exam 3 (review slides) Flashcards
asexual vs sexual reproduction
asexual reproduction: a single individual passes all of its genes to its offspring without fusion of gametes
asexually reproducing individuals gives rise to clone, offspring that are genetically identical to parent
sexual reproduction: 2 parents give rise to offspring that have unique combinations of genes inherited from 2 parents
offspring vary genetically from their siblings and both parents
each pair of homologous chromosomes includes _______________
1 chromosome from each parents
how many chromosomes in human somatic cells and how many are autosomes? also what chromosomes determine sex of offspring?
- 46 chromosomes in a human somatic cell
- 2 sets of 23: one set from mother, one set from father
- XX is female, XY is male
diploid & haploid cell
diploid cell has 2 copies of each chromosome = 2n (formed by mitosis)
for humans, diploid number is 46
haploid cells contain only copy of each chromosome = n (formed by meiosis)
nonsister chromatids vs sister chromatids
main difference in structure
sister chromatids are two exactly similar copies of a chromatid, with the same genes (only aa or BB)
non-sister chromatids are chromosome couples having the same length, patterns and position of the centromere, but have mixed genes (like a B)
in a cell in which DNA synthesis has occurred, each chromosome is _______________
each __________ chromosome consists of 2 _______________
replicated
replicated
identical sister chromatids
how is the number of daughter cells different in mitosis and meiosis?
mitosis produces 2 daughter cells, whereas meiosis produces 4 daughter cells
explain the difference between meiosis I and meiosis II, which occurs first?
meiosis I occurs first
meiosis I (reductional division): homologous chromosomes pair up and separate, resulting in 2 haploid daughter cells with replicated chromosomes
meiosis II (equational division): sister chromatids separate resulted in 4 haploid cells with unduplicated chromosomes
what are homologous chromosomes? (for your knowledge)
pairs of chromosomes that carry genes for the same traits, with one chromosome inherited from each parent
synapsis
pairing up of homologous chromosomes during meiosis, forming structures called tetrads, where each chromosome aligns with its corresponding partner from the opposite parent before genetic material is exchanged between them (crossing over)
slide says: DNA breaks are repaired, each broken end is joined to corresponding segment of the nonsister chromatid, producing crossovers (nonsister chromatids exchange DNA segments)
when does crossing over occur?
prophase I
what is chiasmata?
plural of chiasma, X-shaped point of attachment where paired homologous chromosomes exchange genetic material
what is a tetrad?
2 pairs of homologous chromosomes next to each other
each pair of chromosomes forms a tetrad, a group of 4 chromatids
- each tetrad usually has 1 or more chiasmata
mitosis _______ the number of chromosome sets, while meiosis _________ the number of chromosomes sets
conserves; reduces
what 3 events are unique to meiosis that all occur in meiosis I?
- synapsis and crossing over in prophase I
- alignment of homologous pairs at the metaphase plate: whereas in mitosis individual chromosomes line up at the metaphase plate
- separation of homologous chromosomes during anaphase I: sister chromatids of each duplicated chromosome remain attached, whereas in mitosis chromatids separate
what are the 3 mechanisms that contribute to genetic variation?
- independent assortment of chromosomes
- crossing over
- random fertilization
how do you carry out a test cross and what is it used for?
- to determine the genotype
testcross: breeding individual of unknown genotype with a homozygous recessive individual
- if any offspring display recessive phenotype, unknown parent must be heterozygous
law of segregation (Mendel)
each individual organism has two alleles for each gene & alleles segregate during the formation of gametes
result: each gamete carries only one allele for each gene, and when fertilization occurs, the offspring inherits one allele from each parent. This process contributes to the variation in traits among offspring.
chat gpt answer ^
how did mendel derive his law of segregation and law of inheritance?
