BSCI222 - Mendelian Genetics

What is pangenesis?

Model of inheritance of genetic information proposed by Darwin

• All parts of the body produce small bits “gemmules” that go through the blood system and collect reproductive organs to be transferred to gametes

What was Gregor Mendel’s role in Mendelian Genetics?

1860’s sweet pea hybridization

Applied mathematical analysis (frequencies of trait segregation in crosses)

Predicted existence of traits encoded in discrete units

What is a gene?

A basic unit of biological information (encodes a protein)

What is an allele?

An alternative form of a single gene

What is a locus?

A designated location on a chromosome (ex. to find a gene)

What is a genotype?

The actual genetic makeup of an individual (ex. sequence variation at a gene)

What is the phenotype?

An observable characteristic or trait due to a sequence variation at a gene

What is heterozygous?

A genotype in which the two alleles are different (ex. Aa)

What is homozygous?

A genotype in which the two alleles are the same (ex. AA or aa)

What are reciprocal crosses?

Crosses in which the phenotype of each sex in the parents is reversed as compared with the original cross (tests role of sex on inheritance)

What is a test cross?

Means of determining the genotype of individual with a dominant phenotype (is it AA or Aa) by crossing it with a homozygous recessive (aa)

A? x aa

• if get 4/4 dominant then AA

• if get 2/4 dominant then Aa

What is a monohybrid cross?

A cross involving a single trait

What is the law of segregation?

Two alleles coding the same trait in an individual (ex. YY, Yy, yy) separate during gamete formation so that a gamete only gets one from each parent

What is a dihybrid cross?

Cross involving two traits!

What is the law of independent assortment?

Different pairs of alleles separate independently of each other during gamete formation.

What is the multiplication rule?

P(A) AND P(B) = P(A) x P(B)

What is the addition rule?

As long as both event are mutually exclusive: P(A) OR P(B) = P(A) + P(B)

What are chi-square tests?

x² = ∑ [(observed # - expected #)²/ (expected #)]

How do you derive expected #?

# of offspring x fraction with phenotype (from punnett)

How do you calculate degrees of freedom?

df = # phenotypes - 1

Use this to find the critical value at 0.05

How do you use the x²?

If x² > critical value

• data fits the model within statistical variation (ACCEPT VALUES AS LIKELY)

If x² < critical value

• data does not fit the model (REJECT VALUES)