mendelian inheritance of single gene defects Flashcards Preview

2020 MHS Genetics Unit2 > mendelian inheritance of single gene defects > Flashcards

Flashcards in mendelian inheritance of single gene defects Deck (68)
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1

causes of single-gene defects

  1. missense point mutation
  2. nonsense point mutation
  3. RNA synthesis/processing mutations
  4. small deletions/insertions (few bases)
  5. large deletions/insertions
  6. abnormal recombination
    1. recombination
    2. unequal crossover

2

a given DNA segment on a chromosome

locus

3

alternative versions of a gene

alleles

4

the most common allele in the population

wild-type

5

an allele that differs from the wild type by mutations

mutant/variant allel

6

there are two or more relatively common alleles in the population (>1% occurrence in population)

polymorphism

7

the set of alleles that constitute an individuals genetic make-up

genotype

8

the observable expression of an individuals genotype. In medicine, it means the expression of the disease

phenotype

9

What type of mutation is this an example of?

  1. sickle cell disease
    1. Glu6Val mutation

missense point mutation

  1. a mutation hat changes an amino acid in the primary structure

10

Duschenne muscular dystrophy

nonsense point mutation

  1. a mutation that creates a sttop codon - leading to a shortened proteins
    1. 250+ mutations of this type

11

what type of mutation is this 

beta-thalassemia

  1. mutation in the promoter region

RNA synthesis/processing mutations

  1. mutations in the promoter of the gene
    1. beta thalassemia patients have mutations in the promoter region of hemoglobin beta genes, which leads to diminished (or lack of ) beta chain synthesis
  2. mutation that influences pre-mRNA splicing (exons are spliced out or a region of an intron becomes part of the coding sequence)

12

what type of mutation leads to a deletion/insertion divisible by 3.

small deletions/insertion (few bases)

  1. can lead to missing or extra amino acids.
    1. if the number of nucleotides deleted/inserted is divisible by 3
  2. can lead to chage in reading fram (frame shift mutation)
    1. if the number of nucleotides deleted/inserted is not dividable

13

May involve multiple exons or an entire gene is gone or moved

Large deletion/inserttions

  1. can involve multiple exons or an entire gene
    1. ~75% of the known defects in Duchenne muscular dystrophy
    2. BUI~90% of alpha thalassemeias are due tot thte deletion (loss) of at least one of the hemoglobin alpha genes

14

what are the causes of 

  1. Duchenne muscular dystrophy 
  2. betathalassemas
  3. alpha thalassemias

  1. duschenne muscular dystrophy
    1. large deletions/insertions
  2. beta thalassemias
    1. RNA synthesis/processing mutations
  3. alpha thalassemias
    1. large deletions/insertions

15

describe the two types of abnormal recombinatiton

  1. recombination 
    1. exchange of genetic material between homologous sequences of chromosomes
  2. unequal crossover 
    1. exhange of genetic material between mispaired sistter chromatids or chromosomes ( when they pair through non-identical regions)
    2. may lead to large deletions, duplications

16

hemophilia A is an examples of what type of single-gene defect?

adnormal recombination

  1. inversion
  2. abnormal recombination occurs between homologous sequencs on the same chromosome 
  3. leading to a duplication or inversion

hemophilia A is due to the inversion of the coagulation factor 8 gene from exon 1 to exon 22

  • ~50 of sever hemophila A

17

describe the following variants

18

the visualization of the inheritance pattern of a phenotype with in the family

19

what genotype is a male with a variant allele on his X chromosome?

hemizygote

20

if not all individuals with a given genotype manifest the pheotype(disease), what does that say about its penetrance?

th variant allele has reduced penetrance

21

22

define and explain penetrance vs expressivity

  1. penetrance
    1. the probability that a variant allele has any phenotypec expression
  2. expressivity
    1. the severity of the expressed phenotype
    2. mild vs severe

23

what can influence penetrance and expressivitty of a disease?

  1. age
  2. environment factors
  3. other genes

24

what is the penetrance when 8 out of 10 people with same genotype has any kind of symptom of the disease?

the penetrance of the disease is 80%

25

what is mendelian inheritance pattern based on?

  1. based on
    1. the chromosomal location of the trait
      1. autosomal
      2. X-linked
    2. the dominance of the trait
      1. recessive 
      2. dominant

26

usually affects males and females equally

autosomal

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affects males and femals at different ratios

X-linked

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the wild type allele is dominant, only homozygotes are affected.

recessive

29

the variant allele can be both heterozygoud and homozygous.

dominant

  1. possibilities
    1. incomplete dominance
      1. homozygotes have more sever symptoms
    2. codominance
      1.  at least two alleles expresses the phenotype

30

with the given pedigree, determine the inheritance pattern.

  1. autosomal recessive disorders
    1. phenotype
      1. manifests only in homozygotes
      2. usually manifestes in siblings and not tparents or offspring
    2. both parents have o be att least heterozygote
    3. equally affects males and females