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an orderly process during which a parent cell divides into genetically identical daughter cells.
2 parts: interphase and cell division
2 main parts of cell cycle
-Interphase: Most of cell cycle spent here; divided into 3 stages
G1: before DNA synthesis
S: DNA synthesis
G2: after DNA synthesis
-Cell division: mitosis and cytokinesis
is the phase of the cell cycle phase when chromosomal duplication and cell division result in 2 daughter cells receiving exactly the same # and kinds of chromosomes as a parent cell (dipoid->diploid)
-the physiological process of growth, repair, and immune response require cells to undergo mitosis and multiply.
is a process of chromosomal reduction and cell division that ultimatly results in the formation of 4 genetically different daughrer cells, each with half as many chromosomes as the parent cell (diploid->haploid)
-involves 2 divisions: meiosis I and meiosis II
-takes place to form gametes, the haploid sperm and egg
the fusion of the chromosomal content of the haploid sperm and egg to form a diploid embryo (zygote-cell resulting from the union of egg and sperm)
-occurs during interphase when the DNA making up the entire genome replicates with enzyme unzipping each of the 2 parental strands, new nucleotides move in to compliment each parental strand and join together to make a new DNA strand. Each parent serves as a template for a new strand. 2 sister chromatids held together at centromere completing reproduction of genetic info to be transmitted to next generation of cells.
Division: nuclear contents divide and sister chromatids divide to become 2 individual chromosomes, one for each daughter cell. Each daughter cell gets a complete set of chromosomes and is diploid (2n), then cytokinesis occurs with the division of the parents cytoplasm
Meiosis I process
homologous chromosomes (one from each parent) pair together in synapsis.
-non-sister chromatids often exchange material (aka crossing over or recombination)
-next, homologous chromosomes of each pair separate, each daughter cell receiving one member of each pair
-reduces the # of chromosomes to half so each daughter cell haploid (1n)
-random distribution (aka independent assortment) of maternal and paternal homologous chromosomes to the daughter cells
Meiosis II process
-Chromosomes in haploid number, but still duplicate so now division of each cell now separates the sister chromatids into 2 daughter cells that are haploid (1n)
-crossing over exchange of genetic material during meiosis I results in recombination
-independent assortment during meiosis I with random distribution of homologous parental chromosomes into daughter cells
-fertilization when one egg, containing 223 possible combos of maternal chromosomes and one sperm containing 223 possible combos of paternal, unite to form a zygote
is one of two or more alternate forms of a gene ar a given locus, occur in pairs with one from mother and one from the father
-represented by a letter and be dominant (T) or recessive (t)
A single gene trait that is determined by the alleles ar a single locus. Genotype for a single gene trait on an autosomal chromosome can be:
-homozygous dominant: 2 dominant alleles (TT)
-homozygous recessive: 2 recessive alleles (tt)
-heterozygous: 1 dominant and 1 recessive (Tt)
masks the expression of a recessive gene and is expressed whether in homo or heterozygous state
probability of offspring inheriting a particular combination of alleles, and thus a particular phenotype for a trait determined by those alleles can be determined using this
x-link inherited: allele is carried on x chromosome
y-link inherited: allele is carried on y chromosome
Most sex linked traits are x-linked with exception of gene that actually determines sex (SRY) on Y.
Sex-determining region of Y (SRY) gene
gene that determines sex, located on the Y chromsome
Due to this gene encoding a transcription factor that intitiates a series of gene activations leading to formation of testes from embryonic cells of urogenital ridge
-absence of this gene, ovaries begin to develop in same area around 11 weeks
Hereditary or Genetic Disease
a disease resulting from an abnormality in an individual's genome due to a defect in either a chromosome or an individual gene
-most hereditary diseases are transmitted on autosomal chromosomes
Congenital Disease and Congenital Defect
refers to any abnormality present at birth, even though the problem may not be detected until sometime after birth
2-3% of all newborns have this and an additional 2-3% are not recognized at birth
Etiologies of Congenital Diseases
broadly classified as genetic, environmental, or a combination of the two
non-genetic, environmental agents that can cause intrauterine injury leading to the development of congenital disease. Include drugs, chemicals, radiation, and pathogens. ex. DES or radiation
-embryo most vulnerable between 3rd and 8th week when organ systems forming
failure of homologous chromosomes to separate in first or second meiosis division during the formation of the germ cells
-can involve autosomal or sex chromosomes, and result in abnormal distribution of chromosomes amongst germ cells so one extra or one lacking ex. monosomy and trisomy
Nondisjunction in autosomal chromosomes
rarely seen as absence of an autochromosomal chromosome generally results in the loss of genes required for development and, as a result, the embryo is aborted ex. Down Syndrome most common
most common autosomal trisomy, 3 copies of chromosome 21
-nondisjunction in oogenesis (egg formation) account for 95% of the cases, frequency increases with age of mother
-characterized by congenital cardiac malformation, defects in other organ systems, developmental disabilities, increased incidence of leukemia and accelerated aging, Gart gene for mental retardation
Nondisjunction in sex chromosomes
extra Y: no significant effect
absent Y: body configuration is female
extra X in female: little effect, one x inactivated
extra X in male: adverse effects on male development
Variations in normal number of sex chromosomes often associated with reduced intelligence.
(X) Women, short of stature, broad neck and chest, mental retardation, underdeveloped sex organs, absence of breasts and usually sterile
Triple X Syndrome
(XXX) Somewhat common with usually normal sexual development. Fertility and intelligence may be normal or decreased.
(XXY) Men can have underdeveloped sex organs, have breasts, large hands, long arms and legs, can have normal or some degree of mental retardation. Can go unrecognized. Infertility is most common feature and its estimated 2% of infertile men have this syndrome.
Androgen Insensitivity Syndrome (AIS)
aka testicular feminization syndrome, a genetic condition in which an XY male zygote can develop a phenotypical female adult, or varying degrees of sexual ambiguity
-it is a failure of androgen (testosterone) receptors to function, resulting in failure of male reproductive tract to develop
Changes in chromosome structure
-deletions: when chromosome breaks during meiosis and broken piece is lost
-translocations: movement of chromosome segments from one chromosome to another non-homologous chromosome
-duplications: presence of chromosome segment more than once in same chromosome
-inversions: occur when segment of chromosome is inverted 180 degrees
translocation 9;22 best-known neoplasm-associated chromosomal abnormality associated with chronic myelogenous leukemia (CML)
Autosomal dominant diseases
are expressed in the heterozygous state so if either parent carries an abnormal gene there is a
-1:2 chance offspring will receive disease and be affected by disease.
-Male and female are equally affected
Autosomal recessive diseases
are only expressed in homozygous individuals
-both parents must carry the abnormal gene
-then there is a 1 in 4 chance of infant receiving both genes and being affected by the disease
-Also, a 1 in 2 chance of child being heterozygous for gene, in which case they could be unaffected, but act as a carrier of the disease
-male and female equally affected
ex. Cystic Fibrosis
autosomal recessive single gene disease, most common lethal genetic disorder in the US
-gene responsible is cystic fibrosis transmembrane conductance regulator (CFTR) that regulates transport of chloride ions across plasma membrane
-severity of CF symptoms is partly based on the location and type of CF gene mutation a person has with most common being cystic fibrosis delta F508 mutation, a deletion of 3 base pairs in the coding sequence for this gene
X-linked hereditary disease
usually affect males as they have a single x chromosome that carries the mutation, and thus a recessive allele will be expressed. In females, the effect of the mutation may be masked by the second healthy copy of the X chromosome so they are only carriers of the disease. Most are recessive. ex. muscular dystrophy
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