Genetics

1
Genetics
2
(No Transcript)
3
(No Transcript)
4
Refresh students by discussing Mendels major
concepts of dominance and segregation (162-174).

• The factors that control heredity are individual
  units called genes, which are inherited from
  each parent (through sexual reproduction).
• The genes may be dominant or recessive.
• The two forms of each gene are segregated during
  the formation of reproductive cells.
• Genes for different traits may assort
  independently

5
Define the following terms associated with
genetics

• .
• Trait characteristic of an organism
• Gene a heredity unit that contains a code for a
  sequence of amino acids in a protein chain.
• Allele the alternate or contrasting forms of a
  gene.
• Dominant the gene that is expressed whenever it
  is present in the cell.
• Recessive the gene that is hidden. It is not
  expressed unless a homozygous condition exists
  for the gene.
• Gamete sexual reproductive cell.
• Fertilization the fusion of two gametes.
• Phenotype a physical trait in an organism.
• Genotype the combination of dominant and/or
  recessive genes present in cells.
• Homozygous two identical alleles for a given
  trait.
• Heterozygous two different alleles for a given
  trait.

6
Demonstrate how a Punnett square can be used to
predict the results of a genetic cross
(Mono/Dihybrid crosses) (170-174).

• Setting up the problem.
• Determine the traits used.
• Determine the dominant vs. recessive trait.
• Determine the letters for each trait.
• Express the cross and determine the gametes
  formed.
• Set up the Punnett Square.
• Place the 2 female gametes across the top, the 2
  male gametes down the side.
• Determine the offspring fill in the squares.
• Follow the column straight up to find gamete from
  female parent.
• Follow row across to find gamete from male
  parent.
• Sample problem Show the cross between a
  homozygous blue flowered plant and a homozygous
  white flowered plant. Blue is dominate to white.
• Traits blue flowers, white flowers
• Blue is dominant to white
• Blue B
• White b
• BB x bb
• The Punnett Square

7

• Note the dominant trait is always written first
• BB and bb are the parental or P1 generation.
• Sample problem If Bb x bb, half will be
  heterozygous (Bb), half homozygous recessive
  (bb).
• Note Phenotype ratio 22.

8

• DIHYBRID CROSSES  A dihybrid cross is a cross
  between two individuals identically heterozygous
  at two loci for example, AaBb/AaBb. A dihybrid
  cross is often used to test for dominant and
  recessive genes in two separate characteristics
• In the pea plant, two characteristics for the
  peas, shape and color, will be used to
  demonstrate an example of a dihybrid cross in a
  punnett square. R is the dominant gene for
  roundness for shape, with lower-case r to stand
  for the recessive wrinkled shape. Y stands for
  the dominant yellow pea, and lower-case y stands
  for the recessive green color. By using a punnett
  square (the gametes are RY, Ry, rY, and ry)
• The result in this cross is a 9331 phenotypic
  ratio, as shown by the colors, where yellow
  represents a round yellow (both dominant genes)
  phenotype, green representing a round green
  phenotype, red representing a wrinkled yellow
  phenotype, and blue representing a wrinkled green
  phenotype (both recessive genes).

9

• Differentiate between the diploid and haploid
  condition of a cell and identify the diploid (2n)
  and haploid (n) chromosome number in human cells
  (121153).
• The number of chromosomes in a body cell of an
  organism is the diploid number. In human, this
  number is 46. Half of the diploid number is
  called the haploid number. In humans, this number
  is 23 and is found only in the gamete cells. A
  cell that is diploid contains both sets of
  homologous chromosomes (one set from each
  parent). Thus, haploid cells contain only a
  single set of chromosomes.
• Explain how gender is determined (122)
• Gender is determined by the combination of sex
  chromosomes inherited in the zygote. More
  specifically, it is the sex chromosome within the
  sperm that is the determining factor (it provides
  either an X or Y). Also, it has been discovered
  that the Y chromosome carries a single gene, TDF
  (Testis Determining Factor) that determines
  maleness. (Girl XX, Boy XY)

