Genetics

1.        Gregor Mendel

 

  1. A monk in the 1800’s
  2. Studied pea plants
  3. Planned experiments
  4. Made observations which are the foundation of genetics.
  5. Used math to describe biology for the first time.

 

2.        Principles of Genetics

  1. When parents differ in a trait, the offspring show only one trait.
  2. Offspring of parents differing in some trait will produce eggs or sperm, half with the trait of one parent and half with the trait of the other.
  3. The fact that an organism carries genetic material for one trait does not mean it carries the genetic information for any other trait (independent assortment).

 

3.        Dominance

  1. Mendel studied 7 characteristics in pea plants each which could be expressed in 2 forms.
  2. The form observed is called PHENOTYPE. (How offspring look).
  3. Examples of phenotype in pea plants.

i.                     seed form, round or wrinkled

ii.                    color of seed content, yellow or green

iii.                  color of seed coat, white or gray

iv.                  color of unripe seed pods, green or yellow

v.                   shape of ripe seed pods, inflated or restricted

vi.                  length of stem, short or long

vii.                position of flower, axial or terminal

 

  1. Took two pure strains that differ in only one characteristic, i.e. seed color.
  2. Parents called P1, offspring called F1, offspring of the F1 generation called F2.
  3. P1                 yellow x green
  4. Result: No blending, no yellowish green offspring, instead F1 was all yellow.
  5. The trait that appears in the F1 is DOMINANT. Yellow is a dominant trait.
  6. The trait that does not appear in the F1 is called RECESSIVE. Green is recessive.
  7. One factor is preventing the expression of the other. This is known as the principle of Dominance.
  8. When F1 is crossed with the F1 the recessive trait reappears in the F2.  However the ratio of dominant vs. recessive is consistent.
  9. F2 x F2. Those with recessive traits only produced recessive offspring but those that were dominant made both dominant and recessive offspring.  3:1 ratio dominant to recessive.
  10. Cross.  Yellow x Green.  Yellow is dominant and green is recessive.  P1 Yellow x Green.  F1 Yellow, F2 3 Yellow; 1 Green

 

4.        Genes

  1. Every trait is controlled by two factors, one from each parent.
  2. The unit of inheritance is called a gene.
  3. The alternative form of a gene are called alleles.
  4. The alleles of a gene are at specific locations called loci on chromosomes.
  5. Yellow and Green are examples of alleles of the same trait.
  6. One allele is dominant and one is recessive.
  7. There is a difference between what kind of information you have (GENOTYPE) and what you look like (PHENOTYPE).
  8. 3:1 pattern seen at F2 is only possible if alleles separate during the formation of gametes.
  9. Principle of segregation-two alleles for a trait separate when gametes are made.

 

5.        A closer look

  1. The parents are a pure strain Also known as HOMOZYGOUS.
  2. RR xrr
  3. Both alleles code form the same form of the trait. But ½ of the genes come from each parent.
  4. F1: Rr the alleles code for different forms of the trait (HETEROZYGOUS).
  5. Genotype                              Phenotype                            Gametes

RR homozygous                       round                                     R

rr homozygous                       wrinkled                                 r

Rr heterozygous                       round                                     R or r

 

     F.  F2 Rr x Rr

  1. Punnett Square with Genotype, Phenotype and gametes table.

 

6.        Principal of Independent Assortment

  1. Plants with 2 characteristics called dihybrids.
  2. Example: Round and wrinkled seeds and Yellow and Green seeds.
  3. The two traits don’t influence each other.
  4. P1                RRYY x rryy
  5. F1                RrYy
  6. F2                Table 9:3:3:1 phenotypic ratio
  7. Segregation of genes for one characteristic was not affected by the other gene.
  8. Being round has no effect on whether you are yellow.
  9. Each pair of alleles segregate individually during gamete formation.

 

7.        Test Cross

  1. Cross your unknown with a homozygous recessive.
  2. If unknown is dominant homozygous the all the F1 will carry the unknown trait.
  3. If unknown is dominant heterozygous ½ F1 will be dominant and ½ will be recessive.

 

8.        Beyond Mendel

9.        Chromosomal theory of inheritance.

  1. Chromosomes are not identical but come in a variety of sizes and shapes.
  2. Chromosomes come in pairs called homoloques.
  3. At meiosis, each gamete gets the same # and kind of chromosomes.
  4. When chromosomes line up at metaphase, there is no way to tell which way the maternal or paternal chromosomes will go. This is independent assortment.
  5. Traits must be associated with chromosomes.
  6. There are more traits than chromosomes so many traits must be on a chromosome.

