AP Biology Exam Review

How many chromosomes are there in somatic cells of an animal in which 2n= 16? How many chromosomes are in its gametes?

16, 8

In n= 16, how many chromosomes are there in diploid somatic cells? How many sets of homologus chromosomes are in the gametes?

32, 1

If 2n= 32, how many chromatids are there in a cell after duplication has occured prior to cell division? What is the difference between sister chromatids and non sister chromatids?

64, Sister chromatids are two exactly similar copies of a chromatid. Sister chromatids have the same genes. Non-sister chromatids are chromosome couples having the same length, patterns and position of the centromere.

Stages of Meiosis 1

Prophase 1: Centrosome movement, spindles form, the nuclear envelope breaks down, and chromosomes condense. Crossing over occurs, microtubules from one pole attach to kinetochores, microtubules move the homologous pairs toward the metaphase plate

Metaphase 1: Pairs of homologous chromosomes are arranged at the metaphase plate, and one chromosome faces each pole. Each pair lines up independently of the others. Both chromatids of a homolog attach to kinetochore microtubules from one pole, the chromatids of the other homolog attach at the other pole

Anaphase 1: Breakdown of proteins that are responsible for sister chromatid cohesion along chromatid arms, chromatids separate. Homologs move toward opposite poles. Chromatids move as a unit toward the same pole.

Telophase 1/ Cytokenisis: Forms two haploid daughter cells, cleavage furrow, chromosomes decondensed, nuclear envelope reforms

No duplication occurs between meiosis 1 and 2

Stages of Meiosis 2:

Prophase 2: Spindle apparatus forms

Metaphase 2: Chromosomes are positioned at the metaphase plate

Anaphase 2: Breakdown of proteins holding the sister chromatids together. The chromatids move toward the poles as individual chromosomes

Telophase 2/ Cytokinesis: Nuclei form, chromosomes decondensed, four daughter cells are produced each haploid, and four daughter cells are genetically different from the parent.

Compare Mitosis and Meiosis

DNA Replication: Mitosis= occurs during interphase before mitosis begins. Meisos= Occurs during interphase before Meisos 1 but not Meiosis 2

Number of Divisions: Mitosis= One. Meiosis= Two

Synapsis of homologous chromosomes: Mitosis= does not occur. Meiosis= occurs during prophase 1 along with crossing over between non sister chromatids

Number of daughter cells and genetic composition: Mitosis= Two, genetically identical to each other and the parent. Meiosis: Four, each haploid, genetically different.

How are the chromosomes in a cell at metaphase of mitosis similar to and different from the chromosomes in a cell at metaphase 2 of meiosis

Metaphase- Can be diploid or haploid

Meiosis- haploid

Desrcibe the process of crossing over

During prophase 1, duplicated homologs pair up and crossing over occurs. DNA molecules of two non sister chromatids are broken at coresponding points and chromatin of the chromosomes starts to condense. A zipper like protein complex (synaptonemal comples) forms and attached one homolog to another while the chromatin continues to condense. When the complex is fully formed, the two chromatids are said to be in synapsis. During synapsis, the DNA breaks close up and each end is joined to its corresponding segment. After the synaptonemal complex disassembles but the homologs remain attached due to cohesion. The points of crossover are called chiasmata. Pairing or crossing over does not occur in mitosis

How does meiosis generate genetic variation?

Random fertalization, mutations, independent assortment

What is the evolutionary signifigance of a speices that switches from sexual to asexual reproduction due to their enviroment?

Shows yhat organisms can adapt to their enviroment- survival of the fittest, they do what works best for them

What is the phenotypic and genotypic ration of a cross between a TT tall plant is crossed with a tt dwarf plant? What if the tall plant was Tt?

TTtt: P= 1, G=1

Tttt: P=1:1 G=1:1

TTPPxttpp phenotype and genotype of the f1 and f2 generations

f1: 1:1 f2: p= 9:3:3:1 g=1:2:2:2:1:2:2:1:2:1

Determine the probability of obtaining offspring with indicated genotype: Cross AaBbCcxAaBbcc offspring aabbcc

1/32

List all the possible genotyoes for the following blood groups A, B, AB, O

A- I^A I^A, I^A I

B- I^B I^B, I^B I

AB- I^AI^B

O- ii

What is the probability that mating between two carries will produce an offspring with a recessivley inherited disorder?

1/4

What is the probablity that a normal child will be a carrier if produced by two heterozygous parents?

1/2

Incomplete dominance and epistasis are both terms that define genetic relationships. What is the most basic distinction between them?

Epistasis is a relationship between alleles of two different genes. Whereas dominance refers to the relationship between two variants or alleles of the same gene.

