Unit one Flashcards
What are the stages of the cell cycle?
Interphase ( G1, S, and G2) and M phase
What happens during Interphase of the cell cycle
G1: the cell grows
G0: non dividing stage the cell may enter
G1/S checkpoint: after this the cell is committed to dividing
S: DNA duplicates
G2/M checkpoint
What happens during the M phase of the cell cycle?
After G2/M checkpoint the cell can divide. Mitosis and cytokinesis (cell division) take place.
What are the phases of mitosis?
Interphase, Prophase, Prometaphase, Metaphase, Anaphase, Telophase
What is occurring during interphase?
The nuclear membrane is present and the chromosomes are relaxed.
What is occurring during prophase?
Chromosomes condense. Each chromosome possesses two chromatids. The mitotic spindle forms
What occurs during prometaphase
The nuclear membrane disintegrates. Spindle microtubules attach to chromatids
What occurs during metaphase?
Chromosomes line up on the metaphase plate
What occurs during anaphase?
Sister chromatids separate and move toward opposite poles
What occurs during telophase
Chromosomes arrive at spindle poles. The nuclear membrane re-forms, and the chromosomes relax.
What occurs during cytokinesis?
Cytoplasm divides. In plant cells, a cell wall will form. In meiosis when the cytoplasm divides to produce 2 cells each has half the original number of chromosomes
What are the stages of meiosis?
Meiosis 1: Prophase 1, Metaphase 1, Anaphase 1, Telophase 1
Meiosis II: Prophase II, Metaphase II, Anaphase II, Telophase II –> products
What occurs during prophase I?
Chromosomes begin to condense and the spindle forms. Homologous chromosomes pair. Crossing over takes place, and the nuclear membrane breaks down.
What occurs during metaphase I?
Homologous pairs of chromosomes line up along the metaphase plate
What occurs during anaphase I?
The two chromosomes (each with two chromatids) of a homologous pair separate and move toward opposite poles
What occurs during telophase I?
Chromosomes arrive at the spindle poles
What happens during interkinesis?
In some types of cells, the spindle breaks down, chromosomes relax, and a nuclear membrane re-forms, but no DNA synthesis takes place.
What occurs in prophase II?
Chromosomes condense, the spindle forms, and the nuclear membrane disintegrates
What occurs during metaphase II?
Individual chromosomes line up on the metaphase plate
What occurs during anaphase II?
Sister chromatids separate and move as individual chromosomes toward opposite spindle poles
What occurs during Telophase II?
Chromosomes arrive at the spindle poles; the spindle breaks down and a nuclear envelope reforms
differentiate between prokaryotes and eukaryotes in regards to nucleus, genome, and membrane bound organelles
prokaryotes: no nucleus, relatively small cell diameter (1-10 micrometers), usually one circular DNA molecule, DNA is not complexed with histones in bacteria but some histones in archaea, relatively small amount of DNA, no membrane bound organelles
Eukaryotes: contain a nucleus, relatively large cell diameter (10-100 micrometers), multiple linear DNA molecules, DNA is complexed with histones, relatively large amount of DNA, contains membrane bound organelles
explain binary fission
reproduction of a prokaryotic cell. The circular chromosome replicates at the origin of replication. The new replicated chromosomes move to opposite ends of the cell. A new cell wall forms producing two cells with identical chromosomes.
what is a diploid organism
diploid organisms have two complete sets of chromosomes in each cell. cells that carry two sets of genetic information are diploid. Humans are diploid, they have 23 pairs of chromosomes but 46 chromosomes
what are homologous chromosomes
two chromosomes of a homologous pair are alike in structure and size and each carry genetic information for the same set of characteristics.
what is the difference between a homologous pair and sister chromatids
a homologous pair is a pair of chromosomes that have information for the same trait but they are not copies of each other
Sister chromatids are two copies of one chromosome linked together at the centromere.
what are sister chromatids
To prepare for cell divison each chromosome replicates, making a copy of itself. Sister chromatids are held together at the centromere. Each sister chromatid consists of a single molecule of DNA
what is the purpose of mitosis and what is the purpose of meiosis.
the purpose of mitosis is to produce 2 genetically identical cells. Mitosis ensures that one of the two sister chromatids from each replicated chromosome passes into each new cell.
The purpose of meiosis is to create gametes with half the genetic material as the parent cell. To create gametes for sexual reproduction, that are not exact copies of each other
what is the result of meiosis
1 cell produces 4 genetically variable cells whose chromosome number has been halved from the original cell. (if the parent cell has 24 chromosomes, the daughter cell will have 12)
what is the difference in the 2 divisions that happen in meiosis
at the end of meiosis I the chromosome number has been halved and crossing over (genetic recombination) has occurred.
