My Classroom Material 143 - BIOLOGY JUNCTION

Dichotomous Keying

Dichotomous Keying

Introduction to Dichotomous Key Maker:

The identification of biological organisms can be greatly simplified using tools such as dichotomous keys. A dichotomous key maker is an organized set of couplets of mutually exclusive characteristics of biological organisms. You simply compare the characteristics of an unknown organism against an appropriate dichotomous key. These keys will begin with general characteristics and lead to couplets indicating progressively specific characteristics. If the organism falls into one category, you go to the next indicated couplet. By following the key and making the correct choices, you should be able to identify your specimen to the indicated taxonomic level.

Couplets can be organized in several forms. The couplets can be presented using numbers (numeric) or using letters (alphabetical). The couplets can be presented together or grouped by relationships. There is no apparent uniformity in presentation for dichotomous keys.

Sample keys to some common beans used in the kitchen:

Numeric key with couplets presented together. The major advantage of this method of presentation is that both characteristics in a couple can be evaluated and compared very easily.

1a.	Bean round	Garbanzo bean
1b.	Bean elliptical or oblong	Go to 2

2a.	Bean white	White northern
2b.	Bean has dark pigments	Go to 3

3a.	Bean evenly pigmented	Go to 4
3b.	Bean pigmentation mottled	Pinto bean

4a.	Bean black	Black bean
4b.	Bean reddish-brown	Kidney bean

Alphabetical key with couplets grouped by relationship. This key uses the same couplet choices as the key above. The choices within the first and succeeding couplets are separated to preserve the relationships between the characteristics.

A.	Bean elliptical or oblong	Go to B
	B. Bean has dark pigments	Go to C
	C. Bean color is solid	Go to D
	C. Bean color is mottled	Pinto bean
	D. Bean is black	Black bean
	D. Bean is reddish-brown	Kidney bean
	B. Bean is white	White northern
A.	Bean is round	Garbanzo bean

Rules for Using Dichotomous Keys:

When you follow a dichotomous key, your task becomes simpler if you adhere to a few simple rules of thumb:

Read both choices in a couplet carefully. Although the first description may seem to fit your sample, the second may apply even better.
Keep notes telling what sequence of identification steps you took. This will allow you to double-check your work later and indicate sources of mistakes, if they have been made.
If you are unsure of which choice to make in a couplet, follow both forks (one at a time). After working through a couple of more couplets, it may become apparent that one fork does not fit your sample at all.
Work with more than one sample if at all possible. This will allow you to tell whether the one you are looking at is typical or atypical. This is especially true when working with plants – examine more than one leaf, branch, cone, seed, flower,…etc.
When you have keyed out an organism, do not take your effort as the final result. Double check your identification scheme, using your notes. Find a type specimen (if available) and compare your unknown to the type specimen. If a type specimen is unavailable, find a good description of the indicated taxonomic group and see if your unknown reflects this description.
When reading a couplet, make sure you understand all of the terms used. The best keys will have a glossary of technical terms used in the key. If a glossary is unavailable, find a good reference work for the field (textbook, biological dictionary,…etc.) to help you understand the term.
When a measurement is indicated, make sure that you take the measurement using a calibrated scale. Do not “eyeball” it or take a guess.

Exercise 1:

Using a container of beans, use one of the dichotomous keys above to identify the beans. Glue the beans to the card provided and label them with their common name. Indicate what steps you followed to arrive at your answer. Turn the card in to your instructor. Compare your answers to the instructor’s descriptions and type specimen.

Exercise 2:

Obtain samples of the snack chips provided. Develop a dichotomous key to identify the snacks. In your notebook, keep track of the characteristics you used to differentiate between the different snack families. What are the values of the characteristic for each snack food?

Exercise 3:

Use the dichotomous key to conifers provided below to identify conifers.

