Download ex: sex-linked traits on

This activity was done as a jigsaw. The worksheets were run on colored paper (ex: sex-linked traits on
blue, incomplete dominance on pink, and codominance on yellow) and passed out to the students. The
students then formed groups based on the color of their paper (ex: all blue together, all yellow together,
all pink together). They then read the front of their sheet and used the new knowledge to complete the
back together. The answers of each group were checked for accuracy. After a while the students
moved to form new groups, this time with one of each colored paper in the group (ex: groups of 3; one
blue, one yellow, and one pink). Each student then took turns summarizing/explaining the front of the
sheet and then guiding/helping the others through the back.
***Students seem to struggle with sex-linked traits the most so I tried to make sure that those papers
were handed out to some of my stronger students!
Pera 0405: Other traits
Name__________________________ Date________________________ Color__________________
Incomplete Dominance: The story of snapdragons
So far all of the genes/traits we have discussed in class have followed normal genetic rules.
Pure dominant individuals show the dominant trait, pure recessive individuals show the recessive trait,
and hybrids show the dominant trait. There are a few traits that do not follow these rules.
Snapdragon (flower) color is one of the traits that follows different rules. If you mate a pure red
snapdragon with a pure white snapdragon you might expect to find a pure dominant, a pure recessive,
and two hybrids. This is not the case… open the bags on your table to discover what all of the
offspring of a cross between a pure red and a pure white plant will look like.
Ok so now you are wondering how this is possible. It happens because snapdragon flower
color shows incomplete dominance. This means that neither red nor white dominant and neither red
nor white is recessive. They both will be shown. In the case of pink snap dragons the red gene is
making some red pigment and the white gene is making some white pigment and the resulting flower
looks pink. Since snapdragon color doesn’t follow the normal rules their genes are written a little
differently. You use the large letter C to represent color and a superscript letter to represent the gene
that the plant has. For example CW is a white gene and CR is a red Gene
CR CR = a red snap dragon
CR CW = a pink snap dragon
CW CW = a white snap dragon
Punnett squares are completed the same as genes that follow the normal rules of
dominance/recessiveness except this time you use the code above for each of the genes. An example is
provided below.
CW
CR
CR
R
CW
W
C C
CR CW
R
W
C C
CR CW
Pera 0405: Other traits
When you cross a red
snapdragon with a white
snapdragon you will have
100% pink snapdragons.
Now try the questions on the back of this sheet. When you return to your group your job will be to
explain incomplete dominance to your table and help them complete the back of their sheet.
Incomplete Dominance: the hybrid phenotype is between the phenotypes of both the parents.
Ex: Snap dragons
Red
White
CW
CW
CR
CR CW
CR CW
CR
CR CW
CR CW
100% pink
Now try these…
Pink
R
W
C C
% red: _______________
Pink
% pink: ______________
CR CW
% white: _____________
White
CW CW
% red: _______________
Pink
CR CW
% pink: ______________
% white: _____________
Red
Pink
CR CR
CR CW
% red: _______________
% pink: ______________
% white: _____________
Pera 0405: Other traits
Name__________________________ Date_______________________ Color___________________
Codominance: The story of Roan cows
So far all of the genes/traits we have discussed in class have followed normal genetic rules.
Pure dominant individuals show the dominant trait, pure recessive individuals show the recessive trait,
and hybrids show the dominant trait. There are a few traits that do not follow these rules. Cow
color is one of the traits that follows different rules. If you mate a pure white cow with a pure
red/brown cow you might expect to find a pure dominant, a pure recessive, and two hybrids. This is
not the case… open the bags on your table to discover what all of the offspring of a cross between a
pure red/brown and a pure white cow will look like.
Ok so now you are wondering how this is possible. It happens because cow color shows
codominance. This means that neither red nor white takes over and neither red nor white are hidden.
They are both equal. A cow that has a red/brown gene and a white gene will have some red/brown fur
and some white fur so farmers call them roan cattle. Since roan cow color doesn’t follow the normal
rules their genes are written a little differently. You use capital R to represent the red gene and capital
W to represent the white gene. Since they are both equally as powerful they are both represented by
their own capital letter.
RR = a red/brown cow
RW = a roan cow
WW = a white cow
Punnett squares are completed the same as genes that follow the normal rules of
dominance/recessiveness except this time you use the code above for each of the genes. An example is
provided below.
