BIOL 2500 - Topic 6 (part 6)

Null hypothesis for X² analysis to infer linkage

The ratio does not differ from the ratio expected for unlinked genes (1:1:1:1)

Conclusion if X² is higher than the critical value

The ratio differs from 1:1:1:1, with fewer recombinants and more parentals than expected, meaning it is linked

Reverse usage of maps

You can use genetics maps to determine the gametic frequencies

Factors that affect recombination in genomes

1.) Sex

2.) Age, temperature-dependent variation.

3.) Genetic hotspots and coldspots

Underestimation of map distances

1.) They tend to underestimate the physical distance between genes, such as undetected double frossovers

2.) The further apart the syntenic genes, the more inaccurate it usually is

3.) This is why RF1 + RF2 ≠ RF3

Differences in recombination due to sex

1.) Homogametic individuals tend to have more crossing over, such as in humans, because there’s more area for recombination to occur

2.) Heterogametic individuals tend to have less crossing over

Recombination in Drosophila

Recombination is exclusive to females only and does not occur in males

Hot spots

Spots where recombination occurs more often than average, based on the number of nucleotides present

Cold spots

1.) Spots where recombination occurs less often than average, based on the number of nucleotides present

2.) They usually occur in genes/spots that are highly conserved, such as genes coding for rRNA (would not want this to change)

Genetic recombination map

It maps the relative position of genes based on recombination frequencies, measured by map units

Physical genetic map

The actual position of the genes, based on the nucleotide sequences, measured in kbp

Use of recombination and physical genetic maps

Using both can help us understand chromosomal structures and gene functions