How Much Do You Remember???

Character

A heritable feature

Trait

A variant for a character

True-breeding

Plants that produce offspring of the same variety when they self-pollinate

Hybridization

Crossing of two true-breeding varieties

P Generation

Parental generation; the true-breeding parents

F1 Generation

First filial generation; hybrid offspring from the P generation

F2 Generation

Second filial generation; offspring of F1 hybrids that self-pollinate

Allele

Alternative versions of a gene

Dominant allele

When 2 alleles at a locus are different, it determines the organism’s appearance

Recessive allele

When two alleles at a locus are different, it has no noticeable effect on the organism’s appearance

*both alleles must be recessive to see this trait

Law of Segregation

The two alleles for a heritable character separate during gamete formation and end up in different gametes

*an egg or sperm only gets one of the two alleles that are present in the somatic cells

Punnett Square

A diagram for predicting the allele composition of offspring from a cross between individuals of known genetic makeup

*Practice…

Homozygous

An organism having a pair of identical alleles for a character

Heterozygous

An organism that has two different alleles for a gene

Phenotype

An organism’s traits

Genotype

And organism’s genetic makeup

Test Cross

Breeding of a recessive homozygote with an organism of dominant phenotype but unknown genotype to determine the unknown genotype

Monohybrid

Organism that is heterozygous for one character

Dihybrid

Organism that is heterozygous for two characters

Law of independent assortment

Each pair of alleles segregates independently of other pairs of alleles during gamete formation

Laws of Probability and Inheritance Patterns

Laws of Probability

Probability: 1 = will occur, 0 = will NOT occur

Probabilities of all possible outcomes must add up to 1. For a coin,

If the sides are both “heads,” the probability of landing on that side is 1; and the probability of landing on “tails” is 0.

If the coin has two different sides, there is a ½ chance of landing on a particular side.

For a stack of 52 different cards, there is a 1/52 chance that you will select any given card, and there is a 51/52 chance of selecting a card other than the one you want.

Outcome is not affected by previous trials.

Laws of Probability

Just as each coin toss’s outcome is independent of the others, so the alleles of a gene segregate into gametes independently of another gene’s alleles. (law of independent assortment)

Two rules will help predict the outcome of the fusion of gametes: Multiplication Rule

Addition Rule

Multiplication Rule

Take the individual probabilities of the given outcome and multiply them together Example: For a monohybrid cross Rr x Rr (R is dominant and r is

recessive) the possibility of each allele for a particular gamete being given to the offspring is ½.

The probability of both gametes giving the same allele to the offspring is ½ x ½ = ¼.

Addition Rule

Add the individual possibilities together when determining if one of two or more mutually exclusive events is going to occur.

For example: In a monohybrid cross (Rr x Rr), the probability of the dominant allele being passed on by one of the gametes is ½ x ½ = ¼ , and the probability of the dominant allele being passed on by the other gamete ½ x ½ = ¼ .

Probability of a heterozygote (Rr): ¼ + ¼ = ½.

Solving Complex Genetics Problems with the Rules of Probability

Extending Mendelian Genetics for a Single Gene: the Spectrum of Dominance Complete Dominance – heterozygote and dominant homozygote

are indistinguishable

Mendel’s pea crosses (white OR purple, round OR wrinkled)

Codominance – both phenotypes are exhibited at the same time

Human blood surface molecules (MN has M AND N molecules)

Incomplete Dominance – phenotype is between the phenotypes of the parents

Snapdragons with red and white parents have pink offspring

Multiple Alleles

Human Blood Type: A, B, AB, O

Determined by which of two carbohydrates (A or B) are found of the surface of a person’s red blood cells

An enzyme (I) attaches the carbohydrates

I adds A, I adds B, i adds neither

Each person has 2 alleles, so there are 6 possible genotypes and 4 phenotypes

A B

Genotype

Phenotype

The End