Chromosomal Basis of Inheritance II Flashcards
What is the purpose of GWAS?
To identify which parts of the genome are responsible for certain diseases or conditions.
How do GWAS work?
By comparing DNA from thousands of patients to DNA from thousands of control subjects genetic differences (such as allelic differences or differences in single nucleotide polymorphisms or SNPs) that partially account for the phenotypic differences between the two groups can be identified.
When is recombination frequency best correlated with genetic distance?
This relationship is better established over short distances than over long distances.
What happens in nondisjunction?
Pairs of homologous chromosomes do not separate normally during meiosis. As a result, one gamete receives two of the same type of chromosome, and another gamete receives no copy. The other chromosomes are usually distributed normally.
What happens if nondisjunction occurs during meiosis I?
You get an abnormal number of chromosomes in all of the gametes.
What happens if nondisjunction occurs during meiosis II?
Some gametes are affected and others are not.
What causes aneuploidy?
It is a result of the fertilization of gametes in which nondisjunction occurred.
What is the result of aneuploidy?
It results in monosomic (2n-1) and trisomic (2n+1) individuals.
For most alterations of chromosome number, what is the result?
The organism is non-viable (trisomies and monosomies are the main reason for human pregnancy loss). Most of the viable ones are associated with some serious disorders.
What is Down syndrome?
An aneuploid condition that results from three copies of chromosome 21. It affects about one out of every 830 children born in the United States.
What causes Patau syndrome?
Trisomy of chromosome 13.
What are the symptoms of Patau syndrome?
Serious eye, brain, circulatory defects as well as cleft palate. Children rarely live more than a few months.
What causes Edward’s syndrome?
Trisomy of chromosome 18.
What are the symptoms of Edward’s syndrome?
Almost every organ system affected, and children generally do not live more than a few months.
What are the symptoms of trisomy of the X chromosome?
Healthy and fertile, usually cannot be distinguished from normal female except by karyotype. Slightly taller than average.
What causes Klinefelter syndrome?
Having two X chromosomes and one Y chromosome (XXY)
What are the symptoms of Klinefelter syndrome?
Unusually small testes, sterile, breast enlargement and other feminine body characteristics.
What causes Turner syndrome?
Also known as monosomy X, this is the result of having only one X chromosome and no Y. (XO)
What are the symptoms of Monosomy X (Turner syndrome)?
The only known viable monosomy in humans. Phenotypically female, but sterile due to lack of female organ maturation.
What are the symptoms of having one X and two Y chromosomes (XYY)?
Healthy and fertile, tend to be taller than average. Phenotypically male.
What is triploidy syndrome?
There are three chromosomes for every chromosome. This typically results in miscarriage or death within the first year of life.
What are accessory, dispensable, supernumeray, or B chromosomes?
Some organisms (eg fungi, insects), aside from a core set of chromosomes, also contain chromosomes present in some but not all individuals. These accessory chromosomes are not essential for survival.
What are core chromosomes?
These are chromosomes that carry essential genes that encode housekeeping functions such as cellular metabolism and reproduction; they evolve slowly.
What do accessory chromosomes do?
They show high mutation rates, the acquisition of foreign genes, copy number polymorphisms, and frequent rearrangements; they evolve fast (“the 2-speed genome”)
