Study Guide Questions Flashcards
Define mutagen.
An agent that raises rate of mutation above spontaneous rate.
Define mutation.
Change in DNA
What is the approximate incidence of spontaneous mutation (on a per gene per cell division basis)?
About 1/100,000 per gene per cell
Define and distinguish between point mutations and frameshift mutations.
Point mutations: Substitution of one base pair for another, which can lead to substitution of one amino acid for another.
Frameshift mutations: Insertion or deletion of a base pair, which usually changes several amino acids in protein.
Is sickle cell anemia a point or frameshift mutation?
Point mutation
What protein is defective in sickle cell anemia?
hemoglobin
Individuals heterozygous for the sickle cell allele are more resistant to the disease ___________ than individuals who have 2 copies of the normal allele.
Malaria
Describe the Ames Test. What is it used to detect? Why does it use liver extract?
Mix the chemical you want to test with bacteria and liver enzymes. Monitor bacteria and see how many bacteria get a mutation in a specific gene. The more mutations a chemical causes in bacteria, the more it will cause in us.
What are some effects of the atomic bomb and/or Chernobyl from a genetics/mutation point of view?
Liver extract simulates conditions in the body by providing enzymes that may degrade harmless substances into mutagens
What nuclear disaster occurred in 2011?
Fukushima Dai-ichi nuclear disaster: Earthquake and tsunami caused a meltdown in cores of 3 nuclear reactors.
What is the average radiation exposure per year from naturally occurring sources in the US? What is the average exposure per year from all sources?
US: 3 mSv per year
All sources: 6.2 mSv per year
What is considered to be a “safe” level of radiation exposure in a work environment?
About 4.5 Sv = LD 50/60
max of 50 mSv in any one year
How many millisieverts of exposure are there in a full body CT scan? For a chest x-ray? Similar statistics – see notes
CT scan: 10 mSv
Chest x-ray: 0.10 mSv
Dental x-ray: 0.005
Mammogram: 0.42
What does LD50/60 stand for? And what is the radiation exposure level for the LD50/60 in humans?
The dose at which 50% of people will die in 60 days.
________% of pregnancies spontaneously miscarry
15%
Define and distinguish between the following: Hereditary Defect, Congenital Defect, Phenocopy
Hereditary Defect: transmissible from cell to cell (or parent to child)
Congenital Defect: present at birth (due to genes, environment or both)
Phenocopy: condition resulting from environmental factors that mimics a genetic condition (ex. vitamin D induced rickets)
Define and distinguish between the following: Carcinogen, Mutagen, Teratogen
All are the physical or chemical agent that causes:
Carcinogen: cancer (ex. radiation, tobacco, some chemicals)
Mutagen: change in DNA (mutation) (ex. x-rays, UV light)
Teratogen: birth defects (congenital malformation).
Alcohol acts as a (pick one: carcinogen, mutagen, teratogen) during prenatal development.
teratogen: Fetal Alcohol Syndrome
What problems can develop in the child when the mother uses alcohol or thalidomide or DES or accutane during pregnancy?
Alcohol: Fetal Alcohol Syndrome causes distinctive facial characteristics, poor memory, attention problems, mental retardation.
Thalidomide: Causes limb deformitis esp. shortened flipperlike arms and legs.
DES: Increases incidence of adenocarcinoma of cervix and vagina and increased risk of breast cancer in daughters or testicular cancer in sons.
What type of alteration occurs to the chromosomes in each of the following types of aberrations? Deletions, Duplications, Inversions, Translocations
Deletion: missing part of chromosome
Duplication: extra copy of part of chromosome
Inversion: part of chromosome removed, turned around and put in backwards
Translocation: 2 chromosomes that are not homologous exchange part of their arms
Which of the following (duplication, deletion, inversion, reciprocal translocation, Robertsonian translocation) is responsible for each disorder below? o Familial Down Syndrome o Burkitt’s Lymphoma o Cri du chat o William Syndrome
Familial Down Syndrome: Robertsonian Translocation between chromosomes 21 and 14
Burkitt’s Lymphoma: Reciprocal translocation
Cri du chat: Deletion (part of chr. 5)
William Syndrome: Deletion (missing 26 genes on chr. 7)
What is the chromosomal basis of each of the following disorders? Down Syndrome, Patau Syndrome, Edward Syndrome, Turner Syndrome, Klinefelter Syndrome
Down Syndrome: 3 copies of chromosome #21
Patau Syndrome: 3 copies of chromosome #13
Edward Syndrome: 3 copies of chromosome #18
Turner Syndrome: abnormal # of sex chromosomes (X0)
Klinefelter Syndrome: abnormal # of sex chromosomes
Approximately 1 in _____ live births has a chromosome disorder
150
Approximately ____% of miscarried fetuses have a chromosome disorder
50%
Approximately ____% of institutionalized mentally retarded individuals have a chromosome disorder.
6%
Be able to describe each and distinguish between Mendel’s Laws of Random Segregation and Independent Assortment.
Law of Random Segregation: Heterozygous individuals produce 2 gamete types equally frequently.
