Check6. State Why do traits change over time?

Antibiotic Resistance in Bacteria

Antibiotic

Resistant bacteria

Nonresistant bacteriaNew resistant and

nonresistant bacteria

are treated with the

same antibiotic.

An antibiotic is added to a population

of bacteria. A few of the bacteria

already have mutations that enable

them to resist the antibiotic.

The antibiotic kills most of

the nonresistant bacteria.

The surviving bacteria

reproduce.

The antibiotic now affects only a

small percentage of the bacteria.

The surviving bacteria continue

to reproduce. Most of the

bacteria are resistant to the

antibiotic.



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Extinction and Conservation BiologyYou already have read that for evolution by natural

section to occur, variation within a population is needed. A population with diversity can survive changes in its environment and persist through time. But what happens when a population lacks variation among its individuals and the environment changes? The population might lose its ability to reproduce successfully and fail to survive. When the last individual of a species dies, the species has undergone extinction.

Today, many species are threatened with extinction. A species’ habitat might have been altered or destroyed. Some species have been hunted to extinction. For others, new species introduced into many habitats make it difficult for some native species to survive and reproduce.

A relatively new field of science focuses on saving species. Conservation biology is a branch of biology that studies why many species are in trouble and what can be done to save them. Sometimes scientists’ knowledge of genetics helps species that are in danger of extinction. For example, by 1995, the population of Florida panthers was between 20 and 30 individuals. The population had lost much of its natural variation and was struggling to survive.

Fortunately, scientists’ understanding of genetics and heredity saved the population from extinction. Scientists introduced into the Florida population several female panthers from a population in Texas. This was done to increase genetic diversity in the Florida population. By 2003, the Florida panther population had increased to 80 individuals, and the effort was considered a success.

8. Name one animal species that is in danger of becoming extinct.

Reading Check9. Explain Why did scientists introduce panthers from Texas into the Florida panther population?

SCIENCE USE V. COMMON USEintroduceScience Use to bring a substance or organism into a habitat or a population

Common Use to make someone known to others



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Mini Glossary

Reread the statements at the beginning of the lesson. Fill in the After column with an A if you agree with the statement or a D if you disagree. Did you change your mind?

What do you think

END OF LESSON

Log on to ConnectED.mcgraw-hill.com and access your textbook to find this lesson’s resources.

ConnectED

adaptation: an inherited trait that increases an organism’s

chance of surviving and reproducing in a particular

environment

conservation biology: a branch of biology that studies

why many species are in trouble and what can be done

to save them

evolution: change over time

extinction: occurs when the last individual of a species dies

natural selection: the process by which individuals with

variations that help them survive in their environment live

longer, compete better, and reproduce more than those

individuals without these variations

variation: a slight difference in inherited traits among

individuals in a population

1. Review the terms and their definitions in the Mini Glossary. Write a sentence that explains the difference between an adaptation and a variation.

2. Use the graphic organizer below to identify three factors that contribute to extinction.

3. An environment supports a species of beetle. Some beetles are green, some brown. Because of a drought, birds see green beetles and eat them more often than brown beetles. Over time, which color would you expect to become more common? Why?

Extinction



A column in the

periodic table is

called a group.

A row in the

periodic table is

called a period.

The number in parentheses is the mass number of the longest lived isotope for that element.

PERIODIC TABLE OF THE ELEMENTS

Gas

Liquid

Solid

Synthetic

1

2

93 4 5 6 7

1

2

3

4

5

6

7

Lanthanide series

Actinide series

8

Thorium

90

Th232.04

Cerium

58

Ce140.12

Protactinium

91

Pa231.04

Praseodymium

59

Pr140.91

Uranium

92

U238.03

Neodymium

60

Nd144.24

Neptunium

93

Np(237)

Promethium

61

Pm(145)

Plutonium

94

Pu(244)

Samarium

62

Sm150.36

Americium

95

Am (243)

Europium

63

Eu151.96

Francium

87

Fr(223)

Cesium

55

Cs132.91

Rubidium

37

Rb85.47

Potassium

19

K39.10

Sodium

11

Na22.99

Lithium

3

Li6.94

Hydrogen

1

H1.01

Radium

88

Ra(226)

Barium

56

Ba137.33

Strontium

38

Sr87.62

Calcium

20

Ca40.08

Magnesium

12

Mg24.31

Beryllium

4

Be9.01

Actinium

89

Ac(227)

