Exam 1 Review (Bio 375- Genetics) Flashcards
Prokaryotic cell
no nucleus; no paired chromosomes (haploid); typically single circular chromosome consisting of a single origin of replication; single chromosome is replicated with each copy moving to opposite sides of the cell; no histone proteins complexed to DNA
Eukaryotic Cell
nucleus present; paired chromosomes common (diploid); typically multiple linear chromosomes consisting of centromeres, telomeres, and multiple origins of replication; chromosomes are replicated but require mitosis or meiosis to ensure that chromosome migrates to the proper location; histone proteins are complexed to DNA
three predominant stages of interphase of cells active in the cell cycle
G1 -> S Phase -> G2
G1 (Gap 1)
cell grows and synthesizes proteins necessary for cell division; once the cell passes the G1/S checkpoint then the cell is committed to divide
S phase
DNA replication takes place
G2 (Gap 2)
additional biochemical reactions take place that prepare the cell for mitosis; once the cell passes the major G2/M checkpoint it enters into mitosis
G0
nondividing stage; found in cells prior to G1/S checkpoint; cells may exit active cell cycle to enter this nondivision stage
checkpoints
function to ensure that all cellular components (such as important proteins and chromosomes) are present and functioning before the cell moves to the next stage of the cell cycle; if components are missing or not functioning, then these will prevent the cell from moving to the next stage; these prevent defective cells from replicating and malfunctioning
checkpoints of cell cycle
G1/S checkpoint (occurring during G1 prior to S phase); G2/M checkpoint (occurring during G2 prior to mitosis); and spindle-assembly checkpoint (occurring during mitosis)
meiosis processes responsible for genetic variation
crossing over, random distribution
point during meiosis at which crossing over takes place
begins during the zygotene stage of prophase I and is completed near the end of prophase I
point during meiosis at which random distribution of chromosomes to daughter cells takes place
anaphase I of meiosis
spermatogenesis
primordial diploid germ cells divide mitotically to produce diploid spermatogonia that can either divide repeatedly by mitosis or enter meiosis. spermatogonium that entered prophase I of meiosis is called a primary spermatocyte and is diploid. upon completion of meiosis I, two haploid cell called secondary spermatocytes are produced. upon completing meiosis II, the secondary spermatocytes produce a total of four haploid spermatids. the spermatids then mature to yield sperm.
oogenesis
primordial diploid cells divide mitotically to produce diploid oogonia that can divide repeatedly by mitosis or enter meiosis. oognonium that entered prophase I of meiosis is called a primary oocyte and is diploid. upon completion of meiosis I, the cell divides but unequally. one of the newly produced haploid cells receives most of the cytoplasm and is called the secondary oocyte. the other haploid cell receives only a small portion of the cytoplasm and is called the first polar body. ultimately, the secondary oocyte will complete meiosis II and produce two haploid cells. one cell, the ovum, will receive most of the cytoplasm from the secondary oocyte. the smaller haploid cell is called the second polar body. typically, the polar bodies disintegrate and only the ovum is capable of being fertilized
acrocentric chromosome
a chromosome with the centromere located very close to one end
metacentric chromosome
Chromosome in which the two chromosome arms are approximately the same length
submetacentric chromosome
A chromosome in which the centromere establishes a long arm and a short arm– in which the centromere is halfway between the top and the middle of the chromosome
telocentric chromosome
Chromosome in which the centromere is at or very near one end.
