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Biology 1406 > Chapter 14 Notes > Flashcards

Chapter 14 Notes Flashcards

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1
Q

Mendel discovered the

A

basic principles of heredity by breeding garden peas in carefully planned experiments

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2
Q

Advantages of pea plants for genetic study

A
  • There are many varieties with distinct heritable features, or characters (such as flower color); character variants (such as purple or white flowers) are called traits
  • Mating can be controlled (via cross pollination)
  • Each flower has sperm-producing organs (stamens) and an egg-producing organ (carpel)
  • Cross-pollination (fertilization between different plants) involves dusting one plant with pollen from another
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3
Q

Mendel chose to track only those characters that occurred in

A

two distinct alternative forms.

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4
Q

He also used varieties that were true-breeding

A

(plants that produce offspring of the same variety when they self-pollinate)

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5
Q

In a typical experiment, Mendel mated two contrasting, true-breeding varieties, a process called

A

hybridization

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6
Q

The true-breeding parents are the

A

P generation

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7
Q

The hybrid offspring of the P generation are called the

A

F1 generation

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8
Q

When F1 individuals self-pollinate or cross- pollinate with other F1 hybrids, the

A

F2 generation is produced

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9
Q

When Mendel crossed contrasting, true-breeding white- and purple-flowered pea plants,

A

all of the F1 hybrids were purple

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10
Q

When Mendel crossed the F1 hybrids,

A

many of the F2 plants had purple flowers, but some had white

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11
Q

Mendel discovered a ratio of about

A

three to one, purple to white flowers, in the F2 generation

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12
Q

Mendel reasoned that

A

only the purple flower factor was affecting flower color in the F1 hybrids

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13
Q

Mendel called the purple flower color

A

a dominant trait and the white flower color a recessive trait

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14
Q

The factor for white flowers was not diluted or destroyed because

A

it reappeared in the F2 generation

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15
Q

Mendel observed the same pattern of inheritance in

A

six other pea plant characters, each represented by two traits

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16
Q

What Mendel called a “heritable factor” is what we now call

A

a gene

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17
Q

Alternative versions of genes account for variations in inherited characters

A

For example, the gene for flower color in pea plants exists in two versions, one for purple flowers and the other for white flowers

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18
Q

These alternative versions of a gene are now called

A

alleles

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19
Q

Each gene resides at a

A

specific locus on a specific chromosome

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20
Q

For each character, an organism inherits two alleles, one from each parent.

A

Mendel made this deduction without knowing about the role of chromosomes

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21
Q

The two alleles at a particular locus may be

A

identical, as in the true-breeding plants of Mendel’s P generation

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22
Q

Alternatively, the two alleles at a locus may

A

differ, as in the F1 hybrids

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23
Q

If the two alleles at a locus differ, then one (the dominant allele) determines the

A

organism’s appearance, and the other (the recessive allele) has no noticeable effect on appearance

-In the flower-color example, the F1 plants had purple flowers because the allele for that trait is dominant

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24
Q

(now known as the law of segregation):

A

the two alleles for a heritable character separate (segregate) during gamete formation and end up in different gametes

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25
Q

Thus, an egg or a sperm gets only one of the two alleles that are present in the organism.

A

This segregation of alleles corresponds to the distribution of homologous chromosomes to different gametes in meiosis.

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26
Q

Mendel’s segregation model accounts for the 3:1 ratio he observed in

A

the F2 generation of his numerous crosses

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27
Q

The possible combinations of sperm and egg can be shown using a Punnett square,

A

a diagram for predicting the results of a genetic cross between individuals of known genetic makeup

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28
Q

A capital letter represents a dominant allele, and a

A

lowercase letter represents a recessive allele

-Potential gametes are on the outside of the square

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29
Q

Punnett Square Steps

A

Step 1- Write the genotypes of the parents
Step 2- Determine the gametes each parent can produce
Step 3- Place the gametes on the outside of the punnett square
Step 4- Fill in the boxes

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30
Q

An organism with two identical alleles for a character is said to be

A

homozygous for the gene controlling that character

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31
Q

An organism that has two different alleles for a gene is said to be

A

heterozygous for the gene controlling that character

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32
Q

Unlike homozygotes, heterozygotes are not

A

true-breeding

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33
Q

Because of the different effects of dominant and recessive alleles,

A

an organism’s traits do not always reveal its genetic composition

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34
Q

Therefore, we distinguish between an organism’s phenotype, or physical appearance, and its

A

genotype, or genetic makeup

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35
Q

In the example of flower color in pea plants,

A

PP and Pp plants have the same phenotype (purple) but different genotypes

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36
Q

How can we tell the genotype of an individual with the dominant phenotype?

