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

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

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 4 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

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)