At the end of meiosis II the cell division has been completed so it goes from 2 haploid cells to 4 haploid cells
TLDR; meiosis I is reduction/division, meiosis II is equational division (similar to mitosis)
how is genetic variation produced through meiosis
crossing over which occurs in prophase I and it is the exchange of genetic material between non-sister chromatids
Random separation of homologous chromosomes occurs in anaphase I after random alignment during metaphase I.
how does cohesin control the separation of chromosomes and chromatids in mitosis and meiosis
cohesin is a protien that holds chromatids together and it is key to the behavior of chromosomes in mitosis and meiosis.
cohesin has a single ring like structure that encircles and holds together sister chromatids. It is loaded on to the chromosome in the S phase and persists through G2 and early mitosis. During anaphase in mitosis cohesion along the entire length of the chromosome is broken down by separate, which allows sister chromatids to separate.
The forms of cohesion in meiosis and mitosis differ. At the beginning of meiosis, the meosis-specific cohesin is found along the entire length of the chromosomes arms. In anaphase I cohesin along the chromosomes arms is broken, allowing the two homologs to separate. Cohesin at centromere is protected by shugoshin which prevents the separation of the two sister chromatids during anaphase I. Shugoshin is degraded by the end of metaphase II and sister chromatids separate during anaphase II.
how are gametes formed in humans
male spermatogenesis occurs from puberty through adulthood and produces 4 sperm cells for each round of meiosis
Female oogenesis actually begins prior to birth and is not complete until after fertilization. Only 1 egg is produced for each round of meiosis
what is a gene
an inherited factor (encoded in the DNA) that helps determine a characteristic
What is an allele?
One of two or more alternative forms of a gene
What is a locus?
a specific place on a chromosome occupied by an allele
What is a genotype
a set of alleles possessed by an individual organism
Define the concept of dominance
when two different alleles are present in a genotype, only the trait encoded by one of them — the “dominant” allele is observed in the phenotype
what is the principle of segregation
(Mendel’s first law) each individual diploid organism possesses two alleles for any particular characteristic, one inherited from mom and one from dad. These two alleles segregate (separate) when gametes are formed and one allele goes into each gamete
what are the genotypic and phenotypic ratios for a cross between AA and aa
genotypic: all Aa
phenotypic: all A
what is the genotypic and phenotypic ratios of a cross between Aa and aa
genotypic: 1/2 Aa; 1/2 aa
phenotypic: 1/2 dominant; 1/2 recessive
give the genotypic and phenotypic ratios of a cross between Aa and Aa
genotypic: 1/4 AA; 1/2 Aa; 1/4 aa
phenotypic: 3/4 dominant; 1/4 recessive
give the genotypic and phenotypic ratios of a cross between Aa and AA
genotypic: 1/2 AA; 1/2 Aa
phenotypic: all dominant
What is the multiplication rule and when is it used
the multiplication rule states that the probability of two or more independent events taking place together is calculated by multiplying their independent probabilities.
The key indicator for applying this rule is the word and; additionally, the two events must be independent meaning the outcome of one will not influence the outcome of the other
What is the addition rule and when it is used
the addition rule states that the probability of any two or more mutually exclusive events is calculated by adding the probabilities of the events.
the key indicator of this rule are the words either and or. For this rule to be valid the events of must be mutually exclusive meaning that one event excludes the outcome of the other
what is conditional probability
when information modifies or conditions the probability you are working with conditional probability. An example would be what is the probability a cross between Aa and Aa will produce AA but aa is lethal. The answer would be 1/3 because the fourth event cannot occur.
what is a testcross and how is it used
a testcross is used to analyze genetic crosses. One individual of an unknown genotype is crossed with an individual who is homozygous recessive for the trait in question. The testcross reveals the genotype of the unknown individual.
What is the principle of independent assortment
(Mendel’s second law) states that the alleles at different loci separate independently from one another.
This is an extension of the principle of segregation. The separation is independent of the separation of alleles other loci
What is the Chi-square goodness of fit test
it is used to evaluate the role of chance in producing deviations between observed and expected values. It indicates that the probability that the difference between the observed and expected value is due to chance. It must always be applied to numbers of progeny not proportions or percentages.
