Inheritance Patterns

Question 1

Shape of males in pedigree drawing

Answer 1

Square

Question 2

Shape of females in pedigree drawing

Answer 2

Circle

Question 3

In a pedigree drawing, what do partners have between them?

Answer 3

Partners have a line between them

Question 4

In a pedigree drawing, what do siblings have above them

Answer 4

Siblings have a line above them

Question 5

In a pedigree drawing, who are shaded?

Answer 5

People who are affected are shaded

Question 6

In a pedigree drawing, who have dots inside?

Answer 6

Carriers have dots inside

Question 7

In a pedigree drawing, what do double lines mean?

Answer 7

Are a consanguineous couple(Same blood)

Question 8

What does SB on a pedigree drawing mean?

Answer 8

Still born baby

Question 9

What does the diamond symbol in a pedigree drawing represent?

Answer 9

Means unknown sex

Question 10

What do small triangle symbols in a pedigree drawing represent?

Answer 10

Spontaneous abortion

Question 11

What does a triangle with a line going through it represent?

Answer 11

Represents therapeutic abortion

Question 12

What represents identical twins, non-identical twins?

Answer 12

Identical twins have diagonal lines and a line between them Non identical twins have only diagonal lines

Question 13

What does a diamond with the letter P inside represent?

Answer 13

Represents someone who is pregnant of a child with an unknown sex

Question 14

What symbol represents no offspring?

Answer 14

Question 15

In what form are autosomal dominant inheritance?

Answer 15

Clearly in heterozygous form

Question 16

How many generations are affected by autosomal dominant inheritance?

Answer 16

Multiple generations are affected by autosomal dominant inheritance

Question 17

What will most individuals with autosomal dominant inheritance have?

Answer 17

Most will have an affected parent

Question 18

What is the risk to offspring for autosomal dominant inheritance?

Answer 18

50% risk to offspring

Question 19

Characteristics of autosomal dominant inheritance

Answer 19

-Most individuals have an affected parent -Males and females are equally likely to inherit -An affected individuals siblings/children whom aren’t affected, do not carry the mutation and cannot pass it on to their offspring

Question 20

FEATURES OF AUTOSOMAL DOMINANT INHERITANCE What is penetrance and incomplete penetrance?

Answer 20

Penetrance is the percentage of individuals who carry the mutation and develop symptoms of the disorder -Many dominant disorders show age dependent penetrance Incomplete penetrance is when you have the genotype, but not phenotypically expressed

Question 21

FEATURES OF AUTOSOMAL DOMINANT INHERITANCE What is variable expressivity?

Answer 21

Variation in several symptoms of disorders between individuals with the same mutation

Question 22

FEATURES OF AUTOSOMAL DOMINANT INHERITANCE What varies between autosomal dominant disorders?

Answer 22

De novo mutation rate varies considerably between autosomal disorder conditions

Question 23

FEATURES OF AUTOSOMAL DOMINANT INHERITANCE What is somatic mosaicism?

Answer 23

• Mutn arising at early stage in embryogenesis
• Present in only some tissues/cells (e.g can just be in neuronal cells or skin cells resulting in a difference in the way the disease is presented)

Question 24

FEATURES OF AUTOSOMAL DOMINANT INHERITANCE What is germ line mosaicism?

Answer 24

It is when new mutations arise during oogenesis or spermatogenesis -Mutation present in variable proportion of gametes and can be transmitted to offspring

Question 25

FEATURES OF AUTOSOMAL DOMINANT INHERITANCE What is anticipation?

Answer 25

Worsening of disease severity in successive generations -Characteristically occurs in triplet repeat disorders

Question 26

In what form is autosomal recessive inheritance?

Answer 26

Clearly in homozygous form

Question 27

Who aren't affected by autosomal recessive inheritance?

Answer 27

Carriers aren't affected

Question 28

What sexes are affected by autosomal recessive inheritance?

Answer 28

Both sexes affected

Question 29

How many generations are affected by autosomal recessive inheritance?

Answer 29

Usually one generation affected

Question 30

What may be a factor of autosomal recessive inheritance?

