Honors Biology Semester 2 Exam

Ch. 12, Ch. 13, Ch. 19, Ch. 20, Ch. 22, Ch. 23, Ch. 24, Ch. 25, Ch. 26, Ch. 27, Ch. 28, Ch. 39, Ch. 40

Gregor Mendel

“Father” of genetics, Austrian Monk, studied math and science, became an abbot

Monohybrid crosses

a cross that follows a single trait with 2 variations

Dominant trait

trait that was expressed

Recessive Trait

trait that was not readily expressive

True breeding

A Plant that, when self pollenating, always produces offspring with the same trait as itself

P Generation

2 true breeding plants with contrasting traits are crossed

F1 Generation

offspring of P generation, hybrids

F2 Generation

Offspring of members of F1 generation (when self-pollinating) show a 3:1 ratio of traits

Gene

A segment of DNA that codes for a specific trait

Allele

Members of gene pairs

Principle of Dominance

one member of a gene pair can hide, or mask, the other’s effect (Dominant (T) and Recessive (t) alleles)

Principle of Segregation

The 2 alleles for a gene segregate during gamete formation and are rejoined at random, one from each parent, during fertilization

Genotype

the genetic make up of an organism, Ex. Aa Bb Cc Dd

Phenotype

The physical expression of a genotype, Ex. Brown hair or Blue eyes

Homozygous

having 2 of the same alleles

Heterozygous

having 2 different alleles

Punnet Square

chart/diagram used to determine probable distribution of inherited traits in the offspring

Monohybrid cross

one characteristic is followed

Principle of Independent Assortment

In a cross, the alleles of a gene segregate independently of other genes, as a result, gene pairs found on chromosomes assort independently of one another

Testcross

individual with unknown genotype is crossed with the homozygous recessive genotype, presence of recessive phenotype means test individual is heterozygous

Phenotypic Plasticity

Different phenotypes are possible for the same genotype due to the environment

Polygenic Traits

traits controlled by two or more genes

Pleiotropic

alleles with more than one effect on a phenotype

multiple alleles

a gene with more than 2 alleles, more common

Incomplete dominance

phenotype of heterozygote is intermediate between 2 homozygotes

Codominance

Heterozygous phenotype expresses both parent phenotypes, without blending. Creates a 3rd phenotype, which changes predicted outcomes

Epistasis

The effects of one gene can influence another gene

Thomas Hunt Morgan

• Worked with fruit flies

• saw mutant male with white eyes

• more common in males than females

• determined white eyes were on the X chromosome

• showed segregation of a trait was connected to segregation of chromosomes

Chromosomal sex determination

male gametes (sperm cells) determine sex of the offspring

Genomic imprinting

the phenotype of a specific allele is expressed when it comes from one parent but not the other

Organellar inheritance

inheritance of genes located on the DNA of organelles in mitochondria and chloroplasts

Mitochondrial

Inherited by mother, genes affect ATP production, mostly causes disorders of muscles and nerves

Chloroplast

also usually maternally inherited, affects production of chlorophyll and other pigments

Sex-linked Inheritance

some genes are only on the Y or on the X chromosome

Sex Linkage

Presence of a gene on a sex chromosome

Linked genes

2 or more genes located on the same chromosome, tend to be inherited together

“Crossing Over”

during meiosis can separate linked genes to rearrange allele combinations, creates genetic recombination

Chromosome Map

shows the linear sequence of genes on a chromosome

Alfred Sturtevant

a student of Morgan that used crossing over data to construct a chromosome map of Drosophila

Map Unit

2 genes that are separated by crossing over 1% of the time are considered 1 map init apart

Deletion

part or all of a chromosome is lost (breakage)

Inversion

segment of chromosome breaks off and then reattaches to the SAME chromosome, but in reverse orientation

Translocation

a piece of chromosome breaks off and reattaches to a DIFFERENT chromosome

Nondisjunction

failure of a chromosome to separate from its homologue during meiosis, result is 1 gamete receives an extra chromosome and the other gamete is 1 short.

Pedigrees

a diagram/graph of matings and offspring over multiple generations for a single specific trait (family tree)

Single Allele Traits

controlled by a single allele of a gene single dominant alleles account for more than 200 human traits

Single Allele Recessive

expressed only when 2 copies of recessive ALLELE are present (1 from mom and 1 from dad)

Sex Influenced Traits

presence of male or female sex hormones influences the expression of these traits, a male and female can have the same genotype but the sex influenced trait will be expressed in only one sex

Genetic Markers

a short section of DNA that is known to be closely associated to a particular gene, used to predict of people have a strong chance of getting a disease.

Multiple Allele Traits

controlled by 3 or more alleles of the same gene that code for a single trait

Polygenic Traits

controlled by 2 or more GENES, most human traits are controlled this way

X-Linked Traits

Genes are found only on the X chromosome, there are 100’s of these

Genetic Screening and Counseling of parents

may be requested by prospective parents with concerns, can do: karyotyping, blood tests, DNA testing

Genetic Screening of the Fetus

Doctors con diagnose more than 200 genetic disorders before the baby is born

Genome

full set of information (genes) that are on the chromosome

Gene Therapy

Mostly experimental, only used for diseases that have no other treatments

Heredity

hereditary traits are controlled by genes on the chromosomes inherited from our parents

Gene

section of a chromosome and chromosomes are made mainly of protein and DNA

Fredrick Griffith (1928)

tested 2 strains of s. pneumonia bacteria in mice

Goal- develop vaccine against virulent (disease causing) strain

   S- causes pneumonia and R- is harmless

heat killed S cells did not harm mice, but when mixed these with R cells the mice got sick

Results- heat killed S cells transformed the R cells

What molecule in the S cells was transferred between the cells?

