Sex Chromosomes and Linkage Flashcards
Pedigrees
allow for a visual representation of the specific trait of interest
23 pairs of chromosomes consisting of over _____________ base pairs of DNA
3 billion
it is predicted there is more than ___________ protein coding genes and genes coding for ______________
20,000
functional RNA molecules
Sex Chromosomes
- X and Y chromosomes that are non-homologous
- small regions at the tips of the X and Y chromosome allow these chromosomes to pair and segregate like homologous chromosomes during meiosis
X chromosomes have multiple functions that are unrelated to __________
sex determination
Sex-linked gene
gene located on either sex chromosome
-expression of the phenotype may depend on the sex of the individual
Hemizygous
the rule of dominance and recessiveness no longer apply, this occurs because males have only one X chromosome meaning they have only one locus for this allele
Haemophilia
blood clotting disorder that is X-linked recessive
- results from a mutation in a gene that encodes for a necessary protein that is required for blood clotting
- most people affected are males and most females are carriers of the trait
Linked Genes
- genes that are positioned close together on the same chromosome
- tend to be inherited together and do not segregate independently
- the linkage can be broken during chiasmata in meiosis
Recombination of Alleles
- if linked genes are far enough apart, different allele combinations will be generated during crossover events
- if the linked genes are right beside each other, crossing over won’t occur
Linkage Maps
created to show the relative distance between genes on a chromosome
How SNPs are helpful in creating high-density maps
- high density maps can be created by looking at SNPs that don’t lie in coding regions
- using human genome maps we can find out the approximate location of the disease gene
