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GGE > Genetics 1 - Inheritance Patterns > Flashcards

Genetics 1 - Inheritance Patterns Flashcards

1
Q

essential learning outcomes

A
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2
Q

Klippel-Feil Syndrome clinical symptoms

A

webbed neck

high arched palate

normal carrying angle

low set hairline - mid thoracic spine

congenital protrusion from skull

pectus excavatum

no organomegaly

kyphoscoliosis

significant restricted range of movement cervical and thoracic spine

SOB - minimal exertion

acute kidney injury

thoracic aortic aneurysm and thoracoabdominal aneurysm

dilation of aortic arch

bilateral pulmonary hyperinflation

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3
Q

what causes symptoms of Kippel-Feil Syndrome

A

congenital fusion of any 2 of 7 cervical vertebrae

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4
Q

Klippel-Feil Syndrome - mutations of what genes

A

GDF6

GDF3

MEOX1

(bone development)

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5
Q

Klippel-Feil Syndrome inheritance pattern

A

can be autosomal dominant or recessive (depends on gene involved)

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6
Q

Huntington disease inheritance pattern

A

autosomal dominant pattern

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7
Q

characteristics of Huntington

A

progressive neuronal loss - loss of neurons in basal ganglia

disease onset usually 30’s or 40’s

survival for 15-20 yrs after 1st symptoms

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8
Q

gene associated with Huntington

what sort of mutation is it

A

HTT gene

Polyglutamine/repeat expansion mutation

Trinucleotide repeat - repeat for CAG (makes glutamine)

Multiple copies of CAG

Non functional huntington protein

The more repeats you have, the earlier you are likely to display symptoms and more severe the phenotype will be

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9
Q

anticipation of Huntington

A

offspring may have earlier onset/more severe phenotype than parent due to further expansion of the repeat

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10
Q

risk for children - Huntington

A

27-35 repeats

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11
Q

incomplete penetrance - Huntington

A

36-39 repeats

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12
Q

no of repeats needed to develop Huntington

A

40+

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13
Q

how to screen for Huntington

A

preimplantation and prenatal diagnosis

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14
Q

select the non-hereditary, congenital diseases from the following list

A
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15
Q

rank these concepts in order of appearance

A
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16
Q

autosomal inheritance

A

not sex dependent

allele located on 1 of 22 autosomes

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17
Q

X-linked inheritance

A

clear pattern of sex dependent inheritance

allele located on the X chromosome

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18
Q

pedigree interpretation

A
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19
Q

what’s the pattern of mendelian inheritance

A

recessive

neither of Alexei’s parents have the condition

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20
Q

X linked recessive pattern - Mendelian inheritance

A

character is typically manifested in male offspring of UNAFFECTED offspring

not in offspring of affected males

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21
Q

X linked recessive basis - Mendelian inheritance

A

genetic locus is on an X chromosome

female has 2 X chromosomes

non-functional allele on 1 X chromosome means

  • 1 functional allele for a woman
  • no functional allele for a man
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22
Q

how can a female with carrier mother display classical haemophilia A

A

de novo mutation in the “good” allele

or

daughter of haemophiliac father and carrier mother

also by UPD of maternal X or by skewed X-inactivation of paternal X

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23
Q

vit D resistant rickets also known as

inheritance pattern

A

X-linked hypophosphatemic rickets (XLH)

X linked dominant

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24
Q

what is the only known Y linked character

A

maleness

50% chance that each child of an affected male will manifest the character

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25
Q

what pattern of mendelian inheritance is this

A

autosomal recessive

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26
Q

what pattern of mendelian inheritance is this

A

both males and females affected so probably not X linked

affected in every generation

AUTOSOMAL DOMINANT

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27
Q

e.g. of a dichotomous trait

A

cleft chin - dominant

1 gene (MENDELIAN)

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28
Q

mendelian

A

1 gene involved

29
Q

polygenic/multifactorial

A

character is determined by a large no of genes and the interaction of expression of those genes with the environment - not Mendelian

height

shoe size

eye colour

intelligence

30
Q

environmental influence - trait independent of such factors

A

Huntington

always associated with an expressed trait

31
Q

T2D and environment

A

genetic predisposition to develop T2D but if one watches their diet, unlikely to develop it

32
Q

incomplete penetrance

A

penetrance = probability of a genotype/trait being expressed

phenotype only expressed in a fraction of the population with the genotype

33
Q

variable expressivity

A

variation in phenotype expression when penetrance is complete

a range of symptoms displayed in individuals with the same fully penetrant genotype

34
Q

what happens when penetrance is incomplete but high

A

the disease will appear to be Mendelian but may occasionally appear to skip a generation

most obvious for autosomal dominant inheritance

35
Q

what happens when penetrance is low

A

mendelian patterns are often very difficult to appreciate in the absence of large extended pedigrees

