BIOL 1201 Exam 3 Easley LSU

Meiosis

A type of cell division that reduces the chromosome number by half, producing haploid gametes.

homologous chromosomes

pairs of chromosomes with same genes, one from each parent.

sister chromatids

Replicated forms of a chromosome joined together by the centromere and eventually separated during mitosis or meiosis II.

diploid (2n)

2 sets of chromosomes

haploid (n)

An organism or cell having only one complete set of chromosomes.

synapsis

Pairing of homologous chromosomes during prophase I.

crossing over

the exchange of genes between homologous chromosomes, resulting in a mixture of parental characteristics in offspring, during prophase 1.

independant assortment

the random orientation of homologous chromosomes along the metaphase plate during metaphase I

gametes

reproductive cells (sperm and egg)

zygote

fertilized egg

alternation of generations

A life cycle in which there is both a multicellular diploid form, the sporophyte, and a multicellular haploid form, the gametophyte; characteristic of plants and some algae.

Fertilization

Fusion of an egg and sperm cell

genetic variation

Differences among individuals in the composition of their genes or other DNA segments

mendels law

First Law: Law of Segregation

-States that "There are two allels and hat half of the total number of alleles are contributed by each parent organism."

Second Law: Law of Independent Assortment

-States that "Traits are passed on randomly and are not influenced by other traits ."

~Exception to this is linked traits

dominant alleles

An allele whose trait always shows up in the organism when the allele is present.

recessive alleles

An allele that is masked when a dominant allele is present

chromosome theory of inheritance

A basic principle in biology stating that genes are located on chromosomes and that the behavior of chromosomes during meiosis accounts for inheritance patterns.

sex-linked inheritance

pattern of inheritance in which certain characteristics carried on the X chromosome inherited from the mother are transmitted differently to her male and female offspring

linkage

a phenomenon in which alleles that are located in close proximity to each other on the same chromosome are more likely to be inherited together

Recombination

the genetic process by which one chromosome breaks off and attaches to another chromosome during reproductive cell division

Nondisjuction in Meiosis I

homologous chromosomes fail to separate

aneuploidy

Abnormal number of chromosomes.

polyploidy

condition in which an organism has extra sets of chromosomes

Roles of RNA polymerase

able to separate the DNA, allow an RNA-DNA duplex to form, elongate the transcript nucleotide by nucleotide, release the finished transcript, and restore

the original DNA double helix

promoters

region of DNA that indicates to an enzyme where to bind to make RNA

terminators

RNA sequences that provide the signal to RNA polymerase for stopping transcription

RNA processing

Modification of RNA primary transcripts, including splicing out of introns, joining together of exons, and alteration of the 5' and 3' ends.

capping

-Modified guanosine attached to 5' end

-Needed for mRNA to exit nucleus and bind ribosome

splicing

the process of removing introns and reconnecting exons in a pre-mRNA

translation

Process by which mRNA is decoded and a protein is produced

Role of ribosomes in translation?

- Attaches to mRNA and houses tRNA, allowing codon-anticodon complementary base pairing

- Allows peptide bonds to form between amino acids

Role of tRNA in translation

tRNA molecules deliver exactly the right amino acid called for by each codon on the mRNA; anti-codons

role of anticodons

base pair with the codon on a strand of mRNA during translation

point mutation

gene mutation in which a single base pair in DNA has been changed

frameshift mutation

mutation that shifts the "reading" frame of the genetic message by inserting or deleting a nucleotide

central dogma

DNA -> RNA -> Protein

genomic inprinting

Variation in phenotype depending on whether an allele is inherited from the male or female parent.

character

a heritable feature that varies among individuals, such as flower color

trait

each variant for a character

gene

A segment of DNA on a chromosome that codes for a specific trait

allele

Different forms of a gene

incomplete dominance

A pattern of inheritance in which two alleles, inherited from the parents, are neither dominant nor recessive. The resulting offspring have a phenotype that is a blending of the parental traits.

