Biology Exam 3

blending theory of inheritance

inheritance of traits from two parents produces offspring with characteristics that are intermediate between those of the parents

continuous variation

inheritance pattern in which a character shows a range of trait values with small gradations rather than large gaps between them

discontinuous variation

inheritance pattern in which traits are distinct and are transmitted independently of one another

hybridization

process Mendel performed, mating two individuals that differ with the goal of achieving a certain characteristic in their offspring

P0

the parental generation in a cross

F1

first filial generation

trait

variation in the physical appearance of a heritable characteristic (plant height, seed texture)

reciprocal cross

a paired cross in which the respective traits of the male and female in one cross become the respective traits of the male and female in the other cross

dominant traits

Traits that always show in a person even if only one gene of the pair is inherited for the trait, remain unchanged in hybridization

recessive traitss

become latent, disappear in the offspring of a hybrid

product rule of probability

The chance of two or more independent events occurring together is the product of their chance of occurring separately

allele

gene variations that arise by random mutation and exist at the same relative locations on homologous chromosomes

phenotype

observable traits expressed by an organism (appearance)

genotype

underlying genetic makeup of an organism

homozygous

Having two identical alleles for a particular gene

Heterozygous

An organism that has two different alleles for a trait

monohybrid

A cross between individuals that involves one pair of contrasting traits

test cross

a cross between a dominant expressing individual with an unknown genotype and a homozygous recessive individual; the offspring phenotypes indicate whether the unknown parent is heterozygous or homozygous for the dominant trait

incomplete dominance

in a heterozygote, expression of two contrasting alleles such that the individual displays an intermediate phenotype

codominance

in a heterozygote, complete and simultaneous expression of both alleles for the same characteristic

Example of incomplete dominance

red x white = pink

Example of codominance

in certain varieties of chicken, the allele for black feathers is codominant with the allele for white making the chicken have speckled white and black feathers

wild type

An individual with the normal (most common) phenotype.

x-linked

A gene carried on the X chromosome. If a male inherits an X-linked recessive trait from his mother, he expresses that trait because the Y from his father has no counteracting gene. Females are more likely to be carriers of X-linked traits but are less likely to express them.

hemizygous

the presence of only one allele for a characteristic, as in X-linkage; hemizygosity makes descriptions of dominance and recessiveness irrelevant

recessive lethal

inheritance pattern in which an allele is only lethal in homozygous form, the heterozygote may be normal or have some altered, nonlethal phenotype

dominant lethal

inheritance pattern in which an allele is lethal both in the homozygote and heterozygote, this allele can only be transmitted if the lethality phenotype occurs after reproductive age

law of dominance

In many traits one allele is dominant over the other allele. The "weaker (recessive" allele is only expressed when it is paired with another recessive allele

law of segregation

Mendel's law that states that genes segregate equally into gametes such that offspring have an equal likelihood of inheriting any combination of factors, reason we can use Punnett squares

law of independent assortment

the law that states that genes separate independently of one another in meiosis, every combination of alleles is equally likely to occur

linkage

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

epistasis

antagonistic interaction between genes such that one gene masks or interferes with the expression of another

DNA transformation

process in which external DNA is taken up by a cell

bacteriophage

A virus that infects bacteria

Chargaff's Rule

Different species have equal amounts purines (A and G), and pyrimidines (C and T), Amount A = Amount T, Amount C = Amount G

purines

Bases with a double-ring structure.
Adenine and Guanine

pyrimidines

Cytosine and Thymine, single-ring structure

In DNA, phosphate is connected to the ____ of the sugar

5' carbon

In DNA, OH group is connected to the _____ end of the sugar

3' carbon

Adenine and thymine form ________

2 hydrogen bonds

Guanine and cytosine form ____

3 hydrogen bonds

dideoxynucleotide

type of nucleotide used during DNA sequencing to terminate synthesis (ddNTPs)

gel electrophoresis

technique used to separate DNA fragments of different sizes

histones

protein molecules around which DNA is tightly coiled in chromatin, rich in amino acids

heterochromatin

Eukaryotic chromatin that remains highly compacted during interphase and is generally not transcribed.

semi-conservative method of replication

each of the two parental DNA strands acts as a template for new DNA to be synthesized. Post replication each double-stranded DNA has one old, one new strand

dna polymerase

Enzyme in DNA that adds nucleotides one-by-one to the growing DNA strand that is complementary to the template strand

nucleoside triphosphate (NTPs)

serve as the source of DNA nucleotides and the source of energy to drive polymerization

DNA Polymerase 1

rocesses RNA primers during lagging-strand synthesis and fills small gaps during DNA repair reactions

DNA polymerase 2

involved in DNA repair processes, catalyzes the repair of nucleotide base pairs

DNA polymerase 3

remains in the replication fork on the template strand and continuously adds nucleotides to the new complementary strand as the fork progresses, DNA polymerase III adds DNA nucleotides to the primer(s), synthesizing the DNA of both the leading and the lagging strands.