chromosome alignment in metaphase of mitosis
lined up with centromeres on the metaphase plate
(mitosis) G2
4n number of DNA and 2n number of chromosomes - DNA molecules were replicated in S phase
(meiosis) metaphase I
4n number of DNA and 2n number of chromosomes - neither homologous chromosomes nor sister chromatids have separated
(mitosis) prophase
4n number of DNA and 2n number of chromosomes
(meiosis) anaphase I
4n number of DNA and 2n number of chromosomes - homologous chromosomes separate and begin moving to opposite ends of cell, but sister chromatids do not separate
(meiosis) anaphase II
2n number of DNA and 2n number of chromosomes - sister chromatids separate, resulting in temporary doubling of chromosome number in haploid daughter cell
(meiosis) Prophase II
2n number of DNA and n number of chromosomes - daughter cells are haploid
(mitosis) after cytokinesis (during telophase)
2n number of DNA and number of chromosomes - daughter cells enter G1 after mitosis
(meiosis) after cytokinesis (during telophase II)
n number of DNA and number of chromosomes
determining diploid number
determine number of centromeres present within a cell that contains homologous pairs of chromosomes, recalling that each chromosome possesses a single centromere
location/presence of a centromere
determined by attachment of spindle fibers to chromosome
anaphase of meiosis I
separation of homologous pairs of chromosomes
anaphase of mitosis
cell contains diploid chromosome number for species, but sister chromatids have separated to result in a doubling of chromosome number within cell
anaphase II of meiosis
sister chromatids are being separated, but there are no homologous chromosomes present within the cell
independent assortment
occurs during anaphase I of meiosis
separation of chromatids
occurs during anaphase of mitosis and anaphase II of meiosis
crossing over
occurs during prophase I of meiosis
bivalent pairs line up on metaphase plate
occurs during metaphase I of meiosis
spermatogonium
2n number of DNA and number of chromosomes (assuming that it is in G1 prior to S phase)
first polar body
2n number of DNA and n number of chromosomes (it is a product of meiosis I so it will be haploid, but sister chromatids have not separated so each chromosome consists of two sister chromatids)
primary oocyte
4n number of DNA and 2n number of chromosomes (it is stopped in prophase I of meiosis, so homologues have not yet separated and each chromosome consists of two sister chromatids)
secondary spermatocyte
2n number of DNA and n number of chromosomes (it is the product of meiosis I and has yet to enter meiosis II, so it will be haploid because the homologous pairs were separated in meiosis I but each chromosome is still composed of two sister chromatids)
principle of segregation (mendel’s first law)
states that an organism possesses two alleles for any one particular trait and that these alleles separate during the formation of gametes; ie one allele goes into each gamete; explains that homologous chromosomes segregate during anaphase I of meiosis
concept of dominance
when two different alleles are present in a genotype, only the dominant allele is expressed in the phenotype
incomplete dominance
when different alleles are expressed in a heterozygous individual, the resulting phenotype is intermediate to the phenotypes of the two homozygotes
principle of independent assortment
genes for different characteristics and at different loci segregate independently of one another; an extension of the principle of segregation
principle of segregation vs principle of independent assortment
principle of segregation indicates that the two alleles at a locus separate; principle of independent assortment indicates that the separation of alleles at one locus is independent of the separation of other pairs at other loci
principle of independent assortment relation to meiosis
in anaphase I of meiosis, each pair of homologous chromosomes separates independently of all other pairs of homologous chromosomes. assortment of homologues explains how genes located on different pairs of chromosomes will separate independently of one another
testcross
cross between an organism with an unknown genotype and an organism with a recessive phenotype
binomial equation
(n!/s!t!)p^sq^t
chi square test
sum of (observed-expected)^2/expected
XX-XO system of sex determination
females have two copies of sex-determining chromosome, whereas males have only one copy. males must be considered heterogametic because they produce two different types of gametes with respect to the sex chromosome: either containing an X or not containing an X
XX-XY system vs ZZ-ZW system of sex determination
in XX-XY system, males are heterogametic and produce gametes with either an X chromosome or a Y chromosome; in ZZ-ZW system, females are heterogametic and produce gametes with either a Z or a W chromosome
pseudoautosomal region
region of similarity between X and Y chromosomes that is responsible for pairing the X and Y chromosomes during meiotic prophase I
inheritance of genes in pseudoautosomal region vs inheritance of other Y-linked characteristics
genes in this region are present in two copies in males and females and thus are inherited like autosomal genes; whereas other Y-linked genes are passed on only from father to son
tortoiseshell cats
have two different alleles of an X-linked gene: X+ (non-orange / black) and X° (orange)… patchy distribution results from X-inactivation during early embryo development. each cell of early embryo randomly inactivates one of the two X chromosomes, and the inactivation is maintained in all of the daughter cells. so each patch of black fur arises from a single embryonic cell that inactivated X° and each patch of orange fur arises from an embryonic cell that inactivated X+
Barr body
darkly staining bodies in nuclei of female mammalian cells; Mary Lyon hypothesized that they are inactivated (condensed) X chromosomes. by inactivating all X chromosomes beyond one, female cells achieve dosage compensation for X-linked genes