Oswald Avery (1944)

series of experiments- treated heat killed bacteria to destroy different molecules (proteins, lipids, carbohydrates, RNA, DNA)

tested each type of treated bacteria in mice-transformation of cells occurred in each case except with DNA

Results- the transforming principle is that DNA is the hereditary material

Hershey-Chase (1952)

used bacteriophages-

a type of virus that infects bacteria, has a DNA core and protein coat

used radioactive isotopes to label the DNA and protein

proved that the DNA was what the virus injected into the bacteria

confirmed DNA is the molecule of heredity

Friedrich Miescher (1869)

extracted a material made of nitrogen and phosphorous from nuclei of human cells and fish sperm, called it nuclein

now known as nucleic acid

What is DNA made of?

•deoxyribonucleic acid

a nucleic acid made of

nucleotides that have 3 parts-

5-carbon sugar (deoxyribose),phosphate group, nitrogenous base

nucleotides are linked into long chains by covalent bonds between the sugar of one and the  phosphate of another

this forms the  “backbone” or side chains with the bases sticking out

Purine bases

adenine and guanine, double ring of carbon and nitrogen atoms

Pyrimidine bases

cytosine and thymine, single ring of carbon and nitrogen atoms

What are the complementary bases?

adenine with thymine, and cytosine with guanine

Rosalind Franklin and Maurice Wilkins (1950)

Used X-ray diffraction to show that DNA had a helix shape

Watson and Crick (1950s)

—teamed up in the early 1950’s

—used work from other scientists like Rosalind Franklin, did no experiments

—their final model showed the structure of DNA and how it could replicate

—won the Nobel Prize in 1962

•2 strands of nucleotides known as the phosphodiester backbone

• hydrogen bonds hold the base pairs together, linking the 2 strands together

•shape formed is a double helix

Meselon and Stahl (1958)

evaluated 3 possible models for DNA replication

conservative, semiconservative, dispersive

semiconservative replication was confirmed

each new DNA has an original strand and a new strand

requires a template (parental DNA), nucleotides and enzymes

Replication fork

DNA split into 2 strands

Helicase

enzyme that breaks the hydrogen bonds holding the bases together

DNA polymerase

joins new nucleotides to the existing nucleotides by producing sugar-phosphate bonds

Order of how the nucleotides are added in DNA replication

5’ to 3’

Okasaki fragments

chunks of the lagging strand

ligase

connects the okasaki fragments

telomeres

protects the ends of chromosomes

mismatch repair (MMR)

fixes mis paired bases during replication

photorepair

uses photolyase to repair damage from UV light

Exclusion repair

removes and replaces a damaged section of DNA

Archibald Garrod (1902)

through testing he proposed that inherited diseases are due to enzyme deficiencies

George Beadle and Edward Tatum (1941)

induced mutations in bread mold using X-rays that made the mold unable to make arginine

found that each mutant had a defective enzyme

proposed- one gene/one enzyme hypothesis

—Today- one gene/ one polypeptide hypothesis- relationship between genotype and phenotype, useful but not the whole story

RNA

—a nucleic acid like DNA

—synthesized from a DNA template

—Differences between RNA and DNA

different sugar- Ribose

 single stranded

 contains uracil in place of thymine

—disposable copy of a piece of DNA

many times it is a copy of a single gene

Messenger RNA (mRNA)

carries information for making proteins from the DNA (in nucleus) to  ribosomes (in the cytoplasm)

Ribosomal RNA (rRNA)

combine with proteins to form ribosome subunits that allow for translation

Transfer RNA (tRNA)

carries amino acids to the ribosomes

Transcription (RNA)

making RNA from DNA

Initiation (RNA)

transcription factor recognizes and binds to a promotor (specific sequence on DNA)

Elongation (RNA)

RNA polymerase II moves along DNA, adds the correct (complimentary) nucleotides to new RNA, moves from 5’ to 3’

Termination (RNA)

RNA polymerase II reaches a “stop” sequence on the DNA (may be past end of a gene), and disengages from the  DNA

The RNA is called the primary transcript

RNA processing

primary transcript is processed into mature mRNA

a 5’ cap and a 3’ poly-A tail is added (add stability and reduce degradation)

splicing- cut out noncoded (intron) sections and connect the coding sequences (exons)

Proteins

made of long chains of amino acids called polypeptides,

used for growth and repair,

the sequence of amino acids determines the shape which ultimately determines the function of the protein

Crick and Brenner (1961)

determined how to read the genetic code

codon- 3 bases on mRNA that corresponds to an amino acid, 64 possible codons

code is read in groups of 3 nucleotides continuously

Nirenberg and Khorana (1961-1966)

matched each codon to an amino acid

Translation

mRNA is converted into the sequence of amino acids that make up protein

Initiation (amino acid)

mRNA transcribed in the nucleus moves into the cytoplasm and attaches to a ribosome

initiation complex forms- a tRNA carrying the amino acid methionine pairs with the start codon AUG on the mRNA

initiation factors and ribosomal subunits are also needed

Elongation (amino acid)

making the polypeptide chain

1. matching of tRNA anticodon with mRNA codon

2. a peptide bond joins adjacent amino acids and separates amino acid from tRNA

3. translocation of ribosome- moves the tRNA’s and mRNA so next tRNA/ mRNA interaction can happen

Termination (amino acid)

at a stop codon the ribosome releases protein

the components of translation come apart-

ribosome separates from the last tRNA and the mRNA

Replication

copying DNA before cell division, each strand of original copy is a template for a new strand

Mutations

a heritable change in the sequence of DNA

Germ-cell Mutations

occur in an organism’s gametes/reproductive cells/germ cells.  These mutations do NOT affect the organism itself, but may affect the offspring.  Ex. Spina Bifida