- law of segregation derived by following a single trait
- heterozygous for 1 character (single gene of interest), monohybrid cross
- law of inheritance by following 2 character traits at the same time
- heterozygous for both characters (2 genes of interest)
dihybrid cross: a cross between 2 F1 dihybrids, determines whether 2 characters are transmitted to offspring together as a unit or independently
law of independent assortment (mendel)
- using a dihybrid cross, Mendel developed the law of independent assortment
states that each pair of alleles segregates independently of any other pair of alleles during gamete formation
- applies only to genes on different, nonhomologus chromosomes or those far apart on the same chromosome
- genes located near each other on the same chromosome tend to be inherited together
mendel’s model (thats the name of this slide but really im asking what those 2 important points about genes are but I dont think he discovered this stuff)
- alternative vision of a gene = allele
- different alleles have different DNA sequences at the same locus on a pair of homologous chromosomes
- each gene resides at a specific locus on a specific chromosome
- DNA at locus can vary slightly in its nucleotide sequence, which can affect the function of encoded protein and this an inherited character of organism
describes mendel’s experiments with the white and purple flowers
- Mendel crossed contrasting, true-breeding white-and purple flowered pea plants (P generation) = all F1 hybrids were purple
- Mendel crossed F1 hybrids = many of F2 plants had purple flowers, but some had white
- Mendel discovered a ratio of about 3 purple flowers to 1 white flower in F2 generation (3:1)
3 degrees of dominance for alleles
complete dominance: occurs when phenotypes of heterozygote and dominant homozygote are identical (one allele completely masks the other)
incomplete dominance: phenotype of F1 hybrids is somewhere b/w phenotypes of the 2 parental varieties (ex. red and white parent flower have pink offspring)
codominance: 2 dominant alleles are both expressed (ex. AB blood type)
define these terms: homozygote, heterozygote, phenotype, and genotype
homozygote: an organism with 2 identical alleles for a gene
heterozygote: an organism with 2 different alleles for a gene
phenotype: physical appearance
genotype: genetic makeup
Tay-Sachs disease and inheritance pattern
fatal inherited disorder that causes dysfunctional enzymes to be produced, causing accumulation of lipids in the brain
autosomal recessive
bolded on the slides:
- in heterozygotes, one normal copy of the gene still produces enough of the Hex-A enzyme to prevent significant lipid buildup in their cells ( at biochemical level, phenotype (enzyme activity level) is incompletely dominant)
- heterozygotes produce equal numbers of normal and dysfunctional enzyme molecules, but still sufficient to prevent symptoms of Tay-Sachs (at molecular level, alleles are codominant)
pleiotropy
the ability of a single gene to have multiple phenotypic effects (a single gene can affect multiple, seemingly unrelated traits)
ex. a gene that plays a role in the development of a specific protein. This protein may have different functions in various tissues or cells throughout the body. As a result, a mutation in this gene could lead to various effects or abnormalities in different parts of the organism.
pleiotropic alleles are responsible for multiple symptoms of certain hereditary diseases, such as cystic fibrosis and sickle-cell disease
chromosome theory of inheritance
explains how traits are passed on from generations
- genes are found on specific loci (location sites) on the chromosomes
- chromosomes undergo segregation and independent assortment
Thomas Hunt Morgan’s experiments and conclusions
- 1st solid evidence that proved the existence of sex-linked genes and supported chromosomal theory of inheritance (that specific genes are associated with specific chromosomes)
- conducted experiment with fruit flies
wild type, or normal phenotype was dominant in fruit flies (red eyes)
trait alternative to wild type were mutant phenotypes (white eyes) - cross bred them and learned that eventually, more males had white eyes than females = sex linked inheritance pattern
transmission of X-linked recessive traits
- fathers pass X-linked alleles to all of their daughters but to none of their sons
- mothers can pass X-linked alleles to both sons and daughters
name 3 disorders caused by X-chromosomes (sex linked)
- color blindness
- Duchenne muscular dystrophy
- hemophilia
(not bolded on slide but seems like good info)
nondisjunction
pair of homologous chromosomes do not separate normally during meiosis
