mitosis

Question 1

Define karyotype, haploid and homologous

Answer 1

Karyotype: morphology of a cells characteristics
a normal karyotype has 22 pairs of homologous pairs of autosomal chromosomes plus 1 pair of sex determination chromosomes (females XX, males Xy) so 23 homologous pairs= 46 chromosomes meaning that the typical cell in the human body consists of a diploid (2N=46 chromosomes)

HAploid is N=23 this is the number of chromosomes from each parent
each chromosome is homologous to its sister

Question 2

Genotype vs Phenotype vs Allele

Answer 2

Genotype: a persons biochemical genetic makeup, genotypic differences are mediated by differences between the 2 allels comprimising each homologous pair

Phenotype: mediated by genotype AND environment, its a biochemical, anatomic, physiological or behavioral TRAIT
The genome has 25k genes expression of these genes into proteins they encode confers phenotype

Allele: the genome has 2 homologous copies of each gene one from each member of the pair, each copie is the allele

Homozygous recessive diseases: CF, albinisim, PKU, Taysachs

Question 3

Mitosis

Answer 3

the final stage of the cell cycle, after S phase DNA is 4 N. The goal of mitosis is to precisely restore the 2N condition. The M phase is activated in late G2 when Cyclin B/CDK1 is de phosphorylated by the phosphatase CDC25 (B-CDK1 is phosphorylated by Wee1) B-CDK1 can migrate into nucleus and phosphorylate: centrosomes-> mitotic spindle, nuclear lamins->nuclear envelope breakdown, histones-> chromatin condensation

Stages of mitosis:
Prophase: B/CDK1 -> condensins-> Condense DNA 10^4x
Metaphase: chromatids align at the equator
Anaphase: APC degrades cohesin, then chromatids move
Telophase: 2 daughter nuclei are formed via Karyokinesis
Cytokinesis: 2 daughter cells are formed

Question 4

Prophase

Answer 4

Early prophase: B-CDK1-> condensin-> chromatid condensation. CentroSOMES move to spindle poles

Late prophase: B-CDK1-> nuclear envelope breaks down, 3 kinds of microtubules emanate from the centroSOMES:
1 astral (look like a star)
2. Kinetechore: attach to cetroMERE
3. polar, dont attach the chromatids

Question 5

Metaphase

Answer 5

Sister chromatids go to equator, attached to kinetechore microtubules

chemotherapy: vineblastine inhibits microtubule assembly (binds tubulin) and taxol inhibits microtubule disassembly

Metaphase distintinction from meiosis: the homologous chromosomes do not pair up in mitosis

Question 6

Anaphase

Answer 6

is initiated by APC (anaphase-promoting complex), in the kinetechore, apc degrades securin releasing separase, which then degrades cohesin permitting the release of the sister chromatids

Sister chromatids move to opposit poles via a push pull mechanism.

Push: elongation of polar microtubules
Pull: shortening of the kinetechore microtubules

Question 7

Telophase and cytokinesis

Answer 7

telophase: kinetochores extinct, polar tubules continue to elongats, nuclear envelope reforms via lamin B in a process called karyokinesis
cytokinesis: cleavage furrow pinches off enaploing cellls to separate

Question 8

Mitosis differences

Answer 8

1 division-> 2 cells, number of chromosomes stays the same (diploid 2n-> 2n), 1 s phase per 1 division, homologous chromosomes do not pair, no cross over, centormeres that bind chromatids separate at anaphase the daughter cells genotypes are identical to parental genotype (conservative)

Question 9

Meiosis differences

Answer 9

2 divisions-> 4 cells, number of chromosomes reduced to haploid (1n 23 chromosomes), 1 S phase per 2 divisions, homologous pairs DO pair at prophase 1, at least 1 crossover per homologous pair. Centromeres separate only at anaphase 2, daughter cells are variable

Question 10

mitosis v meiosis differences in chromosome alignment in metaphase

Answer 10

in mitosis paired chromatids representing each duplicated chromosome are independently situated on the equatorial plate in metaphase

In meiosis -1 each chromosome present as 2 sister chromatids pairs up with its homologous partner during prophase 1 this facilitates crossing over (only 23 slots are occupied on the equatorial plate
the homologous chromosomes separate in anaphase1 , but the sister chromatids dont separate until anaphase 2

Question 11

Mendels 1st law

Answer 11

the segregation law: Resultant from meiosis: each gamete recieves one allele or the other never both from the parental cell

Each allel is segregated into a separate gamete

Question 12

Mendels 2nd law

Answer 12

independent inheritance law
during gamete formation, alleles that encode different traits assort independently of each other

so height and eye color are inherited independently

meiosis 1 is when independent assortmet occurs