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COB Genetics > Lec 6. Extensions to Medels Rules > Flashcards

Lec 6. Extensions to Medels Rules Flashcards

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1
Q

Y-Linked characteristics are only present in

A

males

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2
Q

Why is the Y chromosome so small compared to the X chromosome?

A

Y chromosome lost DNA over time

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3
Q

What is important for the sex determination in SRY?

A

Y chromosome

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4
Q

What is the theory of the origin of the Y chromosome?

A

Evolved from an ordinary pair of autosomes but over time the Y chromosome lost genes.

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5
Q

What are four example of Y linked diseases?

A

Male infertility, Hypertrichosis pinnae (hairy ear), Retinitis pigmentosa, XYY syndrome

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6
Q

What is the XYY syndrome?

A

male has an extra Y, having 47 chromosomes. Causes increased height, learning disabilities, aggressive acne, aggressive behavior.

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7
Q

What happens if the SRY gene gets translocated?

A

Gets stuck on the X chromosome making the males XX. Results in infertility.

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8
Q

Where do sex linked traits usually originate from?

A

on the sex chromosome, usually the X

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9
Q

What is X-linked recessive inheritance?

A

Mutation in a gene on the X causes the phenotype to be expressed in males.

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10
Q

What is dosage compensation?

A

Inactivation of 1 X chromosome to compensate for different X dosage between the sexes.

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11
Q

What is the Lyon Hypothesis?

A

Suggests that dosage compensation in mammals is by inactivation of all but one X chromosome in cells with more than one X chromosome. Ex: bar body.

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12
Q

What is Mosaicism?

A

Condition in which cells within the same person have a different genetic makeup. Ex: when different X chromosomes are inactivated in neighboring cells.

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13
Q

What is Xic?

A

X inactivation centers are counted

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14
Q

How does X inactivation work?

A

If two or more X chromosomes are present, Xist is turned on, and its RNA product coats one of the X’s RANDOMLY.

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15
Q

When is the X inactivation process undone?

A

During meiosis

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16
Q

List the most common X-linked recessive disorders

A

Red-green color blindness, Hemophilia A&B, Duchenne & Becker’s muscular dystrophy, X-linked Ichthyosis, XLA, and Glucose-6-phosphate dehydrogenase deficiency. Fragile X.

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17
Q

What is Hemophilia A?

A

blood clotting disorder caused by a mutation of the Factor VIII gene. Most common

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18
Q

What is Hemophilia B?

A

A blood clotting disorder caused by a mutation of the Factor IX. Least common

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19
Q

Duchenne muscular dystrophy is associated with what gene mutation?

A

Dystrophin

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20
Q

Which X-linked recessive disorder is a milder form of Duchenne?

A

Becker’s muscular dystrophy

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21
Q

What is X-linked ichthyosis?

A

a form of ichthyosis caused by a hereditary deficiency of the STS enzyme

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22
Q

What is X-linked agammaglobulinemia (XLA)?

A

these pts dont generate mature B cells.

23
Q

What is glucose-6-phosphate dehydrogenase deficiency?

A

Causes nonimmune hemolytic anemia in repsonse to a number of causes, most commonly infection or exposure to certain medication, chemicals, or foods.

24
Q

Can a male cat ever be calico?

A

Yes, XXY

25
Q

True or False? Hemophilia A and B are X linked and usually inherited from a Male carrier

A

False. Usually carried from a Female carrier.

26
Q

Approximately 1/3 of women carrying the hemophilia gene experience bleeding episodes why?

A

Random x inactivation and random bad luck that the bad chromosome got copied

27
Q

A woman who is red/green color blind has children with a man with normal vision. What is the probability that their 1st child will be color blind?

A

1/2 because Mom is going to produce gametes that have the defective gene that have color sensitivity. All of her kids will get the X chromosome but the dad will also give his X, thus 1/2. All females will not be color blind but all males will be colorblind.

28
Q

What are Mendel’s three laws?

A

Principle of segregation, independent assortment and concepts of dominance and recessive.

29
Q

True or False? There are no exceptions in Mendel’s laws

A

False. There are some exceptions.

30
Q

What is an exception to independent assortment?

A

Genes on the same chromosome are linked and may NOT segregate independently

31
Q

What is Genetic linkage?

A

Tendency of the alleles that are located close together on a chromosome to be inherited together during meiosis. Linked genes will segregate together and not obey Mendel’s independent assortment (2nd law).

32
Q

What is the exception to Genetic linkage?

A

If the alleles are far enough apart they can segregate independent from one another.

33
Q

What is linkage disequilibrium?

A

Non-random association of alleles at different loci.

34
Q

When are loci said to be in linkage disequilibrium?

A

When the frequency of association of different alleles is higher or lower than what would be expected if the loci were segregating independently.

35
Q

What is the result of a single-gene disorder?

A

Of a single mutated gene

36
Q

Which is responsible for the greatest number of individuals that will need clinical interventions because of genetic diseases? A single-gene disorder or Multifactorial inheritance?

A

Multifactoral inheritance.

37
Q

What are polygenic traits?

A

Traits that are produced by the interplay of many sets of genes. Ex: height.

38
Q

What is Non-Mendelian inheritance?

A

Pattern of inheritance in which traits do not segregate in accordance with Mendel’s laws.

39
Q

What is an example for non-mendelian inheritance?

A

Direction of shell coiling in some snail species.

40
Q

How is the direction of shell coiling a good non-mendelian inheritance example?

A

The direction of shell coiling of some snails is determined by maternal genetic effects. A protein is carried in the cytoplasm that initiates coiling during early development. This protein causes the phenotype of her offspring to reflect her genotype regardless of their genotype.

41
Q

Why do scientiests care about snail chirality?

A

Initiation of polarity. Since establishing polarity is one of the earliest and most important events in embryological development.

42
Q

What is an allele?

A

Genes at the same locus, two versions of the same gene

43
Q

What are the three types of dominance?

A

Complete dominance, incomplete dominance and codominance.

44
Q

Mendel’s traits all exhibited what type of dominance?

A

Complete dominance

45
Q

Define complete dominance

A

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

46
Q

Define incomplete dominance

A

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

47
Q

Define codominance

A

Phenotype of the heterozygote includes the phenotypes of both homozygotes

48
Q

Define penetrance

A

the % of individuals having a particular genotype that express the expected phenotype.

49
Q

Define expressivity

A

the degree to which a character is expressed

50
Q

What is complete penetrance?

A

Everyone who inherits the disease causing alleles has some symptoms.

51
Q

What is incomplete penetrance?

A

Some individuls dont express the phenotype even though they inherit the alleles.

52
Q

What is variable expression?

A

Symptoms vary in intensity in different people.

53
Q

What is a good example of incomplete penetrance?

A

Human polydactyly

54
Q

What is a good example of variable expression?

A

human polydactyly. since it can be 2 or 3 extra digits.

COB Genetics (32 decks)

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