as a result, 1 gamete receives 2 of the same type of chromosome, and another gamete receives no copy
mapping distance between genes using recombination data
- Alfred Sturtevant, one of Morgan’s students, constructed a genetic map (an ordered list of the genetic loci along a particular chromosome)
- Sturtevant predicted that the further apart the 2 genes are, the higher the probability that a crossover will occur between them and therefore higher the recombination frequency
distance between genes expressed as map units, 1 map unit 1% recombination frequency
aneuploidy & polyploidy
aneuploidy: offspring have an abnormal number of a particular chromosome (monosomy or trisonomy), results from fertilization of gametes in which nondisjunction occurred
polyploidy: organism had more than 2 complete sets of chromosomes, more common in plants than humans
in plants, associated with increased vigor, larger size, and more adaptability (used for evolution in agriculture) but harmful in animals bc associated with developmental abilities
4 allegations of chromosome structure
deletion: removes a chromosomal fragment (ABC becomes AC)
duplication: repeats a segment (ABC becomes ABBC)
inversion: reverses orientation of a segment (ABC becomes CBA)
translocation: moves a segment from one chromosome to a non homologous chromosome (ABC goes to MNO segment)
first 2 occur during crossing over in meiosis
describe structure of DNA + the 4 nitrogenous bases
DNA is a polymer of nucleotides, each consisting of:
- nitrogenous base
- sugar
- phosphate group
nitrogenous bases:
- adenine (A)
- thymine (T)
- guanine (G)
- cytosine (C)
erwin chargaff (1950)
reported that DNA composition varies from one species to the next = became evidence for DNA being genetic material
Chargaff’s Rules:
1. the base composition of DNA varies between species
2. in any species, the number of A and T bases is equal and the number of G and C bases is equal
structure of DNA (5’ and 3’ & antiparallel)
- 5’ end of DNA strand is the end that has a phosphate group attached to the 5th carbon of the sugar molecule
- 3’ end refers to the end that has a hydroxyl group (-OH) attached to the 3rd carbon of the sugar molecule
- the two DNA strands run in opposite directions, which is known as antiparallel orientation
Watson and Crick
built models of a double helix of DNA
- at first they thought bases paired like with like (A with A) but this did not result in uniform width (either too wide or too small)
- at the end, found out that actually paired purine (A or G) with pyrimidine (C or T) = resulted in uniform width
describe these terms:
1. helicase
2. single strand binding protein
3. topoisomerase
4. primase
5. DNA pol III
6. DNA pol I
7. DNA ligase
helicase: unwinds parental double helix at replication forks
single-strand binding protein (SSB): binds to and stabilize the separated DNA strands, preventing them from re-forming the double helix
Topoisomerase: “molecular scissors” that cut and reseal the DNA strands to release tension, helps prevent DNA from tangling during unwinding
Primase: synthesizes short RNA primers on the DNA template, providing a starting point for DNA polymerase to begin synthesizing a new DNA strand (think of it as a rough sketch)
DNA pol III: main enzyme for synthesizing the new DNA strand during replication, adds nucleotides to the 3’ end of the growing DNA chain
DNA pol I: removes the RNA primers and replaces them with DNA nucleotides during the synthesis of the lagging strands, “clean-up crew” that removes temporary structures (RNA primers) and fills in the gaps
DNA ligase: joins Okazaki fragments on the lagging strand, sealing the gaps between them and creating a continuous DNA strand
leading and lagging strand
DNA polymerase can only synthesize in the 5’ to 3’ direction
leading strand: synthesized continuously and smoothly toward the replication fork in 5’ to 3’ direction
lagging strand: synthesized in short, discontinuous segments called Okazaki fragments away from the replication fork in 5’ to 3’ direction
describe the 7 steps of DNA replication
- Helicase unwinds the parental double helix.
- Molecules of SSB stabilize the unwound template strands.
- The leading strand is synthesized continuously in the 5’ to 3’ direction by DNA pol III.
- Primase begins synthesis of the RNA primer for the Okazaki fragments.
- DNA pol III adds the missing DNA fragments between the RNA primer.
- DNA pol I removes RNA primers from the 5’ end replacing it with DNA nucleotides.
- DNA ligase joined the pieces together and seals them all together.
how does proofreading and repairing DNA occur during DNA synthesis?
