Test 3 Flashcards
Nature of DNA in Eukaryotic Organisms
- in shape of high coiled linear chromosomes
- 46 chromosomes in humans
- 2 meters of DNA coiled in nucleus
What are chromosomes composed of?
- chromatin (protein DNA complex)
Characteristics of Chromosomes (in humans)
- 23 distinct shapes/types
- 2 chromosomes of each tyoe (Type A - Type W)
- 2 complete sets of 23
- 23 paternal chromosomes
- 23 maternal chromosomes
A(paternal) & A(maternal)
- homologous chromosomes
- contain the same gene
- not genetically identical
- same gene, different version
Allele
different versions of the same gene
Ploidy
the number of sets of chromosomes
ex:
diploid - 2 sets
haploid - 1 set
triploid - 3 sets
Haploid Number
the number of chromosomes in a complete set
Cell cycle
events between formation of cell and division of cell
1. interphase (majority of the cell cycle)
2. mitosis (nuclear division)
3. cytokinesis (cytoplasmic division) (goes back to interphase)
zygote formation
egg (haploid) + sperm (haploid) = zygote (diploid)
How many stages does interphase have?
3:
1. Gap 1 (G1)
2. S (synthesis)
3. Gap 2 (G2)
Gap 1
- cell growth
- normal cell stuff
- enzyme production (necessary for DNA replication
What is G0?
cells that never exit G1
cells that never divide
S stage
- chromosomes replicate
- MTOC replicates centrioles (MTOC is replicated)
- dyad is created
Dyad
- pair of sister chromatids (identical)
- held together by a centromere that contains a kinetochore
Centromere
structure in a chromosome that holds 2 sister chromatids together
Kinetochore
protein that forms on a chromatid during cell division that allows it to attach to a spindle fiber on a chromosome
Gap 2 (G2)
- mitochondria/chloroplasts divide
- massive production of tubulin
- chromosomes start to coil more
How many phases are in mitosis?
5
Prophase
- chromosomes become completely condensed
- centrioles move to opposite ends of the cell
a. produces polar microtubules (connects the centrioles and will pull the chromosomes apart)
b. produces aster fibers (connects centrioles to cell membrane)
Prometaphase
- nuclear membrane degenerates
- MTOCs provide kinetochore microtubules (connects chromosomes to microtubules)
Metaphase
- kinetochore microtubules arrange dyads in an independent assortment manner in the center of the cell
a. this is the metaphasic plate
Anaphase
- centrosomes break apart
- chromatids get pulled towards opposite ends of cell
- polar microtubules lengthen so the cell lengthens
- spindle apparatus; microtubules involved in mitosis (polar, aster, kinetochore)
Telophase and Cytokinesis
- chromosomes reach end of the cell
- nuclear envelope forms
- spindle apparatus disappears
- chromosomes de-condense
- belt of actin around metaphasic plate constricts and pinches cell in half
- cleavage furrow forms (in animal cells)
Gametogenesis
- cells undergo meiosis to form gametes
Prophase 1
- same as in mitosis
PLUS - homologous chromosomes hydrogen bond to each other to create a tetrad (bivalent)
- 23 tetrads at the end of prophase 1
Bivalent
a pair of homologous chromosomes (4 chromatids)
Synapse
the pairing of homologs
Crossing over
- homologous chromosomes exchange segments with each other
- occurs 50-70 times per bivalent
- responsible for genetic variability
Metaphase 1
- same as mitosis
- kinetochore microtubules arrange dyads in in the center of the cell
a. this is the metaphasic plate
Anaphase 1
- homologs separate and dyads are pulled to opposite ends
Telophase 1 and Cytokinesis
- same as in mitosis EXCEPT:
1. nuclear membrane does not reform
2. chromosomes stay condensed
Independent Assortment
- random orientation of homologs at the metaphasic plate
- parental sets of chromosomes do not stay together through meiosis 1
Meiosis 2
Prophase 2 - same as mitosis
Metaphase 2 - same as mitosis (23 dyads instead of 46)
Anaphase 2 - same as mitosis (23 dyads instead of 46)
Telophase 2 and Cytokinesis - same as mitosis
What is the result of gametogenesis?
Gametes
What is a polar body?
little haploid bags of chromosomes
Why is the egg that is produced in oogenesis so large?
Egg must be large enough to provide nutrients for 5 days
-occurs in a protective environment
Plant cell divison
- no centrioles in MTOC
- no aster fibers
- cytokinesis occurs through cell plate formation
- division starts in middle and spreads outward
Gene pair
2 copies of the same gene on homologous chromosomes
Locus
physical location of a gene on a chromosome
Dominant allele
allele that is always fully expressed when present
Recessive allele
only expressed if gene pair consists of 2 versions of that allele
Homozygous pair
gene pair that consists of the same alleles
Heterozygous pair
gene pair that consists of different alleles
Genotype
allele make-up of gene pair
phenotype
physical expressions of the genotype
Mendelian genetics
the study of inheritance
Facts about Mendel
- studied in a monostery as a monk
- was a mathmetician
- studied inheritance of 7 traits in pea plants
Monoecious
- have both female and male reproductive parts
- able to self-fertilize
Monohybrid Crosses
- true breeding crossing
- phenotype ratio is 3:1
Truebreeding
- produces offspring of the same phenotype
Mendel’s 1st Law / Principle of Segregation
- individuals have 2 factors (alleles) for each trait
- factors segregate during gamete formation so that each gamete only gets one of those factors
- deduced the diploid nature of eukaryotic organisms (meiosis)
- 3:1 ratio for the offspring of heterozygotes
Dyhybrid Crosses
- 9 genotypes
- 4 phenotypes
- 9:3:3:1
What explains why dihybrid and monohybrid crosses works?
- any sperm is equally likely to fertilize an egg
Mendel’s 2nd Law
- law of independent assortment
- traits are inherited independently of each other because of independent assortment
How did Mendel get “lucky”?
- all traits for the peas were on separate chromosomes
- all traits for the peas only had 2 alleles
- all traits for the peas were controlled by one gene
Linkage
- genes for 2 traits on the same chromosome
- genes are inherited dependently
- only way to stop linkage is by crossing over