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37 Cards in this Set

  • Front
  • Back
Genes
- program specific traits
- are segments of DNA
- most genes prgram cells to synthesize specific enzymes and other proteins that produce an organisms inherited traits
Each chromosomes consists of...
- a single DNA molecule in association with various proteins
Locus
- a specific location on the chromosome that codes for a gene
Homologous Chromosome
- two chromosomes carrying genes that control for the same inherited characteristics
- a set of paternal chromosomes
What is the complete set of chromosomes called?
Diploid number
Diploid number
- total number of chromosomes
- humans 2n = 46
Autosomes
- 22 pairs of chromosomes that are homologous
Meiosis
- reduction of the genetic material from 2n to 1n; diploid to haploid
- 2 nuclear divisions for one round of DNA replication
Meiosis creates
- haploid germ cells ( egg or sperm) from a diploid parent cell
- increased genetic variety due to crossing over events
First division of meiosis separates...
homologous chromosomes
the second round of meiosis...
- separates sister chromatids
Pre- Meiosis 1 (interphase)
- sister chromatid formation
- centrosome replication
- still in uncolied chromatin form
Meiosis 1 Prophase 1
- chromosomes condense
- homologous chromosomes pair up (tetrad formation)
- synapsis (special proteins attach homologous chromosomes together)
- several sites crossing over occurs
- spindles form from each centrosome and spindle fibers attached to kinetochores on the chromosomes begin to move the tetrads around
-
Synapsis
- special proteins
- pairing of homologous chromosomes; tetrad formation
- crossing over between chromatids
Meiosis 1 (Metaphase 1)
- tetrads are rearranged at teh metaphase plate
- microtuble attach to kinetochore of one chromosome from each pole
-
Meiosis 1 (Anaphase 1)
- homologous chromosomes separate and are pulled toward opposite poles
- migration of chromosomes to opposing poles
- sister chromatids are intact
Telophase 1 & Cytokensis
- movement of homologuous chromosomes continues until there is a haploid set at each pole
- each chromosome consists of linked sister chromatids
- haploid sister chromatids

Cyto --> cleavage furrow no further replication
Meiosis 2 (Prophase 2)
- no DNA replication
- spindle apparatus forms attaches to kinetochores of each sister chromatids
- move towards metaphase plate
- Spindle fibers from on pole attach to the kinetochore of one sister chromatid and those of the other pole to the other sister chromatid
Meiosis 2 (Metaphase 2)
- metaphase plate composed of haploid sister chromatids
Meiosis 2 (Anaphase 2)
- centromeres of sister chromatids separate
- sisters travel towards opposite poles
- individual daughter chromosomes (aka a single chromatid) move toward opposite poles
Meiosis 2 (telohase 2)
- separated sister chromatids arrive at opposite poles
- nuclei from around the single haploid chromatids
Meiosis 2 (Cytokensis 2)
- separation of cytoplasm
- four haploid daughter cells which are genetically different
Crossing over during meiosis occurs in what phase?
Prophase 1
What is a non disjunction event?
- alteration of chromosome number due to failure to separate in meiosis 1 (homologous separation) or meiosis 2 (sister chromatid separation)
Key note on gametes...
- the fact that homologous chromosomes can bear two different kinds of genetic information for the same characteristic is what really makes gametes different
Crossing Over
- DNA molecules of two chromatids each belonging to another homologous pair of chromosome break at the same place

- two broken chromatids join together in a new way (recombination of maternal and paternal genetic material)

- homologous chromosomes separate in anaphase I new segment from each homolog

- meiosis 2 sister chromatids separate each going to a different gamete
Factors Affecting Variability
- genetic recombination
- independent orientation
- random fertilization
Common Chromsomal Aberrations
- Trisomies (extra chromosome)

- Monosomies (messing one chromosome)
Karyogram
- ordered display of of magnified images of an individuals chromosomes arranged in pairs starting with the longest
- often prepared with lymphocytes
Typical analysis of Karyotype
- number
- length
- location of G bands
- placement of centromeres
Trisomy 21
- Downs
- extra CHR 21
- with trisomy 13 most common chromosome number abnormality
- 1 out of every 700
- risk increases as mother ages > 35
- suspected to occur after fertilization
Trisomy 13
- extra 13 CHR
- 1/5000 births
- still born or infant death
Sex chromosome nondisjunction
- less dramatic effects
- probably due to the lesser number of genes carried on Y chromosome and the inactivation of one X chomosome in females
One extra Y chromosome ...
- larger stature
- borderline intelligence
- sever social behavioral disturbances
XXY
Klinefelter
- abnormally small testes and sterility
- often accompanied by breast enlargement
XXX
- super female (mult X)
- limited fertility
- mostly phenotypically normal
1 of every 1000

XXX mostly normal

XXXX mildly retarded
X5 severe disability
XXX
- super female (mult X)
- limited fertility
- mostly phenotypically normal
1 of every 1000

XXX mostly normal

XXXX mildly retarded
X5 severe disability