1. I will review DiHybrid Crosses & then learn Sex-Linked Crosses
ISN p.152
MT 16, The Genetics of Life
Thurs
TOPIC:
MY GOAL:
GET ON
TSSK
I will review DiHybrid Crosses & then learn Sex-Linked Crosses
Turn to your DiHybrid Cross HW…

2. Bottom of ISN p. 152 – Work it! T T P p x T t P P TP Tp TP Tp TP tP
Genotype Phenotype TP Tp TP Tp
TTPP=4
TTPp=4
TtPP=4
TtPp=4 TP tP
TTPP
TTPp
TtPP
TtPp
Tall, Purple = 16

3. DiHybrid Cross TOP of ISN p. 152 – Work it!
T T P p x T T P P TP Tp TP Tp
Genotype Phenotype TP
TTPP
TTPp
TTPP=8
TtPp=8
Tall, Purple = 16

4. Your 2nd Job Today ISN page155
WRITE in ANSWERS
X or Y
X or Y, X
XY, XX
You will use the ‘key’ provided to work the Sex Linked Punnett Square on ISN p.154 after I explain…

5. Autosomes vs Sex Chromosomes
Notes, ISN p.155
Autosomes vs Sex Chromosomes
Sex Xsomes =
Xsome pair #23
XX = F
XY = M
Autosomes =
Xsome pairs #1-22
Amniocentesis 5

6. MALES determine the sex of the offspring!
46 Chromosomes total in humans!
2 are sex xsomes:
XX or XY
Eggs = X or X
sperm - X or Y
Sperm determines sex of the offspring X X X Y
GIRL
BOY

7. Sex Linked Traits
Traits found ONLY on the Sex Xsomes  specifically the X
EXAMPLES:
Colorblindness…
Hemophilia…
Muscular Dystrophy…
Traits found on Autosomes – the first 22 pair - are written as letters like Dd or FF (dimples & freckles)
But when a trait is on the Sex Xsome, you change the way you write the gene… 

8. How do you represent Sex-Linked genes?c C C
X X
X Y
As a superscript:
The genes are attached or LINKED to the X sex chromosomes! That’s why they are written as superscripts. No disorders are linked to the ‘Y’ xsomes because it is so small

9. What is a “Carrier”? Why are they “normal”?
Notes ISN page 155
What is a “Carrier”? Why are they “normal”?
Carrier = only F = do NOT exhibit trait, just carry it & MIGHT pass it on
XYor XY C c c C
C C c c
X X or X X or X X
So why can’t men be carriers AND why do more men have Sex-Linked Genetic Disorders???? c c c
X X
X Y

10. Sex Linked Punnett Square
Cross a Heterozygous Normal Color Vision Female with a colorblind male.
XCXc x
XcY

11. XCXc x XcY Xc Y XC Xc XC Xc Xc Xc Xc Y XC Y Genotype Phenotype ?1
F, Carrier = 25% XC Xc Xc Xc
Xc Xc=
Xc Y 1
F, CB = 25%
XCY= 1
M, Normal = 25% Xc Y
Xc Y= XC Y 1
M, CB = 25% ?

12. Your 3rd Job Today ISN page154
WORK the 2 Sex Linked
Punnett Squares
1st = Color Vision
2nd = Hemophilia
Use the Keys on ISN p.155

13. XcY x XCXC XC Xc Y XC Xc XC Y XC Xc XC Y XC Genotype Phenotype2
Carrier are NORMAL! = 50% XC Xc XC Y XC
XC Y = 2
M, normal vision = 50% XC Xc XC Y XC
% children w/ normal vision???
100%

14. XhXh x XHY Xh XH Y XH Xh Xh Y Xh Y XH Xh Genotype Phenotype2
Carrier = 50% Xh XH Xh Xh Y
Xh Y = 2
M, hemophilia = 50% Xh Y
50/50 chance children will be normal XH Xh

15. Be the change you wish to see in the world
Study a bit each night..
HOMEWORK
Be the change you wish to see in the world 15 15