Download Linked Genes and Gene Mapping

Linked Genes and Gene Mapping
**pick up packet off front table
Mendel
• Law of independent assortment- during
meiosis pairs line up on plate independent of
pair above.
– AND genes are on separate chromosomes
What if they weren’t on diff
Chromosomes? What would we
See in the offspring?
Linked Genes
• 2 or more genes found on same chromosome
• Inherited together frequently
Given 2 chromosome options…
Which scenario would give you more
Frequent linked inheritance?
WHY?
WHY?
• Genes close together often travel together
• Less chance for “close genes” to be split
during crossing over
How to determine if genes are really
linked?
• KEY: Look at recombinants in offspring of cross
• EX: In fruit flies, tan body color is dominant to black and normal wing
shape is dominant to vestigal wings. A hybrid male is crossed with a black
vestigal winged female.
Calculate Recombination Frequency
• Formula
• < 50% = __________________
• > 50% = __________________
• 100% = __________________
Gene Mapping
• 1% recombo frequency = 1 MPU (cM)
• Example:
– Recombination frequency of genes A and C is 17%
while the frequency of genes A and B is 7%. Map
the chromosome AND identify how far apart
genes B and C are located.
Linkage Practice
A Wild type fruit fly (heterozygous for gray body
and normal wings) is mated with a black fly with
vestigial wings.
OFFSPRING:
778- wild type
785- black-vestigial
158- black- normal wings
162- gray body-vestigial wings
What is the recombination frequency between
these genes? Are they linked? Why/Why not?
A Wild type fruit fly (heterozygous for gray body
and red eyes) is mated with a black fly with
purple eyes.
OFFSPRING:
721- gray body/red eyes
751- black body/purple eyes
49- gray body/purple eyes
45- black body/red-eyes
What is the recombination frequency between
these genes? Are they linked? Why/Why not?
Determine the sequence of genes along a
chromosome based on the following
recombination frequencies:
A-B = 8 map units
A-C = 28 map units
A-D = 25 map units
B-C = 20 map units
B-D = 33 map units
Determine the sequence of genes
along a chromosome based on the
following recombination frequencies:
A-C = 20 map units
A-D = 10 map units
B-C = 15 map units
B-D = 5 map units