Lec 6. Extensions to Medels Rules Flashcards
Y-Linked characteristics are only present in
males
Why is the Y chromosome so small compared to the X chromosome?
Y chromosome lost DNA over time
What is important for the sex determination in SRY?
Y chromosome
What is the theory of the origin of the Y chromosome?
Evolved from an ordinary pair of autosomes but over time the Y chromosome lost genes.
What are four example of Y linked diseases?
Male infertility, Hypertrichosis pinnae (hairy ear), Retinitis pigmentosa, XYY syndrome
What is the XYY syndrome?
male has an extra Y, having 47 chromosomes. Causes increased height, learning disabilities, aggressive acne, aggressive behavior.
What happens if the SRY gene gets translocated?
Gets stuck on the X chromosome making the males XX. Results in infertility.
Where do sex linked traits usually originate from?
on the sex chromosome, usually the X
What is X-linked recessive inheritance?
Mutation in a gene on the X causes the phenotype to be expressed in males.
What is dosage compensation?
Inactivation of 1 X chromosome to compensate for different X dosage between the sexes.
What is the Lyon Hypothesis?
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.
What is Mosaicism?
Condition in which cells within the same person have a different genetic makeup. Ex: when different X chromosomes are inactivated in neighboring cells.
What is Xic?
X inactivation centers are counted
How does X inactivation work?
If two or more X chromosomes are present, Xist is turned on, and its RNA product coats one of the X’s RANDOMLY.
When is the X inactivation process undone?
During meiosis
List the most common X-linked recessive disorders
Red-green color blindness, Hemophilia A&B, Duchenne & Becker’s muscular dystrophy, X-linked Ichthyosis, XLA, and Glucose-6-phosphate dehydrogenase deficiency. Fragile X.
What is Hemophilia A?
blood clotting disorder caused by a mutation of the Factor VIII gene. Most common
What is Hemophilia B?
A blood clotting disorder caused by a mutation of the Factor IX. Least common
Duchenne muscular dystrophy is associated with what gene mutation?
Dystrophin
Which X-linked recessive disorder is a milder form of Duchenne?
Becker’s muscular dystrophy
What is X-linked ichthyosis?
a form of ichthyosis caused by a hereditary deficiency of the STS enzyme
What is X-linked agammaglobulinemia (XLA)?
these pts dont generate mature B cells.
What is glucose-6-phosphate dehydrogenase deficiency?
Causes nonimmune hemolytic anemia in repsonse to a number of causes, most commonly infection or exposure to certain medication, chemicals, or foods.
Can a male cat ever be calico?
Yes, XXY
True or False? Hemophilia A and B are X linked and usually inherited from a Male carrier
False. Usually carried from a Female carrier.
Approximately 1/3 of women carrying the hemophilia gene experience bleeding episodes why?
Random x inactivation and random bad luck that the bad chromosome got copied
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?
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.
What are Mendel’s three laws?
Principle of segregation, independent assortment and concepts of dominance and recessive.
True or False? There are no exceptions in Mendel’s laws
False. There are some exceptions.
What is an exception to independent assortment?
Genes on the same chromosome are linked and may NOT segregate independently
What is Genetic linkage?
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).
What is the exception to Genetic linkage?
If the alleles are far enough apart they can segregate independent from one another.
What is linkage disequilibrium?
Non-random association of alleles at different loci.
When are loci said to be in linkage disequilibrium?
When the frequency of association of different alleles is higher or lower than what would be expected if the loci were segregating independently.
What is the result of a single-gene disorder?
Of a single mutated gene
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?
Multifactoral inheritance.
What are polygenic traits?
Traits that are produced by the interplay of many sets of genes. Ex: height.
What is Non-Mendelian inheritance?
Pattern of inheritance in which traits do not segregate in accordance with Mendel’s laws.
What is an example for non-mendelian inheritance?
Direction of shell coiling in some snail species.
How is the direction of shell coiling a good non-mendelian inheritance example?
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.
Why do scientiests care about snail chirality?
Initiation of polarity. Since establishing polarity is one of the earliest and most important events in embryological development.
What is an allele?
Genes at the same locus, two versions of the same gene
What are the three types of dominance?
Complete dominance, incomplete dominance and codominance.
Mendel’s traits all exhibited what type of dominance?
Complete dominance
Define complete dominance
Phenotype of the heterozygote is the same as the phenotype of one of the homozygotes
Define incomplete dominance
Phenotype of the heterozygote is intermediate (falls within range, blending) between the phenotypes of the two homozygotes
Define codominance
Phenotype of the heterozygote includes the phenotypes of both homozygotes
Define penetrance
the % of individuals having a particular genotype that express the expected phenotype.
Define expressivity
the degree to which a character is expressed
What is complete penetrance?
Everyone who inherits the disease causing alleles has some symptoms.
What is incomplete penetrance?
Some individuls dont express the phenotype even though they inherit the alleles.
What is variable expression?
Symptoms vary in intensity in different people.
What is a good example of incomplete penetrance?
Human polydactyly
What is a good example of variable expression?
human polydactyly. since it can be 2 or 3 extra digits.