A Key to Selected North American Native and Introduced Conifers

01a	Leaves needle-like	Go to 02
01b	Leaves flattened and scale-like	Go to 27

02a	Leaves are in clusters	Go to 03
02b	Leaves are borne singly	Go to 15

03a	Two to five leaves in a cluster	Go to 04 Genus Pinus
03b	More than five leaves in a cluster	Go to 14

04a	Leaves mostly 5 in a cluster	White Pine (Pinus strobus)
04b	Leaves 2 or 3 in a cluster	Go to 05

05a	Leaves mostly 3 in a cluster	Go to 06
05b	Leaves mostly 2 in a cluster	Go to 08

06a	Leaves twisted, less than 5 inches long	Pitch Pine (Pinus rigida)
06b	Leaves straight, more than 5 inches long	Go to 07

07a	Leaves 5-10 inches long, cones very thorny	Loblolly pine (Pinus taeda)
07b	Leaves mostly over 10 inches long, cones unthorned	Longleaf pine (Pinus palustris)

08a	Leaves mostly longer than 3 inches	Go to 09
08b	Leaves mostly shorter than 3 inches	Go to 11

09a	Leaves rigid, bark grayish	Black pine (Pinus nigra)
09b	Leaves narrower than 1.6mm; bark reddish brown or brown	Go to 10

10a	Cones thornless, twigs brown	Norway pine (Pinus resinosa)
10b	Cones thorny, twigs whitish	Shortleaf pine (Pinus echinata)

11a	Leaves mostly wider than 1.5 mm	Go to 12
11b	Leaves mostly narrower than 1.5 mm	Go to 13

12a	Leaves mostly longer than 35 mm	Mugho pine (Pinus mugo)
12b	Leaves mostly shorter than 35 mm	Jack pine (Pinus banksiana)

13a	Twigs whitened	Virginia pine (Pinus virginiana)
13b	Twigs not whitened	Scotch pine (Pinus sylvestris)

14a	Leaves deciduous, clusters of 20-40	Larch (Larix sp.)
14b	Leaves persistent, stiff, and four sided	True cedar (Cedrus sp.)

15a	Needles short and sharp	Giant Sequioa (Sequioadendron giganteum)
15b	Needles longer than 12 mm	Go to 16

16a	Tiny pegs on twigs	Go to 17
16b	No pegs on twigs	Go to 22

17a	Pegs square, needles sharp	Go to 18 Genus Picea
17b	Pegs round, needles flat and blunt	Hemlock (Tsuga sp.)

18a	Leaves dark green or yellow green	Go to 19
18b	Leaves blue-green	Go to 20

19a	Branchlets droop	Norway spruce (Picea abies)
19b	Branchlets do not droop	Red spruce (Picea rubens)

20a	Leaves at right angles to stems	Blue spruce (Picea pungens)
20b	Leaves point forward	Go to 21

21a	Leaves about 12 mm long, seed cones 15-32 mm in length, crown narrow and pointed	Black spruce (Picea mariana)
21b	Leaves about 19 mm long, seed cones 50 mm in length, spire-like crown	White spruce (Picea glauca)

22a	Buds large and pointed	Douglas fir (Pseudotsuga sp.)
22b	Buds small and rounded	Go to 23

23a	Terminal buds round and clustered	True fir (Abies sp.)
23b	Terminal buds not clustered	Go to 24

24a	Needles white underneath	Go to 25
24b	Needles green underneath	Go to 26 Genus Taxus

25a	Needles pointed	Redwood (Sequoia sempervirens)
25b	Needles blunt	Hemlock (Tsuga sp.)

26a	Leaves 18 mm long or less with inconspicuous midrib	American Yew (Taxus canadensis)
26b	Leaves 25 mm long or more with conspicuous midrib	Japanese Yew (Taxus cuspidata)

27a	All leaves short and sharp	Giant Sequioa (Sequioadendron giganteum)
27b	Some leaves not sharp	Go to 28

28a	Cones round	Go to 29
28b	Cones not round	Go to 31

29a	Cones soft and leathery	Juniper (Juniperus sp.)
29b	Cones woody	Go to 30

30a	Cones under 12 mm in diameter	False cypress (Chamaecyparis)
30b	Cones over 12 mm in diameter	Cypress (Cuppressus)