Answer 30

May be consanguinity

Question 31

What are compound heterozygotes?

Answer 31

-2 mutations in the same gene however these mutations are different

Question 32

What is a homozygote?

Answer 32

-2 mutations in the same gene however these mutations are identical

Question 33

What are the features of autosomal recessive inheritance?

Answer 33

-Trait often found in clusters of siblings -All offspring of affected person are obligate carriers

Question 34

Chromosomes in men and women

Answer 34

Men-XY Women-XX

Question 35

What are the affects on BOTH genders of X-linked inheritance?(Recessive)

Answer 35

- Women are carriers and are unaffected - No male to male transmission - Men will give their Y chromosome to their son

Question 36

What are the affects on BOTH genders of X-linked inheritance?(Dominant)

Answer 36

-Women are affected -Males are more severely affected

Question 37

What type of genes are never passed from father to son?

Answer 37

X-linked genes never passed from father to son

Question 38

In X-linked recessive inheritance, who are the obligate carriers?

Answer 38

All daughters of affected males are obligate carriers

Question 39

In X-linked recessive inheritance, what do children of carrier females have a chance of inheriting mutant alleles?

Answer 39

Children of carrier females have a 50% chance of inheriting mutant alleles

Question 40

What is skewed X-inactivation in X-linked recessive inheritance?

Answer 40

* **_Skewed X-inactivation:_** normally most genes on one of a woman’s X-chromosomes are inactivated * generally random but ~10% of women have uneven or skewed X-inactivation. * Healthy X chromosome is switched off, resulting in the expression of more unhealthy X chromosomes in cells which can lead to manifesting carriers. * **_Manifesting carriers:_** manifest (showing), heterozygous carrier however healthy X chromosome has been switched off resulting in the symptoms shown. * e.g. cardiomyopathy in Duchenne Muscular Dystrophy (mothers of unhealthy boys may be manifesting carrier

Question 41

Who are manifesting carriers?

Answer 41

manifest (showing), heterozygous carrier however healthy X chromosome has been switched off resulting in the symptoms shown. e.g. cardiomyopathy in Duchenne Muscular Dystrophy (mothers of unhealthy boys may be manifesting carrier

Question 42

Y linked inheritance

Answer 42

Always and only passed through fathers to sons

Question 43

* What is a mutation? * What is a pathogenic mutation? * Where can mutations be found?

Answer 43

**Mutation** = Change in genetic material **Pathogenic Mutation** = results in the alteration of the function of the gene product and can cause a disease phenotype Mutations can be found in coding DNA, Non-Coding DNA(promoters and introns)

Question 44

What do a pathogenic mutation result in?

Answer 44

Results in an alteration of the function of the gene product and can cause disease

Question 45

What is a silent mutation?

Answer 45

A base change has no change in the amino acid

Question 46

What is a nonsense mutation?

Answer 46

* Introduction of a stop codon resulting in a truncated protein. * Can cause removal of functional parts of protein. * However, mRNA strand can sometimes be degraded via **nonsense mediated decay**

Question 47

What is the difference between in-frame and frameshift mutations?

Answer 47

* **In frame** = protein product machinery can continue to read the DNA sequence after the mutation. May result in sections with protein missing however the overall function remains * **Frameshift** = insertion or deletions of bases of DNA, disrupts the reading frame so the wrong amino acid is put in place, entire sequence following the mutation will be disrupted or read incorrectly In-frame (multiple of three) or frameshift (not multiple of three)

Question 48

What is pleiotropy?

Answer 48

Specific mutation that is affecting multiple systems e.gmosaicism, expressivity, penetrance (one gene will code and control the phenotype or expression of several different and unrelated traits) *Pleiotropy is most often a bad thing, as many diseases are due to a gene controlling so many traits at once. For example, phenylketonuria is a disease caused by pleiotropy.*

Question 49

What does Hemizygous mean?

Answer 49

Hemizygous: Having only a single copy of a gene instead of the customary two copies. All men are **HEMIZYGOUS** for anything on the X chromosome