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SFM - Exam #2 > GENE - Principles of Genetic Inheritance > Flashcards

GENE - Principles of Genetic Inheritance Flashcards

1
Q

Describe autosomal dominant pedigrees

A
  • affected offspring have one affected parent
  • unaffected individuals do not transmit trait (no silent carriers)
  • trait expected in every generation at 50%
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2
Q

Describe autosomal recessive pedigrees

A
  • 2 copies of mutant allele is required
  • if one copy is present, individual is only a carrier
  • if two carriers procreate, 25% offspring will be unaffected, 25% will be affected and 50% will be an unaffected carrier
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3
Q

Describe X-linked recessive pedigrees

A
  • females rarely affected; primarily heterozygous carriers
  • unaffected males don’t transmit trait
  • males express phenotype with 1 allele, whereas females need 2 alleles present
  • no father-son transmission, as males receive Y chromosome from father
  • if mother expresses recessive phenotype, all of her sons will be affected
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4
Q

What is lyonization?

A
  • When an additional X chromosome is inactivated (not transcribed)
  • Pattern of inactivation is random and occurs separately in individual cells during development
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5
Q

Describe mitochondrial inheritance pedigrees

A
  • mitochondria are inherited only through mother
  • affected females transmit to all offspring
  • affected males transmit to NONE of their offspring
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6
Q

What is the mitochondrial threshold effect?

A

The severity of mitochondrial mutation correlates to the presentation of the disease. There is a threshold number that must be crossed in order for disease to present.

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7
Q

What does LHON stand for?

A

Leber hereditary optic neuropathy

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8
Q

What occurs in the mitochondrial disorder, LHON?

A

Degeneration of retinal ganglion cells, leading to a dark circle in field of vision

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9
Q

What does MERRF stand for?

A

Myoclonic epilepsy and ragged red fibers

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10
Q

What occurs in a MERRF mitochondrial defect?

A
  • mutation in gene encoding for tRNA of lysine

- disrupts synthesis of cyctochome-c oxidase

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11
Q

What are the signs and symptoms of MERRF?

A

Myoclonus dinated muscle movement, cerebral ataxia, seizures, myopathy, and dementia

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12
Q

What does MELAS stand for?

A

Mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes

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13
Q

What happens when a MELAS mitochondrial disorder is present?

A
  • most common mitochondrial inherited disease
  • affect many systems, including brain, nervous system, and muscles
  • may cause stroke and dementia, diabetes, deafness, cognitive impairment, short stature, and migraines
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14
Q

What does euploid mean?

A

Cells have a normal number of chromosomes

Haploid gametes and diploid somatic cells

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15
Q

What does nondisjunction mean?

A
  • Abnormal separation of homologous chromosomes or sister chromatid
  • occurs at anaphase of mitosis, meiosis I or meiosis II
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16
Q

What is polyploidy?

A
  • Cells contain a complete set of extra chromosomes in a cell
  • Incompatible with human life, often seen in plants
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17
Q

What is aneuploidy?

A
  • Cells contain a missing or additional individual chromosome
  • Monosomy and trisomy
18
Q

What is the karyotype of Turner Syndrome?

A

45, XO

19
Q

What are some of the signs and symptoms of Turner Syndrome?

A

Short stature, ovarian hypofunction, premature ovarian failure, infertility, webbed neck, extra skin, low hairline, lymphedema, and cardiovascular defects
Possible developmental delays

20
Q

What is the karyotype of Klinefelter Syndrome?

A

47, XXY

21
Q

What are the signs and symptoms of Klinefelter Syndrome?

A
  • Varying degrees of cognitive, social, behavioral, and learning difficulties
  • Primary hypogonadism (low testosterone), small and/or undescended testes
  • Gynecomastia, infertility, less dense body hair
  • Variability in X numbers can increase symptoms (48, XXXY; 49 XXXXY)
22
Q

What is another name for Trisomy 21?

A

Down Syndrome

23
Q

Which chromosomes affected by trisomy are compatible with life? Which are not?