31a	Cones resemble rosebuds	White cedar or arbor vitae (Thuja)
31b	Cones resemble duck bills	Incense cedar (Calocedrus)

Conifers to Identify:


1. Name:	2. Name:

3. Name:	4. Name:

5. Name:	6. Name:

7. Name:	8. Name:

9. Name:	10. Name:

11. Name:	12. Name:

13. Name:	14. Name:

15. Name:	16. Name:

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Ecology Worksheet Bi

Ecology

Chapter 19 Ecology

1. What is ecology?

2.. What is the most significant environmental change that is taking place today?

3. What is the sixth mass extinction?

4. What is the ozone layer, what does it do for earth, & what is happening to this layer & why?

5. Explain the green house effect.

6. List in order the ecological levels of organization.

7. What is the biosphere, tell where it extends, & tell why it is so important?

8. Define ecosystems & give an example.

9. What is a community?

10. What is a population?

11. What is the simplest ecological level of organization?

12. Use figure 19-6 on page 364 & explain how Lyme disease affects organisms in an ecosystem.

13. What are biotic factors & list them?

14. What are abiotic factors & list them?

15. Are abiotic factors constant? Explain by giving an example.

16.Organisms are able to survive within a _____________ range of environmental conditions.

17. Graphing the range of conditions an organism can survive is called a __________________ Curve.

18.When organisms adjust their tolerance to abiotic factors, the process is called ___________.

19. Explain how dormancy & migration help organisms escape unsuitable environmental conditions.

20. Define niche

Chapter 20 Populations

21. What is meant by population size?

22. What is meant by population density?

23. Name the 4 processes that determine whether a population will grow, shrink, or remain the same size.

24. What are immigration & emigration & how do they affect population size?

25. What are limiting factors & give some examples?

26. What affect does inbreeding have on small populations?

Chapter 21 Community Ecology

27. Interactions among species are called ____________.

28. List the 5 types of symbioses.

29. Define predator & prey & give an example.

30. What is mimicry & give an example?

31. Define these terms — parasitism, parasite, host, ectoparasites, & endoparasites.

32. When niches overlap, _________________________ results so more than one species are using the limited resources.

33. What are mutualism & commensalism?

34. Define succession.

35. Name & describe the 2 types of succession.

36. What are pioneer species & why are they important?

37. What is a climax community?

Chapter 22 Ecosystems

38. What are producers & what is another name they may be called?

39. What is biomass, why is it important, how does it accumulate, & what is its rate of accumulation called?

40. What is gross primary productivity?

41. All heterotrophs would be ______________________.

42. Define & give an example of each of these consumers — herbivore, carnivore, omnivore, detritivores, & decomposer.

43. Whenever one organism eats another, ________________ is transferred.

44. What are trophic levels?

45. All _______________ belong to the first trophic level, _______________ belong to the
Second trophic level, and the _______________ of herbivores belong to the third trophic level.

46. How many trophic levels do most ecosystems contain?

47. What is a food chain & what always begins the chain?

48. Write an example of a food chain.

49. What is a food web?

50. Draw a diagram of a food web that has at least 4 food chains.

51. Approximately __________ percent of the total energy consumed at one trophic level is incorporated into the organisms in the next level.

52. In terms of energy passage, why will there be many more producers than herbivores and fewer large carnivores than small carnivores?

53. What are biogeochemical cycles, why are they important, & name three?

54. Draw & explain the water cycle. Be sure to color your diagram!

55. List & define the 3 important processes in the water cycle.

56. What is groundwater?

57. What 2 processes form the basis for the carbon cycle?

58. Draw & explain the carbon cycle. Be sure to color your diagram!

59. What purpose do decomposers have in the carbon cycle?

60. Why do organisms need nitrogen?

61. Draw & explain the nitrogen cycle. Be sure to color your diagram!

62. Organisms such as ________________ convert _________________ gas into compounds
Called __________________ during the process known as________________________.

