KH

Introduction to Genetics

Mendel

  • Born in Austria in 1822.

  • Added flowers and pea pods to the plant.

  • Fascinated with pea plants.

  • Worked as a monk in the monastery gardens.

What did Mendel do & discover?

  • Conducted breeding experiments with pea plants.

  • Observed patterns of inherited physical characteristics.

  • Some characteristics were expressed more than others.

  • A factor must pass from parent to offspring.

Why was Mendel's work not recognized as important at the time it was published?

  • Because genes and chromosomes had not been discovered yet.

Genetic Keywords

Allele

  • Alternative form of a gene.

  • Example: Doodle of DNA.

Dominant

  • This type of allele is always expressed if it is present.

Recessive

  • This type of allele is only expressed if there are 2 recessive alleles present.

Homozygous

  • This is when both alleles of a gene are the same (both TT or tt).

Heterozygous

  • This is when the alleles of a gene are different.

Genotype

  • This describes the alleles that an organism contains.

Phenotype

  • This describes the physical characteristics displayed by an organism.

Punnett Squares

  • A genetic diagram.

  • Deals with probability.

Example: Smooth vs. Wrinkled Peas

  • A heterozygous pea plant is crossed with a homozygous recessive pea plant.

  • Smooth peas (R) are dominant over wrinkled peas (r).

  • Objective: Work out the probability of each offspring genotype and phenotype for this trait using a Punnett Square.

Steps for Using a Punnett Square

Step 1: Work out the Genotypes of the Parents

  • Parent 1 Genotype: Rr (heterozygous)

  • Parent 2 Genotype: rr (homozygous recessive)

Step 2: Split Up Each Parent's Alleles

  • Each parent can only pass on one allele to the offspring.

Step 3: Work out Possible Offspring Genotypes

  • Read across and down to work out the possible offspring genotypes in each quarter of the square.

Step 4: Phenotype for Each Genotype

  • Determine the phenotype (smooth or wrinkled) for each resulting genotype in the Punnett square.

Step 5: Probability of Each Phenotype

  • Express the probability as a percentage, fraction, or ratio.

Results:

  • Probability of smooth pea plants: 50%

  • Probability of wrinkled pea plants: 50%

  • Ratio of smooth to wrinkled pea plants: 1:1