Topic 1 Heredity: Mendelian Genetics

Question 1

• Scientist Gregor Mendel discovered the basic principles of heredity through extensive experiments with pea plants. The concepts outlined in this section relate Mendel’s findings from his peas which are broadly applicable in the field of genetics.

Answer 1

Note

Question 2

• Mendel crossed pea plants, which basically means two plants exchanged genetic information to give rise to a new generation. The main types of crosses to know for the OAT include monohybrid, dihybrid, and test crosses
  i. Monohybrid cross - two organisms with variations at one gene of interest are crossed
  ii. Dihybrid cross - two organisms with variations at two genes of interest on different chromosomes are crossed
  iii. Test cross - when the genotype of an organism expressing the dominant phenotype is unknown, the unknown organism is crossed with a homozygous recessive organism to determine if the unknown is homozygous dominant or heterozygous dominant

Answer 2

Crosses

Question 3

• A technique that uses probability rules to determine the outcomes of either monohybrid or dihybrid crosses and the subsequent expected frequencies
• To set up a Punnett square, the genotype of both parents are listed outside the box, and the resultant combinations are written inside the boxes
• Remember, Punnett squares follow probability rules, so, referring to the image above, the chances of getting the genotypes NN, Nn, and nn, respectively, are 50%, 50%, and 0%. Punnet squares can also be used for dihybrid crosses, which are slightly more complicated
• To determine the probabilities of
  offspring in dihybrid crosses, it is usually easier to calculate the probability of each gene separately, and then multiply the probabilities.

Answer 3

Punnett Squares

Question 4

• Blending of expressions of alleles

- For example, a red flower and white flower are crossed to result in a unique heterozygous pink offspring

Answer 4

Incomplete Dominance

Question 5

• Both of the inherited alleles are completely expressed

- For example, blood types A and B can show as AB if both are expressed

Answer 5

Codominance

Question 6

• Blood groups have four possible phenotypes, the codominant A, B, and O, leading to four possible genotypes and phenotypes
  i. AO → type A
  ii. BO → type B
  iii. AB → codominant AB type
  iv. OO → type O

Answer 6

Multiple Alleles