Studying Chromosomes Flashcards
What are chromosomes?
Long DNA molecule with part or all of the genetic material of an organism.
What is cytogenetics?
What is X-inactivation?
One of the two X chromosomes in each of the female’s somatic cells is inactive
The inactivated X chromosomes become heterochromatin
The inactivated X chromosome will condense into a so-called Barr-body
What does a G-banding karyotype give information about?
The number of chromosomes
The structure of chromosomes
Regions of euchromatin and heterochromatin
Chromosomal aberrations and translocations
What are 4 complete sets of chromosomes in a single cell called?
Tetraploidy
Patients with Down Syndrome have an extra chromosome 21, what is this referred to as?
Trisomy 21
Give an example of monosomy
45, X
(any number at the beginning)
What is reciprocal translocation?
Two non-homologous chromosomes exchange parts
Define genome
All of an organism’s genetic information in DNA (or in some viruses, RNA)
What are genes?
Genes are a small part of the genome coding for many different RNAs including mRNA for proteins and rRNA for ribosomes
What is Chromatin?
DNA and associated proteins that make up the chromosomes
What is forward genetics and what is reverse genetics?
Forward: Phenotype to Genotype
Reverse: Genotype to Phenotype
Explain what karyotyping is
The study of chromosomes of a single organism, geneticists arrange micrographs of the stained chromosomes in homologous pairs of decreasing size to produce a karyotype
How are metaphase chromosomes classified?
Number of chromosomes
Size of chromosomes
Morphology of chromosomes
Banding pattern
Regions of heterochromatin and euchromatin
What 2 chemical stains are used to aid karyotyping?
Quinacrine (Q banding) and Giemsa (G-banding) can be used to differentially stain chromosomes to reveal species-specific banding patterns.
Explain Giemsa staining (G-banding)
The short arm is designated ‘p’ (petite)
Each band has an identifier number
The long arm is designed ‘q’ (the next letter in the alphabet)
Explain what metacentric, submetacentric, and acrocentric chromosomes are
Metacentric = chromosomes have short and long arms of roughly equal length with the centromere in the middle
Submetacentric = Chromosomes have sort and long arms of unequal lengths with the centromere more towards one end
Acrocentric = Chromosomes have a centromere very near to one end and have very small short arms. They frequently have secondary constrictions on the short arms that connect very small pieces of DNA, called stalks and satellites, to the centromeres. The stalks-satellites contain genes that code for rRNA
Explain the term ploidy cells
Number of chromosomes in a cell
Two sets of chromosomes (diploid cell)
One set of chromosomes (haploid cell)
Humans have 23 Paris of chromosomes (46 in total)
22 Paris are autosomes and 1 pair is sex chromosomes (XX and XY)
Explain the term diploid cells
Diploid cells contain 2 complete sets (2n) of chromosomes
Diploid cells reproduce by mitosis making daughter cells that are exact replicas
Skin, blood, muscle cells (somatic cells)
Explain the term haploid cells
Haploid cells have half the number of chromosomes (n) as diploid - i.e a haploid cell contains only one complete set of chromosomes
Haploid cells are the result of the process of meiosis, a type of cell division give rise to haploid germ cells
Cells used in sexual reproduction - sperm and egg (gametes)
Explain the term polyploidy
Polyploidy is multiple sets of chromosomes present
Common in plants, but are rare in animals
In humans, it is pathological and leads to early death
Give some visible alterations of chromosomes produced by chromosome-specific mechanisms
Constitutional changes (germline in origin) all the cells/tissues hold the same abnormality
Somatic changes (e.g. certain cancers)
Numerical changes - cells with an extra chromosome or a deficiency in chromosomes
Structural changes
Explain what clinical cytogenetics is
The study of the relationship of chromosomal alterations and genetic disease in humans
Explain what Trisomy 12 (T12), Trisomy 13 (T13) and Trisomy 18 (T18) are. How can we find out if someone has these?
T12 - Down Syndrome
T13 - Patau’s Syndrome
T18 - Edward;s Syndrome
Prenatal Screening