If a man with AB bloodtype married a woman with O bloodtype, what will the fractions of their childrens blood types be?

25% chance of havinf A, B, AB, or O blood type

With unlinked genes, an equal number of parental and recombinant offspring are produced. With linked genes, are more or fewer parental than recombinant produced?

More. Linked genes are more likely to be inherited together, meaning they will be more similar to the parent than if they were inherited seperatly and ended up in different locations.

What is the difference between trisomy and a triploidy organism?

Trisomy is a condition where you have an extra copy of one chromosome. Triploidy is a condition where you have an extra set of chromosomes.

What does wild type mean?

Most common type found in the population

Why are males more effected by X linked disorders?

Males only have one X chromosome, meaning if the chromosome contains a disorder, they will 100% get that disorder. Females have two, depending on which one is expressed verus condensed, they have a 50% chance of getting the disorder

Why are specific alleles of two genes that are farther apart more likely to show recombination than those of two closer genes?

Close linked genes are more likely to be inherited together, prohibitinh recombination. if genes are far apart, they can go to different loci and recombine differently

Sex-linked dominant, sex-linked recessive, autosomal dominant, and autosomal recessive

X and Y are sex chromosomes. Dominant inheritance occurs when an abnormal gene from one parent causes disease, even though the matching gene from the other parent is normal. The abnormal gene dominates. But in recessive inheritance, both matching genes must be abnormal to cause disease.

Autosomal dominant traits pass from one parent onto their child. Autosomal recessive traits pass from both parents onto their child. Autosomal refers to the 22 numbered chromosomes as opposed to the sex chromosomes

Hershey and Chase

DNA is hereditary material

Structure of the DNA molecule

Deozyribose sugar, phosphate, nucleic acid bases. Double helix, 5→ 3

Describe the enzymes involved in DNA replication

Topioisomerase: Relives strain ahead of the replication fork

Helicase: unwinds/ untwists strands

Single stranded binding protein- keeps strand from re-joining

DNA Pol 1: removes RNA primers and fills the gaps between Okazaki fragments.

DNA Pol 3: major replicative polymerase, functioning in the synthesis both of the leading strand of DNA and of Okazaki fragments by the extension of RNA primers.

Ligase: Glue okazaki fragments together

Contrast leading vs lagging strand

Leading goes toward the replication fork, continuous

Lagging creates okazaki fragments, going away from the fork and takes longer

Describe a chromosomes components

DNA tightly coiled many times around proteins called histones

Differences between DNA and RNA

Deoxyribose, double helix, thymine

Ribose, single stranded, uracil

Key steps of transcription

Initiaion: Polymerase binds to promoter, DNA strands unwind, the polymerase initiates RNA synthesis st the starting point of the template strand

Elongation: Polymerase moves downstream, unwiding DNA and elongating the RNA in a 5’ → 3’ direction. The DNA starts to reform its double helix after the transcription bubble passes

Termination: RNA transcript is releases and the polymerase deattaches from the DNA

What is a promoter?

DNA sequence where the RNA polymerase attaches and initiates transcription

Describe RNA proccessing

At the 5’ end, a G-cap is added. At the 3’ end, a poly-A-tail is added. They both can faciliatate and export mature mRNA, protect the mRNA from degradation, and help ribosomes attach to the 5’ end when the mRna reaches the cytoplasm.

Introns are also cut out by nuclease and exons are rejoined together by ligase

Introns versus exons

Exons are the coding parts, introns are the non coding parts that will be cut out of the squence during RNA processing- this process is called RNA splicing

Alternative RNA spicing is dependent on which sections are considered exons vs introns

The protein that cuts out the introns are called spliceosomes

Describe the process of translation

A molecule of mRNA is moved through a ribosome, codons are translated into amino acids. tRNA molecules have an anticodon on their end and are also attached to a amino acid, they pair the codon with the amino acid to form a growing polypeptide chain.

A P and E sites

A site accepts an incoming tRNA bound to an amino acid. The P site holds a tRNA that carries a growing polypeptide (the first amino acid added is methionine (Met)). The E site is where a tRNA goes after it is empty, meaning that it has transferred its polypeptide to another tRNA

Describe how a polypeptide is secreted into the endomembrane system

The polypeptides destined for the endomembrane system are marked by a signal peptide. This is recognized by a signal-recognition particle which escorts the ribosome to a receptor protein built into the ER membrane.

Summarize the trp-operon

Repressible operon, its transcription is usually on but can be repressed or inhibited when tryptophan binds allosterically to a regulatory protein.

Describe the lac-operon

Inducible operon, its transcription is usually off but can be turned on by allolactase. An inducer inactivates the repressor

Lactose present, repressor inactive, operon on

Lactose not present, repressor active, operon off

What is cell type specific transcription?

