OBJ - Medical Genetics I: Introduction to Medical Genetics

Question 1

Explain Mendel’s insights into the nature of inheritance and how traits are transmitted from parent to offspring.

Answer 1

Law of segregation
Law of Independent Assortment
Punnet Square

Question 2

List the stages of meiosis and describe the behavior of chromosomes at each stage; explain how the behavior of chromosomes in meiosis accounts for Mendel’s laws.

Answer 2

Meiosis = physical basis for Mendel’s laws

Meisosis I

1) Prophase I - Replication of DNA -> 4n (but 2n-squared)
2) Metaphase I - Synapsis - line up in middle
3) Anaphase I - Segregation into sister chromatids
4) Telophase I

Meiosis II - sister chromatids separate (each has 2n or n-squarded)

1) Prophase II
2) Metaphase II
3) Anaphase II
4) Telophase II - each is haploid = n

Crossing Over - adds genetic diversity

Question 3

Describe the basic organization of chromosomes and list the major components and their characteristics.

Answer 3

Telomere - ends of chromosome

Centromere - center of chromosome, where they link/crossover

G-banding -

Short arms = p (petit)
Long arms = q

Location ID’d by Chromosome #, arm, & band/sub-band “7q31.33”

Question 4

Describe the normal human karyotype and define the terms used to describe chromosome morphology.

Answer 4

Karyotype: chromosomal constitution

total #
Sex chromosomes
any chromosomal abnormalities (extra/missing)

i.e. 46, XY = male or 46, XX = female
47, XX, +21 = 47 total chromosomes, female, extra 21 chromosome = Down’s

del = deletion             46, XY, del(4)(p14) 
dup = duplication
inv = inversion
ins = insertion
i = isochrome
t = translocation

i.e 46,XY, ins(7;8)(q21.2;q24.1q22) Male with insertion into chr. 7 q21.2 of a fragment
q24.1-q22 from chr. 8
(know for recognition only)

Question 5

List the types of chromosome aberrations and explain how they arise; describe the most common chromosome aberration syndromes in humans and discuss associated risk factors

Answer 5

Numerical Abnormalities:
- Aneuploidy = incomplete set of chromosomes; loss/gain of 1+ chromosomes
- Polyploidy = 1+ additional SETS of chromosomes (i.e 3 sets of 26 chromosomes)
- Euploidy = exact multiple of chromosomes
(polyploidy falls under euploidy)

Nondisjunction: chromatids don’t split at centromere -> trisomy & monosomy

Trisomy 16 most common -> but never survives gestation

Structural Abnormalities - breakage/incorrect rejoining of chromosomes

Balanced - no loss/gain of ESSENTIAL material
Unbalanced - Loss/gain of ESSENTIAL material

• Translocations - transfer of a segment of a chromosome from 1 to another (change in chromosome #) = balanced
  Reciprocal
  Robersonian Translocation = short arm to
  different chromosome
• Inversions
• Isochromosomes - double strand breaks into
  2x short arms & 2x long arms
• Insertions
• Deletions
• Duplcations
• Microdeletions - William’s syndrome (not visible to microscope, but affect person)

Question 6

Genetics

Answer 6

the study of heredity

Question 7

Genetic Disease

Answer 7

a disease caused by a mutation in the genetic material (DNA)

Question 8

Congenital Disease

Answer 8

a disease that is present at birth

Question 9

Epigenetics

Answer 9

the study of changes in gene function that occur without a change in the DNA of this gene

Question 10

Chromosomal disorders

Answer 10

wrong number of chromosomes
i.e. Down’s

“Normal” cause of still births & preganacy loss

Question 11

Single gene disorders

Answer 11

• alteration of single gene
• typically congenital
• may/may not be heritable (b/c don’t make it to child bearing age)

Question 12

Multifactorial disorders

Answer 12

i.e. cancer, Heart disease, diabetes (some sort of hereditary disposition/component

Question 13

Allele

Answer 13

Gene variant

Question 14

Hemizygotes

Answer 14

1 allele is present instead of 2

**if recessive allele -> gets expressed b/c only one

Question 15

Law of segregation

Answer 15

if genetically is Aa; 1/2 are A & 1/2 are a

Question 16

Law of Independent Assortment

Answer 16

every allele has same probability of being chosen

Punnet Square

Question 17

Carrier

Answer 17

heterozygote for recessive disorder

Question 18

Genotyoe

Answer 18

genetic/allelic composition

i.e. Aa

Question 19

Phenotype

Answer 19

observable expression

Pink, Red or White flower

Question 20

Polymorphism

Answer 20

the existence of multiple alleles for a particular gene ( ≥ 1% frequency for each allele)

Question 21

Codominance

Answer 21

the expression of each allele can be detected

ABO blood types -> AB = codominant b/c can both be expressed simultaneously