10.     Sex linkage

  1. Studied in Drosophila Melangaster  otherwise known as a fruit fly.
  2. Flies are easily mutated using cold, heat, x-rays, chemicals, or radioactivity.
  3. Normal flies have red eyes, and are called wild type.
  4. A mutant fly has a white eye.
  5. P1 is red eye female x white eye male
  6. F1 All red eyes
  7. F2 3470 red eye and 782 white eyes. Not 3:1.
  8. All the white eyes are male, 2459 red eye female and 1011 red eye male.
  9. Maybe only males can have white eyes.
  10. Original white eye male x red eye daughter
  11. 129 red female, 132 red males, 86 white male, 88 white female.
  12. Chromosomes may assort independently but genes may not. Sex and eye color could be linked.
  13. XrXr x XwY  punnett square
  14. Drosophila has 4 chromosomes; 2 autosomes, 2 sex chromosomes.
  15. In female one X chromosome forms a barr body and is inactivated

11.     Gene linkage and Crossover

  1. 2 traits on different chromosomes will sort independently.
  2. 2 traits on the same chromosome will tend to be passed together.
  3. When genes are on same chromosome it is called gene linkage.
  4. Black body(b) and curved wing (c)are  on the same chromosome.
  5. Beige (B) and normal(C)
  6. BBCC xbbcc expect ½ BC and ½ bc
  7. But you get 37 % BC, 37 % bc , 13% bC and 13% Bc
  8. Body color and wings are on the same chromosome. The alternative alleles are on homoloques.
  9. Chromosomes are able to exchange genes. Recombination in Meiosis.
  10. Sex linked traits, eye color in fruit flies, color blindness in humans, muscular dystrophy, hemophilia.

12.     Chromosome Mapping

  1. If genes are arranged linearly those closer would  become seperated via chrossover less often.  Being close increases the probability of being passd as a unit.
  2. % crossover is proportional to the distance between 2 genes. % crossover is # of crossovers between 2 genes per 100 prophase opportunities.

 

13.     Mutations

  1. X rays, UV light, Chemicals
  2. Chemical mutatgens include cigarette smoke, automobile exhaust, cleaning agents, pesticides, charcoaled steak.
  3. Gene mutations are point mutations can occur during DNA replication.
  4. Sickle cell anemia.
  5. Addition or subtraction of nucleotide, or change the nucleotide.
  6. Chromosome Mutations
  7. Deletions
  8. Inversions
  9. Duplications
  10. Mutations can be beneficial to natural selection.

14.     Stability of DNA

  1. Base pairing makes DNA resistant to change.
  2. DNA repair systems.
  3. Skin cancer is failure of DNA repair systems.

15.     Really Beyond Mendel

  1. incomplete dominance red and white flower produces pink flower.
  2. Multiple alleles ie ABO blood system
  3. Epistais, one gene masks the effects of another. Mouse coat color. When albino gene is homozygous the black and brown coat color does not develop.
  4. Polygenic inheritance. Genes have additive effect, for example height.
  5. Variation. Genotype may be expressed differently in different environment, or different sex, and aging or from which parent the gene was inherited from.

16.     Population Genetics

  1. The frequency of alleles for any characteristic will remain unchanged in a population through any number of generations unless some outside force acts on the populationl.
  2. Hardy-Weinberg priciple  p2 + 2 pq + q2

 

Advances in Genetics

1.        Cloning genes

  1. Restriction Enzymes
  2. Ligase
  3. Insert and Vector
  4. Growth in Bacteria

2.        PCR

  1. DNA separated by heat
  2. Primer anneals to DNA
  3. DNA polymerase extends primer.
  4. Repeat

3.        Molecular Mug Shots

  1. DNA from crime.
  2. Cut with restriction enzymes.
  3. Run on gel.
  4. DNA transferred to nitrocellulose.
  5. Single –stranded probe used to bind to complementary fragments.
  6. X-ray film detects pattern, or fingerprint.

 

4.        Diagnosis of Disease

  1. Restriction Enzymes can be used to find mutations in genes.
  2. Alzheimers and Huntigtons disease.

5.        Advances in Agriculture

  1. crops resistant to inscects, bacteria, fungi and unsuitable growing conditions.
  2. Increase size edible parts.
  3. Increase nutrition.

6.        Gene Replacement Therapy

  1. Replacing defective genes with normal genes.
  2. 1990 a 4 year old girl was given  gene to bosst her immune system.
  3. Corrected cellular defect of cystic fibrosis by adding normal protein.