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3) Genetics > Chapter 4: Extensions and Modifications of Basic Principles > Flashcards

Chapter 4: Extensions and Modifications of Basic Principles Flashcards

1
Q

What states does sexual reproduction alternate between?

A

Haploid and diploid states

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2
Q

What produces haploid gametes?

A

Meiosis

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3
Q

What produces a diploid zygote?

A

Fertilization (fusion of gametes)

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4
Q

How do male and female gametes differ?

A

In size and shape

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5
Q

How many pairs of chromosomes do humans have? How many autosomes?

A
  • 23

- 22

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6
Q

What chromosome do males possess? What about females?

A
  • Male: XY

- Female: XX

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7
Q

What is the SRY gene? Which chromosome is it located on?

A
  • Y chromosome
  • Causes the development of male characteristics
  • Females do NOT possess the SRY gene
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8
Q

Which experimentation allowed us to discover that the SRY gene encoded for male characteristics?

A
  • In mice, the SRY gene was knocked-down, which resulted in the loss of male characteristics in a male mouse
  • When the SRY gene was inserted in a female, the mouse gains male characteristics
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9
Q

What allows the X and Y chromosome pairing in males?

A
  • X and Y chromosomes are homologous at the pseudoautosomal regions
  • Similarity is enough to allow pairing of X-Y chromosomes
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10
Q

What is the ratio of XX-XY sex determination?

A

1:1 sex ratio

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11
Q

What is the prevalence of Turner syndrome?

A

1 in 3000 females

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12
Q

What are the symptoms of Turner syndrome?

A
  • Short
  • Low hairline
  • Broad chest
  • Normal intelligence
  • Most likely sterile
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13
Q

What is the genetic problem in Turner syndrome? What is the cause?

A
  • Women only have a single X chromosome in their cells (XO)

- Due to problems at the cohesion level, the homologous chromosomes don’t dissociate, which creates unbalanced gametes.

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14
Q

What is the prevalence of Klinefelter syndrome?

A

1 in 1000 males

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15
Q

What are the symptoms of Klinefelter syndrome?

A
  • Small testes
  • Reduced facial and pubic hair
  • Tall
  • Sterile
  • Normal intelligence
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16
Q

What is the genetic problem in Klinefelter syndrome?

A
  • Men have a Y chromosome and two or more X chromosomes in their cells (XXY, XXXYY, XXXY)
  • Due to non-disjunction as in Turner syndrome
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17
Q

What is the prevalence of Poly-X (Triplo-X) syndrome?

A

1 in 1000 females

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18
Q

What are the symptoms of Poly-X syndrome?

A
  • No distinctive features
  • Tall and thin
  • Few are sterile (incidence is only slightly higher)
  • Few are mentally challenged (incidence is only slightly higher)
  • Often, women live their lives without knowing they have Poly-X
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19
Q

What is the genetic problem in Poly-X?

A
  • Multiple X chromosomes (XXX, XXXX, XXXXX)

- The severity of intellectual disability increases as the number of X chromosomes increases beyond 3

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20
Q

What is androgen-insensitivity syndrome?

A
  • When a person who is genetically male (one X and one Y chromosome) is resistant to male hormones (called androgens)
  • The person has some or all the physical traits of a woman, but the genetic makeup of a man
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21
Q

What organism uses the XX-XO sex determination system?

A

Grasshoppers

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22
Q

In the XX-XO sex determination system, what is a male and what is a female? What might males also possess?

A
  • Female: XX
  • Male: XO (heterogametic) or X (hemigametic)
  • There is no O chromosome - the letter O signifies the absence of a sex chromosome
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23
Q

What organism uses the ZZ-ZW sex determination system?

A

Birds, snakes, amphibians, fish

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24
Q

In the ZZ-ZW sex determination system, what is a male and what is a female? What might males also possess?

A
  • Female: ZW (heterogametic)

- Male: ZZ (homogametic)

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25
Q

What is a genic sex-determining system? What is it found in?

