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Block 2 > Genetics lecture 2 > Flashcards

Genetics lecture 2 Flashcards

1
Q

What are the different classifications of human genetic disorders?

A
  1. Single gene disorders
  2. Chromosomal disorder
  3. Multifactorial or polygenic disorders
  4. Mitochondrial disorder
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2
Q

What id the law of segregation?

A

Alleles segregate from each other in the formation of gametes, 1/2 the gametes carry one allele, and the other 1/2 carry the second allele.

At fertilization, gametes are randomly combined

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3
Q

What is the principle of independent assortment?

A

Genes for different traits assort independently of one another in the formation of gametes

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4
Q

What is the exception to the 2 Mendel’s laws?

A

The 2 rules only work if each trait is located on a different chromosome and if the traits are independent

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5
Q

How do diploid organisms get their alleles?

A

Inherit one allele from each parent

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6
Q

What are the different degrees of relatives? What is precent of genes in common in each degree?

A
  1. First degree: 50% (parents, sibling and children)
  2. Second degree: 25% (grandparents, uncles, aunts, nephews, grandchildren, half-siblings)
  3. Third degree: 12.5% (1st cousins)
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7
Q

What is recurrent risk?

A

The likelihood that a trait or disorder present in one family member will occur again in other family members in the same or subsequent generations

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8
Q

What are the most common classes of genetic diseases?

A
  1. Enzyme defects: almost always recessive
  2. Defects in receptor proteins
  3. Transport defects
  4. Disorders of structural proteins
  5. Neurodegenerative disorders
  6. Mitochondrial diseases
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9
Q

What is autosomal dominant inheritance?

A
  1. one allele is altered
  2. homozygous lethal
  3. no carriers
  4. most affected individuals are heterozygous
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10
Q

What are the rules of transmission for autosomal dominant disorders?

A
  1. Affected individuals are observed in each generation, creating a vertical pattern of inheritance. Affected individuals always have an affected parent
  2. The recurrence risk is 1/2 of the children born to a single affected parent will be affected
  3. Unaffected people have normal children
  4. Both males and females can be affected and can pass the abnormal gene to their offspring
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11
Q

What are the common alterations in dominant disorders?

A
  1. Haploinsufficiency
  2. Gain-of-function
  3. Dominant-negative effect
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12
Q

What is haploinsufficiency?

A

Reducted dosage of the wild-type allele is not enough for the normal function of the protein

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13
Q

What is gain-of-function?

A

The gene product of the mutated allele gains a new abnormal function

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14
Q

What is dominant-negative effect?

A

The mutated allele (misshapen protein) acts with the gene product of the wild-type allele and inhibits its function

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15
Q

What is autosomal recessive disorder?

A
  1. When BOTH alleles are altered

2. Affected individuals inherit one copy from each parent, so both parents are heterozygous for the disease

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16
Q

What are the rules of transmission for autosomal recessive disorders?

A
  1. The trait may be found in siblings
  2. Parents are usually healthy but carry one altered allele
  3. Horizontal pattern of inheritance
  4. The recurrence risk is 1/4 of having a second affected child since both parents are heterozygous
  5. The trait may appear as an isolated event
  6. Parents of affected children may be related
  7. Males and females are equally affected
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17
Q

What is special about recessive diseases?

A

One copy of the gene product is enough to provide the appropriate function. The affected gene is often an enzyme

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18
Q

What is special about X-lined inheritance?

A
  1. Since males have only one X chromosome (hemizygous), they can only pass the gene onto their daughters
  2. X-linked diseases can be dominant or receissive
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19
Q

What are the rules of transmission for X-linked recessive disorders?

A
  1. There is no male-to-male transmission; males only pass on the Y chromosome to their sons. Affected males will transmit the gene to all of their daughters
  2. The disease can skip a generation
  3. Affected males have phenotypically normal offspring but their daughters are obligated carriers
  4. Affected males get affected genes from their mothers
  5. Female carriers will pass the abnormal gene to 1/2 of their offspring. Sons that inherit the gene will be affected and daughters will be carriers like their mothers
  6. Female carriers may be mildly symptomatic due to unequal inactivation of the X-chromosome
  7. Unaffected males do not transmit the disorder
  8. Males only need 1 copy to be affected
20
Q

What are the characteristics of a dominant X-lined disease?

A
  1. Both males and females are affected
  2. Fathers will pass the gene to ALL of their daughters, but NONE of their sons
  3. The pattern of inheritance from a mother is the same as autosomal dominant
  4. Frequently lethal in males
21
Q

What are some characteristics of mitochondrial inheritance?

