Human Genetics and Inheritance Patterns - Genetics 5 Flashcards
What makes up a genome, and which of these make up genes?
- Repeated sequences
- Non-coding sequences (NOT INTRONS)
- RNA coding and regulatory sequences - genes
- Introns - genes
- Protein-coding regions - genes
What could the non-coding sequences of DNA be for?
Pseudo-genes that are still evolving - a DNA sequence that resembles a gene but has been mutated into an inactive form over the course of evolution. So it is a copy of the active gene
What could the repeated sequences in DNA be for?
Perhaps it is left over genes from past viral infections
Human Karyotype
Typical chromosome arrangement in human cells.
Diploid
Cell with two complete sets of chromosomes.
Aneuploidy
Numerical chromosome imbalance in cells (difference in number of chromosomes).
Trisomy
a chromosomal condition characterised by an additional chromosome
Trisomy 13
Condition with three copies of chromosome 13.
X Monosomy
Single X chromosome, no second sex chromosome.
Turner Syndrome.
Klinefelter Syndrome
Trisomy XXY
Jacob’s syndrome
Trisomy XYY
Triple X syndrome
Trisomy XXX
Why are there little symptoms of trysomy XXX?
Having an extra X chromosome does not cause a disbalance in sexual characteristics as the extra proteins are all for female development
Why does jacob’s have little to no symptoms compared to turner and klinefelte syndrome?
The extra Y chromosome produces more proteins for male development but this doesn’t cause lot of problems as there is no compatition with the other Y chromosome. Male development still occurs.
What would the sex of someone with X monosomy be?
They would still be female, however with a lower concentration of female hormones so they may be infertile or not go through their entire puberty. Suggests that female development requires both X chromosomes.
Why does Trisomy XXY (klinefelter) have more severe impacts than Trisomy XYY or XXX?
In trisomy XXY there is more competition between the female and male sex hormones since the amount of both produced is equal. This results in more pronounced phenotypes and symptoms. In the others there is greater testosterone or oestrogen so singular sex puberty can occur.
Edwards Syndrome
Triomy 18. 1 in 5000
Patau syndrome
Trisomy 13, 1 per 16,000
Down syndrome
Trisomy 21, 1 per 1000.
Live Births with aneuploidy are possible with
Possible with trisomy 13, 18, 21, or XXY and monosomy X.
Why are some aneuplodies compatible with life and others aren’t?
Aneuploidies in smaller chromosomes are less likely to have a big impact because the chromosomes contain less genes. As a result the organism can survive.
Explain step 1 of non disjunction in meiosis I of ovum development.
- Prophase - after DNA replication, homologous chromosomes undergo pairing, synapsis and recombination, and arrest at the diplotene (dictyte) stage. This arrest is a pause in the cell cycle of the oocyte.
Explain step 2 of non disjunction in meiosis I of ovum development.
- Dictyate arrest - oocytes remain in meitotis arrest until the female reaches maturity and the oocyte has completed an extensive growth following follicle formation. The older the female the longer the chromosomes have been held together.
Explain step 3 of non disjunction in meiosis I of ovum development.
- Divisions - lutenizing hormone (LH) surge that triggers ovulation also causes resumption of completion of the first meitotic division in the periovulatory oocyte. As anaphase I occurs, inaccurate division of the homologous chromosomes is more likely if the oocyte has been in arrest for a long period of time the chohesins holding them together do not break off properly. As a result aneupodolies are more likely in mature women. The ovulated egg is arrested at the seconds meitotic metaphase, and anaphase onset and completion of meiosis II only occur if the egg is fertilised.
How would you expect an X-linked ressesive allele disorder to manifest in families?
- More common in males
- No father-son transmission
- The son of a female carrier has a 50% chance of having the disease
How would you expect an X-linked dominant disorder to manifest in families?
There are no carriers, female or male.
* Male/female equally at risk
* Affected mother has 50% chance passing on disease contaning X to offspring.
* Affected father will pass on X to all daughters (no father-son transmission)
Autosomal Dominant Disorders
Autosomal = non sex chromosome
Eg Huntington’s Disease
* Affected individuals in every generation.
* Males-females equally affected
* 50% chance offspring being affected
Autosomal Recessive Disorders
Eg Cystic fibrosis Phenylketonuria
* Requires both parents to be carriers.
* Skips a generation
* Both parents must be heterozygous carriers
* 25% chance being affected
Pre-implantation Genetic Diagnosis (PGD)
Parents without underlying fertility issues wull be offered IVF with PGD. HFEA is licensed to do IVF screening for over 600 genetic disorders.
The cells are biopsied to see if they are genetically fine, the fine ones are inserted into the mother.
Ethical issues - selection of phenotypes suggests designer babaies issue.
