Genetics Foundations, Chromosomes, Chromosomal Abnormalities, Imprinting (Lectures 11,12,21)

Question 1

law of independent assortment

Answer 1

any two genes will be inherited as independent units

the exception is linked genes

Question 2

pleiotropy

Answer 2

a single mutation affects different organ systems

Question 3

incomplete penetrance

Answer 3

the possibility that an individual can carry a particular genotype, but never show symptoms of the disease

Question 4

nucleosome

Answer 4

• composed of 8 histone proteins
• structure around which DNA is wrapped to be condensed into chromatin
• the tighter a segment of DNA is wrapped around a nucleosome, the more difficult it transcriptional machinery to reach
• ie, a building block of a chromosome

Question 5

law of segregation

Answer 5

allele pairs separate during gamete formation

Question 6

linked genes

Answer 6

if 2 genes are very close together on the chromosome, they can be inherited together, and can only be separated by recombination events that occur during meiosis
the probability of recombination btw two loci is directly proportional to the physical distance that separates them on the chromosome (the closer they are, the less likely they will be separated)

Question 7

heterochromatin

Answer 7

tightly wound DNA, genes are not actively transcribed

Question 8

euchromatin

Answer 8

loosely wound DNA, genes are actively transcribed

Question 9

incomplete dominance

Answer 9

each genotype has a different phenotype

Question 10

sporadic mutation

Answer 10

individuals expose themselves to an environmental factor that phenotypically mimics, or phenocopies, a condition present in a family

Question 11

karyotype

Answer 11

-Chromosomes stained with Giemsa stain in metaphase
-Dark bands are gene poor, have heterochromatin (also AT rich regions)
Light bands have euchromatin

Question 12

When to karyotype / profile chromosomes

Answer 12

1. Problems in early growth and development
2. Stillbirth and neonatal death
3. Infertility
4. Family history
5. Neoplasia
6. Pregnancy for mother of advanced maternal age

Tissue source: blood, cheek swab, amniocentesis

Question 13

aneuploidy

Answer 13

• abnormal number of chromosomes (ie, like 45, 47)

- differs by a fraction of the genome, not by multiples of the genome

Question 14

Mitotic (post-zygotic) nondisjunction

Answer 14

establishes an abnormal line of cells within an otherwise normal individual

Question 15

non-invasive pre-natal screening

Question 16

meiotic nondisjunction

Answer 16

• a single chromosome is mis-segregated in the gamete

- occurs in oocytes more often than spermatocytes

Question 17

Turner syndrome

Answer 17

only viable monosomy (X)
diagnosis at birth or puberty
webbed neck, short stature, lymph edema in hands and feet
infertility, amenhorrea, normal intelligence

Question 18

klinefelter syndrome

Answer 18

• trisomy XXY
• long limbs
• hypogonadism (small genitalia)
• gynecomastia
• infertility (no germ cells)
• behavioral, IQ difficulties

Question 19

balanced rearrangements

Answer 19

genomic content is shuffled such that everything remaining is the same copy number (of genes)

examples include: inversions, translocations: Robertsonian + reciprocal

Question 20

unbalanced rearrangements

Answer 20

net loss/gain of genomic content

examples include: translocations, duplications, deletions

Question 21

inversions

Answer 21

-occur when a chromosome experiences one or two double-stranded breaks, and the liberated fragment is re-inserted into the chromosome in the opposite orientation

two main types:
-paracentric: not involving the centromere

• pericentric: involving the centromere
• breakpoints in the chromosome can disrupt the a gene’s function

Question 22

reciprocal translocation

Answer 22

• when two or more chromosomes has dsDNA breaks and the material is exchanged before the breaks are repaired
• DNA relocates to a new chromosome with no net gain or loss of material
• A notable translocation is between chromosomes 9 and 22, which harbor a novel fusion protein resulting from joining of two genes at the break point (bcr-abl fusion protein results in increased and mislocalized tyrosine kinase activity, resulting in the development of chronic myelogenous leukemia, CML).

Question 23

spectral karyotyping (SKY)

Answer 23

• individual probe sets labeled in 24 different colors for each unique chromosome
• makes it easy to determine origin of “extra” DNA
• Easier to characterize translocations

Question 24

Cri-du-Chat syndrome

Answer 24

• terminal deletion of chromosome 5 (5p15)
• Loss of this chromosome segment causes patients to cry with a characteristic cat-like sound and develop intellectual disability, microcephaly, epicanthal folds, low set ears, and heart defects

Question 25

chromosomal microarray (CMA)

Answer 25

• fetal DNA is analyzed to determine if loci are over- or -under represented in the sample
• high resolution method of counting copies of genomic loci
• More effective at detecting small-scale chromosomal changes that can be missed by traditional karyotype analysis
• Can’t detect balanced rearrangements because it is not able to provide spatial info about chromosome arrangement

Question 26

Edwards syndrome

Answer 26

trisomy 18

Question 27

Patau syndrome

Answer 27

trisomy 13