Section: 3.6
Name:
Opening Activity:
Latin Root Word:
Review of Old Information:
Incomplete Dominance or Codominance?
a)Birds can be blue, white, or white with blue-tipped feathers.
b) Flowers can be white, pink, or red.
c) A Hoo can have curly hair, spiked hair, or a mix of both curly and spiked.
d) A Sneech can be tall, medium, or short.
3. In Smileys, eye shape can be starred, circular, or a circle with a star. Write the genotypes for the
pictured phenotypes
4. Show the cross between a star-eyed and a circle eyed. What are the phenotypes of the offspring?
____________ What are the genotypes? __________
6. A man with type AB blood is married to a woman with type O blood. What are all the possible blood
types of their children?
New Information:
I.
Sex determination
i. Remember, during meiosis all chromosomes are split and each cell gets one half of a homologous pair. 1. You get half your father’s chromosomes and half of your mothers. ii. This is also how it works with sex chromosomes. The sex chromosomes for humans are _________________. 1. Female genotype is _________ 2. Male genotype is _________ Human inheritance patterns are significantly MORE complex than that of a fruit fly. Complete the table
below making sure that each inheritance pattern is defined and has an example.
Inheritance Pattern
Description
Trait or Disorder Influenced
Dominant:
More than 200 traits are controlled by the autosomal
dominant condition and more than 250 traits by the
autosomal recessive; the single allele of a gene codes for
the single trait.
Huntington’s Disease,
Dwarfism, Cataracts
Recessive:
Albinism, Cystic Fibrosis
Multiple-allele Traits
Traits where three or more alleles (characteristics) of the
SAME gene code for a single trait.
Traits or characteristics that are controlled by more than
one gene.
X-Linked Traits
Colorblindness, Hemophilia,
Muscular Dystrophy
Sex Influenced Trait
Baldness
Nondisjunction
Activity:
Part 1: Sex-Linkage
Complete the questions using the instructions below:
As many of you know boys are different than girls. In humans sex is determined by the twenty-third pair of
chromosomes known as “sex chromosomes”. If you have two X-shaped (XX) chromosomes you are destined to be a female.
If you have an X and a Y-shaped (XY) chromosomes, you are destined to be a male. Since the X and Y chromosomes carry
different information, any genes found on the X chromosomes are referred to as sex-linked genes. Therefore, women will
have two alleles for these genes because they have two (XX)
chromosomes. On the other hand, men have only one allele for each of these genes because they have only one X
chromosome (XY).
Sample Problem:
In fruit flies, the gene for eye color is carried on the X chromosome which is a sex chromosome (sex-linked). The
allele for red eyes is dominant over the allele for white eyes. If a white-eyed female fruit fly is mated with a red-eyed male,
predict the possible offspring.
1. Since the female has white eyes, she must be “X X ”. The male is red-eyed and because he has only one X
chromosome, he has only one allele for eye color. His eyes are red so he must be RY. means he only has one allele
for eye color, so he must be “X Y”. Since the allele “R” is present on the X chromosome only, and there is no
other allele for eye color because the male other sex chromosome is a Y chromosome.
r
r
R
2. For sex-linked traits we need to list the genotype in a different fashion. We must identify the individual as being male
or female according to their sex chromosomes. Females are XX, and males are XY. Sex-linked traits are only found on
the X chromosome, therefore the letters are placed as superscripts (above) the X chromosome. Therefore the
genotype for the female fly is X X and the male is X Y. You can use shorthand notation rr x RY, but sometimes this
can be confusing.
r
r
R
3. The Punnett square for the parent flies are shown below.
X
X
r
r
XX
XX
R
r
R
r
X
⎢
⎢
Y
R
X Y
X Y
r
r
4. The genotypic ratio is
1 XX
R
:
r
1 XY
r
5. The individual X X will be a female because she has two X chromosomes. She will have red eyes because she has Rr.
The individual with X Y will be a male because he has the X and Y chromosomes. He will have white eyes because
he has only one allele and it is “r”. So from this cross you would expect all of the females to have red eyes and all
of the males to have white eyes.
R
r
r
Complete the following problem below:
1. Hemophilia is a sex-linked trait. A person with hemophilia is lacking certain proteins that are necessary for normal
blood clotting. Hemophilia is caused by a recessive allele so use “N” for normal and “n” for hemophilia. Since
hemophilia is sex-linked, remember a woman will have two alleles (NN or Nn or nn) but a man will have only one
allele (N or n). A woman who is heterozygous (a carrier) for hemophilia marries a normal man:
a. What are the genotypes of the parents?
b. Make a Punnett square for the above cross.
Genetics - X Linked Genes
**In fruit flies, eye color is a sex linked trait. Red is dominant to white.**
1. What are the sexes and eye colors of flies with the following genotypes?
X X _________ X Y __________ X X __________
R
r
R
r
r
X X ____________ X Y ____________
R
R
r
2. What are the genotypes of these flies:
white eyed, male ____________ red eyed female (heterozygous) ________
white eyed, female ___________ red eyed, male ___________
3. Show the cross of a white eyed female X X with a red-eyed male X Y .
r
r
R
4. Show a cross between a pure red eyed female and a white eyed male.
What are the genotypes of the
parents:
___________ and _______________
How many are:
white eyed, male ____
white eyed, female ____
red eyed, male ____
red eyed, female ____
5. Show the cross of a red eyed female (heterozygous) and a red eyed male.
What are the genotypes of the parents?
___________ & ________________
How many are:
white eyed, male ____
white eyed, female ____
red eyed, male ____
red eyed, female ____
Math: What if in the above cross, 100 males were produced and 200 females. How many total red-eyed
flies would there be? ________
6. In humans, hemophilia is a sex linked trait. Females can be normal, carriers, or have the disease. Males
will either have the disease or not (but they won’t ever be carriers)
X X
X X
X X
Show
H
H
H
h
h
h
= female, normal
X Y = male, normal
= female, carrier
= female, hemophiliac
X Y= male, hemophiliac
the cross of a man who has hemophilia with a woman who is a carrier.
H
h
What is the probability that their children will have the disease? __________
7. A woman who is a carrier marries a normal man. Show the cross. What is the probability that their
children will have hemophilia? What sex will a child in the family with hemophilia be?
8. A woman who has hemophilia marries a normal man. How many of their children will have hemophilia,
and what is their sex?
Calico Cat Genetics
9. In cats, the gene for calico (multicolored) cats is codominant. Females that receive a B and an R gene
have black and oRange splotches on white coats (calico). Males can only be black or orange, but never
calico.
Here’s what a calico female’s genotype would look like: X X
B
R
Show the cross of a female calico cat with a black male?
What percentage of the kittens will be black and male? _________
What percentage of the kittens will be
calico and male? _________
What percentage of the kittens will be calico and female? _________