Genetics exam 1

The idea of the Homunculus was from the ancient Greeks who believed the sperm contains a tiny, fully formed human. The egg provides a place for the homunuculus to grow, i.e. the egg does not provide any traits. What is the issue with this theory?

All the progeny would be identical copies of their father.

Explain the theory of blended inheritance. What made this theory misleading?

• LIke mixing paint

• Parental traits become “mixed” and forever changed

• It could not explain obvious differences between biological siblings nor the persistence of variation within extended families.

What were the keys to Mendel’s success?

1. Excellent model organism

2. Discreet traits

3. Pure-breeding lines

4. Controlled matings

5. Large numbers of offspring and statistical methods

Define a monohybrid cross:

outcross between two plants that differ by a single alternative trait

Define parental generation (P) in Mendelian terms:

original pure-breeding lines used for the cross

Define first filial (F1) generation in Mendelian terms:

Offspring resulting from the monohybrid cross

Define second filia generation (F2) in Mendlian terms:

Offspring resulting from the self-fertilization of the F1 generation

How did the first monohybrid cross that Mendel did disprove the blended inheritance model?

In all monohybrid cross, the hybrid was indistinguishable from one of the parents.

How did the first monohybrid crosses disprove the homunuclus model?

When Mendel conduted reciprocal crosses, he found that it did not matter whether the egg or sperm contributed to the trait (i.e. genetic material is from both parents, not only father).

Define Mendel’s law of segregation

• The two alleles of a gene separate from each other in making gametes (egg and pollen)

• Also, gametes unite at random

What were the ratios for genotypes and phenotypes when Mendel self-crossed the F1 generation to create the F2?

Ratio of genotypes: 1:2:1 YY: Yy: yy

Ratio of phenotypes: 3:1 yellow:green

You have two yellow peas. How might you distinguish the YY pure-breeding yellow peeds form the Yy hybrid yellow peas, if they look the same?

Perform a test cross with a pure-breeding homozygous recessive individual

Probability equation

Explain the product rule?

The probability of two independent events occuring simultaneously is the product of each of the respective proabilities

e.x. p(getting two heads in a row) is p(H) x p(H) = 0.5×0.5= 0.25

Explain the sum rule

The probability of either one or the other of two mutually exclusive outcomes occuring is the sum of their individual probabilities

Explain Mendel’s law of independent assortment

During gamete formation, alleles of different genes assort independently of each other

How can we apply Mendel’s law of independent assortment to predicting dihybrid frequencies, i.e. a cross with two different genes?

we can find the probability for EACH geneto calculate the probability for BOTH (the product rule)

What is the genetic definition of an allele?

An alternative form of a gene

What is the molecular definition of an allele?

A gene variant that differs by DNA sequence

Why are most mutant alleles recessive?

The dominant allele determines a normally functioning protein, while the recessive allele does not specify a functional protein (usually).

Monohybrid crosses helped Mendel explain which of his two laws?

• Law of Segregation

• Disproved Blending theory - The green peas reappeared in the F2 generation following the F1 self-cross.

Dihybrid crosses help to explain which of Mendel’s two laws?

• Law of Independent assortment

• An allele for one gene will not have an effect on an allele for another gene

What are some traits of a recessive disease?

1) generation skipping

2) consanguineous mating often reveals recessive trait

3) affected children from unaffected parents (carriers)