What is the purpose of a P value
P= probability that the deviation between expected and observed values are due to chance.
high p= chance alone produced the differences in observed and expected numbers
low p= some other factor produced the differences in observed and expected numbers
what is the difference between sex chromosomes and autosomes
sex chromosomes differ between males and females
autosomes are non sex chromosomes and they are the same between males and females
How are the X and Y chromosome able to pair up in meiosis
Even though they are different in size and content they are homologous at their pseudoautosomal regions which allows them to find each other and pair up during Prophase I
How is sex determined in organims
sex determination varies depending on the species. Many species use the XX, XY determining system (like humans). However, sex is determined in some species by the number of X chromosomes and there are no Y chromosomes. Some species’ sex is determined by environmental conditions. And in other species, there is a specific gene that determines sex, rather than sex chromosomes.
How is sex determined in humans
it is determined by the SRY gene on Y chromosome (not by the whole Y chromosome). Without the SRY gene the gonads will develop into ovaries
what is genotype and phenotype of sex chromosomes in Klinefelter syndrome
genotype: xxy
phenotype: male
what is the genotype and phenotype of sex chromosomes in Turner syndrome
genotype: XO
phenotype: female
what is the genotype and phenotype in triple x syndrome
genotype: xxx
phenotype: female
what is the genotype and phenotype in xyy male syndrome
genotype: xxy
phenotype: male
What is the cause of androgen insensitivity syndrome
women with androgen insensitivity syndrome have x and y chromosomes. Testosterone must bind to an androgen receptor in order to stimulate the development of male characteristics, but with the absence of testosterone female characteristics develop. In androgen insensitivity there is nothing for the testosterone to bind to so the body develops as a female.
What is the difference between x-linked and y-linked traits
x-linked traits: genes on the x chromosome can be passed from mother or father
y-linked: genes on the y chromosome. Can only be passed from father to son and will always be passed from father to son
what is a reciprocal cross and how does it apply to sex-linked traits
a reciprocal cross crosses a male and female with different phenotypes and then does it again with the phenotypes corresponding to the opposite sex. This will help indicate if a trait is sex linked or not.
What is nondisjunction
the failure of chromosomes to separate properly during anaphase
What is dosage compensation
only 1 x chromosome is expressed in each cell of female mammals. Which X is inactivated is random and set early in development. In cells with more than 2 X chromosomes, all but one X will become inactivated
What is a Barr Body
Inactivated X chromosome that appears as a condensed, darkly staining body in the nuclei of most cells of female placental mammals.
How are heterozygous females mosaics for x-linked traits such as a tortoiseshell cat
Xa or XA depending on which X gets inactivated, some cells express a, others A
What are the three different types of dominance
Complete dominance: phenotype of the heterozygote is the same as the phenotype of one of the homozygotes
Incomplete dominance: phenotype of the heterozygote is intermediate between the phenotypes of the two homozygotes
Codominance: phenotype of the heterozygote includes the phenotypes of both homozygotes
What is penetrance
the percent of individuals having a particular genotype that express the expected phenotype
what is expressivity
degree to which the phenotype is expressed
what are lethal alleles
an allele that causes death at an early stage of development often before birth
define multiple alleles
presence of more than two types of alleles at a locus
what is gene interaction
interaction between genes at different loci. more than one locus determines a trait
define gene interaction with epistasis
gene interaction in which one gene masks the effect of another gene at a different locus
What is dominant epistasis and what is recessive epistasis
in dominant epistasis only one copy of the dominant epistatic gene is needed to mask the effects. In recessive epistasis two copies of the recessive gene is needed to mask the effects
what is a sex-influenced trait
a trait coded by autosomal genes whose expression is influenced by the sex of an individual. Dominant in one sex and recessive in the other.
what is a sex limited trait
a trait encoded by autosomal genes but its expression is limited to one sex
what is cytoplasmic inheritance
traits encoded by genes found in the cytoplasm (mitochondrial or chloroplast genes) and therefore are only inherited from the female parent
what is genetic maternal effect
phenotype of offspring is determined by genotype of the mother. Genes are still inherited by both parents, but only maternal parent influences phenotype
What is genomic imprinting
expression of a gene depends on the sex of the transmitting parent
what is anticipation
a genetic trait becomes more strongly expressed, or is expressed at an earlier age, as it is passed from generation to generation
what is a phenocopy
when environmental factors produce a phenotype that is the same as a phenotype produced by a genotype
what is the difference between pleiotropy and polygenic
pleiotropy: one gene affects multiple characteristics
polygenic: characteristics encoded by genes at many loci
