Mendelian Inheritance of Disease

Question 1

What is mendelian inheritance of disease?

Answer 1

inheritance patterns of single gene diseases are referred to as mendelian
mendelian trait is a mutation in one gene
runs in families
common are cystic fibrosis, sickle cell disease

Question 2

what is meiosis? what is result of it?

Answer 2

• sex cell division
• produces 4 haploid (1n) gametes (eggs/sperm) from a single diploid cell (2n)
  haploid has single chromosome

Question 3

describe the process of meiosis

Answer 3

diploid cell –> 4 haploid gametes
DNA (23 pairs) one from each parent replicate (46 total)
* 22 autosomes and one pair of XX or XY
sister chromatids (identical copies) attach at cetromere
• maternal & paternal copies of each chromosome AKA Homologous chromosomes pair with each other and line up
recombination and metaphase plate alignment occur
random chromosome orientation + recombination lead to independent assortment
first homologous chromosomes separate then sister chromatids-> 4 gametes ready to be fertilized

Question 4

random chromosome orientation and recombination leads to … where all pairs of genes separate independently of one another during meiosis unless close together on the same chromosome

Answer 4

independent assortment

Question 5

during meiosis I .. separate and during meiosis II … separate

Answer 5

homologous chromosomes

sister chromatids

Question 6

each person has 2 different … of a gene, one on each homologous chromosome

• it is a form of a gene
• any two will differ in sequence in some way

Answer 6

allele

Question 7

homozygous vs heterozygous

Answer 7

homozygous- person inherited same allele

heterozygous - person inherited two different alleles

Question 8

how to vizualize inheritance patterns?

Answer 8

punnett square

Question 9

form of inheritance that is caused by genes that are not on sex chromosomes 
can be dominant (1 allele causes the disease) 
or recessive (2 alleles cause the disease)

Answer 9

autosomal inheritance

Question 10

this type of inheritance is caused by a gene on the X or Y chromosome

• different outcomes if the mother or father has the disease allele
• inherited in a sex-biased manner (doesn’t happen in autosomal)

Answer 10

X-linked (can be recessive or dominant) 
Y linked (not common)

sex biases in inheritance indicates it is sex linked

Question 11

analysis used to look at family tree annotated with pattern of inheritance
• males represented as squares
• females as circles
• shading means affected
• carrier has dot in middle of square or circle

Answer 11

pedigree analysis

Analysis:
can the phenotype skip generations?
* if yes - the trait is likely to be recessive
* if no - trait is likely to be dominant
is there a sex bias in inheritance?
* if yes - sex linked trait
* if no - autosomal

Question 12

what is penetrance? what is meant by 100% or complete penetrance?

Answer 12

penetrance is the amount of people with a genotype that exhibit the associated phenotype
* there’s a spectrum (light off and on)
complete penetrance means that 100% of individuals with the disease will express the associated phenotype

Question 13

What are 2 interactions that contribute to why variation in phenotypes occurs among individuals who share the same genotype?

Answer 13

1. genetic interaction

2. environmental interaction

Question 14

what is expressivity? what is variable expressivity

Answer 14

expressivity is the degree of phenotypic expression of a trait (light dimmer)

variable expressivity is when the degree of phenotypic expression differs among individuals with the same genotype

Question 15

when a trait seems to skip a generation what could be the two reasons?

Answer 15

the recessive pattern of inheritance or incomplete penetrance of a dominant allele

Question 16

what is HCM or hypertrophic cardiomyopathy and its associated cause?

Answer 16

HCM is a thickening of the muscle in the heart wall with no obvious cause
(happens to a lot of pro athletes) sudden deaths/heart failure
inherited - autosomal dominant

in patients with HCM - the cardiac muscle is so thick
• the septum (separates 2 ventricles) is enlarged
• outer wall of left ventricle also enlarged

Question 17

records the electrical signal from the heart to check for different heart conditions
* uses electrodes placed on skin

Answer 17

EKG - electrocardiogram

Question 18

checks how your heart’s chambers and valves are pumping blood through your heart
* uses ultrasound

Answer 18

Echo - echocardiogram

Question 19

if a pedigree shows male -> male transmission then you know it cant be .. what form of inheritance?

Answer 19

X-linked bc men only pass on their Y to their sons not the X