10

• Distinguish between sex chromosomes and
  autosomes(122).
• There are 23 pairs of chromosomes in humans.
  Twenty-two pairs are autosomes, and one pair is
  the sex chromosome. The X chromosome is larger
  that the Y and it has extra genes on it that code
  form regular body traits.
• Explain the inheritance of sickle-cell anemia
  (176-180).
• An amino acid substitution results in the sickle
  shape of the red blood cells. This causes the red
  blood cells to have low oxygen carrying capacity,
  and deprive tissues of oxygen. This can be fatal.
  The cell shape is elongated and curved, hence the
  sickle name. This is in lieu of the biconcave
  disk shape of normal cells. This disease is found
  almost exclusively in the African-American
  population and affects about 1 out of every 623
  A.A. infants born in the U.S. The disease exists
  in individuals who are homozygous heterozygous
  individuals do not exhibit symptoms of the
  disease, but are considered carriers and have a
  resistance to malaria

11

• Identify the causes of Downs, Turners, and
  Klinefelters syndromes and identify them by
  their karyotypes (122-123).
• Nondisjunction is the failure of chromosomes to
  separate properly during one of the stages of
  meiosis. XXY produces Klinefelters syndrome
  (male appearance, underdeveloped testis, enlarged
  breasts, usually sterile, often mentally
  retarded). XO is Turners syndrome (female
  anatomically and physiologically, rudimentary
  ovaries, no menstruation or ovulation). YO seems
  to be fatal, none have been found. Other multiple
  sex chromosomes usually produce some
  abnormalities. Downs syndrome (G trisomy, three
  21 chromosomes) produces mental retardation and
  distinctive facial characteristics.

12

• Distinguish between sex-linked and autosomal
  disorders, Incomplete dominance, and Codominance
  (171, 175-178, 180).
• Sex-linked diseases are inherited through one of
  the "sex chromosomes" -- the X or Y chromosomes.
• Autosomally inherited diseases are inherited
  through the non-sex chromosomes (autosomes),
  pairs 1 through 22.
• Dominant inheritance occurs when an abnormal gene
  from ONE parent is capable of causing disease
  even though the matching gene from the other
  parent is normal. The abnormal gene dominates the
  outcome of the gene pair.
• Recessive inheritance occurs when BOTH matching
  genes must be abnormal to produce disease. If
  only one gene in the pair is abnormal, the
  disease is not manifest or is only mildly
  manifest. However, the genetic predisposition to
  disease can be passed on to the children.
• Examples (X-linked recessive),Color blindness ,
   hemophilia A , Duchenne muscular dystrophy,
  (X-linked dominance)
  Retinitis pigmentosa , Rett syndrome , Vitamin D
  resistant rickets

13

• X-linked diseases usually occur in males. Males
  have only one X chromosome, so a single recessive
  gene on that X chromosome will cause the disease.
  Although the Y chromosome is the other half of
  the XY gene pair in the male, the Y chromosome
  doesn't contain most of the genes of the X
  chromosome and therefore doesn't protect the
  male. This is seen in diseases such as hemophilia
  and Duchenne muscular dystrophy.
• Females can get an x-linked recessive disorder,
  although it would be very rare. An abnormal gene
  on the X chromosome from each parent would be
  required, since a female has 2 X chromosomes.
• For an autosomal dominant disorder
  
  
  
  If one parent has an abnormal
  gene and the other parent a normal gene, there is
  a 50 chance each child will inherit the abnormal
  gene, and therefore the dominant trait.
• Examples Achondroplasia (dwarfism), Huntington
  disorder, neurofibromatosis, Polydactyly, Marfan
  syndrome

14

• For an autosomal recessive disorder
  
  
  