- DNA polymerase proofread newly made DNA, replacing any incorrect nucleotides
- In mismatch repair of DNA = repair enzymes replace incorrectly paired nucleotides that have evaded the proofreading process
- in nucleotide excision repair, a nuclease cuts out and replaces damaged stretches of DNA
triplet code
series of nonoverlapping, three-nucleotide words that are translated into a chain of amino acids, forming a polypeptide
also called codons
how are codons coded
one of the 2 DNA strands, the template strand, provides a template for ordering the sequence of complementary nucleotides in an RNA transcript
during translation, the mRNA base triplets are read in the 5’ to 3’ direction
each codon specific the amino acid (one of 20) to be placed at the corresponding position along a polypeptide
transcription (promoter and transcription unit) and translation
transcription: first stage of gene expression, complementary RNA copy of a segment of DNA (called mRNA), done by RNA polymerase
- DNA sequence where RNA polymerase attaches is called the promoter (kinda like the starting point), takes place in nucleus
- the stretch of DNA that is transcribed is called a transcription unit
translation: converting the information in mRNA into a sequence of amino acids, forming a protein (takes place in ribosomes) using tRNA
how do eukaryotic cells modify RNA after transcription?
- enzymes in the eukaryotic nucleus modify pre-mRNA before genetic messages are dispatched to the cytoplasm
- in most cases, certain interior sections of the molecule are cut out and the remaining parts are spliced together - introns removed through RNA splicing
introns vs exons
introns: noncoding segments in a gene that are usually spliced out
exons: expressed segments that are translated into amino acid sequences
structure and function of transfer RNA (tRNA)
- tRNA helps translates mRNA message into protein, they transfer amino acids to the growing polypeptide in a ribosome
- each tRNA carries a specific amino acid on one end and an anticodon on the other end (anticodon = base-pairs with a complementary codon on mRNA)
the 3 binding sites for tRNA on a ribosome
P site: holds the tRNA that carries the growing polypeptide chain
A site: holds the tRNA that carries the next amino acid to be added to the chain
E site: exit site, where discharged tRNAs leave the ribosome
what determines the shape of a protein?
gene determines the primary structure, and the primary structure in turn determines shape
bolded on the slide:
during synthesis, a polypeptide chain begins to coil and fold spontaneously into a specific shape: a 3-D molecule with secondary and tertiary structure
silent, missense, and nonsense mutations
silent mutation: have no effect on amino acid produced by codon because of redundancy in the genetic code
missense mutations: still code for an amino acid, but not the correct amino acid
nonsense mutations: change an amino acid codon into a stop codon
- most lead to a nonfunctional protein
how are polypeptides targeted to specific locations?
- polypeptide synthesis always begins in the cytosol
- polypeptides destined for the ER or for secretion are marked by a signal peptide
- a signal-reception particle (SRP) binds to the signal peptide, SRP escorts the ribosome to a receptor protein built into the ER membrane
steps from that diagram on the slide:
1. polypeptide synthesis begins
2. SRP binds to signal peptide, halting synthesis (important to halt so that SRP has time to engage with it)
3. SRP binds to receptor protein at a pore
4. SRP detaches and polypeptide synthesis resumes
5. signal-cleaving enzyme cuts off signal peptide
6. completed polypeptide folds into final conformation
what is an operon & the 2 types
entire stretch of DNA that includes the operator (on-off switch), the promoter, and the genes that they control
repressible and inducible operons:
repressible operon: usually on but can be turned off by binding of repressor to the operator
ex. trp operon (tryptophan)
inducible operon: usually off but can be turned on
ex. lac operon
in what type of pathways do inducible and repressible enzymes usually function?
inducible enzymes usually function in catabolic pathways
repressive enzymes usually function in anabolic pathways
histone acetylation and DNA methylation
histone methylation: adding acetyl groups to histone proteins which loosens grip on DNA, allowing for transcription to occur (enhancing gene expression)
DNA methylation: adding methyl groups to DNA bases, condensing chromatin and reducing transcription (repressing gene expression)
- “do not disturb” sign
enhancers & activators
enhancers: specific DNA sequences that boost gene expression
activators: proteins that bind to these enhancer regions, acting like helpers to increase the activity of nearby genes
together, they play a crucial role in regulating the level of gene expression in cells
oncogenes
normal genes in a cell that have the potential to become cancer genes if they are mutated
- otherwise code for cell growth and division
