chapter 15,16,17 Flashcards by mckenna harris

Explain how Mendel’s hypothesis of inheritance differed from the blending theory of inheritance.

blending theory- traits from parents blend together in offspring
mendels hypotheis- traits are inherited as discrete units (genes) that do not blend but segregate and recombine

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Differentiate between character and trait.

character- a heritable feature- flower colour
trait- a specific variant of a character- purple

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State in your own words Mendel’s Law of Segregation

each individual has two alleles for a gene, one from each parent, and these alleles separate during gamete formation, so each gamete only carries one allele

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Distinguish between genotype and phenotype; heterozygous and homozygous; dominant and recessive.

genotype- genetic makeup
phenotyp- physically appearance
homozygous- two identical alleles- PP or pp
heterozygous- two different alleles-Pp
dominant- expressed in heterozygous state
recessive- expressed in homozygous

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State, in own words, Mendel’s Law of Independent Assortment.

genes of different traits assort independently during gamete formation meaning the inheritance of the gene does not affect

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Explain how independent assortment, crossing over and random fertilization contribute to genetic variation in sexually reproducing organisms.

Independent assortment- random rearrangement of the chromosomes
Crossing over- genetic exchange between homologous chromosomes
Random fertlization- any sperm can fertilize any egg.

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Give an example of incomplete dominance and explain why it does not support the blending theory of inheritance

Example- red (RR) x white (rr)= pink (Rr) this does not support the blending theory because pink and pink can still produce red and white.

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Explain how phenotypic expression is affected by complete dominance, incomplete dominance and codominance

Complete dominance-one allele masks the other.
Incomplete dominace- blended phenotype
Codominace- both alleles fully expressed.

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Define and give examples of pleiotropy.

One gene affects multiple traits

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Explain, in own words, what is meant by “one gene is epistatic to another” and how this affects the phenotypic ratio of a dihybrid cross.

One gene mask the other

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Describe a simple model for polygenic inheritance.

Multiple genes affect a single trait. Hair colour for example

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Describe how environmental conditions can influence the phenotypic expression of a character.

Siamese cats are good examples of this because their fur colour depends on a temperature-sensitive enzyme.

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Given a simple family pedigree, deduce the genotypes for some of the family members.

Dominant traits- appears in every generation
Recessive traits- can skip generation
Sex-linked traits- more common in males if x-linked

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Explain how the chromosome theory of inheritance differs from Mendel’s theory of inheritance.

Mendel theory- traits are inherited as discrete factors (genes) that segregate and assort independently.
Chromosome theory- genes are located on chromosomes, which undergo segregation and independent assortment during meiosis.

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Describe the inheritance of a sex-linked genes such as color-blindness, Duchenne muscular dystrophy, and hemophilia.

Sex linked genes are located on sex chromosomes x or y. most x-linked affecting males more than females.
Examples- colour blindness and hemophilia.
Sex linked genes are located on sex chromosomes x or y. most x-linked affecting males more than females.
– A recessive x-linked allele in males is expressed because there is no second x to mask it. So there is not other option.

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Describe the process of X inactivation in female mammals.

One x chromosome in each female cell is randomly inactivated (forms barr body) patchy fur color is a good example of this.

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Define linkage and explain why linked genes do not assort independently

Linked genes- are located close together on the same chromosome
They do not follow mendels law of indepedant assortment because these genes tend to be inherited together

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Distinguish between parental and recombinant phenotypes.

Parental phenotype- offspring look like one of the parents
Recombinant phenotype- offspring have new trait combination due crossing over

Explain how crossing-over can unlink genes.

Occurs in prophase 1 of meiosis
Homologous chromosomes exchange genetic material
The further apart two genes are, the more likely they are to be separated by crossing over.

Map a linear sequence of genes on a chromosome using recombination frequencies from experimental crosses.

Recombination frequency %= # of recombinant offspring/total offspring x 100
Genes far apart=high recom frequency
Genes close together- low recom frequency

Distinguish among nondisjunction, aneuploidy and polyploidy; explain how these major chromosomal changes occur and describe the consequences.

Nondisjunction- failure of homologous chromosoms or sister chromatids to separate in meiosis
Aneuploidy- abnormal chromosome number eg- trisomy 21
Polyploidy- extra full sets of chromosomes eg- triplody 3n

Distinguish between trisomy and triploidy

Trismony 2n +1- extra copy of a single chromosome eg-down syndrome
Triploidy 3n- entire extra set of chromosomes

Describe what is meant by the following terms: deletions, duplications, translocation sand inversions

Deletion- loss of a chromosome segment
Duplication-extra copy of segment
Inversion- reversed segment
Translocation- segment moves to non-homologous chromosome

Summarize experiments performed by the following scientists that provided evidence that DNA is the genetic material

Frederick did the transformation experiment worked with pneumoniae and found that s strain could transfer to R strain
Hershey and chase used radioactive isotopes to label DNA and protein in viruses.
Erwin chargaff- found base-pairing rules a,t,c,g bases.

List the three components of a nucleotide.