  When both parents are carriers of an autosomal
  recessive trait, there is a 25 chance of a child
  inheriting abnormal genes from both parents, and
  therefore of developing the disease. There is a
  50 chance of each child inheriting one abnormal
  gene (being a carrier).
• Examples  Galactosemia (the inability to
  metabolize lactose), cystic fibrosis,
  phenylketonuria, xeroderma
  pigmentosa, Tay-Sachs disease, Sickle cell
  disease
• INCOMPLETE DOMINANCE  A heterozygous condition
  in which both alleles are partially expressed,
  often producing an intermediate phenotype.
  (sometimes called partial dominance)
• For example, when a snap dragon with red flowers
  is crossed with a snap dragon with white flowers,
  a snap dragon with pink flowers is
  produced.ORLike in Caucasians, the child of
  straight haired parents and a curly haired parent
  will have wavy hair Straight and curly hair are
  homozygous dominant traits and wavy hair is
  heterozygous and is intermediate between straight
  and curly

15

• CODOMINANCE  In codominance, neither phenotype
  is completely dominant. Instead, the heterozygous
  individual expresses both phenotypes. A common
  example is the ABO blood group system. The gene
  for blood types has three alleles A, B, and i.
  i causes O type and is
  recessive to both A and B. The A and B alleles
  are codominant with each other. When a person has
  both A and B, they have type AB blood.

16
Interpret human pedigrees to determine the
inheritance and probability of human genetic
disorders (176).The parental generation is at
the top of the pedigree, and the offspring are on
the next line, connected by a line. Marriages are
shown by a line between one of the offspring and
a new circle or square, not connected above. The
grandchildren will be two lines down, and
traceable to their parents form direct lines.
17

• Identify advances in genetic technology and the
  ethical responsibilities that follow. (238-242)
• With the increasing strides in genetic
  engineering comes more responsibility and ethical
  concerns involving the safety with this type of
  advancement in altering both plant and animal
  genetic make-up. There are many benefits and
  risks involved with genetically modified crops
  and animals, which scienctists, the public, and
  other agencies must work together to evaluate.
• In the twentienth century, advances in plant
  breeding started using the principles of genetics
  to select plants. Today, genetic engineers can
  change/add favorable characteristics to a plant
  by manipulating the plants genessuch as
  developing bigger/tastier crops, being able to
  tolerate drought and different climates,
  heat/cold, adapting to different soils, resistant
  to insects, and improving the nutritional values
  of the crop plants, etc
• Soon after the advances with crop plants, farmers
  started using genetic engineering to improve and
  modify the farm animals. Altering growth hormone
  amounts in the animals diet increased many things
  such as weight, milk production, etc Another
  way gene technology is used with animals is
  adding in human genes to farm animals in order to
  get human proteins produced in their milk. The
  proteins are then sold for pharmaceutical
  purposes. These animals are called transgenic
  animals because they have foreign DNA in their
  cells.

18

• Cloning is also a very controversial topic in
  this field. Scientists turn to cloning as a way
  to create herds of identical animals that can
  make medically useful proteins. They have
  successfully cloned animals since 1996, but most
  have not survived due to many different technical
  complicationsbecause of these technical and
  ethical problems, efforts to clone humans are
  illegal in most countries.
• Launch of Human Genome Project (1988)
• First mammal cloned (sheep, in Scotland, by Ian
  Wilmut) (1996)
• Legislation to ban cloning dies in US Senate
  after heavy lobbying by the biotech industry.
  Senators are told that human cloning wouldn't be
  technically possible for "at least 10 years
  (1998)
• A child conceived in part to provide therapeutic
  tissues for an earlier-born sibling is born.
  Techniques of preimplantation genetic diagnosis
  are used to ensure that the child does not itself
  carry the disease. The press erroneously hails
  the child as the world's first "designer baby
  (2000)

19
(No Transcript)
20

• US congressional hearings begin on legislation
  banning human cloning(2001)
• Scientists at Texas A M University announce
  that they cloned a cat in December, the first
  cloning of a house pet(2002)
• The first complete sequence, accurate to 99.999,
  of the genetic code of a single human is
  announced (2003)
• A horse is cloned(2003)
• Korean researchers announce that they have
  succeeded in cloning human embryos and extracting
  stem cells from them.
• A mouse is born with two female parents and no
  male parent (2004)
• Use of preimplantation genetic diagnosis (PGD) to
  provide stem cells for children suffering from
  non-genetic diseases.(2004)