W
R
R
RW
RW
W
RW
RW
Pera 0405: Other traits
When you cross a red/brown
cow with a white cow you
will have 100% roan cows.
Now try the questions on the back of this sheet. When you return to your group your job will be to
explain Codominance to your table and help them complete the back of their sheet.
Codominance: both genes are equally expressed in hybrid individuals.
Ex: Roan Cows
Red
White
W
W
R
RW
RW
R
RW
RW
100% Roan
Now try these…
Roan
Roan
RW
RW
% red: _______________
% roan: ______________
% white: _____________
White
Roan
WW
RW
% red: _______________
% roan: ______________
% white: _____________
Red
Roan
% red: _______________
RR
RW
% roan: ______________
% white: _____________
Pera 0405: Other traits
Name_______________________ Date____________________ Color_________________
Sex-linked traits: The story of male pattern baldness
The sex of an individual is determined at the time fertilization takes place. The 23rd chromosome
pair determines sex in humans. If the offspring has a 23rd pair that matches or is XX then it will be a
female. If the 23rd pair does not match or is Xy it will be a male. The egg cell always contains an X
chromosome and the sperm carries either an X or y. Because of this fact it is the father’s genetic
contribution that determines the sex of the baby.
X X = female
X y = male
As you can tell by the diagram to the right the y
chromosome is much smaller than the X
chromosome and therefore the male is missing the
second copy of any gene that is carried on the upper
portion of the X chromosome.
Sex-linked traits are genes that are carried on the upper region of the X chromosome. Sex linked
traits show up more often in men since men only have one X chromosome and therefore only need to
inherit one copy of the gene to show the recessive genotype. Some sex-linked traits in humans are
colorblindness (the inability to decipher colors), hemophilia (a disease where your blood will not clot or
stop bleeding), and baldness (all of these sex linked traits are recessive). Since sex linked traits are
different depending on the sex of the individual it is important to include the sex in the genotype or a
punnett square.
The diagram below represents all of the possible genotypes for sex-linked traits.
XhXh
XX
Normal Female Female hemophiliac
XhX
Female Carrier Normal Male
Xy
Xhy
Male hemophiliac
** a female carrier is a female who does not show the trait but has on copy they can send to their offspring.
Punnett squares are done similarly for sex-linked traits. You still begin by placing the parent genes on the
outside of the square (top and left), only this time you use the X, Xh, and y symbols (use a superscript c for
colorblindness and a superscript b for baldness). Below a punnett square has been done for you crossing a
normal male and a female carrier of hemophelia.
X
y
Xh
XhX
Xhy
X
XX
Xy
The offspring will be:
25% female carriers (XhX)
25% normal females (XX)
25% hemophiliac males (Xhy)
25% normal males (Xy)
This couple has a 25% chance of having a baby with
hemophilia. If the child is a girl it cannot have hemophilia.
Now try the questions on the following page. When you return to your group your job will be to explain
sex linked traits to your table and help them complete the back of their sheet.
Pera 0405: Other traits
Mate a mother that is colorblind (XcXc) with a normal father (XY).
X
Xc
Xc
y
What percent of their offspring will be:
Color blind males: _______________
Normal males: __________________
Color blind females: _____________
Normal females: ________________
Female carriers of the colorblind gene: ____________
What are the chances of this couple having a child that
will be colorblind? ____________________________
Mate a bald man (Xby) with a female that is a carrier of the bald gene (XbX).
What percent of their offspring will be:
Bald males:___________________
Normal males: ________________
Bald females: _________________
Normal females:_______________
Female carriers of the bald gene:_________________
What are the chances of this couple having a child that
will go bald? _________________________________
1. Explain why sex linked traits are seen more often in males. _______________________________
______________________________________________________________________________
2. What is a female carrier? _________________________________________________________
______________________________________________________________________________
3. Which parent’s genes determine if the son will be bald? _________________________________
______________________________________________________________________________
4. How would it be possible to get a bald female? Would her mom and dad have to be bald? ______
______________________________________________________________________________
______________________________________________________________________________
5. Below draw models of the X and Y chromosomes and show where the sex linked traits are
located.
Pera 0405: Other traits