A

Such an individual could be either homozygous dominant or heterozygous

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37
Q

The answer is to carry out a testcross:

A

breeding the mystery individual with a homozygous recessive individual

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38
Q

If any offspring display the recessive phenotype,

A

the mystery parent must be heterozygous

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39
Q

all kids dominant =

A

AA (homozygous)

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40
Q

1/2 kids dominant

1/2 kids recessive =

A

Aa (heterozygous)

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41
Q

Phenotype

A

physical appearance (like the color)

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42
Q

Genotype

A

genetic makeup (like the Bb, BB, bb letter stuff)

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43
Q 
BB genotype 
(two capital letters) =
A

homozygous dominant

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44
Q 
bb genotype
(two lower case letters) =
A

homozygous recessive

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45
Q 
Bb genotype
(one capital and one lower case letter) =
A

heterozygous

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46
Q

Mendel derived the law of segregation by

A

following a single character

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47
Q

The F1 offspring produced in this cross were monohybrids,

A

individuals that are heterozygous for one character

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48
Q

A cross between such heterozygotes is called a

A

monohybrid cross

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49
Q

Mendel identified his second law of inheritance by

A

following two characters at the same time

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50
Q

Crossing two true-breeding parents differing in two characters produces

A

dihybrids in the F1 generation, heterozygous for both characters

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51
Q

A dihybrid cross, a cross between F1 dihybrids, can determine

A

whether two characters are transmitted to offspring as a package or independently

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52
Q

Using a dihybrid cross, Mendel developed the

A

law of independent assortment

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53
Q

The law of independent assortment states that

A

each pair of alleles segregates independently of each other pair of alleles during gamete formation

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54
Q

Strictly speaking, this law (law of independent assortment) applies only to genes on different,

A

nonhomologous chromosomes or those far apart on the same chromosome

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55
Q

Genes located near each other on the same chromosome tend to be

A

inherited together

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56
Q

Mendel’s laws of segregation and independent assortment reflect the

A

rules of probability

57
Q

When tossing a coin, the outcome of one toss has no impact on the outcome of the next toss

A

In the same way, the alleles of one gene segregate into gametes independently of another gene’s alleles

58
Q

The multiplication rule states that

A

the probability that two or more independent events will occur together is the product of their individual probabilities –AND-

59
Q

The addition rule states that

A

the probability that any one of two or more exclusive events will occur is calculated by adding together their individual probabilities –OR-

60
Q

We can apply the multiplication and addition rules to predict

A

the outcome of crosses involving multiple characters

61
Q

In calculating the chances for various genotypes,

A

each character is considered separately, and then the individual probabilities are multiplied

62
Q

What’s the probability of getting an individual with the genotype AABbCc? From a cross of AaBbCc x AaBbCc

A 
-1st- Break each trait apart
AA – probability ¼
Bb – (Bb =1/4 OR bB = ¼) probability ½
Cc – (Cc = ¼ OR cC = ¼) probability ½
-Now decide to add or multiply? AND = multiply
¼ x ½ x ½ = 1/16 ANSWER
63
Q

The relationship between genotype and phenotype is rarely as simple as

A

in the pea plant characters Mendel studied

64
Q

Many heritable characters are not determined by only one gene with two alleles

A

However, the basic principles of segregation and independent assortment apply even to more complex patterns of inheritance

65
Q

Inheritance of characters by a single gene may deviate from simple Mendelian patterns in the following situations:

A
  • When alleles are not completely dominant or recessive
  • When a gene has more than two alleles
  • When a gene produces multiple phenotypes
66
Q

Complete dominance occurs when

A

phenotypes of the heterozygote and dominant homozygote are identical

67
Q

In incomplete dominance,

A

the phenotype of F1 hybrids is somewhere between the phenotypes of the two parental varieties

((cross two traits and there will be a mixture of something. like cross red and white and get pink))

68
Q

In codominance,

A

two dominant alleles affect the phenotype in separate, distinguishable ways
Ex: AB blood type

((like there being two color stripes on something))

69
Q

A dominant allele does not subdue a recessive allele; alleles don’t interact that way

A

Alleles are simply variations in a gene’s nucleotide sequence

For any character, dominance/recessiveness relationships of alleles depend on the level at which we examine the phenotype

