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GENETICS CH. 11-14
WHO ARE YOU WHO ARE YOU WHO ARE YOU WHO ARE YOU WHO ARE YOU WHO ARE YOU
In this unit you will learn the basics of genetics. There will be a lot of information that will help you
understand why you are the way you are. You will practice the concepts through a series of word
problems and ethical situations. It is a tough unit but one that you can apply to your every day living.
Enjoy.
OBJECTIVES: The student will be able to:
1. Relate genetics back to the nucleus and its function
2. Describe a chromosome pair and its parts and how it relates to the laws of genetics.
3. Define, explain and use the law of dominance, segregation and independent
Assortment.
4. Relate genetics to meiosis, gamete formation, fertilization, crossing over, etc.
5. Do a simple genetic profile
6. Make a pedigree and by following several traits, explain it
7. Do genetic problems dealing with monohybrid, codominance, multiple allele,
blood typing, sex-linked, sex influenced, pedigrees, and probabilities.
8. Explain some of the different genetic mutations and genetic diseases
9. Differentiate between gene and chromosome mutations
10. Give a brief description of Mendel's work
11. Explain genetic continuity and variation in terms of heredity
12. Explain how the environment influences gene expression.
TERMINOLOGY: The first set of terminology will be on the Terminology Test. It is important to
understand and be able to work with these terms in order to do genetic problems and understand
genetics in general.
allele
heterozygous
codonimant
homozygous
dominant
law of dominance
recessive
progeny
gene
filial
genetics
F1, F2
genotype
phenopype
----------------------------------------------------------X,Y
karyotype
variation
oncogene
crossing over
nondisjunction
sex-linked
sex chromosomes
amniocentesis
genetic counceling
ultasonography
diabetes mellitus
down syndrome
punnett square
carrier
recessive
haploid (1n)
gamete
diploid (2n)
law of independent assortment parent
law of segregation
offspring
multiple alleles
ratios
probability
hemoplhilia
sickle-cell anemia
galactosemia
PKU
tay-sachs
colorblindness
klinefelter syndrome
turners syndrome
fetalscopy
gene mutation
chromosome mutation
mutagen
ASSIGNMENTS and GRADING:
1. Read ch. 11, 14 Notes should be taken and all terms defined.
2. A large number of problems will be assigned (handout and from the text). These will
take a large amount of time as you master how to do them. They will be checked
on occasion, sometimes for grade and other times for understanding.
3. A genetic profile of your family and extended family (or friend's) and a pedigree
using this data. An explanation will accompany and explain your research.
4. A written test will be given on the terms and a simple monohybrid cross to check
for understanding of the basic material. All students MUSTpass this test with a C grade
before they will be allowed to take the other tests.
5. Several written tests will be given each containing word problems and terms. These
tests may be taken over, but only once and must be done within 2 school days.
The tests will not be the same, but similar covering the same information.
EXTRA CREDIT: 1.For the student who wants to go beyond in their understanding, you can check with
the teacher, and will be given several DIHYBRID crosses to learn how to work out on your own. This is
only for the students who understand the other material taught. 2. Read ch 13 and do the worksheets
that accompany that material. Also you must do a small research paper with it. Ask the teacher.
REVIEW OF MEIOSIS
The purpose of meiosis is to reduce the number of chromosomes in half, from the diploid number to the haploid
number and to produce gametes (sperm and eggs). This is found happening in the ovaries of the female and the
testis of the male.
RULES FOR FIGURING OUT GENETIC PROBLEMS
1. Write out the symbols
Ex: B = black, b = white (Dominant-recessive trait )
R = red, W = white, RW = pink
(Co-dominant and Incomplete dominace traits)
X = hemophilia, X = normal (Sex-linked traits)
2. Write out the genetic cross using genotypes
Ex: Aa x Aa = ___________
B__ x B___ = Bb,.B___
3. Ask: What is the question. What am I to try and find out?
4. Figure out the problem by:
a. Making a punnett square
b. Working backwards and forwards through the double recessive traits.
THE PARTS OF A GENETIC PROBLEM AND PUNNETT SQUARE
Example 1.
B= brown eyes
b = blue eyes
Bb x bb
Bb, bb
½ Bb
½ bb
½ brown eyes
½ blue eyes
Example 2
AABB x aabb
16/16 AaBb
Aa x Aa
P1 x P1
¼ AA, ½ Aa, ¼ aa
F1
F1 x F1
F2
SUMMARY OF CELL TYPES AND HAPLOID/DIPLOID.