63. Bodies of dead organisms contain mainly in _________________ & _________________.

64. Wastes such as __________________ & _______________ also contain nitrogen that must be recycled.

65. ________________ recycle nitrogen from dead organisms & wastes by changing it into
______________________. The process is called ________________________.

66. Explain nitrification & denitrification.

67. Plants can absorb ____________________ from the soil, but animals obtain nitrogen from
their ___________________.

68. Define biome.

69. List the 7 major biomes.

70. Why don’t mountains belong to any one biome?

71. What is a tundra, where are they found, & tell organisms that would be found tree?

72. What is permafrost & how does it control plant life in the tundra?

73. What are taigas, where would they be found, & what type of vegetation dominates this area?

74. Plants & animals in the taiga must be adapted for long __________________, short
_________________, & ________________________ soil.

75. List some typical animals of the taiga.

76. What characterizes a temperate deciduous forest?

77. Deciduous forests have 4 pronounced ____________________ with _________________
summers, _______________________ winters, and__________________________ than the
taiga.

78. Grasses dominate what biome?

79. Why aren’t there more trees on grassland?

80. What are grasslands called in each of these areas —– North America, Asia, South America, & southern Africa?

81. Describe the soil of grasslands. Because of the soil condition, how is much of the grassland used?

82.What type of animals would be found on grassland?

83. What periodically occurs across grasslands & why doesn’t it kill the grasses?

84. Approximately how much rainfall do deserts receive each year?

85. Are deserts always hot? Explain.

86. What adaptation must desert vegetation make to survive?

87. What types of adaptations must desert animals make to conserve water?

88. What are savannas & where are the best known savannas found?

89. Describe temperature & rainfall on savannas?

90. Name some herbivores & carnivores found on a savanna.

91. Describe the rainy season on a savanna & tell what special problem this poses for the animals & plants there?

92. What are tropical rain forests & where are they located?

93. Rain forests have stable, year-round ______________________ & abundant ____________.

94. Plants in the rainforest must constantly compete for what?

95. Explain the canopy & epiphytes in a rainforest.

96. Describe the plant & animal life in a rainforest.

97. Tropical rainforests are more commonly called _____________________.

98.Oceans cover what percent of the earth’s surface?

99. Draw, label, & color the zones found in the ocean (see figure 22-16). Define each term labeled on your drawing.

100. What are intertidal organisms exposed to & name some intertidal organisms.

101. Which zone in the ocean is the most productive & why?

102. What small organisms are found in the neritic zone & why are they important?

103. In tropical areas, what forms in the neritic zone & why are they important?

104. Which ocean zone has fewer species & why?

105. Where does most of the earth’s photosynthesis take place?

106. Animals in the aphotic zone feed on what?

107. Organisms living deep in the ocean must cope with what 2 problems? Give some examples of deep ocean animals & explain how they adapt to their environmental problems.

108. What are volcanic vents, when were they discovered, & describe the organisms found there?

109. What are estuaries & what special problem do estuary organisms face?

110. What characterizes freshwater zones & give several examples?

111. Name & describe the 2 categories into which ecologists divide lakes 7 ponds?

112. Define a river & describe organisms found there?

Chapter 23 Environmental Science

113. Where do upwellings occur & how are they helpful?

114. Describe the event known as El Nino & tell its effect.

115. Describe chlorofluorocarbons effect on the ozone layer & tell why we should be concerned?

116. Define biodiversity.

117. Define conservation biology & use migratory birds to explain an example of this new discipline?

118. Sometimes species are reintroduced into areas. Use the Gray wolf & describe its reintroduction in the United States.

119. Where are the Everglades located & what is being done to restore them?

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Chromosome Notes

Chromosomes Linkage

Genes on the same chromosome are linked.

Example: Unlinked Genes

G = gray body

g = black (ebony) body

R = red eyes

r = purple eyes

The diagrams below show that the locus for body color (G or g) is on a different chromosome than the locus for eye color (R or r). These two loci will assort independently to produce either GR and gr gametes or Gr and gR gametes.

cross: GgRr X ggrr

gametes: GR, Gr, gR, gr X gr

Ratio expected: 1:1:1:1

Example: Linked Genes

Suppose G and R are linked as shown below. If the body color and eye color loci are on the same chromosome, they will not assort independently unless crossing-over occurs frequently.

