ch 9 - inheritance

• what are genes?


  discrete "heritable" factors
• what does heredity mean?

  traits being passed from parent to offspring
• what are genetics?


  the science of heredity
• what are characters?


  a heritable feature
• what is a trait?

  a variant of character
• what is a monohybrid cross?

  mating parents with ONE characteristic
• what are punnett squares?

  used to show possible offspring traits
• two alleles for each trait:

  dominant allele: the expressed allele - P, recessive allele: the non expressed allele - p
• homozygous means?


  organisms with (2) identical alleles for a characteristic; true-breeding: PP (homozygous dominant) pp (homozygous recessive) PP X pp --> inherits one for purple (P) and one for white (p)
• phenotype:


  physical or expressed trait, 3 purple: 1 white --> phenotype ratio
• genotype:


  genetic makeup, 1 PP: 2 Pp: 1 pp --> genotypic ratio
• Mendel's 4 hypothesis:

  1. alleles - alternative forms of genes, ex: flower color can be purple or white
  2. there are two alleles inherited from each parent, offspring's can have homozygous alleles (PP or pp), heterozygous alleles (Pp)
  3. when (2) alleles of a pair are different and one is expressed --> heterozygous, dominant & recessive
  4. alleles pairs separate from each other in meiosis. each sperm and egg carriers only unite at fertilization, each contributes it's alleles, offspring's now have (2) alleles for every trait
• the law of independent assortment is revealed by tracking (2) characteristics at one:

  dihybrid cross - mating parents with (2) characteristics
• principal of independent assortment (actual results): 


  alleles of genes are distributed to gametes randomly. genes inherited independently, random orientation of maternal and paternal homologues along the metaphase plate during metaphase I.
• geneticists used to testcross to determine unknown genotype, what is testcross?

  a mating between an individual with an unknown genotype with homozygous recessive; ex) chocolate lab color = bb, black lab color= could be BB or Bb
• what are recessive disorders?


  deafness is an homozygous recessive trait (dd); most genetic disorder are recessive --> cystic fibrosis, albinism, tay-sachs disease, sickle cell anemia, deafness
• what are carriers?


  people who carry one copy for a recessive disorder --> heterozygous Dd
• what are dominant disorders?

  some disorders are due to dominant alleles, ex) extra fingers and toes
• what is achondroplasia?


  form of dwarfism; only heterozygotes with this dominant allele have the disorder --> Aa, homozygous dominant causes death to embryo --> AA (no carriers)

  *some dominant disorders express later in life, so could be passed on, ex) achondroplasia, alzheimer's, huntington's & polydactyl
• what is complete dominance?

  only need (1) dominant allele to express the phenotype
• what is incomplete dominance?

  as in-between phenotype where one allele is not completely expressed over the other allele, ex) hypercholesterolemia - recessive allele (h) causes disease; * incomplete dominance is not "blending"
• human blood has (3):


  has (3) possible alleles --> ABO

  (2) carbohydrates can be found on the surface of RBC --> A & B

  
• A single gene may affect many phenotypic characteristics:

  pleiotropy - one gene controls multiple characteristic, ex) Sickle cell disease- homozygous recessive for sickle cell effects

  **Heterozygotes are carriers but codominant alleles
• single characteristic may be influenced by many genes:

  *Polygenic Inheritance – additive effect of two or more genes on a single phenotypic trait.

  ex) human skin pigmentation -> A,B,C alleles code for dark skin

  incomplete dominance over a, b, c, alleles for light skin

  *other ex) human height, eye color, weight, heart disease
• the environment affects many characteristics:

  many human phenotypes are influenced by genes and environment

  • height & build
  • skin color
  • IQ
  • heart disease & cancer
  • susceptibility to alcoholism & schizophrenia
• what is a sex-linked gene?


  gene located on either sex chromosome (x-linked genes)
• sex-linked disorders affect mostly males:


  men only have to inherit one sex-linked recessive allele for it to express, (from mother)

  women have to inherit (2) sex-linked recessive alleles
• X chromosome carries sex-linked genes for disorders:


  red-green colorblindness

  hemophilia - bleeds excessively when injured

  duchenne muscular dystrophy - progressive weakening of muscles and loss of coordination
• what occurs during S phase?

  DNA is copied/duplicated
• How many homologous pairs of chromosomes does a somatic cell have? How many pairs are autosomal and sex chromosomes?

  23; 22; 1
•   What structure do microtubules come from?

  centrosome
• what is NOT a function of mitosis?

  production of gamete cells
• Does mitosis produce genetically identical or different daughter cells?And how many daughter cells?

  2 identical cells
• true or false: In anaphase of mitosis, homologous chromosomes separate to opposite poles.

  false, sister chromatids separate
• Contact inhibition can be best described as..

  the stopping of cell division when cells start to touch one another
• how many chromosomes does gametes have?

  23
• which of the following does NOT occur during prophase I?

  process where 2 sister chromatids come together as pairs
• during anaphase I, which structures are being separated?

  tetrads
• what's an allele?


  alternative forms of genes on the same locus
• which process does NOT lead to increased genetic variability?

  mitosis