mitosis = nuclear division that produces two daughter cells with thesame number and kinds of chromosomes as the parental cell (cell that divides)chromosome = condensed DNA in the form of a chromatid

-in the dividing cell - chromosome duplicates and is found in the form of two sister chromatids joined by a centromerecell cycle = division of the cell, consists of interphase, mitosis and cytokinesiscytokinesis = division of the cytoplasm and organelles of a cell that has undergone mitosis into two daughter cells chromatin = interphase form of DNA, DNA helices associated with proteins = histones

-each cell (except sex cells) has two complete sets of 23 chromosomes-therefore the cell is said to be diploid and n = 23 (2n = 46)

Interphase: DNA begins to condense, duplicate andform the chromosomal structure (2 chromatids+ centromere)-each cell = 2n (where 2 = 23)

Prophase:movement of centrioles (specializedgroups of microtubules) to the opposite ends(poles) of the cell-appearance of spindle fibers between thecentrioles-fragmentation of the nuclear envelope,disappearance of the nucleolus-complete formation of the spindle = asters (shortmicrotubules from the centrioles), poles with centrioles, and spindle fibers

Metaphase: alignment of chromsomes along thespindle

Anaphase: separation of sister chromatids (calleddaughter chromosomes)-movement of chromosomes to the opposite poles- by the spindle (lengthening and shorteningof spindle fibers)

Telophase: decondensing of DNA, cytokinesisby the formation of a cleavage furrow

Cytokinesis: by the formation of a cleavage furrow-furrow - slight indentation around the circumference of the cell-actin filaments then assemble to form a contractile ring which decreases in size “purse string” mechanism -pinches the cell in half

-genetic diversity at mitosisprovided by crossing over-between non-sister chromatids of 4 chromosomes (tetrad)-results in an exchange of geneticmaterial and diversity

-like mitosis but requires 2 nuclear divisions - cell undergoes meiosis I and II-occurs in the formation of sex cells and results in 4 daughter cells each with half the number of chromosomes as the parental cell (haploid)-ensures genetic diversity - crossing over, different combinations of chromosomes within the resulting sex cells, fertilization results in different combinations

4n = 82n = 4

Meiosis I: similar to mitosis EXCEPT at anaphasewhere duplicated chromosomes DO NOT separate-they travel to the poles as a pair of chromatids-Prophase I - duplication of chromosomes andattraction of homologous pairs of chromosomes(synapsis) forming tetrads-occurrence of crossing-over-Metaphase II - alignment-Anaphase II - separation of chromosome pairs

Meiosis II: similar to mitosis-lining up of chromosomes at Metaphase II-separation of sister chromatids at Anaphase II-cytokinesis at Telophase II

-unequal division of the primary oocyte (2n) forms the secondary oocyte and a polar body-polar body - contains chromosomes butvery little cytoplasm-polar body splits during oogenesis-secondary oocyte develops into the ovum(haploid)-fertilization unites haploid sperm with thehaploid egg - produces diploid individuals

-production of sperm and egg occursthrough meoisis

-from birth - each individual is diploid (containing two copies of the 23 different chromosomes-chromosome charts = karyotypes (display of the 23 chromosome pairs)-pairs 1 through 22 are called autosomes = do NOT determine sex-pair 23 = sex chromosomes (X and/or Y)

-diseases: Huntington’s - chromosome #4 Cystic fibrosis - chromosome #7 Sickle cell anemia - chromosome #11 Tay-Sachs disease - chromosome #15 Amyotrophic lateral sclerosis - chromosome #21

-extra chromosome 21

-polyploidy = extra pair of chromosomes -one gamete is diploid - non-disjunction during meiosis I (homologous pairs fail to separate) or meiosis II (sister chromatids) -results in a triploid celle.g. trisomy 21 = Down’s syndrome (1/770) trisomy 13 = Patau’s syndrome (1/15000) trisomy 18 = Edward’s syndrome (1/4000) trisomy 22 = very rare

-aneuploidy = missing a chromosome pair-occurs in sex chromosomes morefrequently

-because we have two copies of each chromosome - we have two copies of each gene-multiple forms of each gene = alleles-so homologous chromosomes are the same gene for gene - BUT they can be made up ofdifferent alleles of that gene-dominant allele - uppercase letter e.g. E-recessive allele - lowercase letter e.g. e-individual with two identical alleles of one gene on each chromosome = homozygous- individual with two different alleles of one gene on each chromosome = heterozygous e.g. allele E or e -union of sperm and egg with the same alleles = homozygous = EE or ee -union of sperm and egg with different alleles = heterozygous = Ee

-genotype: genetic makeup of an individual

-phenotype: physical or biochemical manifestation of the genotype

-dominant trait: results from the combination of a dominant allele withanother dominant allele (homozygous dominant) or with a recessiveallele (heterozygous dominant)

-recessive trait: results from the combination of two recessive alleles(homozygous recessive)

-Punnett square: frequently used to determine the phenotype of offspringand the odds that a genotype will occur

-75% chance of a dominanttrait resulting-25% chance of a recessivetrait resulting

-results when one allele is notcompletely dominant over another-results in an intermediate phenotype-can also be known as ‘blending’e.g. sickle cell anemia

-irregular RBC shape-caused by abnormal hemoglobin(less soluble)HbAHbA normalHbSHbS sickle cellHbAHbS carrier

-Autosomal recessive disorders: homozygous recessiveCystic Fibrosis - 1/20 Caucasians (carrier - heterozygous), 1/2500 newborns

-mutation in gene that encodes a chloride channel proteinTay-Sachs disease - Jewish descent

-lack of the enzyme hexosaminidase (HexA)Phenylketonuria - 1/5000 newborns

-lack enzyme needed to process the amino acid, phenylalanine-accumulation - neurological failure, mental retardation

-Autosomal dominant disorders: homozygous or heterozygous dominantNeurofibromatosis - 1/3000 people, equally represented

-café-au-lait spots on the skin, mostly mld symptoms-severe symptoms - skeletal deformaties, large head, eye and ear tumors-gene on chromosome 17, controls cell division

Huntington disease - 1/20000 people-progressive degeneration of neurons-gene on chromosome 4 - no known cure

-Sex-linked disorders: contain alleles of genes also-X-linked - contributed by mothere.g. color blindness, muscular dystrophy, hemophilia

-Polygenic disorders: controlled by more than one allele e.g. cleft lip, clubfoot, hypertension, diabetes -more than one allele can control normal traits

e.g. skin color AABB Very dark skin AABB or AABb Dark skin AaBb, AAbb or aaBB Medium skin Aabb or aaBb Light skin aabb Very light skin