In this case, GgRr can produce only two kinds of gametes: GR and gr.

GgRr X ggrr

gametes: GR, gr X gr

If G and R are linked, then whenever you have a G, you have an R. Any gray, purple offspring (G-rr) would result from crossing over because a Gr gamete is needed.

Suppose out of 100 offspring, you got 46 gray, red, 46 black purple, 4 gray purple and 4 black red. Eight percent of the offspring resulted from crossing over. These offspring are recombinant.

Crossing Over

Crossing over is more likely to occur between genes that are far apart. The farther apart genes are, the greater the probability that crossing over will occur between them.

In the example above, we had 8% crossing over.

The percent of recombination (crossing over) can beused as a measure of how far apart genes are. 1% crossing over = 1 map unit.

Example

G = gray body

g = black (ebony) body

R = red eyes

r = purple eyes

Suppose that G and R are linked (on the same chromosome) in a particular individual and g and r are also linked

P1 GgRr X ggrr

If there is no crossing-over, possible gametes for the first parent are GR and gr.

If there is crossing-over, possible gametes are gR and Gr.

the following results were obtained:

How far apart are the G and R loci?

Sex Chromosomes

Humans have 23 pairs of chromosomes (46 total) chromosomes. Two of these are called sex chromosomes, the other 44 are called autosomes.

There are two kinds of sex chromosomes, called the X chromosome and the Y chromosome. The X chromosome is larger and contains many genes. The Y chromosome is much smaller and contains very few genes.

Normally, human females have two X chromosomes (XX) and males have one X and one Y chromosome (XY).

Occasionally, an accident happens in which a person is born with too many or too few sex chromosomes. In these cases, the person will be male if they inherit a Y chromosome and female if they do not.

Examples of four different possibilities that produce males are shown below. The last three are abnormal.

XY
XXY
XXXY
XYY

Examples of four different possibilities that produce females are shown below. Normal females are XX.

X
XX
XXX
XXXX

The cross below shows that normal females produce eggs that have one X chromosome. Half of the sperm produced by normal males have an X chromosome and the other half have a Y chromosome.

XX x XY

This analysis shows that half of the offspring are expected to be male, half are expected to be female.

Chromosomal Determination of Sex

Males

The Y chromosome contains a gene called SRY (for sex-determining region of Y).

Females

Testicular Feminization

The body cells of people with testicular feminization are insensitive to testosterone and therefore develop the female phenotype even though they have a Y chromosome.

It has an X-linked recessive mode of inheritance.

Guevodoces

Guevodoces refers to a condition in which the male phenotype develops after puberty.

It is due to delayed testosterone production.

X-Linkage

Morgan (Columbia U):

P1 red-eyed X white-eyed

F1 all red-eyed

F2 3:1 (red:white) but all white were male

explanation:

These genes are found on the X chromosome but not on the Y chromosome. An XrY male will therefore have red eyes. Details of this cross are below.

P1	XRXR	X	XrY
female	male

gametes: XR (female) and Xr, Y (male)

The offspring produced from the above cross are crossed with each other (below):

F1 XRXr X XRY

gametes: XR and Xr (from female); XR and Y (from male)

F2:

Notice that there are three possible genotypes for females and two possible genotypes for males.

Females		Males
Genotypes	Phenotypes	Genotypes	Phenotypes
XRXR	red	XRY	red
XRXr	red	XrY	white
XrXr	white

X-Linked Inheritance

Males inherit their X chromosome from their mother. Their Y chromosome comes from their father. A male, therefore, cannot pass an X-linked trait to his sons. Males inherit all of their X-linked traits from their mother.

If a male inherits an X-linked recessive trait, it will be expressed because males do not have a homologous X chromosome.

