Human genome and chromosomes Flashcards
State features of the G-light band on chromosomes?
Gene rich
G-C- rich
Early replicating
State features of the G-dark band on chromosomes?
Gene poor
AT-rich
Late replicating
What is the function of telomeres? What type of DNA do they hold?
Where are they located?
Protective DNA and protein Cap
Containes repetitive DNA
Located at the very top and bottom of a chromosome
What is the function and location of a centromeres? What type of DNA does it contain
Location- between the short P arm and long Q arm of chromosomes
Function- keeps sister chromatids together
Attaches sister chromatids to microtubules
Containes repetitive DNA
What is the haploid and diploid chromosome number?
Haploid- 23
Diploid- 46
What are coding and non coding sequences of DNA?
Coding sequences- encode proteins
Non coding sequences- introns, intergenic regions (end of DNA), functional RNA’s (non-coding RNAs, microRNAs),
What are exons and introns?
Exons- encode proteins
Introns- Non- coding - between exons
What are control elements? What is it produced by? Where is it located
sequences that regulate transcription (promoters and enhancers) Produced by non-coding regions of DNA Located at the start of a DNA sequence
What is a psudogene?
Non functional copy of a gene
What are REPETITIVE SEQUENCES?
tandem repeats of closely related DNA sequences
What is the central dogma?
DNA- (transcription)-RNA-(translation)-proteins
What is the meaning of Disomy?
Two copies if a chromosome
Definition of polyploidy
gain of one or more haploid chromosome sets
Translocation meaning/ balanced translocation meaning
Joining of part of one chromosome to a second chromosome.
Balanced- when there is no loss or gain of material after joining
What is a ROBERTSONIAN TRANSLOCATION
Two chromosomes joining at their centromeres. Loss of material
What are the most common autosome abnormalities in babies
Down syndrome
edwards syndrome
patau sydrome
What are the most common sex chromosome abnormalities in new born babies
Turner syndrome
Klinefelter syndrome
Describe the main genetic and clinical features of down syndrome
Trisomy 21 1 in 700 >60% spontaneous abortions Muscle hypotonia single palmar crease learning difficulties congenital heart malformtaions
List the 3 different chromosome patterns which can cause down syndrome
- 3 separate chromosomes 21
- Robertsonian translocation
- mosaicism- normal and trisomy 21 cells
Describe the main genetic and clinical features of Edwards syndrome
Trisomy 21 1 in 3000 many malformations- heart and kidneys clenched hands with overlapping fingers (death in 1 week)
Describe the main genetic and clinical features of PATAU syndrome
1 in 5000 Trisomy 13 many malformtaions - incomplete lobation of brain, cleft lip, congital heart disease (death in 1 week)
Describe the main genetic and clinical features of Klinefelter syndrome
47,XXY
• 1 in 1000 males
• Infertility (testes do not produce sperm)
• Poorly developed 2ndy sexual characteristics in some (lack of testosterone)
• Tall
Describe the main genetic and clinical features of Turner syndrome
45,X • 1 in 5000 females • 99% lost spontaneously • Short stature • Primary amenorrhoea (no periods) (ovaries involute before birth) • Congenital heart disease
Describe the processes of amniocentesis
Genetic testing of cells from the amniotic fluid
• Ultrasound guidance
• 15-18 weeks
Describe the processes of Chorionic villus sampling
Genetic testing of tissue from the placenta (chorionic villi)
• Ultrasound guidance – trans-abdominal or trans-cervical
• 12-14 weeks
State a non invasive way dor down syndrome screening
nuchal translucency
What is X-inactivation? Why does it occur?
During embryonic development- one of the two X-chromosomes in
each cell is randomly inactivated.
The adult female is a mosaic
Ensures only 1 somatic cell has 1 active X chromosome
What is the pseudoautosomal regions of the X-chromosome
An area that contains genes found on the Y chromosome involved in development
Not inactivated
What is the process used for x inactivation? When is it reversed?
Xist- found in X inactivation centre causes chromosome changes, leading to transcriptional inactivation and formtaion of barr bodies
Reversed in Germ cells
What do bar bodies indicate?
Number of inactive chromosomes
Function of Y chromosome
Encodes the “Sex Determining Region of the Y-chromosome” – the
SRY gene
Responsible for male sex determination