- Phosphate group, deoxyribose sugar, nitrogenous bases - Purines- adenine and guanine - Pyrimidines cytosine and thymine - Base-pairing rule- a pairs w t and c pairs with g

Describe the structure of DNA and explain what kind of chemical bond connects the nucleotides of each strand and what type of bond holds the two strands together.

- Double helix - Covalent bonds connect nucleotides within a strand - Hydrogen bonds hold the two strands together

Explain, in your own words, semiconservative replication and describe the Meselson-Stahl experiment.

- DNA strands separate, and each serves as a template - They used n15 and n14 isotopes to prove DNA copies one strand from the original.

Describe the process of DNA replication, including the role of the origins of replication and replication forks.

- First begins at the origin of replication….creates replication forks. - Helicase unwinds DNA - Primase lays down RNA primer - DNA polymerase adds nucleotides 5’ to 3’ direction. - One strand runs 5’ to 3; and the other 3’ to 5’, dna polymerase only synthesizes 5 to 3 leading to.. - Leading strand which is continuously synthesizing and the lagging strand Okazaki fragments synthesizd in pieces.

Explain the roles of DNA ligase, RNA primer, primase, and helicase

- Helicase- unwinds the DNA - Primase- makes RNA primer - DNA polymerase- adds nucleotides and proofreads - DNA ligase- seals Okazaki fragments

Explain the role of DNA polymerase in DNA proofreading and repair.

- DNA polymerase proofreads and fixes errors - Telomeres- non-coding ends of chromosomes (prevent loss of important genes). - Telomerase- extends telomeres (active in stem and cancer cells)

Describe the current model for progressive levels of DNA packing. Heterochromatin and euchromatin

- DNA packing levels- nucleosome (DNA + histone), chromatin fiber, chromosome - Heterochromatin- tightly packed inactive genes - Euchromatin- loosely packed, active genes.

1. Describe early experimental evidence that implicated proteins as the links between genotype and phenotype

- Scientists knew genes-controlled traits but unsure how, Garrod 1902 made the connection btwn disease and enzymes. Each disease was caused by a loss of an enzyme in a metabolic pathway.

2. Explain how experiments done by Beadle and Tatum and Srb and Horowitz identified how genes control metabolism.

- Worked with bread mold and they exposed the mold to x-rays causing mutations. Found that mutant mold could not grow without a pacific amnio acid. This concluded that one gene code for a specific enzyme. - Srb and Horowitz studied mutants in more detail and indefied that specific gene controlled different enzymes in the pathway.

3. Distinguish between "one gene-one enzyme" hypothesis and "one gene-one polypeptide," and explain why the original hypothesis was changed.

- The one gene one enzyme hypothesis was modified because some proteins are not enyzmes, some proteins are made of multiple polypeptides, RNA are modfied and code for different proteins, some genes make RNA but the RNA isn’t used to make proteins

4. Explain how RNA differs from DNA.

- RNA is a ribose, single stranded, AUCG, less stable molecule. DNA is a deoxyribose, double stranded, atcg stable molecule.

5. In your own words, briefly explain how information flows from gene to protein.

- DNA, transcription, mRNA, translation, protein

6. Distinguish between transcription and translation and where they occur in prokaryotes and eukaryotes.

- Transcription and translation occur simultaneously located in the cytoplasm for prokaryotes - Transcription produces pre-rna, gets modified to rna. Rna moves out of nucleus. Translation occurs on ribosome in cytoplasm

7. Define codon, and explain what relationship exists between the linear sequence of codons on mRNA and the linear sequence of amino acids in a polypeptide.

- Codon- a set of 3 nucleotides on mRNA. Each codon codes for one amino acid. - Redundant- multiple codons code for the same amnio acid - Unambiguous- each codon only codes for one amino acid - Its nearly universal shared by almost all living organisms suggest common evolutionary origin

8. Explain the process of transcription including the three major steps of initiation, elongation and termination.

- DNA to mRNA - Initiation- RNA polymerase binds to the promoter - Elongation- RNA polymerase moves along the DNA adding nuceleotides to the 3’end synthesing from 5 to 3. - Termination- signaled by termination sequence on the DNA. RNA polymerase detachs and the nucleotides that pass this go through post-transcriptional modification

9. Explain how eukaryotic mRNA is processed before it leaves the nucleus.

- Before leaving the nucleus, eukaryotic mRNA undergoes - 5’ cap addition- helps ribosome binding - Poly a tail- protects mRNA - Splicing removes introns joins exons

10. Distinguish among mRNA, tRNA, and rRNA.

- mRNA- carries genetic code from DNA to ribosomes - tRNA- brings aa t ribosome, matches codons with anticodons - rRNA- part of ribosomes, helps protein synthesis.

11. Explain the role of aminoacyl-tRNA synthetases

- Helps attach the right aa to its corresponding tRNA which essentially charges the tRNA.

12. describe the process of translation including initiation, elongation and termination and explain what enzymes, protein factors and energy sources are needed for each stage.

- Initiation- ribosome binds to mRNA, first tRNA attaches. - Elongation- codon recognition, tRNA moves into a site. mRNA binds to tRNA. Peptide bonds by ribozyme. tRNA moves from a site to p to e. - Termination- stop codon is reaches a site ribosome detaches