Lecture 5 - Intro to Cytogenetics Flashcards Preview

Unit 1 - Molecular and Cellular Principles of Medicine > Lecture 5 - Intro to Cytogenetics > Flashcards

Flashcards in Lecture 5 - Intro to Cytogenetics Deck (30)
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Role of cytogenetics

Identify chromosomal anomalies that may be associated with disease, contribute to diagnosis and treatment - "gold standard"


Statistics of chromosomal abnormalities?

1/13 conceptions have one, only 6 in 1000 are born. 0.6% of newborns have chromosomal anomaly


Do all chromosomal abnormalities appear early in life?

No, some may become obvious as the person ages


What does one look for in chromosomal abnormalities?

Numerical (not 46 chromosomes) or structural - change in the size or shape of one of the chromosomes


What specimens are needed to diagnose it?

Blood (DNA from leukocytes), amniotic fluid, chorionic villi, bone marrow (oncology), tissue


Describe karyotype anaylsis

Compare chromosomes from metaphase in size, centromere position (metacentric, submetacentric, acrocentric), banding pattern


Describe the parts of the chromosomes

P (short arm), Q (long arm), centromere connecting chromatids, terminated by telomeres.


Describe an acrocentric chromosome

It has modified short arms with stalks containing only multiple copies of rRNA genes that are capped by a modified telomere called a "satellite"


What is a banding pattern?

Chromosomes are stained after mild trypsinization and results in banding - each chromosome has a unique band pattern represented by an ideogram (pattern).


Describe chromosome polymorphisms

the presence of two or more alternative structural forms for a chromosome within a population - inherited as Mendelian characters and can be traced. Not often associated with disease.


Nomenclature for chromosomes

46,XX - normal female, 46,XY - normal male. 45,X/46,XX - mosaic



exact multiples of the haploid set of chromosomes (3N and 4N not possible for life)



gain or loss of chromosomes equaling less than one complete complement



2N + 1 = 47 (Trisomy 13: 47,XX,+13) 47,XXY



2N - 1 = 45 (Monosomy 8: 45,XY,-8) 45,X


What are some ways aneuploidy may occur?

1. Nondisjunction in anaphase 1 of meiosis for 1 chromosome
2. Mitotic errors giving rise to some cells with 3 copies


What is mosaicism?

The result of a mutation that leads to a unique finding in a second cell which establishes a second cell line. Usually the two cell lines differ by this single change. Mosaicism is ACQUIRED.


What are some viable autosomal trisomies?

X, 13, 18, and 21


Trisomy 21

1/700, short stature, low set ears, mental retardation, short hands, eye folds, protruding tongue. Multiple system defects (heart, lung, brain - huge range)


Trisomy 13

Patau Syndrome - 1/4000-10000, failure to thrice, cleft lip/palette, rock bottom feet, polydactyly, heart defect


Trisomy 18

Edwards Syndrome - 1/8000, low birth weight, small mouth jaw, hypoplasia of muscles, crossed fingers


Sex chromosome aneuploidies

Klinefelter syndrome (47, XXY), XYY male, XXX female, Turner syndrome (45,X)


Homogametic and hetergametic

Homogametic (females): have 2 copies of one type of chromosome (X chromosome)

Heterogametic (males): have 1 copy of 2 different types (X and Y)


Describe X and Y chromosomes

Both have areas for recombination at tips, the "pseudoautosomal" region, under which is the TDF (testis determining factor) and SRY (sex determining region) which can occasionally be crossed over


Describe the process of sex determination for a female

Female development is default - females lack the TDF/SRY, ovaries develop, proliferation of Mullerian ducts, regression of Wolffian ducts


Sex determination for a male

TDF/SRY present, testes develop, inhibition of Mullerian ducts which ultimately degenerate. Testosterone produced >> Wolffian duct proliferation


Describe the process of sex determination in general

Due to genes on the X, Y, and autosomes (TDF not the only factor). Occurs early in development, loss of sex chromosome later in life doesn't matter.


Why are females not at a deficit with no Y?

Y chromosome involved mainly with male characteristics


Why are males not at a deficit because of only 1 X?

X inactivation - Barr bodies in somatic cells of females shoes a condensed X chromosome. Happens 3-7 days after fertilization, needed for determination of normal female.


Describe somatic mosaicism

If a female is heterozygous, then there will be subpopulations in her body. Some cells will express the traits on the maternal X and some will express traits on the paternal X. Ex - calico kitties!