70
Q

Tay-Sachs disease is fatal; a dysfunctional enzyme causes an accumulation of lipids in the brain

A
  • At the organismal level, the allele is recessive
  • At the biochemical level, the phenotype (i.e., the enzyme activity level) is incompletely dominant
  • At the molecular level, the alleles are codominant
71
Q

Dominant alleles are not necessarily more common in populations than recessive alleles

A
  • For example, one baby out of 400 in the United States is born with extra fingers or toes
  • The allele for this unusual trait is dominant to the allele for the more common trait of five digits per appendage
  • In this example, the recessive allele is far more prevalent than the population’s dominant allele
72
Q

Most genes exist in populations in more than two allelic forms

(multiple alleles)

A

For example, the four phenotypes of the ABO blood group in humans are determined by three alleles for the enzyme (I) that attaches A or B carbohydrates to red blood cells: IA, IB, and i.

73
Q

The enzyme encoded by the IA allele adds the A carbohydrate,

A

whereas the enzyme encoded by the IB allele adds the B carbohydrate; the enzyme encoded by the i allele adds neither

74
Q

multiple alleles

A

when you have more than 2 alleles of choices

75
Q

Most genes have multiple phenotypic effects, a property called

A

pleiotropy

76
Q

For example, pleiotropic alleles are responsible for the

A

multiple symptoms of certain hereditary diseases, such as cystic fibrosis and sickle-cell disease

77
Q

pleiotropy

A

one gene affects many traits

78
Q

Some traits may be determined by two or more genes

A

Epistasis

Polygenic inheritance

79
Q

In epistasis,

A

a gene at one locus alters the phenotypic expression of a gene at a second locus

80
Q

(epistasis)

For example, in Labrador retrievers and many other mammals, coat color depends on two genes

A
  • One gene determines the pigment color (with alleles B for black and b for brown)
  • The other gene (with alleles C for color and c for no color) determines whether the pigment will be deposited in the hair
81
Q

Quantitative characters are those

A

that vary in the population along a continuum

82
Q

Quantitative variation usually indicates polygenic inheritance

A

an additive effect of two or more genes on a single phenotype

83
Q

Skin color in humans is an example of

A

polygenic inheritance

(eye color is also an example of this)

84
Q

polygenic inheritance

A

many genes influence one trait

85
Q

Another departure from Mendelian genetics arises when the

A

phenotype for a character depends on environment as well as genotype

86
Q

The norm of reaction is the

A

phenotypic range of a genotype influenced by the environment

-For example, hydrangea flowers of the same genotype range from blue-violet to pink, depending on soil acidity

87
Q

Norms of reaction are generally broadest for polygenic characters
Such characters are called multifactorial because

A

genetic and environmental factors collectively influence phenotype

88
Q

An organism’s phenotype includes its physical appearance, internal anatomy, physiology, and behavior.

A

An organism’s phenotype reflects its overall genotype and unique environmental history.

89
Q

Humans are not good subjects for genetic research

A

Generation time is too long
Parents produce relatively few offspring
Breeding experiments are unacceptable

-However, basic Mendelian genetics endures as the foundation of human genetics

90
Q

A pedigree is a

A

family tree that describes the interrelationships of parents and children across generations

91
Q

Inheritance patterns of particular traits can be traced and described using

A

pedigrees

92
Q

Pedigrees can also be used to make predictions about future offspring.

A

We can use the multiplication and addition rules to predict the probability of specific phenotypes.

93
Q

Many genetic disorders are inherited in

A

a recessive manner

These range from relatively mild to life-threatening

94
Q

Recessive inherited disorders

A
  • Albinism
  • Cystic Fibrosis
  • Sickle-cell syndrom/disease
95
Q

Recessively inherited disorders show up only in individuals homozygous for the allele

A

AA and Aa don’t have the disorder

aa does have the disorder

96
Q

Carriers are

A

heterozygous individuals who carry the recessive allele but are phenotypically normal; most individuals with recessive disorders are born to carrier parents (Aa)

97
Q

Most people who have recessive disorders are born to

A

two carrier parents

98
Q

Albinism is a recessive condition characterized by

A

a lack of pigmentation in skin and hair

99
Q

If a recessive allele that causes a disease is rare, then

A

the chance of two carriers meeting and mating is low

100
Q

Consanguineous matings (i.e., matings between close relatives) increase

A

the chance of mating between two carriers of the same rare allele

-Most societies and cultures have laws or taboos against marriages between close relatives

