Chapter 4: Linkage recombination

What if there are genes that are linked and located on the same chromosome?

They will have a recombinant frequency that is less than 50%, resulting in there being a unlikely chance of the crossover event occurring, making them more likely to be inherited together and produce fewer recombinants

What if there are genes that are not linked and located on different chromosomes?

They will have a recombinant frequency that is 50%, resulting in there being a high chance of a crossover event occurring, making them more likely to be inherited independently and produce many recombinants

Which chromatids undergo recombination? What is the result?

2 non-sister chromatids undergo recombination, resulting in a new allelic combination

What is one genetic map unit?

It is the distance between a pair of genes with 1 in 100 meiotic products being recombinants

What is cross over in meiosis?

A process where the chromatids of 2 homologous chromosomes break at the same position and exchange corresponding segments

What is a chiasma?

A cross-shaped structure that forms between two non-sister chromatids

What does the recombination frequency reflect?

the distance between two genes on a chromosome and the likelihood of a crossover event occurring between them

What does the proportion of recombinants correlate to in linkage recombination?

It correlates to the distance separating two gene loci on a chromosome map.

When are the proportions of recombinants and parental types identical during independent assortment?

When two genes are on different chromosomes and follow independent assortment.

What is a three-point test-cross?

A type of cross that enables geneticists to evaluate the linkage between 3 genes and determine gene order all in one cross

What do recombination maps show

They show the loci of genes with known mutant alleles

How are gene positions determined within a recombination map?

It is determined by the recombination frequency during meiosis

• with the frequency being proportional to the distance between two loci, making RF the mapping unit

Why is knowing a gene position on a chromosome crucial?

Its needed for the construction of complex genotypes used in experiments and commercial application

What can a gene position on a chromosome be used to define?

It can be used to define a recombination map at the DNA level

What can geneticists deduce by comparing differences in chromosomal maps?

They can deduce the evolutionary genetic mechanisms that caused genomes to diverge.

What can linkage be used to discover?

It can be used to discover the location of genes associated with specific diseases in a genome

What can the loci of any DNA heterozygosity be used as?

It can be used as a molecular chromosome marker to map gene locations

• And when used to view a disease gene, it’ll appear closely linked to the gene and segregate along with the alleles of the gene

What is a physical map?

A simple genomic DNA map that shows each genes:

• location

• sequence

• Size

• whats between them

• Other landmarks of interest

With the units of distance being # of DNA bases

What does the alignment of a physical map with a recombination map allow for?

It allows for the relative position on both maps to be compared and allows for any phenotypes to be connected with unknown gene functions