chromosomal theory of inheritance - similar chromosomes pair w/ each other during meiosis 

• segregation/independent assortment shown by meiosis I
• number of traits for each organism always more than number of chromosomes
• Thomas Hunt Morgan - performed experiments w/ red/white eyed flies
  • found evidence of sex-linked inheritance
  • proved that genes for traits are found on chromosomes
• males - X/Y chromosomes
• females - X/X chromosomes
• sex-linked trait - found on the X chromosome

genetic recombination - crossing over mixed up genes further 

• physical exchange of chromosomal arms
• crossing over can occur anywhere along the chromosome
• more likely that crossing over occurs between chromosomes that are far apart
• genetic map - measures distance between genes in terms of recombination frequency
  • centimorgan - map unit, distance within which a crossover is expected to happen in 1% of gametes
• three-point cross - involves 3 linked genes (genes so close that they don’t assort independently)
  • wild type - most common allele of a gene, designated by "+"

human genetic map - uses pedigrees and statistics 

• LOD (log of odds ratio) - ratio of probability that 2 genes are linked to probability that they aren’t linked
• anonymous markers - genetic markers that can be detected easily but doesn’t cause a phenotype
  • allows for chromosomes to be mapped
• polymorphisms - differences between individuals in populations

human chromosomes - 46 chromosomes, 23 pairs; divided into 7 groups 

• autosomes - 22 of 23 pairs, perfectly matched in males and females
• sex chromosomes - similar in females, dissimilar in males
• SRY gene - on Y chromosome, plays important role in male sexual development
  • environmental factors can cause changes in sex of adult fishes/reptiles
• Barr body - inactive X chromosome in females (deactivated after sex is determined)
• gap conversion - copies over DNA sequence from other chromosome
  • DNA sections that don’t match are completely discarded
  • Y chromosome consists of palindromes, able to fix itself w/o another DNA sequence (reason why males aren’t extinct)

chromosome number - can cause abnormalities and diseases 

• nondisjunction - failure of sister chromatids to separate correctly
• aneuploidy - loss/gain of a chromosome
• monosomics - humans who lost 1 copy of an autosome, don’t survive development
• trisomics - humans w/ extra copy of autosome, most don’t survive
  • possible to survive w/ 3 copies of chromosome 13, 15, 18, 21, or 22
• Down Syndrome - trisomy 21, occurs in 1/750 children
  • translocation - process that adds a small part of chromosome 21
  • cancer more common in people w/ Down Syndrome
  • possible link to cancer/Alzheimer’s on chromosome 21
  • chances of giving birth to a child w/ Down Syndrome increases as the mother gets older (eggs have more time to mutate)
• Klinefelter syndrome - XXY zygote
  • sterile male w/ many female body characteristics
• Turner syndrome - XO zygote (O means absence of a chromosome)
  • sterile female w/ webbed neck and sex organs that never mature
• Jacob syndrome - XYY zygote
  • fertile males w/ normal appearances
  • chances for disease 20x higher in mental/penal institutions

genetic counseling - determining if parents are at risk of producing children w/ defects 

• checks the genetic state of early embryos
• pedigree analysis - makes it possible to estimate the probability of someone being a carrier from some disease
• amniocentesis - amniotic fluid withdrawn from uterus during 4th month of pregnancy
  • cells then grown in cultures in the lab
  • ultrasound used to determine position of needle/fetus so that the fetus won’t be harmed
• chorionic villi sampling - cells removed from chorion (membrane part of placenta)
  • can be used in 8th week of pregnancy
  • faster than amniocentesis
• karyotype analysis - checks for aneuploidy
• lack of normal enzyme activity >> disorder present