origins of replication

site where DNA replication begins

DNA replication

The process in which DNA makes a duplicate copy of itself.

helicase

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

replication forks

a Y-shaped point that results when the two strands of a DNA double helix separate so that the DNA molecule can be replicated

sing;e-strand binding proteins

protein that binds to single-stranded DNA during replication, helps in keeping the two strands of DNA apart so they may serve as templates

DNA Polymerase

Can only add nucleotides 5' to 3'. Requires a 3' OH group to which it can ad nucleotides

RNA primase

synthesizes an RNA primer that is complementary to template DNA, primers DNA synthesis

primer

a short stretch of RNA with a free 3' end, bound by complementary base pairing to the template strand and elongated with DNA nucleotides during DNA replication

Topoisomerase

prevents overwinding of the DNA double helix ahead of the replication fork as the DNA is opening up, causes temporal nicks in DNA helix, then reseals it

leading strand of DNA

strand that is synthesized continuously in the 5' to 3' direction, synthesized in the direction of the replication fork, can be extended from a single primer

Okazaki fragment

DNA fragment that is synthesized in short stretches on the lagging strand, each require primer to start synthesis. New primer segments are laid down in the direction of replication fork but pointing away from it

lagging strand of DNA

the strand that replicated in short fragments and away from the replication fork

sliding clamp

ring-shaped protein that holds the DNA pol on the DNA strand

ligase

An enzyme that connects two fragments of DNA to make a single fragment

Primase

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

There are ______ origins of replication in eukaryotes while there's only one in prokaryotes

many

How many DNA polymerases are there in eukaryotes compared to prokaryotes?

Eu= 14, pro=5

telomere

DNA at the end of linear chromosomes, unpaired, ends get shorter as cells divide over generations

Telomeres repeat

TTAGG

Telomerase

enzyme that contains a catalytic part and an inbuilt RNA template, functions to maintain telomeres at chromosome ends

mismatch repair

The cellular process that uses specific enzymes to remove and replace incorrectly paired nucleotides.

nucleotide excision repair

A repair system that removes and then correctly replaces a damaged segment of DNA using the undamaged strand as a guide.

induced mutations

result from an exposure to chemicals, UV, or other environmental agent

spontaneous mutation

occur without exposure to any environ

point mutations

changes in a single nucleotide pair of a gene

transition substitution (mutation)

when a purine is replaced with a purine or a pyrimidine is replaced with another pyrimidine

transversion substitution (mutation)

purine replaced by a pyrimidine, or pyrimidine replaced by a purine

silent mutations

have no effect on the amino acid produced by a codon because of redundancy in the genetic code

trinucleotide repeat expansion

a steady increase in the number of copies of a repeated DNA sequence of three nucleotide bases from generation to generation; responsible for genetic anticipation

translocation mutation

mutation in which one part of one chromosome breaks off and attaches to another

central dogma

theory that states that, in cells, information only flows from DNA to RNA to proteins

degeneracy

redundancy of the genetic code; that is, most amino acids are encoded by several codons

codon

A specific sequence of three adjacent bases on a strand of DNA or RNA that provides genetic code information for a particular amino acid

reading frame

On an mRNA, the triplet grouping of ribonucleotides used by the translation machinery during polypeptide synthesis.

nonsense codon

one of the three mRNA codons that specifies termination of translation

plasmid

A small, circular section of extra DNA that confers one or more traits to a bacterium and can be reproduced separately from the main bacterial genetic code.

transcription bubble (prokaryotic transcription)

region of locally unwound DNA that allows for transcription of mRNAs

missense mutation

A base-pair substitution that results in a codon that codes for a different amino acid.

nonsense mutation

A mutation that changes an amino acid codon to one of the three stop codons, resulting in a shorter and usually nonfunctional protein.

nontemplate strand

the strand of DNA that is not used to transcribe mRNA; this strand is identical to the mRNA except that T nucleotides in the DNA are replaced by U nucleotides in the mRNA

initiation site

nucleotide from which mRNA synthesis proceeds in the 5' to 3' direction; denoted with a "+1"

upstream nucleotides

Before initiation site (-)

downstream nucleotides

nucleotides following the invitation site (+)

Transcription, translation, and mRNA degradation occur simultaneously in prokaryotes because

Prokaryotes don't have membrane-enclosed nuclei

Core enzyme of RNA polymerase

Lacks the sigma subunit; responsible for catalytic function. Made up of two alpha units, Beta unit, and beta prime unit. Performs elongation

two alpha subunits in core enzyme

necessary to assemble the polymerase on the DNA

B subunit in core enzyme

bunds to ribonucleic triphosphate that will become part of the mRNA molecule

B' subunit in core enzyme

binds the DNA template strand

sigma (σ) subunit

involved only in transcription initiation, confers transcriptional specificity such that the polymerase begins to synthesize mRNA from an appropriate initiation site
Without σ, the core enzyme would transcribe from random sites and produce gibberish