Lanthanum

57

La138.91

Yttrium

39

Y88.91

Scandium

21

Sc44.96

Rutherfordium

104

Rf(267)

Hafnium

72

Hf178.49

Zirconium

40

Zr91.22

Titanium

22

Ti47.87

Dubnium

105

Db(268)

Tantalum

73

Ta180.95

Niobium

41

Nb92.91

Vanadium

23

V50.94

Seaborgium

106

Sg(271)

Tungsten

74

W183.84

Molybdenum

42

Mo95.96

Chromium

24

Cr52.00

Bohrium

107

Bh(272)

Rhenium

75

Re186.21

Technetium

43

Tc(98)

Manganese

25

Mn54.94

Hassium

108

Hs(270)

Osmium

76

Os190.23

Ruthenium

44

Ru101.07

Iron

26

Fe55.85

Meitnerium

109

Mt(276)

Iridium

77

Ir192.22

Rhodium

45

Rh102.91

Cobalt

27

Co58.93

Hydrogen

1

H1.01

Element

Atomic number

Symbol

Atomic mass

State ofmatter

ES1_ES2_RE_SE_BC.indd 2ES1_ES2_RE_SE_BC.indd 2 3/13/10 6:42:26 PM3/13/10 6:42:26 PM

10 11 12

13 14 15 16 17

18

The names and symbols for elements 113-116 and 118 are temporary. Final names will be selected when the elements’ discoveries are verified.*

Metal

Metalloid

Nonmetal

Recently discovered

Curium

96

Cm(247)

Gadolinium

64

Gd157.25

Berkelium

97

Bk(247)

Terbium

65

Tb158.93

Californium

98

Cf(251)

Dysprosium

66

Dy162.50

Einsteinium

99

Es(252)

Holmium

67

Ho164.93

Fermium

100

Fm(257)

Erbium

68

Er167.26

Mendelevium

101

Md(258)

Thulium

69

Tm168.93

Nobelium

102

No(259)

Ytterbium

70

Yb173.05

Lawrencium

103

Lr(262)

Lutetium

71

Lu174.97

Darmstadtium

110

Ds(281)

Platinum

78

Pt195.08

Palladium

46

Pd106.42

Nickel

28

Ni58.69

Roentgenium

111

Rg(280)

Gold

79

Au196.97

Silver

47

Ag107.87

Copper

29

Cu63.55

Copernicium

112

Cn(285)

Mercury

80

Hg200.59

Cadmium

48

Cd112.41

Zinc

30

Zn65.38

Ununtrium

113

Uut(284)

*

Thallium

81

Tl204.38

Indium

49

In114.82

Gallium

31

Ga69.72

Aluminum

13

Al26.98

Boron

5

B10.81

Ununquadium

114

Uuq(289)

*

Lead

82

Pb207.20

Tin

50

Sn118.71

Germanium

32

Ge72.64

Silicon

14

Si28.09

Carbon

6

C12.01

Ununpentium

115

Uup(288)

*

Bismuth

83

Bi208.98

Antimony

51

Sb121.76

Arsenic

33

As74.92

Phosphorus

15

P30.97

Nitrogen

7

N14.01

Ununhexium

116

Uuh(293)

*

Polonium

84

Po(209)

Tellurium

52

Te127.60

Selenium

34

Se78.96

Sulfur

16

S32.07

Oxygen

8

O16.00

Astatine

85

At(210)

Iodine

53

I126.90

Bromine

35

Br79.90

Chlorine

17

Cl35.45

Fluorine

9

F19.00

Ununoctium

118

Uuo(294)

*

Radon

86

Rn(222)

Xenon

54

Xe131.29

Krypton

36

Kr83.80

Argon

18

Ar39.95

Neon

10

Ne20.18

Helium

2

He4.00


A column in the

periodic table is

called a group.

A row in the

periodic table is

called a period.

The number in parentheses is the mass number of the longest lived isotope for that element.