A
  • No sex chromosomes, only sex-determining genes

- Found in some plants, fungi, protozoans, and fish

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26
Q

Give an example of environmental sex determination in Crepidula fornicata.

A
  • As the environment of the limpet changes, the sex will too

- Males are always at the top of the stack

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27
Q

Differentiate chromosomal, genic, and environmental sex determinations.

A
  • Chromosomal: males and females have chromosomes that are distinguishable
  • Genic: sex is determined by genes, but the chromosomes of males and females are indistinguishable
  • Environmental: sex is determined by environmental factors
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28
Q

Give an example of genic sex determination in Drosophila melanogaster.

A
  • X:A is the ratio of the number of X chromosomes over the number of haploid sets of autosomes
  • Male: 0.5 ratio
  • Female: 1 ratio
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29
Q

How many chromosomes does Drosophila melanogaster have?

A
  • 3 pairs of autosomes

- X and Y

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30
Q

XY and XO produce what sex in Drosophila, if there is AA autosomes?

A

Male

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31
Q

XX and XXY produce what sex in Drosophila, if there is AA autosomes?

A

Female

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32
Q

XXX, XXXY and XXXX produce what sex in Drosophila, if there is AA autosomes?

A

Metafemale

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33
Q

XX produces what sex in Drosophila, if there is AAA autosomes?

A

Intersex

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34
Q

XO produces what sex in Drosophila, if there is AAA autosomes?

A

Metamale

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35
Q

Name some contributions to genetics by Drosophila melanogaster.

A
  • Basic principles of heredity including sex-linked inheritance, multiple alleles, epistasis, gene mapping, etc.
  • Mutation research
  • Chromosome variation and behaviour
  • Population and behavioural genetics
  • Genetic control of pattern formation
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36
Q

What are X or Y-linked genes?

A
  • A locus that is present on either the X or the Y, but not on the other
  • Allows for differences in the segregation of the alleles
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37
Q

What causes the transformation of a “female” into a male during puberty (Guevedoces)?

A
  • They have on the Y chromosome a rare allele of a gene that encodes for an enzyme that is involved in the synthesis of testosterone
  • Since this enzyme is defective, the fetus will not have a first peak of testosterone
  • There will only be a peak of testosterone at puberty, allowing them to grow male genitalia later in life
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38
Q

What is dosage compensation?

A
  • Phenomenon that equalizes the amount of protein produced by X-linked genes in the two sexes
  • The activity of the gene must be equalized in certain organisms
  • Some organism won’t do anything though
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39
Q

Provide examples of dosage compensation.

A
  • Halving the activity of genes (worms)
  • Doubling the activity of genes on the X chromosome of males (fruit flies)
  • Inactivation (placental mammals)
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40
Q

What is the genetic cause behind tortoise cats?

A
  • Found in mostly females (rare for males to be affected)
  • Patch of cells that carry one type of allele for the fur colour
  • Another patch of cells carry a different allele, and produce a different colour
  • Dosage compensation: inactivation of one X chromosome in a given cell (random = patches)
  • Due to the Lyon hypothesis (inactivation of X chromosome)
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41
Q

What is the optimal proof that shows that white eyes in Drosophila are X-linked?

A
  • The proof comes from a RECIPROCAL cross
  • If a male has white-eyes (and female has red), it produces a 3:1/
  • If a male has red-eyes (and female has white), a 1:1 ratio is produced
  • In X-linked inheritance, the ratios are different depending on which sex is carrying the trait
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42
Q

What is a reciprocal cross?

A

A pair of crosses between a male of one strain and a female of another, and vice versa

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43
Q

What are the limitations to the study of genetics in humans?

A
  • Controlled mating is not possible
  • Long generation time
  • Human family size is generally small
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44
Q

What do geneticists often use?

A

Pedigrees

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45
Q

What are the characteristics of a pedigree?

