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MCM Genetics > Mendelian Genetics > Flashcards

Mendelian Genetics Flashcards

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1
Q

Somatic Cells

A

Cells that are not gametes. Contain 2 copies of each chromosome (1-22) and either XX or XY

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2
Q

Autosome

A

Any chromosome not considered a sex chromosome (1-22)

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3
Q

Allosome (Gonosome)

A

Sex chromosomes (X and Y)

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4
Q

Gametes

A

Ova and sperm cells. Contain 1 copy of each chromosome (1-22) and either X or Y.

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5
Q

Haploid

A

Having one copy of each chromosome.

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6
Q

Diploid

A

Having 2 copies of each chromosome.

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7
Q

Homologous Chromosomes

A

The two chromosomes in a diploid pair. Contain the same genes but one is paternal origin and one is of maternal origin.

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8
Q

Gene

A

A sequence of DNA that encodes a specific protein or RNA

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9
Q

Allele

A

One of several alternative forms of a gene sequence at a locus.

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10
Q

Polymorphism

A

When a locus has multiples alleles present in a population. A genetic variant with at least two alleles and occurs in at least 1% of the population.

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11
Q

Locus

A

A specific chromosomal location.

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12
Q

Wild-Type

A

Allele present in the majority of individuals. Not deleterious.

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13
Q

Mutant

A

Allele that differs from the wild-type due to mutation.

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14
Q

Genotype

A

Set of alleles an individual possesses.

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15
Q

Phenotype

A

Expression of the alleles. Protein present in clinical manifestation.

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16
Q

Homozygous

A

Two alleles at a particular locus are identical.

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17
Q

Heterozygous

A

Two alleles at a particular locus are different.

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18
Q

Hemizygous

A

X-linked genes in males.

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19
Q

Pleiotropism

A

A single mutant gene may result in many phenotypic variants.

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20
Q

Oculodentodigital Dysplasia

A

Example of Pleiotropism. A connexion mutation. Clinical Features: Thin nose, microcephaly, microphthalmia, microcornea, microdontia, partial adontia, hand and foot abnormalities.

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21
Q

Mendelian Inheritance

A

Single Gene (20%). Two categories of single-gene inheritance; autosomal and gonosomal.

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22
Q

Complex Inheritance/Multigenic

A

Unsure of specific mode. Complex. 50%

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23
Q

Environmental teratogen

A

Environmental factor. 5%

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24
Q

Chromosomal Imbalance

A

25%

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25
Q

Dominant

A

Allele that is always expressed, even if another allele is present.

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26
Q

Incompletely dominant

A

Expression of two different alleles results in an intermediate phenotype. For example: A red rose is crossed with a white rose. Offspring are pink roses.

27
Q

Codominant

A

Each allele results in an observable phenotype. For example: Blood type.

28
Q

Recessive

A

Requires the presence of two identical alleles to express an observable phenotype.

29
Q

Loss-of-function

A

Reduced production of a gene product or inactive protein. Most common.

30
Q

Gain-of-function

A

Gene product gains new function. Most often toxic properties. Sometimes increased activity (for example receptor activation). Note: Not necessarily a good gain.

31
Q

Recurrence Risk

A

The probability that the offspring of a couple will express a genetic disease.

32
Q

Autosomal Dominant Disorders

A
  1. Disorder is manifested in the heterozygous state
  2. Both males and females affected
  3. Most often affects enzymes, receptors, feedback inhibitors, and structural protein
33
Q

Dominant Negative Allele

A

Mutant allele negatively affects a normal allele. Multimeric proteins

34
Q

Autosomal Dominant Pedigree

A
  1. Disease typically observed over multiple generations.
  2. Skipped generations unlikely to be seen.
  3. Males and Females equally affected.
35
Q

Haploinsufficiency

A

Normal physiology requires more than half of the fully functioning gene product. Can be sporadic, resulting from a new mutation.

36
Q

Penetrance

A

The frequency (%) in which the allele expresses itself phenotypically.

