Modes of Inheritance

Question 1

what are the M’s ?

Answer 1

• Mendelian (most important 1)
• Multifactorial (most important 2)
• iMprinting
• Mitochondrial
• Mosaicism

Question 2

what is penetrance?

Answer 2

• The likelihood of having a disease if you have a gene mutation
• 100% penetrance means you will always get the disease if you have the mutation

Question 3

what are mendelian disorders?

Answer 3

diseases that segregates (spread around) families in manner predected by Mendels law(basically was finding out that we had dominant and recessive genes and about how they came from parents )

= Essentially a disease that is predominantly caused by a change in a single gene

Question 4

what are examples of mendelian inheritance?

Answer 4

-autosomal dominant
-autosomal recssive
-X-linked (mitochondrial = genes only inherited by mother)

Question 5

what level of penetrance does mendelian disorders have?

Answer 5

high penetrance

Question 6

what is multifactorial inheritance?

Answer 6

when more than 1 factor causes a trait or health problem, such as a birth defect or chronic illness. Genes can be a factor, but other things that aren’t genes can play a part, too e.g. Nutrition

Question 7

what are mitochondrial genes?

Answer 7

genes that are inherited only from the mother

Question 8

what are examples of non-mendelian inheritance?

Answer 8

• methylation
• imprinting
• mitochondrial inheritance
• mosaicism

Question 9

autosomal dominant key points

Answer 9

-seen in all generations

-50% risk of affected child if affected parent
-severity variable
-males and female equally affected

Question 10

autosomal recessive key points

Answer 10

-often only 1 generation affected
-1 in 4 risk of infected child if parent carriers

Question 11

X-linked inheritance carriers?

Answer 11

female usually carrier of gene and pass onto male children

Question 12

what is result for children of female carrier of x-linked disease?

Answer 12

-1/2 male children will be affected
-1/2 female will be carriers

Question 13

what is result for children of male carrier of x-linked disease?

Answer 13

-all male children will be normal (no male-male transmission)
-all female will be carriers (as can only pass on affected x chromosome)

Question 14

why can female carrier show only mild features of x-linked disease?

Answer 14

due to x-inactivation, part of affected gene could be inactivated so not as bad symptoms

Question 15

what is pedigree chart symbol for miscarraige?

Answer 15

triangle

Question 16

what is pedigree chart symbol for affected and not affected?

Answer 16

affected = filled in
non-affected = not filled in

Question 17

in most rare diseases is genotype or environment more important?

Answer 17

genotype

Question 18

what is a single nucleotide polymorphism (SNP)?

Answer 18

=alterations in DNA sequence that can effect not diseases like height, weight, hair colour, health factors etc -> these effects are still through gene function

Question 19

how common are SNP’s ?

Answer 19

10 million- they’re every 100-300 base pairs and are each given a unique ID

Question 20

what are copy number variations (CVN’s)?

Answer 20

= extra or missing stretches of DNA
=they can size from a few bases to millions
=deletions or duplications

Question 21

how common are CNV’s?

Answer 21

=highly prevalant (chance of disease)
=over 1500 known ones
=12% of human genome variable

Question 22

how high is penetrance for multifactorial disease?

Answer 22

low for just one mutation

Question 23

what is effect of SNP’s?

Answer 23

most SNP’s have no effect
SNPs that do have an effect are expected to have smaller effects than a rare disease causing mutation (some polymorphisms can completely destroy a gene without causing disease)

Question 24

what is methylation?

Answer 24

-when methyl group on end of cytosine (only happens when opposite guanine)
-it prevents transcription and key in gene regulation, switching genes on and off
-makes mutation more likely
-allows environment to affect genome

Question 25

what is imprinting?

Answer 25

differences in gene expression depending on whether a gene is maternally or paternally inherited (some genes only work if you inherit them from mother/father)
->specific chromosomal regions contain imprinted gnes