A

Trisomy 13, 18, and 21 are compatible with life. The rest are not

24
Q

What are some of the signs and symptoms of Trisomy 21?

A

Short stature, distinct facial features, cardiac defects, duodenal atresia, ventriculomegaly, absent nasal bone, and short limbs

Varying degrees of cognitive impairment

25
Q

What is another name for Trisomy 18?

A

Edwards Syndrome (47, XX/XY,+18)

26
Q

What are the signs and symptoms of Trisomy 18?

A

Microencephaly, prominent occiput, malformed and low-set ears, small mouth and jaw, cleft lip/palate, rocker bottom feet, and overlapping fingers.

Rocker bottom feet is a tell-tale sign of trisomy 18

Approximately 95% of fetuses die in utero, and less than 10% of those born alive survive to 1 year of age.

27
Q

What is another name for Trisomy 13?

A

Patau Syndrome

28
Q

What are the signs and symptoms of Trisomy 13?

A

Severe intellectual disabilities and physical abnormalities, heart abnormalities, kidney malformation, CNS malformation, microcephaly, malformed ears, closely spaced/absent eyes, clenched hands and plydactyly, and cleft lip/palate

29
Q

Define genomic imprinting

A

Alleles that are silenced (not transcribed) such that the gene is expressed only from the non-imprinted allele of the mother or father

30
Q

What is uni-parental disomy?

A

When an individual receives two copies of a chromosome from one parent and no copies from the other parent

Occurs as a random error during meiosis

Can lead to Prader-Willi and Angelman Syndromes

31
Q

What are the symptoms of Pradder-Willi Syndrome?

A

Short stature, hypotonia, small hands/feet, obesity, intellectual disability, uncontrolled eating, and behavioral complications

32
Q

What are the symptoms of Angelman Syndrome?

A

Severe intellectual disability, speech impairment, seizures, ataxic gait, and excitability

33
Q

What causes Prader-Willi Syndrome?

A

Spontaneous deletion/mutation of PATERNAL chromosome 15

34
Q

What causes Angelman Syndrome?

A

Caused by a deletion/mutation in MATERNAL chromosome 15

35
Q

Define penetrance in relation to genetics

A

The probability of expressing a particular phenotype

If < 1.0, genotype is said to have incomplete penetrance

36
Q

Define variable expressivity

A

Trait in which the same genotype can produce phenotypes of varying severity or expression

37
Q

Variable expressivity depends on many environmental factors. Name a few.

A

Diet, exercise, exposure to harmful agents, etc.

38
Q

What are two examples of Variable Expressivity diseases mentioned in lecture?

A

Neurofibromatosis
- Mild expression: cafe-au-lait spots, benign growths on iris, nerve tumors
- Severe expression: thousands of nerve tumors, optic nerve gliomas, learning
disabilities, hypertension, scoliosis, and malignancies

Marfan Syndrome

- Affects connective tissue, subsequently affecting many different systems
- Ectopia lentis and weakened and stretched aorta 
- May lead to aneurysm and aortic dissection
39
Q

What is locus heterogeneity?

A

Single disorder, trait, or pattern of traits caused by mutations in genes at different chromosomal loci

Example: osteogenesis imperfecta (chromosome 7 and 17)

40
Q

Define genotype frequency

A

Number of individuals with a given genotype divided by the total number of individuals in the population

Three possible genotypes: homozygous dominant, homozygous recessive, and heterozygous

Frequencies are denoted as p2, q2, and 2pq

41
Q

Define allele frequency

A

Frequency of occurrence or proportions of different alleles of a particular gene in a given population

Two possible alleles: Dominant and Recessive

Frequencies denoted as p and q

42
Q

What does the Hardy-Weinberg Principle state?

A

Specifies the relationship between allele frequency and genotype frequency

p^2 + 2pq + q^2 = 1

p = dominant allele frequency, q = recessive allele frequency
p^2 = homozygous dominant genotype frequency
q^2 = homozygous recessive genotype frequency
2pq = heterozygous genotype frequency

SFM - Exam #2 (4 decks)

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