ap bio unit 5

• both DNA and RNA carry genetic information
• prokaryotes DO SHOW genetic variation even if they don't participate in sexual reproduction
• linked genes: genes located very close to other genes on the same chromosome can be inherited together
• meiosis: production of gametes (sex cells) from diploid cells

  • daughter cells have HALF the chromosomes
  • diploid to haploid
  • when the sperm and egg join in fertilization, the two haploid sets of chromosomes form a complete diploid set: a new genome
• homologous chromosomes: the similar but nonidentical chromosome pairs an organism receives from its two parents
• meiosis 1: homologous chromosomes separate

  meiosis 2: sister chromatids separate
• prophase 1 of meiosis:

  • chromosomes condense and become visible
  • chromosomes pair up and crossing over occurs
  • common for multiple crossing overs to occur

  
• metaphase 1 of meiosis:

  • homologous pairs, NOT individual chromosomes, line up at the metaphase plate for separation
  • RANDOM ORIENTATION

  
• anaphase 1 of meiosis:

  • same as mitosis, however, each sister chromatid is still attached to one another

  
• telophase 1 in meiosis:

  • same as mitosis
  • newly formed cells are HAPLOID
  • each chromosome has 2 (non-identical) sister chromatids
• meiosis II:

  • mitosis but with haploid cells
  • the sister chromatids separate, making haploid cells with NON-DUPLICATED chromosomes

  
• reasons for genetically different gametes:

  • crossing over in prophase 1
  • random orientation of homologous pairs in metaphase 1
• end of meiosis 1: 2 haploid cells

  end of meiosis 2: 4 haploid cells
• mitosis produces genetically IDENTICAL daughter cells, but meiosis produces genetically UNIQUE daughter cells
• mendel's pea plant experiment results:

  • P generation: tall x short
  • F1 generation: all tall
  • F2 generation: 3 tall: 1 short
• law of segregation:

  • only 1 of the 2 gene copies present in an organism is distributed to each gamete that it makes and the allocation of the gene copies is random
  • occurs in anaphase 1
• law of independent assortment:

  • inheriting an allele has nothing to do with inheriting an allele for any other trait
  • occurs during metaphase 1
• monohybrid cross: heterozygous for one gene

  dihybrid cross: heterozygous for two genes
• independent events- the occurrence of one event does NOT affect the occurrence of another (rolling a 1 on the first dice and a 6 on the second dice)

  mutually exclusive- two events cannot occur at the same time (rolling a 1 and 6 at the same time)
• codominance: two alleles may be simultaneously expressed when both are present

  • ex. red and white flowers
• incomplete dominance: two alleles may produce an intermediate phenotype when both are present

  • ex. pink flowers
• sex linkage: genes carried on sex chromosomes, such as the X chromosome of humans

  • show different inheritance patterns than genes on autosomal (non-sex) chromosomes
• epistasis: the alleles of one gene may mask or conceal the alleles of another gene
• polygenic inheritance: characteristics that are controlled by a number of different genes

  • polygenic traits include height, skin color, hair color, and eye color
• when doing punnett squares between males and females, the Y chromosome has NO ALLELE on it
• X-linked human genetic disorders are much more common in males than in females due to the X-linked inheritance pattern (the X chromosome from the mom is the ONLY allele that shows up in males)
• hemizygous: males are hemizygous for X-linked genes because he has no other gene copy

  • even if the allele is recessive in females, the male will still express that allele
• recombination frequency = (recombinants/total offspring) x 100%
• autosomal chromosome: trait that is located on a NON-SEX chromosome (ex. Aa, RR)
• autosomal dominant trait: present in every generation, not SEX-LINKED

  
• x-linked recessive trait: not necessarily present in every generation, MORE MALES THAN FEMALES

  
• the offspring inherits mitochondrial AND nuclear DNA from their MOTHER, while they ONLY inherit nuclear DNA from their FATHER
• the larger the recombination frequency, the FURTHER the genes are
• mitochondrial and chloroplast DNA are both inherited from the MOTHER
• phenotypic plasticity: the ability of an organism to change its phenotype in response to environmental change

  • allows organisms to better fit a particular environment
• euploid- contains chromosomes correctly organized into complete sets

  aneuploid- missing one or more chromosomes

  • monosomy- 2n-1
  • trisomy- 2n+1

  
• nondisjunction- when homologous chromosomes or sister chromatids fail to separate during meiosis I or II, or during mitosis
• down syndrome- trisomy 21, 3 copies of chromosome 21
• chromosomal rearrangement:

  • duplication- part is copied
  • deletion- part is removed
  • inversion- region is flipped around (opposite direction)
  • translocation- piece of one chromosome gets attached to another
  • reciprocal translocation- swapping of segments
• horizontal gene transfer where genetic information is shared between organisms WITHOUT MATING