A

Every cell contains mitochondria in the cytoplasm. mtDNA is comprised of a small double stranded circle

Mitochondrial genome is very small and only contains a few genes

Only ova cells contribute mitochondria to the developing embryo. So ONLY females can pass on mitochondrial conditions to their children

22
Q

What are the rules of transmission for mitochondrial disorders?

A
  1. Affected mothers pass the disease to all of her children
  2. Affected males don’t pass the disease to their children
  3. Both sexes are equally affected
23
Q

What are the complications in Medelian inheritance?

A

Both environmental and genetic factors can influence the expression of a disease and complicate pedigree interpretation

24
Q

What are the signs that a new mutation has occurred?

A

A case without a family history where the pehnotype matches a well-known genetic disease

25
Q

What is achondroplasia?

A
  1. Autosomal dominant disease
  2. Leading cause of dwarfism
  3. 80% born to parents of normal height
  4. Cause: in most cases, the disorder is due to new mutations in the FGFR3 gene with no family history disease
26
Q

What is Duchenne muscular dystrophy?

A
  1. X-linked recessive disease
  2. Progressive loss of muscle function and weakness, which begins in the lower limbs before 6y/o
  3. Due to muew mutation at the dystrophin gene that leads to loss of the Dystrophin protein
27
Q

What is semidominance?

A

Blending or grading of different genotypes. A phenotype is intermediate between the dominant and the recessive phenotype

28
Q

What is co-dominance?

A

Each allele produces a pphenotype independent of each other

29
Q

Describe the inheritant pattern of ABO blood group?

A

Co-dominance

A alleles produce A antigens on the surface of blood cells
B alleles produce B antigens on the surface of the blood cells
AB blood type expresses both A and B alleles on the surface

30
Q

Describe sickle cell’s inheritance pattern?

A

Co-dominance

Two alleles (HbA and HbB). HbAA individuals are normal. HbSS have he disease and HbAS individuals are mildly anemic and protective for malaria

31
Q

What is polygenic or multifactorial inheritance?

A

Caused by multiple genes interactions or gene and environment interactions

Show a gradient of phenotypes, not all or nothing phenotypes.

Caused by the interaction between a variety of genes as well as environmental factors

32
Q

What is linkage?

A

2 genes are close together on a single chromosome, they tend to be inherited together

The closer they are on a chromosome, the more likely they are inherited together

33
Q

What is variable expressivity?

A

Not all individuals carrying a disease gene express the same phenotype. Affected individuals are genotypically the same, but may exhibit a different combination of the phenotype

Individuals may express all of the symptoms or just a few; however all individuals show some symptoms

34
Q

What is variable penetrance?

A

Describes the percentage of people in a population with a predisposing genotype that are affected.

95% penetrant indicates that 95% of the population with a single disease gene develop the disease while 5% do not.

35
Q

How does age of onset affect Huntington’s disease?

A

Huntington’s disease has a wide age of onset. It’s a dominant neurodegenerative disorder.

Children are rarely affected, but all will develop the disease if they live long enough

36
Q

What is anticipation?

A

Refers to an earlier age of onset and increased severity with each generation

37
Q

What is myotonic dystrophy?

A

Caused by expansion of a trinucleotide CTG repeat in the 3’ untranslated region of a gene encoding a protein kinase on chromosome 19.

The severity of the disease correlates with the number of repeats. The repeated units are unstable and can expand in subsequent generations leading to more severe phenotype

38
Q

What is genetic heterogeneity?

A

Disorders caused by mutations in more than one gene that are seemingly unrelated, but these genes may act at different points in the same biochemical or regulatory pathway

39
Q

What is mosaicism?

A

Individual has a mixture of genetically different cells

Due to mutations that are generated during development. Some cells will have the mutation while others will not.

If this occurs early during development, an individual will have a larger percent of mutant cells compared to if the mutation occurs at a later time

Can be germline if it alters the sperm or egg. Somatic if it alters non-germ cells

40
Q

What is epistasis?

A

Interaction of 2 or more genes to produce a phenotype

41
Q

What is locus?

A

Chromosomal location of a gene or a trait

42
Q

What is an allele?

A

Two or more sequence variants of a gene that are located at the same site on a chromosome

43
Q

What is genotype?

A

Two alleles present at a given locus in an individual.

Homozygote: 2 identical alleles at the locus

Heterozygote: 2 different alleles

44
Q

What is phenotype?

A

Observed clinical, biochemical or physical expression of a genotype, resulting from the interaction of te genotype with the environment

45
Q

What is dominant?

A

Expression of a phenotype that masks the effect of the second allele

46
Q

What is proband?

A

The individual who 1st brings a family to the attention of a geneticist

47
Q

What is consanguinity?

A

2 individuals are consanguineous if they have at lease one common ancestor–no more remote than a great-grandparent

Block 2 (3 decks)

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