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37 Cards in this Set
- Front
- Back
Genes
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- program specific traits
- are segments of DNA - most genes prgram cells to synthesize specific enzymes and other proteins that produce an organisms inherited traits |
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Each chromosomes consists of...
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- a single DNA molecule in association with various proteins
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Locus
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- a specific location on the chromosome that codes for a gene
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Homologous Chromosome
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- two chromosomes carrying genes that control for the same inherited characteristics
- a set of paternal chromosomes |
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What is the complete set of chromosomes called?
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Diploid number
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Diploid number
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- total number of chromosomes
- humans 2n = 46 |
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Autosomes
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- 22 pairs of chromosomes that are homologous
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Meiosis
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- reduction of the genetic material from 2n to 1n; diploid to haploid
- 2 nuclear divisions for one round of DNA replication |
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Meiosis creates
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- haploid germ cells ( egg or sperm) from a diploid parent cell
- increased genetic variety due to crossing over events |
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First division of meiosis separates...
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homologous chromosomes
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the second round of meiosis...
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- separates sister chromatids
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Pre- Meiosis 1 (interphase)
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- sister chromatid formation
- centrosome replication - still in uncolied chromatin form |
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Meiosis 1 Prophase 1
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- 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 - |
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Synapsis
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- special proteins
- pairing of homologous chromosomes; tetrad formation - crossing over between chromatids |
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Meiosis 1 (Metaphase 1)
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- tetrads are rearranged at teh metaphase plate
- microtuble attach to kinetochore of one chromosome from each pole - |
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Meiosis 1 (Anaphase 1)
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- homologous chromosomes separate and are pulled toward opposite poles
- migration of chromosomes to opposing poles - sister chromatids are intact |
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Telophase 1 & Cytokensis
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- 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 |
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Meiosis 2 (Prophase 2)
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- 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 |
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Meiosis 2 (Metaphase 2)
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- metaphase plate composed of haploid sister chromatids
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Meiosis 2 (Anaphase 2)
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- centromeres of sister chromatids separate
- sisters travel towards opposite poles - individual daughter chromosomes (aka a single chromatid) move toward opposite poles |
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Meiosis 2 (telohase 2)
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- separated sister chromatids arrive at opposite poles
- nuclei from around the single haploid chromatids |
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Meiosis 2 (Cytokensis 2)
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- separation of cytoplasm
- four haploid daughter cells which are genetically different |
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Crossing over during meiosis occurs in what phase?
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Prophase 1
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What is a non disjunction event?
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- alteration of chromosome number due to failure to separate in meiosis 1 (homologous separation) or meiosis 2 (sister chromatid separation)
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Key note on gametes...
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- the fact that homologous chromosomes can bear two different kinds of genetic information for the same characteristic is what really makes gametes different
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Crossing Over
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- 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 |
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Factors Affecting Variability
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- genetic recombination
- independent orientation - random fertilization |
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Common Chromsomal Aberrations
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- Trisomies (extra chromosome)
- Monosomies (messing one chromosome) |
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Karyogram
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- ordered display of of magnified images of an individuals chromosomes arranged in pairs starting with the longest
- often prepared with lymphocytes |
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Typical analysis of Karyotype
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- number
- length - location of G bands - placement of centromeres |
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Trisomy 21
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- 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 |
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Trisomy 13
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- extra 13 CHR
- 1/5000 births - still born or infant death |
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Sex chromosome nondisjunction
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- less dramatic effects
- probably due to the lesser number of genes carried on Y chromosome and the inactivation of one X chomosome in females |
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One extra Y chromosome ...
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- larger stature
- borderline intelligence - sever social behavioral disturbances |
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XXY
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Klinefelter
- abnormally small testes and sterility - often accompanied by breast enlargement |
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XXX
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- super female (mult X)
- limited fertility - mostly phenotypically normal 1 of every 1000 XXX mostly normal XXXX mildly retarded X5 severe disability |
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XXX
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- super female (mult X)
- limited fertility - mostly phenotypically normal 1 of every 1000 XXX mostly normal XXXX mildly retarded X5 severe disability |