Banerji_Lab5_linkage

Banerji_Lab5_linkage - Lab 5 - Linkage & Recombination...

Info iconThis preview shows pages 1–11. Sign up to view the full content.

View Full Document Right Arrow Icon
Lab 5 - Linkage & Recombination
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Genes Can Be Linked There are 20,000-25,000 genes in the human genome – so, it can’t be that each gene is on its own chromosome and assorts independently. In many cases, genes travel together in particular allelic sets. [We call this “linkage.”]
Background image of page 2
Because of the way homologous chromosomes line up on the metaphase plate, we expect 4 different types of gametes in equal proportions : [Meiosis in an A/a;B/b individual]
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Another way to say this is that ½ the gametes show the “parental” configuration, while the other ½ show a “recombinant” (non-parental) configuration.
Background image of page 4
What if A and B are close together on the same chromosome? In the absence of crossing over, linked genes stay together. Crossing over can often separate linked genes, however. [“Complete Linkage”] [“Incomplete linkage”]
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
How do we know if genes are “linked” or “independent”? • Independent assortment gives us 4 types of gametes (2 parental and 2 recombinant) in EQUAL FREQUENCIES (1/4:1/4:1/4:1/4) [heterozygote] • Complete linkage gives us 2 types of gametes (both parental) in EQUAL FREQUENCIES (1/2:1/2) • With incomplete linkage… it depends on how close the linked genes are.
Background image of page 6
Linked Genes If the alleles of the A and B genes get mixed and matched 10% of the time, we say that their loci are 10 “centiMorgans” (cM) apart. [Note: “map distance” = frequency of recombination. It doesn’t necessarily have anything to do with the actual, physical distance between the loci.]
Background image of page 7

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Recombination Frequency * The number of recombinant offspring, divided by the total number of offspring (expressed as a percent).
Background image of page 8
Coupling and Repulsion With linkage, it’s not always the case that one parent gives all dominant alleles and the other parent gives all the recessive alleles: A B a B a b A b COUPLING REPULSION Dominant alleles adjacent to each other (same homolog) Dominant alleles diagonally across from each other
Background image of page 9

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
What if 3 genes are on the same chromosome, instead of just 2? • We still look at what kind of gametes are
Background image of page 10
Image of page 11
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 29

Banerji_Lab5_linkage - Lab 5 - Linkage & Recombination...

This preview shows document pages 1 - 11. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online