Each gamete has an equal chance of getting either allele.
Law of Independent Assortment: The migration of alleles of one gene into the gametes does not influence the migration of alleles of a second gene.
Be familiar with the terms: allele, gene, loci
Allele: form of a gene
Gene: segment of DNA
Loci: position on the chromosome
Be able to describe the genetic basis and symptoms of the following disorder: Marfan Syndrome
Dominant gene. Long appendages. Displaced eye lens due to flexible collegen. Heart valve problems and weakened aorta. Pigeon chest.
Be able to work problems similar to:
o How many different gametes can be produced from an individual of genotype AaBBCcdd? What about an individual of genotype aaBbCcDY?
o How many different genotypes would you expect in a cross of the individuals above? How many different phenotypes? What is the probability that the first child is genotype AaBbCcDd? What is the probability that the first child is a male who shows all of the dominant characteristics?
a
Be able to describe the genetic basis and symptoms of the following disorder: Osteogenesis Imperfecta
Dominant gene that affects the production of collagen in bones. 1 gene = multiple characteristics. Variable expressivity. High incidence of bone fractures. Short stature. Weak muscles, loose joints. Blue Sclera. Hearing impairment. Shortened life expectancy in severe forms, normal in mild to moderate forms.
Be able to describe the genetic basis and symptoms of the following disorder: Nail Patella Syndrome
Dominant allele, but about 20% of cases are new mutations.
Pleotropic effects: 1 gene affects multiple traits.
Abnormal development of finger and toenails.
Abnormal or missing patella (kneecap) (slips out of joint).
Other skeletal abnormalities (ex. hips).
High incidence of kidney disease.
High degree of penetrance and variable expressivity.
Define and give an example of each of: penetrance
The per cent of individuals who show the phenotype that is expected for a particular genotype.
100% penetrance if the genotype always causes the expected phenotype.
Ex. Polydactyly
Define and give an example of each of: expressivity
The variation in severity for a particular genetic trait.
Ex. Osteogenesis Imperfecta has variable expressivity.
Define and give an example of each of: epistasis
One trait is controlled by 2 or more genes such that the gene products interact to determine the phenotype of 1 trait.
Ex. Migraines, hearing ability
Define and give an example of each of: pleiotropy
One gene has an effect on several aspects of an individual’s phenotype (one gene affects the phenotype of several traits).
Ex. Osteogenesis Imperfecta and Nail-Patella Syndrome
Not all people of genotype Pp are polydactylous. Is this an example of incomplete penetrance or variable expressivity?
Incomplete penetrance
When are the primary, secondary and tertiary sex ratios measured and what is the approximate value of each?
a
What is the role of the SRY gene in sex development? What chromosome is this gene on?
The sex determining Region of the Y, located on the top part of the Y chromosome.
What is the ovotestes?
Early embryo indifferent stage structures that will develop into either ovaries or testes
When (about how many weeks after fertilization) does the SRY gene begin to direct the ovotestes toward male development?
About 7-8 weeks after fertilization.
Which organs in females correspond to the penis, vas deferens, and testes in males?
Penis: Clitoris
Vas deferens: Fallopian Tubes
Testes: Ovaries
What methods are used to assist in determining the sex of a child at birth? What methods are important in determining gender assignment as individuals are older?
Clinical features. Karyotype to determine if XX or XY Tests for Y chromosome (Y body) Test for Barr Body Ultrasound to see what structures are present internally
What is a Barr Body and how is it used to help identify the sex of an individual?
Inactivated X chromosome.
Inactivation of all except one X chromosome occurs randomly in somatic cells at some point in development. Once activated, all progeny cells have the same X inactivated.
If they have it: female.
Describe the following conditions, their effect on sex characteristic development, the sex chromosome composition of the individuals, the number of Barr bodies present and the effects of each disorder on gender assignment: testicular feminization
a
Describe the following conditions, their effect on sex characteristic development, the sex chromosome composition of the individuals, the number of Barr bodies present and the effects of each disorder on gender assignment: testicular feminization/androgen insensitivity
Description: XY individuals that look like females (sterile).
Effect on development: X Chromosome codes for an androgen receptor. Mutation produces a defective androgen receptor so cells won’t respond properly to make hormone. Male sex development is dependent upon functional androgens.
Sex chromosome: XY
# of barr bodies: 0
Effects on gender: Looks like sterile female: female external genetalia, breast development, no uterus, blind vagina, undescended testes.
Describe the following conditions, their effect on sex characteristic development, the sex chromosome composition of the individuals, the number of Barr bodies present and the effects of each disorder on gender assignment: adrenyl virilism
Description: Can occur later in life leading to development of male secondary sex characteristics (deeper voice, facial hair, more prominent Adam’s apple) and infrequent or absent menstrual periods.
Effect on development: Missing enzyme causes overproduction of male hormones (androgens) by adrenal glands.
Sex chromosome: XX
# of barr bodies: 1
Effects on gender: Male secondary sex characteristics, infrequent/absent menstrual periods.