Females can be carriers of X-linked traits without expressing them because they might carry the dominant allele on the other X chromosome. For example, the following genotype will have a dominant phenotype: XAXa.

Dosage Compensation

Although females have twice as many X-linked genes, the amount of protein produced by these genes is the same in females as it is in males.

Reduced protein production (called dosage compensation) occurs as a result of inactivating one X chromosome by coiling and condensing it. When condensed, it cannot be transcribed, that is, it cannot be used to produce mRNA.

Condensed X chromosomes, called Barr bodies, are visible using ordinary light microscope techniques.

The table below shows the number of Barr bodies in normal cells and in the cells of people with an abnormal number of X chromosomes. Normal males do not have Barr bodies because they only have one X chromosome.

Genetic Condition	# Barr Bodies per Cell
normal male	0
normal female	1
XXX female	2
XXXX female	3
XXY (Klinefelter male)	1

In summary, one X chromosome remains active, the others are inactivated by forming Barr bodies.

Inactivation

Inactivation occurs early in embryonic development (12-16 days).

In females, each cell normally contains two X chromosomes. The X chromosome that is inactivated is determined randomly.

img006.gif (6009 bytes)

img007.gif (6184 bytes)

Once inactivation occurs, all daughter cells of a particular cell have the same X chromosome inactivated.

All of the “pink” chromosomes in the drawing below (left side of diagram) have been inactivated. All future cells produced by this cell will have the pink chromosome inactivated. In the diagram on the right, all of the blue chromosomes have been inactivated. All future generations of this cell will have the blue chromosome inactivated.

img008.gif (6206 bytes)

Females are therefore mosaics with respect to the X chromosome. Patches of body cells will have the maternally inherited X chromosome inactivated and other patches will have the paternally inherited one inactivated.

Example of Mosaicism: Calico Cats

A calico cat has patches of orange and patches of black

X = orange

X1 = black

MALES:

XY = orange

X1Y = black

FEMALES:

XX = orange

X1 X1 = black

X X1 = orange or black patches

All cells descended from an X1 cell (X is inactive) are orange-yellow.

All cells descended from an X cell (X1 is inactive) are black.

Human Example – Anhydrotic Dysplasia

Anhydrotic dysplasia is a disease that results in the absence of sweat glands.

It is inherited as an X-linked recessive disease.

Let X = normal sweat glands and X’ = absence of sweat glands. Normal males are XY. Affected males are X’Y and do not have sweat glands.

Normal females are XX, heterozygous females are XX’ and have patches of skin with sweat glands and patches of skin without sweat glands. Females that are X’X’ do not have sweat glands.

Other Information

Should heterozygous females for colorblindness be able to see color?

Suppose: X = color vision

x = colorblind

The Retina of a heterozygous (Xx) female will have some cells with the “X” inactivated and other cells with the “x” inactivated.

A heterozygous carrier of red-green colorblindness has some colorblind cells in her retina. The non-colorblind cells enable her to see color.

Turner’s syndrome is an abnormality in females where there is only one X chromosome; the other is missing. These people have abnormalities that will be discussed in the next chapter. Why aren’t Turners syndrome females normal? Evidence indicates that some genes in the Barr body remain active. Their DNA is uncoiled and extends from the Barr body. If the Barr bodies of a normal female were missing, she would exhibit Turners Syndrome.

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Crayfish Appendage Table

Crayfish Appendage Table

Appendage	Function	Location	Attach Appendage Here
Antennules	Senses touch & taste; helps crayfish maintain balance	in front of the mouth	.
Antenna	Senses touch and taste	in front of the mouth	.
Mandible or jaw	Crushes food	mouth	.
First Maxilla	Moves food to the mouth	behind the mandibles	.
second maxilla	moves water in the gill chamber	behind the mandibles	.
First maxilliped	Holds food; Senses touch and taste	at ventral and forward part of the thorax region	.
Second maxilliped	Holds food; Senses touch and taste	at ventral and forward part of the thorax region	.
Third maxilliped	Holds food; Senses touch and taste	at ventral and forward part of the thorax region	.
Cheliped	Grasps food	at ventral part of thorax-posterior to the maxillipeds	.
walking leg	locomotion	at ventral part of thorax-posterior to the maxillipeds	.
Swimmeret	1st swimmeret in males transfers sperm to female; females use the 2nd-5th swimmerets to hold eggs & young; locomotion	abdominal region on the ventral side	.
uropod	swimming	posterior or tail end	.
telson	swimming	posterior or tail end	.