A
  • Male: square
  • Female: circle
  • Affected: red
  • Deceased: line crossed
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46
Q

What is an obligate carrier? What is the symbol?

A
  • Carries the gene but does not have the trait

- Red circle in the center of the square/circle

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47
Q

What is a proband? What is the symbol?

A
  • First documented affected family member coming to attention of geneticist
  • P incoming into the shape
48
Q

What is an asymptomatic carrier?

A
  • Unaffected at this time but may later exhibit the trait

- Ex: in Huntington’s disease

49
Q

What is Waardenburg syndrome characterized by?

A
  • Deafness
  • Fair hair
  • Visual problems
  • White forelock
50
Q

How is Waardenburg syndrome inherited?

A

As an autosomal dominant trait

51
Q

What are the characteristics of autosomal recessive diseases?

A
  • Normally appear with equal frequency in both sexes
  • Tend to skip generations
  • More likely to appear among progeny of related parents
52
Q

Cystic fibrosis, sickle cell anemia, and Tay Sachs disease are examples of what?

A

Autosomal recessive diseases

53
Q

What are the characteristics of autosomal dominant traits?

A
  • Appear in equal frequency in both sexes
  • Do not skip generations
  • Affected people have at least one affected parent
54
Q

Huntington’s disease is an example of what?

A

Autosomal dominant disease

55
Q

What is Huntington’s disease?

A

Brain disorder that causes uncontrolled movements, emotional problems, and loss of thinking ability

56
Q

What are the characteristics of X-linked recessive traits?

A
  • Appear more often in males than in females
  • Are NOT passed from FATHER to SON
  • An affected male can pass the allele to a daughter, who is unaffected, and passes it to sons who are
57
Q

Hemophilia and Duchenne muscular dystrophy are examples of what?

A

X-linked recessive traits

58
Q

What is hemophilia?

A
  • Rare genetic bleeding disorder

- Caused by a shortage of certain clotting factors

59
Q

What are the characteristics of X-linked dominant diseases?

A
  • Affect both male and females
  • An affect male must have an affected mother
  • Do not skip generation
  • Affected males pass the trait to all daughters, but none to sons
  • Affected females (if heterozygous) pass the trait on to about half of their sons and daughters
60
Q

What are the characteristics of Y-linked diseases?

A
  • Only in males

- Passed from a father to all his sons

61
Q

Rett syndrome is an example of what?

A

X-linked dominant disease

62
Q

What is Rett syndrome?

A
  • Neurological disorder that mainly affects females

- Caused by mutations in the MECP2 gene located on the X chromosome

63
Q

What is retinitis pigmentosa an example of?

A

Y-linked disease

64
Q

What is retinitis pigmentosa?

A
  • Eye disease that causes severe vision impairment
  • Mutated cells of the retina make defective proteins
  • Gene is linked to the Y chromosome
65
Q

Differentiate X-linked dominant and autosomal dominant pedigrees.

A

In X-linked dominant, whereas affected females can pass on the trait to either sons or daughters, affected males pass on the trait only to all daughters

66
Q

What kind of trait is most likely to appear in a family with consanguinity?

A

Recessive traits

67
Q

Define dominance.

A

Phenotype of the heterozygote is the same as the phenotype of one of the homozygotes

68
Q

Define incomplete dominance.

A

Phenotype of the heterozygote is intermediate (falls within the range) between the phenotypes of the two homozygotes

69
Q

Define codominance.

A

Phenotype of the heterozygote includes the phenotypes of both homozygotes

70
Q

Define penetrance.

A

The proportion of individuals carrying a variant (or allele) of a gene (the genotype) that also express an associated trait (the phenotype)

71
Q

Define expressivity.

A

In those who display the phenotype, it is the degree to which the phenotype is expressed (ex: a little lump of flesh vs. an entire limb)

72
Q

What do multiple alleles at a locus allow for? What is necessary to observe these effects?

