Chapter 17- Mendelian Patterns of Inheritance

Be able to identify and describe a P generation, F1 generation, F2 generation.

• P generation: parents

• F1 generation: hybrid offspring (first generation)

• F2 generation: hybrid offspring (second generation)

True-breeding versus hybrid organisms (from a cross of true-breeding organisms).

true breeding: homozygous for a particular trait, two identical alleles (AA or aa)

hybrid organisms: result of the cross combination of two true breeding alleles with different alleles causing the offspring to become heterozygous (Aa)

How Mendel set up his pea plant crosses – what did he cross together?

he crossed two true breeding plants (AA and aa). 

result: all dominant alleles (Aa)

What phenotypes and ratios did Mendel see in the P, F1 and F2 generations?

P: AA & aa       F1: Aa       F2: Aa & aa

Distinguish between dominant vs. recessive traits and genotype vs. phenotype.

Be able to use and interpret terminology: homozygous dominant (PP), Heterozygous (Pp), Homozygous recessive (pp). 

Know how to complete Punnett squares to predict genetic and phenotypic outcomes given information about parental generation.

Understand what a testcross is, how it works and what it can tell you - Recognize homozygous (PP or pp) versus heterozygous (Pp)

test cross: mystery allele and known  recessive allele

what can it tell you: parents genotypes 

Understand what the Law of Independent Assortment and the Law of Segregation tell us about the relationship of genes (and their alleles) to each other.

Law of Segregation

• alleles separate randomly into reproductive cells during meiosis

• only one allele

• ex. if the plant gets purple gene, it cant get the white gene too

• ex. if the plant gets the dominant gene, it cant be recessive

Law of independent assortment:

• alleles separate randomly into reproductive cells during meiosis

• two different alleles

• ex. plants are round and yellow (dominant) or wrinkled and green (recessive) 

Calculate probabilities of getting complex genotypes and probabilities of getting different offspring in a mating

heterozygous hybrid 

25% homozygous dominant

50% heterozygous dominant 

25% homozygous recessive 

heterozygous dominant & homozygous recessive

 50% heterozygous dominant 

 50% homozygous recessive 

Know when and how to use the Multiplication rule: 

probability of two or more independent events occurring together (for example, the likelihood of getting two different alleles like R and R together from parental gametes at the same time in one offspring); use this rule to calculate the probability of getting a specific genotype in one offspring. These are comparable to a coin toss – each time you toss a coin is independent of the next time you toss a coin.

Know when and how to use the Addition rule: 

probability that one or more mutually exclusive events will occur; each offspring you could get in a mating is a mutually exclusive event that does not impact the other offspring you could get in another mating. However, given the parent’s genotypes, you can only get specific pool of offspring.

Remember a trihybrid Punnett square with 64 possibly offspring – that’s 100% of the potential offspring possible, and when I ask you to predict the probability of specific genotypes of offspring, I’m asking you to find a percentage of all the possible offspring. (Remember also the turn signal example or drawing a specific card or set of cards from a deck.) Use this rule to calculate the probability of getting multiple offspring of different genotypes from a mating. 

Be able to perform monohybrid Punnett squares (one for each set of alleles) to calculate the probabilities of complex genotypes (example: for a trihybrid cross – 3 genes – make 3 individual Punnett squares).