Describe the following conditions, their effect on sex characteristic development, the sex chromosome composition of the individuals, the number of Barr bodies present and the effects of each disorder on gender assignment: congenital adrenyl hyperplasia
Description: Missing enzyme causes over production of male hormones (androgens) by adrenal glands. Can occur before birth to cause newborn XX individuals to have ambiguous sex characteristics.
Effect on development: Enlarged clitoris that may look like a penis but have normal uterus, ovaries and fallopian tubes. At puberty they develop normal female secondary characteristics.
Sex chromosome: XX
# of barr bodies: 1
Effects on gender: Parents may choose to have genital area altered very young. About 70% identify themselves as female.
Describe the following conditions, their effect on sex characteristic development, the sex chromosome composition of the individuals, the number of Barr bodies present and the effects of each disorder on gender assignment: guevedoces
Description: Ambiguous sex at birth (larger than normal clitoris, but not large enough to be a penis). 5 alpha reductase enzyme, low activity so testosterone is not converted to active form at normal level.
Effect on development:
Sex chromosome: XY
# of barr bodies: 0
Effects on gender: Appear more female like, usually raised as female. Puberty: Big change: Clitoris develops into penis due to increase in male hormones and testosterone. Typically switch to male.
Describe the following conditions, their effect on sex characteristic development, the sex chromosome composition of the individuals, the number of Barr bodies present and the effects of each disorder on gender assignment: Turner syndrome
Description: No second X chromosome.
Effect on development: Wide neck, usually sterile.
Sex chromosome: X0
# of barr bodies: 0
Effects on gender: Usually sterile, usually appear as female.
Describe the following conditions, their effect on sex characteristic development, the sex chromosome composition of the individuals, the number of Barr bodies present and the effects of each disorder on gender assignment: Klinefelter Syndrome
Description: Male is born with extra X chromosome.
Effect on development: May have enlarged breasts, voice may not be as deep.
Sex chromosome: XXY
# of barr bodies: 1
Effects on gender: Appear mostly as male, but mostly sterile.
In sex reversal surgeries, which direction is more easily accomplished: Male to female or female to male?
Male to female
Be able to describe the genetic basis and symptoms of the following disorders at the level presented in class: Rett Syndrome
a
Be able to describe the genetic basis and symptoms of the following disorders at the level presented in class: Rett Syndrome
X linked dominant trait.
Due to mutant MECP2 gene (makes a protein that regulates other genes)
Symptoms: Autistic type symptoms
Severity varies (X inactivation)
Boys die soon after birth, girls normal until 6-18 months, then regression on language and motor skills, loss of use of hands followed by compulsive hand washing behavior, etc.
Be able to describe the genetic basis and symptoms of the following disorders at the level presented in class: Congenital Generalized Hypertrichosis
X-linked Dominant
Werewolf syndrome
Extra hair
About 19 in the world
Be able to describe the genetic basis and symptoms of the following disorders at the level presented in class: Amelogenesis Imperfecta
a
Be able to describe the genetic basis and symptoms of the following disorders at the level presented in class: Amelogenesis Imperfecta
X-linked dominant
Males more than females
Enamel crystals are not produced normally
Little to no enamel on teeth.
Be able to describe the genetic basis and symptoms of the following disorders at the level presented in class: Colorblindness
X-linked recessive
Red-green color blindness
Be able to describe the genetic basis and symptoms of the following disorders at the level presented in class: Hemophilia
X-linked recessive
Clotting factor VIII is defective
Be able to describe the genetic basis and symptoms of the following disorders at the level presented in class: Duchenne Muscular Dystrophy
X-linked recessive 1 in 3500 males Defective dystrophin protein that is a structural protein in muscles. Muscle degeneration, paralysis, death. Higher risk of heart problems.
True or False:
o If an abnormal characteristic is considered to be an X-linked dominant trait and the father has the characteristic, his daughter has to have the characteristic also.
a
True or False:
o If an abnormal characteristic is considered to be an X-linked dominant trait and the father has the characteristic, his daughter has to have the characteristic also.
True because the father only has one X to give to the daughter, and that X has the dominant gene.
True or False:
o If an abnormal characteristic is considered to be an X-linked dominant trait and the father has the characteristic, his son must also be affected.
False because the father gives the Y to the son, not the X.
You should expect more than one pedigree problem on the test. Problems done in class are good examples of the types of problems you should expect.
a
True or False:
o If a trait is located on the Y chromosome and the father has the characteristic, approximately half of his sons are expected to have it.
False, all of his sons will have it because he has to give them his Y.
You may be asked to determine genotypes, phenotypes, probability of progeny types from crosses, identify individuals based on the pedigree numbering system, distinguish between types of symbols on pedigrees (married individuals, siblings, twins (monozygotic and dizygotic), consanguineous marriages,proband, etc)
a
You may be asked to draw a pedigree to conform to a word description
a
You may be asked to determine if the shaded trait is dominant, recessive, X-linked, Autosomal, Y linked
Autosomal: Mother and Father unshaded, daughter shaded: shaded is recessive
Autosomal: Mother and Father shaded, daughter unshaded: shaded is recessive
X-Linked: Mother and son are differently shaded, mother is dominant.
