1. Review

2. What is a gamete? Why do we need to know the gamete composition?
Aa 21=2
AaBB 21=2
AaBbCc 23=8
AaBbCC 22=4
We need to know the gamete composition so that we can insert them into the boxes in punnet square
e.g # AaBbCc x AaBbCC
ABC
ABc
AbC
Abc
aBC
aBc
abC
abc

3. Testcross What is a testcross? Why do we do testcross?
- homozygous recessive alleles

4. Sex linked 2 ways to write it, depending on instruction
Eg, assume that PTC is a sex-linked gene.
Ability to taste is dominant XP+/ XP
Inability to taste is recessive XP/ Xp
So, XP+XP+, XP+X , XP+Y are tasters and non-tasters will be XPXP, XPY
Always bear in mind that if they talk about disease, normal means a NONCARRIER XP+XP+, XP+Y

5. Try this
The gene for eye in flies (Drosophila melanogaster) are sex linked. The gene for red eye is dominant over yellow eye. A red eyed male is mated with yellow eyed female. Diagram the cross is the male is heterozygous.

6. Try this
The gene for eye in flies (Drosophila melanogaster) are sex linked. While gene gene for wings are autosomal. The gene for red eye is dominant over yellow eye, gene for vestigial wings is dominant over long wing. A red eyed male fly with vestigial wings is mated with yellow eyed female fly with long wings. Diagram the cross is the male is heterozygous.

7. Map distance and chi-square
How do we determine the ratio
Green pod, starchy 568
Red pod, wrinkle 525
Green pod wrinkle 154
Red pod, starchy 163
1400
Recombinant ??
Ratio ??
Which one is which ??

8. Trihybrid cross- determining map distance
Parent flies were mated
Black body, purple eyes, vestigial wings
Gray body, red eyes, long wings
Producing
Black body, purple eyes, vestigial wings 411
Gray body, red eyes, long wings 412
Black body, purple eyes, long wings 60
Black body, red eyes, long wings 28
Black body, red eyes, vestigial wings 1
Gray body, purple eyes, vestigial wings 30
Gray body, red eyes, vestigial wings 61
Gray body, purple eyes, long wings 2
b+ pr+ vg+
b pr vg

9. Calculate the distance between genes
We know that map distance is
So, we need to calculate the map distance of
Between body and eye color
Between body and wings
Between eye and wing
Recombinant
Total
X 100

10. Between body and eye color
Between body and wing
Between eye and wing

11. But. The actual distance calculated was 18
But.. The actual distance calculated was 18.4 mu, therefore, this is said to experience rare double crossovers.
Therefore

12. Single and Double crossovers