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Chromosomes & Human Inheritance Notes

Chromosomes:

Thomas Sutton in 1902 proposed that genes are located on chromosomes
Called the Chromosome Theory of Inheritance
For most of the life of the cell, chromosomes are too elongated to be seen under a microscope & are called chromatin
Before a cell gets ready to divide, each chromosome is duplicated & condenses into short structures
Each chromosome is composed of a single, tightly coiled DNA molecule
The two DNA strands are homologous (duplicates) and are held together by the centromere
While they are still attached, the duplicated chromosomes are called sister chromatids

Fertilization restores the diploid chromosome number and paired condition for alleles in the zygote
Chromosomes can be categorized as two types — autosomes & sex chromosomes
Autosomes are non-sex chromosomes that are the same number and kind between sexes
Sex chromosomes determine if the individual is male or female
Sex chromosomes in the human female are XX and those of the male are XY
Males produce X-containing and Y-containing gametes; therefore males determine the sex of offspring

Chromosome Numbers:

All animals have a characteristic number of chromosomes in their somatic or body cells called the diploid (or 2n) number.
The gametes or sex cells (egg & sperm) contain half the number of chromosomes as a body cell; known as the haploid number (n) of chromosomes

Diploid (2n) numbers of Organisms
Man	46
Dog	78
Fruitfly	8
Crayfish	200
Corn	20

Pedigrees:

Also called a family tree
Squares represent males and circles represent females
Horizontal lines connecting a male and female represent mating
Vertical lines extending downward from a couple represent their children
A shaded symbol means the individual possess the trait
Half-shaded symbols are carriers

Sex Linkage:

Thomas Hunt Morgan worked with fruit flies & confirmed that genes were on chromosomes
a. Fruit flies are cheaply raised in common laboratory glassware
b. Females only mate once and lay hundreds of eggs
c. Fruit fly generation time is short, allowing rapid experiments
Experiments involved fruit flies with XY system similar to human system
Besides genes that determine sex, sex chromosomes carry many genes for traits unrelated to sex
X-linked gene is any gene located on the X chromosome that are missing on the Y chromosome
X-linked alleles are designated as superscripts to X chromosome
Newly discovered mutant male fruit fly had white eyes

Mutant White-eyed & Wild, Red-eyed

Cross of white-eyed male with dominant red-eyed female yield expected 3:1 red-to-white ratio; however, all white-eyed flies were males
An allele for eye color on the X but not Y chromosome supports the results of the cross
Heterozygous females are carriers that do not show the trait but can pass it on
Males are never carriers but express the one allele on the X chromosome
Red-green color-blindness is X-linked recessive
In humans, another well-known X-linked traits is hemophilia (free bleeders that lack clotting factors in their blood)
One of the most famous genetic cases involving hemophilia goes back to Queen Victoria who was a carrier for the disorder and married Prince Albert who was normal
Their children married other royalty, and spread the gene throughout the royal families of Europe

Example Sex-Linked Problems:

1. What are the results of crossing a colorblind male with a female carrier for colorblindness?

Trait: Red-Green Colorblindness
Alleles: XC normal vision Xc colorblindness
XCXc x Xc Y
	XC	Y	Genotypes:	XCXC ,XCY, XCXc, XcY
XC	XCXC	XCY	Genotypic Ratio:	1:1:1:1
Xc	XCXc	XcY	Phenotypes:	normal vision female, normal vision male, female carrier, colorblind male

