Lecture 5 Flashcards
Haploid
1n
one of each chromosome
ex. gametes
Diploid
2n
two of each chromosome
(usually the normal state)
Tetraploid
4n
four of each chromosome
ex. after replication in mitosis
Aneuploid
a numerical change in part of the genome
ex. trisomy: one extra chromosome, mostly lethal
ex. Down syndrome has an extra chromosome 21
Non-Disjunction
the chromosomes don’t separate properly into separate cells during the splitting
how trisomy/monosomy occurs
can occur at all of the chromosomes at a low frequency
Amniocentesis
taking a small amount of amniotic fluid from the mother in order to determine analyze the chromosomes of the baby
Sex Determination
- Sex Chromosomes–ex. humans and silkworms have XX or XY, drosophila and nematodes X to autosome ratio
- Ploidy–ex. bees, males are haploid, females are diploid
- Environment–ex. sea worm, larvae undifferentiated but depends on where it lands in the ocean
X Chromosome Inactivation
sex determined by Y chromosome in humans, so they’re insensitive to X chromosome aneuploidy, means some X chromosomes can deactivate into Barr bodies
Barr Bodies
dark staining bodies in nuclei of cells, actually the inactive X chromosome in that cell
everyone has one functional X chromosome, the inactivation occurs at a few hundred cells stage, random in each cell
ex. causes Calico cats
X-linked Genes
diseases caused by genes located on the X chromosome are much more likely to occur in males, because they have only one X chromosome
Linkage
during meiosis, genes on the same chromosome tend to be passed together
allows us to guess how closely genes are located
Unlinked Genes
genes that assort independently of one another
Recombinants
new combinations of alleles
Non-recombinants
parental combinations of alleles
Recombination frequency
number of recombinants over total progeny