Codominance

Both alleles are fully expressed in the heterozygote

multiple alleles

more than two alleles exist for a gene in a population (e.g. ABO blood group)

pleiotropy

The ability of a single gene to have multiple effects.

epistasis

one gene affects the expression of another gene

polygenic inheritance

Multiple genes affect a single trait.

law of segregation

allele pairs separate during gamete formation and reunite randomly during fertilization

law of independent assortment

each pair of alleles segregates independently of other pairs during gamete formation

linked genes

Genes located close enough together on a chromosome that they tend to be inherited together.

multiplication rule

the probability of two independent events occurring together is the product of their individual properties

addition rule

the probability of either two mutually exclusive events occurring is the sum of their individual properities

testcross

Breeding an organism of unknown genotype with a homozygous recessive individual to determine the unknown genotype. The ratio of phenotypes in the offspring reveals the unknown genotype.

monohybrid cross

a cross between individuals heterozygous for one character

dihybrid cross

a cross between heterozygous individuals for two characters

sex chromosomes

X and Y chromosomes.

autosomes

Any chromosome that is not a sex chromosome

sex-linked genes

Genes located on the sex chromosomes.

x-linked genes

Genes found on the X chromosome.

y-linked genes

genes found on the Y chromosome

hemizygous

having only one copy of a gene (males with x-linked genes)

X inactivation

Random inactivation of one X chromosome in females.

map units

A measurement of the distance between genes; one map unit is equivalent to a 1 percent recombination frequency.

Interference

the combination of two or more waves that results in a single wave

three-point test crosses

detect double crossing over events and determine gene order on a chromosome

nondisjunction

Error in meiosis in which homologous chromosomes fail to separate.

chromosomal deletions

involve the loss of all or part of a chromosome

chromosomal duplication

A segment of the chromosome is repeated. It's the opposite of deletion,

chromosomal translocation

When part of one chromosome breaks off and attaches to another non homologous, chromosome.

karyotyping

the process of sorting chromosomes into their matched pairs. An important technique for investigating chromosomal disorders

nucleotide

building block of DNA, consisting of a deoxyribose sugar, a phosphate group, and a nitrogenous base (A,T,G,C)

double helix

twisted-ladder shape of DNA, formed by two nucleotide strands twisted around each other

base pairing

the nearly perfect fit between A-T (two hydrogen bonds) and G-C (three hydrogen bonds) nucleotides

semiconservative replication

each new DNA molecule consists of one new strand and one old strand

origin of replication

Site where DNA replication begins.

replication fork

the Y-shaped region where DNA is unwound and replicated

helicase

An enzyme that untwists the double helix of DNA at the replication forks.

single strand binding proteins

proteins that stabilize single-stranded DNA during replication

topoisomerase

enzyme that relives strain ahead of the replication fork

primase

enzyme that synthesizes the RNA primer

DNA polymerase

Enzyme that synthesizes new DNA strands.

leading strand

synthesized continuously in 5' to 3' direction

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

Short DNA segments on the lagging strand.

telomeres

Repeated DNA sequences at the ends of eukaryotic chromosomes. they protect against gene loss during replication.

telomerase

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

chromatin

the complex of DNA and proteins that makes up eukaryotic chromosomes

histones

proteins around which DNA is wound to form nucleosomes

nucleosomes

a structural unit of chromatin, consisting of DNA wrappped around a histone octamer

euchromatin

loosely packed chromatin

heterochromatin

Tightly packed chromatin, transcriptionally inactive.

30nm fiber

nucleosomes associate with each other to form a more compact structure - results from interactions between adjacent histone H1 proteins

chromosome condensation

process by which a duplicated chromosome becomes packed into a more compact structure prior to cell division

transcription

(genetics) the organic process whereby the DNA sequence in a gene is copied into mRNA

RNA polymerase

enzyme that catalyzes transcription

transcription unit

A region of DNA that is transcribed into an RNA molecule.

RNA processing

The modification of mRNA before it leaves the nucleus that is unique to eukaryotes.

pre-mRNA

precursor mRNA; the first strand of mRNA produced by gene transcription that contains both introns and exons

introns

noncoding sequences within pre-mRNA

exons

coding sequences in pre-mRNA