Final Flashcards
Association of Genes and Chromosomes
Red eyes being the dominant phenotype (represented by “X^R”) and white eyes being the recessive phenotype (represented by “X^w”)
Sex Linked-Traits
o Sex-linked traits are those more frequent in either males or females
o They are usually associated with genes on either the X (X-linked) or Y (Y-linked) chromosomes
Mammal Sex chromosomes
X is large, with about 900 genes
Y is small, about 100 genes, highly degraded
During meiosis I, X and Y pair in a single region, the pseudoautosaomal region. The rest of the X/Y are very different from each other, and so do not align with each other.
Homozygous
X-X- shows recessive
Heterozygous
X+X- does not show trait
Hemizygous
X-Y shows recessive phenotype
X+Y does not show phenotype
X Chromosome inactivation
In females, only one of two X chromosomes express genes
Barr Body
One chromosome remains unwound and can express genes, the other is highly condensed
Gene-Linkage
Proximity of two or more genes one a chromosome can affect patterns of inheritance
Gene-Linkage of fruit flies
o The two more common offspring classes represent the parental gametes (alleles in combination found in the parents chromosomes)
o The two less common offspring classes represent transmission of recombinant gametes (chromosomes result from crossing over between homologous chromosomes during meiosis in the F1 females)
Aneuploidy
An incomplete set of chromosomes
Trisomy
One extra chromosome
Monosomy
Missing one chromosome
Nondisjunction
failure of homologous chromosomes (meiosis I) or sister chromatids (meiosis II and mitosis) to separate at anaphase
Down Syndrome
Extra copy of Chromosome 21, Trisonomy 21
“Common” sex chromosome Aneuploids
- XXY: Klinefelter syndrome
- XYY: about 1 in 1000 males, no apparent complications
- XXX: triple X females, no apparent complications
- XO: Turner’s syndrome, the only known viable monosomy in humans
Chromatin
Complex of DNA & proteins
Histones
Primary Proteins
Form octamers (groups of eight) called Nucleosomes
DNA winds around each nucleosome twice, about 150 bp
Euchromatin
Interphase chromosomes are usually in unpacked state
Heterochromatin
Highly Packed State
Inaccessible and so, not expressed
Chargaff’s rule
The rule that in DNA there is an equal amount of A&T and G&C
3 model’s of DNA replication
Conservative, semiconservative, dispersive
Conservative model
This model proposes that the original DNA molecule remains completely intact and a completely new DNA molecule is formed from scratch, essentially creating one “old” DNA and one “new” DNA
Semi-Conservative model
This model suggests that each strand of the original DNA molecule serves as a template to create a new complementary strand, resulting in two new DNA molecules, each containing one strand from the original DNA.
Dispersive model
This model proposes that the original DNA strands become fragmented, and the new DNA is created by mixing pieces of the old strands with new pieces, resulting in a DNA molecule with segments of both old and new DNA interspersed throughout.
Meselson & Stahl 1953
Conducted an experiment that provided conclusive evidence that DNA replicates semi-conservatively
Meselson & Stahl experiment
Tested bacteria using heavy isotope of nitrogen, 15N (normally 14N is lighter)