Alia's Quizlet

linkage

condition in which alleles do NOT show independent assortment because they are so close to each other on a chromosome that cross over event rarely occur between them

genetic recombination

splicing of DNA sequences together to produce new combinations

Nondisjunction

failure of homologous chromosomes to separate during meiosis 1 or of sister chromatids during meiosis 2 or early in mitosis. Result: monosomy or triosomy

wild type

the phenotype for a character most commonly observed in natural populations

Thomas Morgan

Bred fruit flies, and supported the the theory of chromosomal inheritance by finding that a specific gene is carried on a specific chromosome

X linked traits

traits carried on the X chromosome, the recessive trait shows up more commonly in males due to them only having one X

Y linked genes

genes found on the Y chromosome, passed from father to son rel. unchanged, mostly code for sex related genees

hemizygous

A gene present on the X chromosome that is expressed in males in both the recessive and dominant condition

Chromosomal Basis of Inheritance

genes are located on chromosomes and the behavior of chromosomes during meiosis and fertilization accounts for inheritance patterns

Chromosomal Basis of Sex

In humans and other mammals, there are two varieties of sex chromosomes: a larger X chromosome and a smaller Y chromosome

Only the ends of the Y chromosome have regions that are homologous with corresponding regions of the X chromosome

The SRY gene on the Y chromosome codes for a protein that directs the development of male anatomical features

Barr body

A dense object lying along the inside of the nuclear envelope in female mammalian cells, representing an inactivated X chromosome.

What is the physical basis for recombination

The physical basis of recombination between unlinked genes is the random orientation of homologous chromosomes at metaphase I of meiosis, which leads to the independent assortment of the two unlinked genes

genetic map

An ordered list of the genetic loci along a particular chromosome.

linkage map

A genetic map based on the frequencies of recombination between markers during crossing over of homologous chromosomes.

Aneuploidy

A chromosomal aberration in which one or more chromosomes are present in extra copies or are deficient in number.

Monosomy

Chromosomal abnormality consisting of the absence of one chromosome from the normal diploid number

Triosomy

nondisjunction with one more chromosome

Polyploidy

A chromosomal alteration in which the organism possesses more than two complete chromosome sets.

Deletion

A change to a chromosome in which a fragment of the chromosome is removed.

Duplication

a broken fragment may become reattached as an extra segment to a sister or nonsister chromatid, producing a duplication of a portion of that chromosome.

Inversion

A chromosomal fragment may also reattach to the original chromosome but in the reverse orientation, producing an inversion.

Translocation

Change to a chromosome in which a fragment of one chromosome attaches to a nonhomologous chromosome.

Triosomy 21

Down syndrome, result of extra chromosome 21 so the body cell has 47 total chromosomes. Most cases come from nondisjunction in meiosis 1 during homolog separation

Aneuploidy of Sex Chromosomes

-Nondisjunction of sex chromosomes produces a variety of aneuploid conditions

Klinefelter syndrome

A chromosomal disorder in which males have an extra X chromosome, making them XXY instead of XY.

male sex organs but smaller than average testes and produce little of no sperm

taller than average

learning disabilities

XYY syndrome

A chromosomal disorder in which males have an extra Y chromosome.

not really any affects; taller than average

XXX

Trisomy X, slightly taller that average women, may be at risk for learning disabilities

Monosomy X (Turner Syndrome)

X0 females

Sterile

Only known viable monosomy in humans

Cri du chat syndrome

A deletion of the short arm of chromosome 5 associated with an array of congenital malformations, the most characteristic of which is an infant cry that resembles a meowing cat.

Philedelphia chromosome

abnormality of chromosome 22

bone marrow cells that contain philedelphia chromosome are often found in chronic myelogenous leukemia and

translocation of large fragment of chromosome 22 onto chromosome 9

genomic imprinting

a phenomenon in which expression of an allele in offspring depends on whether the allele is inherited from the male or female parent

extranuclear inheritance

extranuclear genes are found in mitochondria and chloroplasts. Defects in mitochondria DNA can reduce cell's ATP production. Mitochondria passed to zygote all come from mother, so all related diseases are mother inherited.

Two mother egg procedure

The chromosomes from the egg of an affected mother could be transferred to an egg of a healthy donor that has had its own chromosomes removed.

Fredrick Griffith (1928)

Proved a process called transformation: genetic material from one cell can be transferred to another cell from studying pneumonia

Oswald Avery, Colin MacLeod, and Maclyn McCarty

Expounded upon Frederick Griffith's Streptococcus pneumoniae experiment, removing all but one of the macromolecules in each determination. Found that DNA was molecule of heritability.

Alfred Chase & Martha Hershey

Used radioactive sulfur and phosphorus to trace the fates of protein and DNA, respectively, of T2 phages that infected bacterial cells. They wanted to see which of these molecules entered the cells and could reprogram them to make more phages.

When proteins were labeled (batch 1), radioactivity remained outside the cells, but when DNA was labeled (batch 2), radioactivity was found inside the cells. Cells containing radioactive phage DNA released new phages with some radioactive phosphorus.

Phage DNA entered bacterial cells, but phage proteins did not. Hershey and Chase concluded that DNA, not protein, functions as the genetic material of phage T2.

Erwin Chargaff

Discovered that DNA composition varies, but the amount of adenine is always the same as thymine and the amount of cytosine is always the same as guanine.