A
  • For a greater variety of genotypes and phenotypes

- Observing a large group is necessary

73
Q

What is the equation that defines the number of possible genotypes if there are multiple alleles at a locus?

A

[n(n + 1)]/2 where n is the number of different alleles

74
Q

What is gene interaction?

A

Two different genes (two sets of alleles) contribute to the determination of a single characteristic (phenotype)

75
Q

Provide an example of gene interaction.

A
  • There are two genes encoding for the enzymes for the synthesis pathway of the pigments of peppers
  • Each locus encodes an enzyme for a specific step in the exact same pathway, allowing them to affect the same characteristic
76
Q

Does gene interaction affect the phenotypic ratio?

A

No

77
Q

Define epistasis.

A

The effect of gene interaction in that one gene masks or hides the effect of another gene at a different locus

78
Q

Explain recessive epistasis in a Labrador retriever.

A
  • The E gene is responsible for taking the pigment from the shaft into the hair
  • If the dog is homozygous for e, it is not capable of pushing the pigment out
  • ee masks the effects of other genes
79
Q

Define recessive epistasis.

A

The Recessivealleles at one locus (aa) mask the phenotypic expression of other gene locus

80
Q

Define dominant epistasis.

A

The dominantallele of one gene masks the effects of either allele of the second gene

81
Q

Explain dominant epistasis in squashes.

A
  • When you have a dominant W allele, the enzyme is not functional
  • The enzyme is responsible for producing the color of compound B
  • The color remains compound A
82
Q

What is duplicate recessive epistasis?

A

Two recessive alleles mask the genotype

83
Q

What is the modified dihybrid phenotypic ratio in recessive epistasis?

A
  • 9:3:4
  • A_B_: 9
  • A_bb: 3
  • aa_B and aabb: 4
84
Q

What is the modified dihybrid phenotypic ratio in dominant epistasis?

A
  • 12:3:1
  • A_B_ and A_bb: 12
  • aaB_: 3
  • aabb: 1
85
Q

What is the modified dihybrid phenotypic ratio in duplicate recessive epistasis?

A
  • 9:7
  • A_B_: 9
  • A_bb, aaB_, aabb: 7
86
Q

Define sex-influenced characteristics.

A
  • Determined by autosomal genes
  • Inherited according to Mendel’s principles
  • Expressed differently in males and females
87
Q

Define sex-limited characteristics.

A
  • Encoded by autosomal genes that are expressed in only in one sex
  • The trait has zero penetrance in the other sex
88
Q

What are the four characteristics of cytoplasmically inherited traits?

A
  1. Present in males and females
  2. Usually inherited from one parent, typically the maternal parent
  3. Reciprocal crosses give different results
  4. Exhibits extensive phenotypic variation, even within a single family
89
Q

Which characteristics do not apply to Mendelian rules?

A

Cytoplasmically-inherited

90
Q

Where are cytoplasmically-inherited characteristics encoded in?

A

Genes found on the mitochondrial or chloroplast genome

91
Q

Why don’t cytoplasmically-inherited characteristics not follow Mendelian rules?

A
  • No mitochondria in the sperm, some in the egg
  • Unequal share of genetic information
  • Information largely acquired from the mother
92
Q

If mitochondrial genome is only acquired by the mother, then wouldn’t there be a large number of individuals with the same mitochondrial genome?

A

No, since the mitochondrial genome undergoes multiple generations, allowing it to be unique for each individual

93
Q

Define the genetic maternal effect.

A

The phenotype of the offspring is determined by the genotype of the mother

94
Q

When do genetic maternal effects arise?

A

When substances present in the cytoplasm of an egg (encoded by the mother’s nuclear genes)

95
Q

Which generation determines the genotype in the genetic maternal effect?

A

The F1 generation mother determines the trait for the F2 generation

96
Q

Define epigenetics.

A

The study of heritable changes in gene expression (active vs. inactive genes) that does not involve changes to the underlying DNA sequence

97
Q

Define genomic imprinting.

