Mendelian Genetics

Sex-linked genes exhibit unique patterns of inheritance 

- x- inactivation regulates gene dosage in females one of the x chromosomes in each cell of the body becomes inactivated by methylation 

    - this inactive chromosome condenses into a Barr Body which lies on the inside of the nuclear envelope 

- linked genes tend to be inherited together because they are located near each other on the same chromosome 

linked genes: located on the same chromosome and therefore tend to be inherited together during cell division

genetic recombination: the production of offspring with a new combination of genes inherited from the parents 

crossing over:  can explain why some linked genes get separated during meiosis, research indicates that the farther apart two genes are on a chromosome, the higher probability that crossing over will occur between them 

linkage map:  genetic map that is based on the percentage of crossover events 

map units: 1-1 recombination frequency 

Alterations of chromosome number or structure cause some genetic disorders. 

nondisjunction: occurs when the members of a pair of homologous chromosomes don't separate properly during meiosis I or sister chromatids don't separate properly during meiosis II. 

    -if faulty gametes engage in fertilization the offspring will have an incorrect chromosome number

-fertilized eggs that have received three copies of the chromosome in question are said to be trisome, if they just received one they are said to be monosomic 

polyploidy:  condition of having more than 2 complete sets of chromosomes, forming a 3n or 4n individual

Karyotype: an individual's collection of chromosomes, used to look for abnormal numbers or structures of chromosomes 

deletion: when a chromosomal fragment is lost, resulting in missing genes 

duplication: when chromosomal segment is repeated 

inversion: occurs when a chromosomal fragment breaks off and attaches to its original position but backward 

translocation:  when the deleted chromosome fragment joins a nonhomologous chromosome

-down syndrome when trisomy 21 is affected, with developmental delays in specific facial features 

-Klinefelter syndrome an aneuploid condition where a male has an extra x chromosome, affected individuals have male organs but are sterile

-turner syndrome a monosomic condition in which females have just one sex chromosome reproductive organs do not mature