2. What are the results of crossing a colorblind male with a colorblind female?

Trait: Red-Green Colorblindness
Alleles: XC normal vision Xc colorblindness
XcXc x Xc Y
	Xc	Y	Genotypes:	XcXc , XcY
Xc	XcXc	XcY	Genotypic Ratio:	1:1 ratio
Xc	XcXc	XcY	Phenotypes:	colorblind female, colorblind male
Phenotypic ratio:	1:1 ratio

Linked genes:

Each chromosomes has 1000’s of genes
All genes on a chromosome form a linkage group that stays together except during crossing-over
Some genes located on the same chromosome tend to be inherited together
Linked genes were discovered by Thomas Hunt Morgan while studying fruit flies
Linked alleles do not obey Mendel’s laws because they tend to go into the gametes together
Crosses involving linked genes do not give same results as unlinked genes

Chromosome Mapping:

Recombinants result from chromosome crossing over during prophase I of meiosis
Geneticists can use recombination data to map a chromosome’s genetic loci (position on a chromosome)
A genetic map lists a sequence of genetic loci along a particular chromosome
Alfred Sturtevant, a student of Morgan, reasoned that different recombination frequencies reflect different distances between genes on a chromosome
The farther apart genes are, the greater likelihood of crossing-over
The closer together two genes are, the less likely of crossing-over occurring
A map unit equals 1% recombination frequency
If 1% of crossing-over equals one map unit, then 6% recombinants reveal 6 map units between genes
To determine the frequency of recombinants, the following formula is used:

	Number of recombinants x 100%
Recombination Frequency	=	———————————————
Total Number of Offspring

Humans have few offspring and a long generation time so biochemical methods are used to map human chromosomes (Human Genome Project)

Chromosome Mutations:

Mutations are changes in genes or chromosomes that can be passed on to offspring
Mutations increase the number of variations that occur
Chromosomal mutations include changes in chromosome number and/or structure
Monosomy occurs when an individual has only one of a particular type of chromosome
Turner syndrome (X0) is an example of monosomy
Trisomy occurs when and individual has three of a particular type of chromosome
Examples of trisomy include Klinefelter’s Syndrome (XXY) and Down Syndrome or Trisomy 21 where the individual has three 21st chromosomes
Both monosomy & trisomy result when chromosomes fail to separate during meiosis; called nondisjunction
Monosomy and trisomy (aneuploidy) occur in plants and animals and may be lethal (deadly)
Polyploidy where the offspring have more than two sets of chromosomes occurs often in plants (3n, 4n …)
Environmental factors including radiation, chemicals, and viruses, can cause chromosomes to break causing a change in chromosomal structure
Inversion occurs when a piece of a chromosome breaks off & reattaches to the same place but in the reverse order
Translocation occurs when a chromosome segment breaks off & attaches to a different chromosome
Deletions occur when the end of a chromosome breaks off & is lost
Cri du chat syndrome (results in retardation & a cat-like cry) is due to a deletion of a portion of chromosome 5
Duplications occur when a section of a chromosome is doubled
Fragile X Syndrome caused by an abnormal number of repeats (CCG) results in retardation & long, narrow face becomes more pronounced with age

Gene Mutations:

Change in genes caused by change in structure of the DNA
DNA bases may be substituted, added, or removed to cause gene mutation
When genes are added or removed, the mutation is called a frame shift mutation

Frame shift mutation

Adding or Removing genes is called a point mutation

point mutation

Sickle cell anemia (red blood cells are C-shaped so can’t carry as much oxygen) is an example of a gene mutation in African Americans

Tay-Sachs (a disorder where the nervous system deteriorates) is a fatal gene mutation in Jewish people of Central European Descent
Phenylketonuria or PKU occurs from the inability of a gene to synthesize a single enzyme necessary for the normal metabolism of phenylalanine and results in death

Category: My Classroom Material

Dichotomous Keying

Introduction to Dichotomous Key Maker:

Twigs whitened

Leaves point forward

White spruce (Picea glauca)

Redwood (Sequoia sempervirens)

Ecology Worksheet Bi

Chromosome Notes

Example: Unlinked Genes

Example: Linked Genes

Example