Bio 141 Exam 3 (DNA replication, mitosis/meiosis, Mendelian genetics)

Helicase

unwinds and separates the parental DNA strands

topoisomerase

breaks, swivels, and rejoins the parental DNA ahead of the replication fork, relieving strain caused by unwinding

RNA primase

synthesizes RNA primers, using the parental DNA as a template

Single-strand binding proteins

stabilize the un-wound parental strands

DNA polymerase III

using parental DNA as a template, synthesizes new DNA strand by adding nucleotides to an RNA primer or pre-existing DNA strand

DNA polymerase I

removes RNA nucleotides of primer from 5’ end and replaces them with DNA nucleotides added from the 3’ end of adjacent fragment 

DNA ligase

joins okazaki fragments of lagging strand; on leading strand, joins 3’ end of DNA that replaces primer to rest of leading strand DNA

Initiation

topoisomerase, helicase, single-strand binding protein

elongation

RNA primase, DNA polymerase III, DNA polymerase I, DNA ligase

termination

shortening of telomeres

conservative model

the tow parental strands reassociate after acting as templates for new strands, thus restoring the parental double helix

semiconservative model

the two strands of the parental DNA separate, and each functions as a template for synthesis of a new, complementary strand

dispersive model

Each strand of both daughter DNA contains mixtures of old and newly synthesized DNA

G₁ phase

Metabolic activity and growth; unduplicated chromosomes

S phase

Metabolic activity, growth, and DNA synthesis; ends with duplicated chromosomes

G₂ phase

Metabolic activity, growth, and preparation for cell division; DNA is still in the form of loose chromatid; the cell checks for any DNA damage and ensures everything is ready for mitosis

Interphase

G₁ phase, S phase, G₂ phase

Mitotic (M) phase

Mitosis and then cytokinesis

cytokinesis

cytoplasm division; Division of cytoplasm, producing two daughter cells; each daughter cell can start a new cycle

in animal cells: a cleavage furrow forms

in plant cells: a cell plate forms

mitosis

nuclear division; Distribution of chromosomes into two daughter nuclei

blending hypothesis

trait from parent 1 + trait from parent 2 = trait in offspring is an even blend (not true)

homozygous

an individual has two of the same allele on each homologous chromosome

heterozygous

an individual has different alleles on homologous chromosome

phenotype

appearance (manifestation of genotype)

genotype

genetic sequence

chromatin

DNA string made of DNA and histones (condensing proteins); loosely-wrapped, free-floating DNA

euchromatin

more loosely arranged than heterochromatin

chromosome

1 molecule of DNA and the proteins that condense the DNA; tightly packed, condensed DNA

replicated chromosome

DNA has been doubled; contains two sister chromatids which are identical

centromere

the area of a chromosome where sister chromatids are held together; located at the center of each sister chromatid

homologous pair (of chromosomes)

same shape, same size, have the same genes; might have different alleles; two chromosomes with the same genetic information and centromere location; diploid only

gene

a unit of hereditary information occurring along a chromosome; specific DNA sequence that codes for a particular trait; always found at a certain spot on a chromosome

allele

a specific version of a gene/different versions of the hereditary information at a gene (represent them as A/a); alternate versions of genes

dominant allele

will determine the appearance whether or not the other allele is present

recessive allele

will not have an influence if the other allele is present; but it doesn’t get diluted or destroyed!

haploid cells

DON’T have homologous pairs

diploid cells

DO have homologous pairs

bidirectional replication

replication occurs in both directions beginning at the origins of replication (left & right)

How is the process of DNA semi-conservative?

Half of the original DNA molecule is preserved in each daughter DNA molecule to create a template for complemtary DNA strands.

How is the process of DNA antiparallel?

since DNA is shaped like a double helix with the two strands running antiparallel to each other

How is the process of DNA complementary?

since each DNA replication is the complement of the previous strand.

How is the process of DNA semi-discontinuous?

since the DNA strand going towards the origin, can’t be replicated continuously, so when DNA is replicated it’s discontinuous since one strand is replicated continuously (leading strand) and the other is replicated discontinuously

replicated/duplicated

a chromosome that has been copied during the S phase of Interphase (1 replicated chromosome)

sister chromatid

½ of the replicated chromosome

ploidy

the number of complete sets of chromosomes in a cell

centrosome

the region in animal cells that organizes the mitotic spindle; contains two centrioles

centriole

microtubule structures in the centrosome

mitotic spindle

microtubule structures that move chromosomes around in mitosis

aster

the short microtubules radiating from the centrosome

kinetochore

protein structure that connects sisterchromatid centromeres to mitotic spindle fibers

cell division

mitosis + cytokinesis

meiosis

results in genetic variation; all the chromosomes from one parent don’t necessarily stick together

advantageous for survival, adaptation, evolution

disadvantageous for mutations

meiosis I

separation of homologous chromosomes (pairs: one each from parent 1 and parent 2); where independent assortment occurs

meiosis II

separation of sister chromatids (similar to mitosis)

allele segregation

alleles separate into different gametes

crossing over

occurs when DNA broken by proteins, synapsis, chiasmata, and recombination occurs; after this occurs, the sister chromatids are no longer identical (same genes but different alleles)

synapsis

DNA joined to a non-sister chromatid (not identical)

chiasmata

x-shaped structure, ensures homologous pairs stay together

recombination

different assortment of traits from parents to offspring

prophase I

crossing over (recombination): the transfer of portions of chromosomes b/w non-sister chromatids

metaphase I

independent assortment of chromosomes (in meiosis I)

anaphase I

the two alleles for a heritable character separate (at some point) during gamete formation and end up un different gametes

independent assortment

different chromosomes from the same parent don’t necessarily stick together (independent of each other)

hybridization

crossing or mating of two true-breeding varieties

Mendel’s Law of Segregation

• Genes have alternate versions (alleles)

• an individual gets one allele of a gene from each parent

• If the alleles differ, one determines the appearance and the other is unnoticeable

• the two alleles for a heritable character separate during gamete formation and end up un different gametes

test cross

reveals if an individual with a dominant phenotype has a recessive allele (reveal the genotype); uses a parent with a recessive phenotype

epistasis

the phenotypic expression of a gene at one locus alters that of a gene at a second locus

polygenic traits

multiple genes produce one trait (ex: monogenic)

pleiotropy

one gene affects multiple traits (ex: pigment and hearing: white-fur blue-eyed cats are often deaf)

sex-linked gene

a gene located on either the x-chromosome or y-chromosome (often X-linked though)

hemizygous

X-linked gene; males only need one copy of the recessive allele to exhibit the phenotype

Barr body

condensed inactive chromosomes (of females in somatic cells)

mosiac (of traits)

occurs when the female is heterozygous for a trait on the X chromosome

parental types

matching offspring (short for phenotypes)

recombinant types/recombinants

non matching offspring (if 50% of offspring are recombinants, there’s a 50% frequency of recombination —> not linked)