PERIODIC TABLE OF THE ELEMENTS

Gas

Liquid

Solid

Synthetic

1

2

93 4 5 6 7

1

2

3

4

5

6

7

Lanthanide series

Actinide series

8

Thorium

90

Th232.04

Cerium

58

Ce140.12

Protactinium

91

Pa231.04

Praseodymium

59

Pr140.91

Uranium

92

U238.03

Neodymium

60

Nd144.24

Neptunium

93

Np(237)

Promethium

61

Pm(145)

Plutonium

94

Pu(244)

Samarium

62

Sm150.36

Americium

95

Am (243)

Europium

63

Eu151.96

Francium

87

Fr(223)

Cesium

55

Cs132.91

Rubidium

37

Rb85.47

Potassium

19

K39.10

Sodium

11

Na22.99

Lithium

3

Li6.94

Hydrogen

1

H1.01

Radium

88

Ra(226)

Barium

56

Ba137.33

Strontium

38

Sr87.62

Calcium

20

Ca40.08

Magnesium

12

Mg24.31

Beryllium

4

Be9.01

Actinium

89

Ac(227)

Lanthanum

57

La138.91

Yttrium

39

Y88.91

Scandium

21

Sc44.96

Rutherfordium

104

Rf(267)

Hafnium

72

Hf178.49

Zirconium

40

Zr91.22

Titanium

22

Ti47.87

Dubnium

105

Db(268)

Tantalum

73

Ta180.95

Niobium

41

Nb92.91

Vanadium

23

V50.94

Seaborgium

106

Sg(271)

Tungsten

74

W183.84

Molybdenum

42

Mo95.96

Chromium

24

Cr52.00

Bohrium

107

Bh(272)

Rhenium

75

Re186.21

Technetium

43

Tc(98)

Manganese

25

Mn54.94

Hassium

108

Hs(270)

Osmium

76

Os190.23

Ruthenium

44

Ru101.07

Iron

26

Fe55.85

Meitnerium

109

Mt(276)

Iridium

77

Ir192.22

Rhodium

45

Rh102.91

Cobalt

27

Co58.93

Hydrogen

1

H1.01

Element

Atomic number

Symbol

Atomic mass

State ofmatter


10 11 12

13 14 15 16 17

18

The names and symbols for elements 113-116 and 118 are temporary. Final names will be selected when the elements’ discoveries are verified.*

Metal

Metalloid

Nonmetal

Recently discovered

Curium

96

Cm(247)

Gadolinium

64

Gd157.25

Berkelium

97

Bk(247)

Terbium

65

Tb158.93

Californium

98

Cf(251)

Dysprosium

66

Dy162.50

Einsteinium

99

Es(252)

Holmium

67

Ho164.93

Fermium

100

Fm(257)

Erbium

68

Er167.26

Mendelevium

101

Md(258)

Thulium

69

Tm168.93

Nobelium

102

No(259)

Ytterbium

70

Yb173.05

Lawrencium

103

Lr(262)

Lutetium

71

Lu174.97

Darmstadtium

110

Ds(281)

Platinum

78

Pt195.08

Palladium

46

Pd106.42

Nickel

28

Ni58.69

Roentgenium

111

Rg(280)

Gold

79

Au196.97

Silver

47

Ag107.87

Copper

29

Cu63.55

Copernicium

112

Cn(285)

Mercury

80

Hg200.59

Cadmium

48

Cd112.41

Zinc

30

Zn65.38

Ununtrium

113

Uut(284)

*

Thallium

81

Tl204.38

Indium

49

In114.82

Gallium

31

Ga69.72

Aluminum

13

Al26.98

Boron

5

B10.81

Ununquadium

114

Uuq(289)

*

Lead

82

Pb207.20

Tin

50

Sn118.71

Germanium

32

Ge72.64

Silicon

14

Si28.09

Carbon

6

C12.01

Ununpentium

115

Uup(288)

*

Bismuth

83

Bi208.98

Antimony

51

Sb121.76

Arsenic

33

As74.92

Phosphorus

15

P30.97

Nitrogen

7

N14.01

Ununhexium

116

Uuh(293)

*

Polonium

84

Po(209)

Tellurium

52

Te127.60

Selenium

34

Se78.96

Sulfur

16

S32.07

Oxygen

8

O16.00

Astatine

85

At(210)

Iodine

53

I126.90

Bromine

35

Br79.90

Chlorine

17

Cl35.45

Fluorine

9

F19.00

Ununoctium

118

Uuo(294)

*

Radon

86

Rn(222)

Xenon

54

Xe131.29

Krypton

36

Kr83.80

Argon

18

Ar39.95

Neon

10

Ne20.18

Helium

2

He4.00


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