Lec 6. Extensions to Medels Rules

Question 1

Y-Linked characteristics are only present in

Answer 1

males

Question 2

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

Answer 2

Y chromosome lost DNA over time

Question 3

What is important for the sex determination in SRY?

Answer 3

Y chromosome

Question 4

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

Answer 4

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

Question 5

What are four example of Y linked diseases?

Answer 5

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

Question 6

What is the XYY syndrome?

Answer 6

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

Question 7

What happens if the SRY gene gets translocated?

Answer 7

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

Question 8

Where do sex linked traits usually originate from?

Answer 8

on the sex chromosome, usually the X

Question 9

What is X-linked recessive inheritance?

Answer 9

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

Question 10

What is dosage compensation?

Answer 10

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

Question 11

What is the Lyon Hypothesis?

Answer 11

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.

Question 12

What is Mosaicism?

Answer 12

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

Question 13

What is Xic?

Answer 13

X inactivation centers are counted

Question 14

How does X inactivation work?

Answer 14

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

Question 15

When is the X inactivation process undone?

Answer 15

During meiosis

Question 16

List the most common X-linked recessive disorders

Answer 16

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

Question 17

What is Hemophilia A?

Answer 17

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

Question 18

What is Hemophilia B?

Answer 18

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

Question 19

Duchenne muscular dystrophy is associated with what gene mutation?

Answer 19

Dystrophin

Question 20

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

Answer 20

Becker’s muscular dystrophy

Question 21

What is X-linked ichthyosis?

Answer 21

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

Question 22

What is X-linked agammaglobulinemia (XLA)?

Answer 22

these pts dont generate mature B cells.

Question 23

What is glucose-6-phosphate dehydrogenase deficiency?

Answer 23

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

Question 24

Can a male cat ever be calico?

Answer 24

Yes, XXY

Question 25

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

Answer 25

False. Usually carried from a Female carrier.

Question 26

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

Answer 26

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

Question 27

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?

Answer 27

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.

Question 28

What are Mendel's three laws?

Answer 28

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

Question 29

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

Answer 29

False. There are some exceptions.

Question 30

What is an exception to independent assortment?

Answer 30

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

Question 31

What is Genetic linkage?

Answer 31

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).

Question 32

What is the exception to Genetic linkage?

Answer 32

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

Question 33

What is linkage disequilibrium?

Answer 33

Non-random association of alleles at different loci.

Question 34

When are loci said to be in linkage disequilibrium?

Answer 34

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

Question 35

What is the result of a single-gene disorder?

Answer 35

Of a single mutated gene

Question 36

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?

Answer 36

Multifactoral inheritance.

Question 37

What are polygenic traits?

Answer 37

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

Question 38

What is Non-Mendelian inheritance?

Answer 38

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

Question 39

What is an example for non-mendelian inheritance?

Answer 39

Direction of shell coiling in some snail species.

Question 40

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

Answer 40

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.

Question 41

Why do scientiests care about snail chirality?

Answer 41

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

Question 42

What is an allele?

Answer 42

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

Question 43

What are the three types of dominance?

Answer 43

Complete dominance, incomplete dominance and codominance.

Question 44

Mendel's traits all exhibited what type of dominance?

Answer 44

Complete dominance

Question 45

Define complete dominance

Answer 45

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

Question 46

Define incomplete dominance

Answer 46

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

Question 47

Define codominance

Answer 47

Phenotype of the heterozygote includes the phenotypes of both homozygotes

Question 48

Define penetrance

Answer 48

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

Question 49

Define expressivity

Answer 49

the degree to which a character is expressed

Question 50

What is complete penetrance?

Answer 50

Everyone who inherits the disease causing alleles has some symptoms.

Question 51

What is incomplete penetrance?

Answer 51

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

Question 52

What is variable expression?

Answer 52

Symptoms vary in intensity in different people.

Question 53

What is a good example of incomplete penetrance?

Answer 53

Human polydactyly

Question 54

What is a good example of variable expression?

Answer 54

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