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
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