A

Genes whose expression is affected by the sex of the transmitting parent

98
Q

What affects the way DNA is expressed in genomic imprinting?

A
  • Whether a gene passes through the egg or the sperm determines how much methylation of the DNA takes place
  • The amount of methylation determines whether the gene is expressed in the offspring
99
Q

Is the male gene or the female gene expressed in Igf2?

A
  • Male gene is expressed

- Female gene is silent

100
Q

Describe an example of how the expression of a genotype may be influenced by environmental effects?

A
  • Certain genes are more solicited at a higher temperature
  • For example, in the Himalayan rabbit, colder temperatures cause black fur at the extremities, and warmer temperatures cause white fur
101
Q

How is sex predicted in a fruit fly? How is sex actually determined?

A
  • Predicted by the X:A ratio

- Actually determined by genes on the X chromosome

102
Q

What is a Barr body?

A

Inactivated X chromosome that appears as a condensed, darkly staining structure in most cells of female placental mammals

103
Q

What is the Lyon hypothesis?

A

If a cell contains more than two X chromosomes, all but one of them is inactivated

104
Q

How many Barr bodies will a male with XXXYY chromosomes have in each of his cells? What are those Barr bodies?

A
  • Two Barr bodies

- Each Barr body is an inactive X chromosome

105
Q

What are the causes of incomplete penetrance and variable expressivity?

A

The effects of other genes and environmental factors that can alter or completely suppress the effect of a particular gene

106
Q

How does incomplete dominance differ from incomplete penetrance?

A
  • Incomplete dominance: heterozygote is intermediate between the homozygotes
  • Incomplete penetrance: some individuals do not express the expected phenotype
107
Q

Define a lethal allele.

A

Allele that causes the death of an individual organism, often early in development, so that individuals do not appear in the progeny of a genetic cross

108
Q

What are the effects of recessive and dominant lethal alleles?

A
  • Recessive: kill individual organisms that are homozygous for the allele
  • Dominant: kill both heterozygotes and homozygotes
109
Q

What are the overall effects of lethal alleles?

A

Modify the ratios of progeny resulting from a cross

110
Q

What is a compound heterozygote?

A

Possesses two different alleles that result in a recessive phenotype

111
Q 
A number of all-white cats are crossed, and they produce the following types of progeny: 12/16 all-white, 3/16 black, and 1/16 gray. What is the genotype of the black progeny?
A) Aa
B) AaBb
C) A_B_
D) A_bb
A

D) A_bb

112
Q

If the ratio is 9:3:4, what gene interaction occurred?

A

Recessive epistasis

113
Q

If the ratio is 9:7, what gene interaction occurred?

A

Duplicate recessive epistasis

114
Q

If the ratio is 12:3:1, what gene interaction occurred?

A

Dominant epistasis

115
Q

What kind of characteristics have a higher penetrance in one sex over another?

A

Sex-influenced characteristics

116
Q

In humans, what will be the phenotype of a person with XXXY sex chromosomes?
A) Klinefelter syndrome
B) Turner syndrome
C) Poly-X female

A

A) Klinefelter syndrome

117
Q

How does incomplete dominance differ from incomplete penetrance?
A) Incomplete dominance refers to alleles at the same locus; incomplete penetrance refers to alleles at different loci
B) Incomplete dominance ranges from 0 to 50%; incomplete penetrance ranges from 51 to 99%
C) In incomplete dominance, the heterozygote is intermediate between the homozygotes; in incomplete penetrance, heterozygotes express phenotypes of both homozygotes
D) In incomplete dominance, the heterozygote is intermediate between the homozygotes; in incomplete penetrance, some individuals do not express the expected phenotype

A

D) In incomplete dominance, the heterozygote is intermediate between the homozygotes; in incomplete penetrance, some individuals do not express the expected phenotype

3) Genetics (16 decks)

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