Chargraff's Rules

(1) DNA base composition varies between species, and (2) for each species, the percentages of A and T bases are roughly equal, as are those of G and C bases.

Maurice Wilkins and Rosalind Franklin

used a technique called X-ray crystallography to study molecular structure of DNA

Watson and Crick

Figured out structure of DNA was a double helix by stealing Rosalind Franklin's work. They thought strands were antiparallel and that phosphate backbone was on the outside. Also believed in semi-conservative model, but could not prove it

conservative model

two parental strands re-associate after acting as templates for new strands thus restoring the parental double helix

semi-conservative

in each new DNA double helix, one strand is from the original molecule, and one strand is new

dispersive model

each strand of both daughter molecules contains a mixture of old and newly synthesized DNA

Meselson-Stahl Experiment

(1958) grew bacteria for one generation with heavy nitrogen, transferred the bacteria to a medium with regular nitrogen for several generations then later separated the DNA by centrifugation and the DNA showed to have split between the DNA strands proving semiconservative replication

Why can't you pair a purine with a purine?

Too wide

Why can't you pair a pyrimidine with a pyrimidine

Too narrow

Purines

Adenine and Guanine

Pyrimidines

cytosine, thymine, uracil

Why can't A bond with C

2 repulsions between NH/NN only one bond capable, not good enough

Why can't G bond with T

Two repulsions and only one bond

Important Bonds

HN, HO, CdbO, CdbN

origin of replication

Site where the replication of a DNA molecule begins, consisting of a specific sequence of nucleotides. Proteins that initiate replication recognize this sequence and attach to DNA, separating strands and opening up replication bubble.

replication fork

A Y-shaped region on a replicating DNA molecule where new strands are growing.

DNA polymerase

Catalyzes the synthesis of new DNA by adding nucleotides to the 3' end of a preexisting chain. Requires primer and template strand.

How does DNA polymerase work?

DNA polymerase catalyzes the POLYMERIZATION of deoxynucleotides into DNA. Only work in 5'--->3' direction. It adds deoxynucleotides to the 3'-OH group.

leading strand

The new continuous complementary DNA strand synthesized along the template strand in the mandatory 5' to 3' direction. TOWARD REP FORK

lagging strand

A discontinuously synthesized DNA strand that elongates by means of Okazaki fragments, each synthesized in a 5' to 3' direction away from the replication fork.

Okazaki fragments

Small fragments of DNA produced on the lagging strand during DNA replication, joined later by DNA ligase to form a complete strand. About 100-200 nucs long in eukaryotes, 1000-2000 in pro

DNA ligase

A linking enzyme essential for DNA replication; catalyzes the covalent bonding of the 3' end of a new DNA fragment to the 5' end of a growing chain.

primase

An enzyme that joins RNA nucleotides to make the primer using the parental DNA strand as a template.

Helicase

Enzyme that untwist double helix at replication fork, separating the two strands and making them available as a template strand

Topoisomerase

Enzyme that functions in DNA replication, helping to relieve strain in the double helix ahead of the replication fork.

single strand binding proteins

A protein that binds to the unpaired DNA strands during DNA replication, stabilizing them and holding them apart while they serve as templates for the synthesis of complementary strands of DNA.

antiparallel

The opposite arrangement of the sugar-phosphate backbones in a DNA double helix.

Why can't DNA polymerase continuously add nucleotides in the same direction on both strands?

DNA polymerase works only in the 5'-->3' direction because if a mistake is made, and the nucleotide is removed from the 5' end, the phosphate is removed with is, and there would be no more phosphate to form the bond

DNA pol I

Removes RNA nucleotides of primer from 5' end and replaces them with DNA nucleotides. Also has 5'-->3' exonuclease capability

Low processivity- leaves template after 20 nucs

slow speed: 10 nucs/sec

Telomeres

Repeated DNA sequences at the ends of eukaryotic chromosomes TTAGGG

Telomerase

An enzyme that catalyzes the lengthening of telomeres in eukaryotic germ cells. AAUCCC

Why are telomeres important?

They provide a buffer against the loss of more valuable DNA

Why must DNA pol 3 have RNA primer

the first few bases may have a very high error rate; thus a replication system that can recognize these bases and remove and replace them later may be favored

DNA polymerase III

In charge of synthesizing nucleotides onto the leading end in the classic 5' to 3' direction.

Very high processivity- it leaves the template only after adding 1000s of nucs

high speed (1000 nuc/sec) and high accuracy because it checks the pairing of the previous nuc before adding the next and thus must have an existing C3 platform to add new nucs

How long is an RNA primer

5-10 nucleotides long

How long is an okazaki fragment

About 1000 nucleotides long in prokaryotes, 100-200 in eukaryotes

Nucleoid

A non-membrane-bounded region in a prokaryotic cell where the DNA is concentrated.

Euchromatin

The less condensed form of eukaryotic chromatin that is available for transcription.

Heterochromatin

DNA that is densely packed around histones. The genes in heterochromatin are generally inaccessible to enzymes and are turned off.

Chromatin diameter

10 nm

Histones

protein molecules around which DNA is tightly coiled in chromatin

Nucleosome

Bead-like structure in eukaryotic chromatin, composed of a short length of DNA wrapped around a core of histone proteins

condensin

protein complex that helps configure duplicated chromosomes for segregation by making them more compact