GN 301 Module 6: Linkage and Codominance

Define **Independent Assortment**:

the migration of the alleles of one gene into a gamete doesn’t affect the migration of alleles at a second gene, as long as they’re on different chromosomes

Define **Linked Genes**:

occurs when genes are on the same chromosome, tend to be transmitted as a single unit

**Crossing Over**

A breakage of chromosomes and an exchange of genes between nonsister chromatids of homologous chromosomes, diversifying genetic information in an individual.

Importance of crossing over in gamete formation

Crossing over helps maximize the genetic diversity of any offspring that result from the eventual union of two gametes during sexual reproduction

Compare/Contrast Parental v Recombinant Gamete Types:

Gametes that are produced without crossing over are the parental types, and gametes produced due to crossing over is a recombinant type
Parental types occur more frequently than recombinant types

Map Distance:

The further apart 2 genes are, the more likely it is that a crossover will occur between them.

Which gamete will be produced most frequently from the individual shown?

aBc is the most likely formed. Parental types are more likely than recombinant (without having to cross over)

Which gamete will be produced least frequently?

aBC is the least likely formed. This is because a crossover would be required between B/b and C/c.

Parental vs Recombinant

The types of gametes that are classified as noncrossover (parental) or crossover (recombinant) types, depends on which alleles were on associated on the same chromosome prior to the crossover.

**Map distances**

the distance between genes on a chromosome

How are map distances measured?

Measured in centimorgans (cM)

Multiple alleles

Multiple alleles occur when there are more than 2 forms of the same gene. Even though there are more than 2 options for alleles, each person can still only have 2 alleles at a given locus.

**Genotype Number**

If you have “N” alleles, you can get (N / 2) (N + 1) different genotypes
2 alleles: (2/2)(2+1) = (1)(3) = 3 different genotypes
3 alleles: (3/2)(3+1) = (1.5)(4) = 6 genotypes
4 alleles: (4/2)(4+1) = (2)(5) = 10 genotypes

Codominance

when both of the alleles at a locus are expressed in the heterozygous individual

MN Blood type locus

These alleles produce proteins found on blood cells

3 possible genotypes: MM, MN, or NN. a person who is heterozygous makes both M and N proteins

codominant

A and B are ___ to each other

dominant

A and B are both ____ to O

recessive

O is ____ to both A and B

Spp. Mom is AO and Dad is AB. What are the possible blood types of their children and in what frequency?

Possible blood types: Type A, Type B, or Type AB

Spp. Mom is AB and has a B child. What can the father’s blood type be?

AB + ? = B
Type B= B0 or BB
Father could be B0, BB, AB, or 00