37
Q

Incomplete Penetrance

A

An individual inherits the allele but is phenotypically normal.

38
Q

Variably Expressed

A

All individuals express the phenotype but to different degrees.

39
Q

Autosomal Recessive Disorder

A
  1. Parents of affected usually unaffected.
  2. Usually completely penetrant.
  3. Onset is usually early in life.
  4. Usually not a new mutuation.
40
Q

Margin of Safety

A

Heterozygous individuals with half the normal content function normally.

41
Q

Autosomal Recessive Pedigree

A
  1. Typically only seen in one generation

2. Males and Females equally affected.

42
Q

Consanguinity

A

The mating of related individuals Individuals who share common ancestors are more likely to carry the same recessive allele.

43
Q

X-Linked disorders

A

Those affecting gonosomes. Most Y-linked disorders cause infertility so this is generally not considered a pattern of inheritance.

44
Q

X-linked recessive disorders

A

Almost all X-linked disorders are recessive. All affected males will be hemizygosity. Heterozygous females usually don’t express the full phenotypic change.

45
Q

X-Linked dominant disorders

A

Few Exist.

46
Q

X-linked recessive pedigree

A

Males are more commonly affected. Skipped generations are common. Male to male transmission not seen.

47
Q

X-linked dominant pedigree

A

Male to male transmission not seen. Heterozygous females are affected so expressed twice as often in females. Skipped generations unusual. No sons but all daughters of an affected male will express the disease.

48
Q

X-Inactivation/Dosage Compensation (General Overview)

A
  1. Inactivates copy of the X chromosome in all somatic cells of females.
  2. Begins during blastocyte formation
  3. Condensed into heterochromatin
  4. Gene regions methylated.
  5. Barr Body
49
Q

Barr Body

A

Highly condensed chromosome visible in the nuclei of interphase cells.

50
Q

X-Inactivation/Dosage Compensation (Rules)

A
  1. Random: 50% chance in each cell that either the maternal or paternal X chromosome is inactivated. Genetic Mosaicism.
  2. Fixed: Once inactivated, every descendent of the cell will have the same X chromosome inactivated.
  3. Incomplete: Some regions not inactivated. Manifesting heterozygotes.
51
Q

Genetic Mosaicism

A

Condition in which cells with different genotypes or chromosome constitutions are present in the same individual.

52
Q

Manifesting heterozygotes

A

Some females will express an X-linked recessive mutation due to X-inactivation.

53
Q

Myotonic Dystrophy

A

Autosomal dominant condition with variable expression in clinical severity and age at onset. Manifests as bilateral cataracts, moderate facial weakness and ptosis, myotonia.

54
Q

SHH Mutation (Sonic Hedgehog)

A

Variable expressivity.Caused by a missense mutation. For example: Mother has a single central upper incisor. Daughter is severely affected with microcephaly, abnormal brain development, hyp-telorism, and cleft palate.

55
Q

Expressivity

A

The severity of expression of the phenotype among individuals with the genotype.

56
Q

Allelic Heterogeneity

A

Different mutations can be responsible for more or less severe expression. Usually not within a family.

57
Q

Pleiotropy

A

A single disease causing mutation affects multiple organ systems.

58
Q

Locus Heterogeneity

A

A single disorder is caused by mutations at different chromosomal loci.

59
Q

Point Mutations

A

Replace one nucleotide with another.

60
Q

Missense mutation

A

Alters the meaning of the sequence such that it encodes a different amino acid. May or may not affect the overall protein structure.

61
Q

Nonsense Mutation

A

Alters the meaning of the sequence to a STOP codon. Protein is truncated. (Stop this nonsense!)

62
Q

Frameshift Mutations

A

Insertion or Deletion into a sequence. If not a multiple of three, entire message is changed in the sequence following it. If a multiple of three, subsequent protein will lose or gain an AA.

63
Q

Trinucleotide Repeat Mutations

A

Amplification of a sequence usually containing Cs and Gs. Dynamic or continually changing during cell division.

MCM Genetics (1 decks)

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