?

Apoptosis

Programmed cell death

What characteristics do viruses share with cells?

they have nucleic acid genomes based on the same genetic code that's used in your cells (and the cells of all living creatures). Also, like cell-based life, viruses have genetic variation and can evolve.

Describe lytic vs lysogenic cycles of viruses

Lytic: the virus introduces its genome into a host cell and initiates replication by hijacking the host's cellular machinery to make new copies of the virus. Once infection is complete, the newly replicated and assembled virus particles are released through lysis of the host cell into the surrounding waters.

Lysogenic: involves the incorporation of the viral genome into the host cell genome, infecting it from within, then being passed to its offspring before switching to lytic and detroying every host.

Summarize darwins mechinisms of natural selection to explain observable patterns of evolution

organisms with heritable traits that favor survival and reproduction will tend to leave more offspring than their peers, causing the traits to increase in frequency over generations.

How is rapid drug resistance an example of natural selection

When bacteria are initially exposed to an antibiotic, those most susceptible to the antibiotic will die quickly, leaving any surviving bacteria to pass on their resistant features to succeeding generations.

How is this statement inaccurate?: Antibiotics have created drug resistance in MRSA

An environmental factor such as a drug does not create new traits, such as a drug resistance, but rather selects for traits among those that are already present in the populations

How does evolution account for similar mammalian forelimbs with different functions?

because such uniquely similar structures could not have happened by chance, these species must share common ancestors at some point.

Describe convergent evolution versus divergent evolution

Divergent evolution is when individuals in one species, or closely related species, acquire enough variations in their traits that it leads to two distinct new species. Convergent evolution on the other hand is when two unrelated species develop similar traits because they live in similar environments.

Why is it necessary to distinguish homology from analogy to refer to phylogeny?

Homologous structures share a similar origin; analogous organs have a similar function.

Describe assumtions and limitations of a molecular clock

molecular clocks work under the assumption that genetic changes occur at a fixed rate. Limitations of molecular clocks include: DNA, RNA, or protein sequences that may change at irregular bursts instead of at a constant rate.

Explain why genetic variation is a prerequisite for evolution

Without variation, traits would not be able to be more suited than others, therefore not being able to evolve/ adapt

Why do only a small fraction of mutations in a population become widespread?

It depends on whether or not they are beneficial, and more suited for the enviroment. The organism that contains the mutation would then reproduce/ survive better and pass down that mutation.

If a population stopped producing sexually, how would the variation differ overtime

There would be no variation as evrything wuld be a clone of the parent

The allele frequencies in a population are A=.6 and a=.4. Predict the genotypic frequencies for the next generation.

AA= 36%

aa= 16%

Aa= 48%

Suppose you are able to determine actual genotype frequencies in the population and find out that these frequencies differ signifigantly from what is expected- what would this indicate

The population is evolving at a non-constnat rate

The frequency of allele a is .45 for a population in Hardy-Weinberg equilibrium. What are the expected genotypic frequencies?

AA: 30%

Aa: 49%

aa: 20%

Distinguish genetic drift from gene flow, how they occur, and their implications for future genetic variation in a population

Genetic drift results from chance fluctuations of allele frequencies from generation to generation; it tends to decrease variation over time. Gene flow is the exchange of alleles between populations; it tends to increase variation within a population but decrease allele frequency differences between populations.

Directional, distruptive, vs stabalizing selection

Directional- prefers one extreme

Disruptive- prefers two extremes, not the middle

Stabalzing- prefers the middle, neither extreme

Why is the the sickle-cell frequency in the gene pool in African Americans so high?

Heterozygous advantage: those who are heterozygous carry the diesease, but also are immune to malaria

Allopatric vs Sympatric speciation

In allopatric speciation, groups from an ancestral population evolve into separate species due to a period of geographical separation. In sympatric speciation, groups from the same ancestral population evolve into separate species without any geographical separation.

How do reproductive barriers arise in each type of speciation?

Pre-zygotic:

• Behavioral- Different mating rituals

• Temporal- Different mating times

• Mechanic- Different morphological features

• Spatial- Different geographic locations

• Gametic- Sperm and egg do not work together

Post-zygotic

• Hybrid inviability- Premature death

• Hybrid breakdown- Reproductive failure that shows up after the f2 generation

• Hybrid sterility- Offspring infertile/ cannot breed

Explain the three possible outcomes for a hybrid zone over time

fusion of parental populations, extinction of one of the parental types, or speciation via “reinforcement.”

Explain the importance of gene flow to the biological species concept

The effect of gene flow is to reduce genetic differences between populations, thereby preventing or delaying the evolution of the populations in different geographical areas into separate species.