36
Q

prevalence of variable expressivity

A

the norm among genetic diseases and is particularly common for disorders that affect multiple organ systems

37
Q

factors that influence penetrance and expressivity

A

age

gender

environmental risk factors

lifestyle risk factors

modifier genes

parents of origin (epigenetic) effects

38
Q

clinical case

A
39
Q

inheritance pattern of hypercholesterolemia

associated genes

A

dominant pattern of inheritance

LDLR gene on Chr 19

40
Q

clinical symptoms of hypercholesterolemia

A

skin lesions (xanthelasmata) present on eyelids and under eyes

MI

xanthomas

41
Q

things to remember

A
42
Q

genome

A

all of the hereditary info that an organism has encoded in its DNA (or for some viruses DNA)

43
Q

chromosome

A

a threadlike structure of DNA and protein (chromatin) found in the nucleus of most living cells

each chromosome has many genes which carry genetic info

human cells have 23 pairs of chromosomes (22 autosomes + our sex chromosomes)

44
Q

gene

A

unit of heredity which is transferred from a parent to offspring and is responsible for a character/trait of the offspring

or a DNA sequence associated with a particular property/encoding for a particular protein

45
Q

allele

A

each of 2 or more alternative forms of a gene that arise by mutation and are found at the same place (locus) on a chromosome

46
Q

homozygous

A

refers to a gene with identical alleles on both homologous chromosomes

47
Q

heterozygous

A

refers to a gene with different alleles on each homologous chromosome

48
Q

phenotype

A

observable physical or biochemical characteristics of an organism, as determined by both genetic makeup and environmental influences

49
Q

genotype of an organism

A

the entire set of allels in an organism that determines the expression of its characteristics or traits

(Which allele do you have at each locus on your chromosomes)

50
Q

trait/character

A

a specific part/relatively discrete element of total phenotype

51
Q

dichotomous characters

A

yes/no

extra fingers, presence or absence of a disease

52
Q

quantitative/continuous characters

A

height

IQ

53
Q

mendelian characters

synonym

A

specific identifiable characters/traits (normal or pathological) that show a fairly clear cut pattern of inheritance

monogenic

the specific character/trait depends mostly on genotype at a single gene locus

given an otherwise normal genetic and environmental background 1 allele at 1 specific locus determines the character

In HETEROZYGOUS state he was able to tell if traits were recessive or dominant

54
Q

mendelian disease

A

Huntington

4p16.3

55
Q

punnett square

A

mother is heterozygous for H allele (dominant pattern of inheritance for monogenic Huntington’s disease character)

father is homozygous for h allele (recessive pattern of inheritance for non HD character)

56
Q

inheritance pattern - CF

A

recessive

terms generally refer to pattern of inheritance of character (phenotype) rather than to the gene

57
Q

dominant and recessive describe

A

functional relationship of 2 different alleles of the same gene in a (compound) heterozygous organism

58
Q

dominant genetic characters

A
59
Q

recessive genetic characters

A
60
Q

fully penetrant condition

A

e.g. Huntington

clinical phenotype is manifested in 100% of the offspring with the appropriate genotype

61
Q

incomplete/reduced penetrance condition

A

e.g. breast cancer in carriers of BRCA1 and BRCA2 genes

clinical phenotype is not observed among all individuals

High risk for breast cancer, but not 100% guaranteed to display breast cancer

62
Q

what influences penetrance

A

penetrance is a complex continuum influenced by other (modifier) genes and non-genetic factors (environment, lifestyle, age, epigenetics)

63
Q

penetrance of mendelian conditions vs multi-factorial

A

Mendelian single gene conditions - more likely to be fully penetrant

Multi-factorial - less than 100% penetrance

64
Q

e.g. variable expressivity

A

even siblings with the same mutation for Cystic Fibrosis have varying degrees of lung and pancreas dysfunction

65
Q

variable expressivity in neurofibromatosis type 1

A
66
Q

incomplete dominance

A

intermediate inheritance in dominant disorders in which 1 allele is not completely expressed over its paired allele (blending of traits)

clinical phenotype of MOST DOMINANT genetic traits in heterozygotes (Aa) is in-between that of wild-type (aa) and mutant homozygotes (AA)

homozygosity for a disease causing mutation (AA) with dominant pattern of inheritance often results in much more severe clinical phenotype

67
Q

e.g. incomplete dominance

A

e.g. achondroplasia (short limbed dwarfism)

heterozygosity for FGFR3 mutation (Ff) = short limbed dwarfism

homozygosity for FGFR3 mutation (FF) = stillborn/early death due to resp failure (underdeveloped ribcage)

68
Q

clinical case - Marfan syndrome

associated gene

symptoms

A

MCQ

69
Q

things to remember

A

GGE (33 decks)

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