Inheritance Patterns

Question 1

What is the symbol for a male on a pedigree?

Answer 1

→ A square

Question 2

What is the symbol for a female on a pedigree?

Answer 2

→ A circle

Question 3

How do you show that two people are partners on a pedigree?

Answer 3

→ There is a line between them

Question 4

How do you show children on a pedigree?

Answer 4

→ There is a line down

Question 5

How do you show siblings on a pedigree?

Answer 5

→ There is a line above connecting them from the top

Question 6

How do you show affected people on a pedigree?

Answer 6

→ They are colored in

Question 7

How do you show carriers on a pedigree?

Answer 7

→ A shaded dot within the shape

Question 8

How do you show a consanguineous couple on a pedigree?

Answer 8

→ A double line joining them

Question 9

What is a stillborn baby of unknown sex on a pedigree?

Answer 9

→ A rhombus with the SB symbol

Question 10

How is a spontaneous abortion shown on a pedigree?

Answer 10

→ a triangle

Question 11

How is a therapeutic abortion shown on a pedigree?

Answer 11

→ A triangle with a line through it diagonally

Question 12

How are twins shown on a pedigree?

Answer 12

→ two shapes coming from the same vertical line

Question 13

How is pregnancy shown on a pedigree?

Answer 13

→ A rhombus with a P inside it

Question 14

What is a rhombus on a pedigree?

Answer 14

→ Unaffected person whose sex is unknown

Question 15

How do autosomal dominant conditions manifest?

Answer 15

→ Heterozygous form

Question 16

What are the 4 key things to look for in an autosomal dominant pedigree?

Answer 16

→ Multiple generations affected
→ Both sexes

→ Male to female and female to male transmission
→ Most will have an affected parent
→ If both parents possess the trait, but it is absent in any of their offspring, then the parents are both heterozygous (“carriers”) of the recessive allele

Question 17

How do you know that an autosomal dominant condition is not carried on the sex chromosome?

Answer 17

→ Both genders are affected

→ Transmission between sexes

Question 18

What is the risk for each child of an affected parent with an autosomal dominant condition?

Answer 18

→ 50% risk

Question 19

What is penetrance?

Answer 19

→ % of individuals who carry the mutation and develop symptoms of the disorder

Question 20

What does a 75% penetrance mean?

Answer 20

→ Someone can have the dominant allele but not phenotypically have the disease
→ Huntingtons

Question 21

What is variable expressivity?

Answer 21

→ Variation in the severity/symptoms of the disorder

Question 22

What is a condition that exhibits variable expressivity?

Answer 22

→ Neurofibromatosis I

Question 23

What is somatic mosaicism?

Answer 23

→ New mutation arises at an early stage of embryogenesis
→ Present in some tissues or cells

→ If the majority of cells are not affected then the disease severity is reduced

Question 24

What is germ line mosaicism?

Answer 24

→ New mutation arises during oogenesis or spermatogenesis
→ Mutation present in variable proportion of gametes

→ Some gametes will have the mutation and some will not

Question 25

Which type of mosaicism can be transmitted to offspring?

Answer 25

→ Germ line mosaicism

Question 26

What is anticipation and what kind of disorders does this occur in?

Answer 26

→ Worsening of the disease severity in successive generations
→ occurs in triplet repeat disorders

Question 27

How do autosomal recessive conditions manifest?

Answer 27

→ Homozygous

→ Compound heterozygous

Question 28

What are the key things to look for in an autosomal recessive pedigree?

Answer 28

→ Carriers (heterozygote) not affected
→ Both sexes affected

→ One generation affected
→ can be consanguinity
→ Affected individual does not have affected parents

Question 29

What is a compound heterozygote?

Answer 29

2 mutations are in the same gene
→ Mutations are different

Vast majority of recessive is compound heterozygosity ​

Question 30

What is a homozygote?

Answer 30

→ 2 mutations in the same gene

→ Identical mutations

Question 31

What is an example of different mutations in genes in a compound heterozygote? (cystic fibrosis)

Answer 31

→ delta F508

→ G542X

Question 32

What is an example of the same mutation in genes in a homozygote? (cystic fibrosis)

Answer 32

→ Delta F508

→ Delta F508

Question 33

What are features of autosomal recessive inheritance?

Answer 33

→ Found in clusters of siblings but not in parents and offspring
→ All offspring of affected person are obligate carriers

Question 34

What is the carrier probability for autosomal recessive inheritance?

Answer 34

→ 2/3 for unaffected siblings of affected person

Question 35

What is the recurrence risk for autosomal recessive inheritance?

Answer 35

→ 1/4 for each sibling of the affected person

Question 36

What are the 2 features of X linked recessive inheritance?

Answer 36

→ Women are unaffected carriers
→ no male to male transmission

Hemizygous- loci on X-chromosome in men

Question 37

What are the 2 features of X linked dominant inheritance?

Answer 37

→ Women are affected

→ Males are more severely affected/lethal

Question 38

Why can women be homo or heterozygous for X linked inheritance?

Answer 38

→ They have 2 copies of the X chromosome

Question 39

Why can men not be homo or heterozygous?

Answer 39

→ They only have a single copy of the X linked gene

Question 40

How are X linked genes never passed?

Answer 40

→ never passed from father to son

Question 41

What are all daughters of affected males with an X linked inheritance?

Answer 41

→ obligate carriers

Question 42

What is skewed X inactivation?

Answer 42

→ The majority of genes on a woman’s X chromosome are inactivate
→ One of the X chromosomes are inactivated in all the cells

→ The healthy X chromosome is switched off more often than not so the mutated protein is expressed

Question 43

What is an example of manifesting carriers in X linked disorders?

Answer 43

→ Some women have symptoms

→ Cardiomyopathy in DMD (Duchenne muscular dystrophy)

Question 44

What is Y linked inheritance always passed from and to and what is an example of this?

Answer 44

→ Father to son

→ Hirsutism

Question 45

What is a mutation?

Answer 45

→ A change in genetic material

Question 46

What is a pathogenic mutation?

Answer 46

→ results in an alteration of the function of the gene product which causes a disease phenotype

Question 47

What are 3 types of mutations?

Answer 47

→ Substitutions
→ Deletions

→ Insertions

Question 48

What is a silent/synonymous change?

Answer 48

→ A nucleotide change without an amino acid change

Question 49

What is a missense mutation?

Answer 49

→ Replacement of a single nucleotide

→ Incorrect amino acid gets produced

Question 50

What is the impact of amino acid substitution?

Answer 50

Physiochemical similarity between two amino acids
→ Functional role of a specific domain of protein

→ Phylogenetic conservation of amino acid amongst diverse species

Question 51

What is a nonsense mutation?

Answer 51

→ Replacement of a nucleotide
→ Stop codon is produced

→ Shortening of protein

Question 52

What does an insertion mutation do?

Answer 52

→ Incorrect amino acid sequence

Question 53

What types of insertion are there?

Answer 53

→ In frame (multiple of 3)

→ Frameshift (not a multiple of 3)

Question 54

What types of deletion are there?

Answer 54

→ In frame (multiple of 3)

→ Frameshift (not a multiple of 3)

Question 55

What do most autosomal dominant disorders show?

Answer 55

age-dependant penetrance. As one gets older, they show symptoms. BRCR 1 breast cancer​

Question 56

What is reduced penetrance?

Answer 56

Reduced penetrance- individuals carry mutation but do not show symptoms​

Question 57

Why are frameshift deletions more dangerous than in-frame?

Answer 57

extremely likely to lead to large-scale changes to polypeptide length and chemical composition, resulting in a non-functional protein that often disrupts the biochemical processes of a cell.