Theme 4A: Mendelian Inheritance

Question 1

What were two of the early theories of inheritance? What are the major issues with these theories?

Answer 1

• Blending inheritance - offspring have traits that are intermediate to their parents (i.e., mixing of traits)
  *This means that variation will be reduced over time (rare traits would disappear)
• Lamarckism - “Inheritance of acquired traits”, so favorable traits acquired by parents are passed on to offspring
  *There hasn’t been an elimination of undesirable traits, such as diseases etc.

Question 2

What type of inheritance was Mendel wanting to test?

Answer 2

• Particulate inheritance

Question 3

What does a parental (P1) generation represent?

Answer 3

• The true-breeding representation of a particular trait, while the filial generation (F1) is produced from the parental generation

Question 4

What’s a monohybrid cross?

Answer 4

• Crossing two individuals that are homozygous for two different alleles of one single trait in order to determine which one is dominant, since the offspring will all be heterozygous and will therefore express the same phenotype.

Question 5

What’s the difference between product rule and sum rule?

Answer 5

• Product rule - The probability of two independent events occuring in succession (multiplying them together)
• Sum rule - The probability that one or the other of two mutually exclusive events will occur is the sum of their individual probabilities

Question 6

What is a test cross used for?

Answer 6

• Used to determine if an individual is heterozygous for a certain trait. Done by mating the unknown individual with the homozygous recessive genotype and observing the offspring

Question 7

What does the separation of alleles reflect in meiosis?

Answer 7

• The separation of chromosomes along the metaphase plate, which occurs at random

Question 8

What are two major flaws with basic mendelian inheritance?

Answer 8

• Dominance in traits is not universally observed!
• Mendel’s theory could not explain variation in traits!

Question 9

What is the difference between incomplete dominance and codominance?

Answer 9

• Incomplete dominance - An intermediate phenotype because one allele is not completely dominant to the other allele, causing the heterozygote to create an intermediate phenotype
• Codominance - Both traits are expressed equally because both alleles have equal effects. Heterozygote exhibits both homozygote phenotypes

Question 10

What type of influences impact the variation of a species, influences that Mendel couldn’t account for?

Answer 10

• Genetic influences
• Environmental influences
  *These created a continuous distribution among populations of species

Question 11

True or false: Two individuals can have the same phenotypes but not the same genotypes

Answer 11

• This is true
• 1 could be heterozygous for a dominant trait while the other could be homozygous dominant for the same trait.

Question 12

What are the main causes of evolution?

Answer 12

• Mutations
• Migration
• Genetic Drift

Question 13

Whats considered the null hypothesis for evolution?

Answer 13

• There will be no change in the allele frequencies over time of a specific trait.

Question 14

What five conditions must me maintained in order for a population to maintain a Hardy-Weinberg eqilibrium? (i.e., undergo no evolution?)

Answer 14

1) No mutations must occur
2) There is no migration
3) The population is inherently large (infinite in theory)
4) Genotypes do not differ in fitness (no natural selection)
5) Mating is completely random