101
Q

Cystic fibrosis is the

A

most common lethal genetic disease in the United States,striking one out of every 2,500 people of European descent

102
Q

The cystic fibrosis allele results in

A

defective or absent chloride transport channels in plasma membranes leading to a buildup of chloride ions outside the cell

103
Q

Cystic fibrosis Symptoms include mucus buildup in some internal organs and abnormal absorption of nutrients in the small intestine

A

Chronic bronchitis, foul stools, recurrent bacterial infections

104
Q

If children with cystic fibrosis remain untreated, the children die before their 5th birthday

A

Treatment options include:

  • Physical chest clearing
  • Daily antibiotic regimens
  • Life expectancy is about 30 years
105
Q

Sickle-cell disease affects

A

one out of 400 African-Americans

106
Q

Sickle-cell disease is caused by

A

the substitution of a single amino acid in the hemoglobin protein in red blood cells

107
Q

In homozygous individuals,

A

all hemoglobin is abnormal (sickle-cell)

108
Q

Sickle-cell disease symptoms include

A

physical weakness, pain, organ damage, and even paralysis

109
Q

Sickle-cell disease and cystic fibrosis are examples of

A

pleiotropy

110
Q

In sickle-cell disease

A

hh- full blown disease
Hh – sickle-cell trait
HH - normal
Heterozygotes (said to have sickle-cell trait) are usually healthy but may suffer some symptoms

111
Q

About one out of ten African Americans has sickle cell trait, an unusually high frequency of an allele with detrimental effects in homozygotes

A

Heterozygotes are less susceptible to the malaria parasite, so there is an advantage to being heterozygous

112
Q

Some human disorders are caused by

A

dominant alleles

113
Q

Dominant alleles that cause a lethal disease are

A

rare and arise by mutation

114
Q

Achondroplasia is a form of

A

dwarfism caused by a rare dominant allele

DD – lethal
Dd- dwarfism
dd – normal height

This is an example where the recessive allele is more common than the dominant allele

115
Q

The timing of onset of a disease significantly affects its

A

inheritance

116
Q

Huntington’s disease is

A

a degenerative disease of the nervous system

117
Q

Huntington’s disease has no obvious phenotypic effects until the individual is

A

about 35 to 40 years of age
Hh - affected
hh-normal

Once the deterioration of the nervous system begins the condition is irreversible and fatal

118
Q

Many diseases, such as heart disease, diabetes, alcoholism, mental illnesses, and cancer have both

A

genetic and environmental components

119
Q

Little is understood about the

A

genetic contribution to most multifactorial diseases

120
Q

Genetic counselors can provide information to prospective parents concerned about

A

a family history for a specific disease

121
Q

Using family histories, genetic counselors help couples determine the odds that their children will have genetic disorders.

A

Probabilities are predicted on the most accurate information at the time; predicted probabilities may change as new information is available.

122
Q

For a growing number of diseases, tests are available that

A

identify carriers and help define the odds more accurately

123
Q

In amniocentesis,

A

the liquid that bathes the fetus is removed and tested

124
Q

In chorionic villus sampling (CVS),

A

a sample of the placenta is removed and tested

125
Q

Other techniques, such as

A

ultrasound and fetoscopy, allow fetal health to be assessed visually in utero

126
Q

Some genetic disorders can be detected at birth by

A

simple tests that are now routinely performed in most hospitals in the United States

  • PKU
  • -Can’t metabolize phenylalanine – diet
127
Q

Huntington’s disease and Achondroplasia are

A

dominantly inherited disorders

128
Q

gene-

A

a heritable unit that determines a character; can exist in different forms

129
Q

allele-

A

an alternative version of a gene

130
Q

character-

A

a heritable feature that varies among individuals

131
Q

trait-

A

a variant for a character

132
Q

dominant allele-

A

determines phenotype in a heterozygote

133
Q

recessive allele-

A

has no effect on phenotype in a heterozygote

134
Q

genotype-

A

the genetic makeup of an individual

135
Q

phenotype-

A

an organism’s appearance or observable traits

136
Q

homozygous-

A

having two identical alleles for a gene

137
Q

heterozygous-

A

having two different alleles for a gene

138
Q

testcross-

A

a cross between an individual with an unknown genotype and a homozygous recessive individual

139
Q

monohybrid cross-

A

a cross between individuals heterozygous for a single character

Biology 1406 (53 decks)

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