Practice: Fill in the chart below by checking the appropriate boxes
CELL TYPE
HAPLOID DIPLOID 1n 2n
Parent
Body cell
Gamete
Sperm
Egg
Sex cell
Zygote
Progeny
Offspring
HOW TO FIGURE OUT GAMETES
The purpose of meiosis is to reduce the number of chromosomes in half, from the diploid number to the
haploid number and to produce gametes (sperm and eggs). This is found happening in the ovaries of the female and
the testis of the male.
How can we figure out what these gametes are?
Example 1
AaBb (parent cell is diploid with a 2n=4. Genes are in pairs)
AB (gametes, sperm and eggs, have one gene of each gene pair with a haploid number (1n) of 2. )
Ab
aB
ab
Example 2
AaBbCc (parent cell, 2n=6)
ABC, ABc, AbC, Abc, (gametes, 1n=3 One gene from each gene pair)
aBC, aBc, abC, abc
Practice: What are the gametes these parents can form?
1. AA
2. Tt
3. TTSSRr
4. TTrr
5. AaBbDD
6. AaBbCcDdEeFfGg (write out three of the many gametes)
PRACTICE DOING GENETIC PROBLEMS USING PUNNETT SQUARES
For each of the problems below do the following:
a. Assign the symbols
b. Write out the genetic cross using genotypes
c. Draw out a punnett square and figure out the progeny
d. Write out the genotypic proportions (ratio.)
e. Write out the phenotypic proportions (ratio.)
1. Cross a homozygous black rat with a homozygous white rat. Black is dominant.
a. B = black, b = white
b. BBxbb
d. 4/4 Bb
e. 4/4 black
2. Cross two heterozygous black rats
a.
b.
d.
e.
3. Cross a hybrid black rat with a white one
a.
b.
d.
e.
4. Cross a hybrid black rat with a homozygous black one.
a.
b.
d.
e.
In the next two problems, the traits show incomplete dominance and co-doninance. You solve them the same way
as before, but they differ in the way the symbols are assigned. There are three options in the phenotype with the
heterozygous being the third color.
1. In guinea pigs, neither yellow or white color dominates. They blend to form a cream color (the heterozygous
condition.) This is a incomplete dominance trait.
Cross a yellow guinea pig with a white one
a. YY = yellow, WW = white, YW = cream
b. YY x WW
d. 4/4 YW
e. 4/4 = cream
Cross a cream guinea pig with a yellow one
a.
b.
d.
e.
2. In dogs, both black and white are dominant colors. They do not blend but rather are both expressed. The
heterozygous condition ends up spotted. This is a co-dominant trait.
Cross two spotted dogs.
a.
b.
d.
e.
GENETICS PROBLEMS
Below are a number of genetic problems for you to try and figure out. Some of these will be very easy
and others will be more difficult. You are to try and do as many of them as possible in order to
understand the concepts being taught in class. Do these on a separate piece of paper. If you get
totally stuck, ask another student to help or go to your teacher. Most of these will have to be done at
home. Some of these will be checked for understanding and others for grade.
PROBABILITIES
1. What is the probability of tossing a coin and getting heads 3 times in a row?
2. What is the chance that the next toss will be heads?
Tails?
3. Looking at the results of this punnett square , what is the probability that the parents will have a blue
eyed baby? What is the probability of the second baby being blue eyed? What is the probability of them
having a brown eyed baby? What is the chance of them having 3 brown eyed babies in a row.
B = brown
b = blue
cross Bb x Bb (parents)
SINGLE TRAIT CROSSES
4. In a certain animal, black fur, B, is dominant to white fur, b. Determine the expected genotypic ratios
and phenotypic ratios resulting from crosses between (a) homozygous black x white, (b) two
heterozygous blacks, and (c) heterozygous black x white.
5. In a strange creature you find purple eyes, P, dominant to yellow, p. Two purple eyed creatures mate
and produce six offspring. Four of them have purple eyes and two have yellow eyes. What are the
genotypes of the parents? The phenotypes? What are the genotypes of the offspring?
6. (harder) In fruit flies, long wing, L, is dominant to short wing, l. Two long winged flies produced 49
short winged and 148 long winged offspring. What were the probable genotypes of the parents? What
proportion of the long winged offspring would be heterozygous?
7. Albinism, the total lack of pigment, is due to recessive gene (aa is an albino). A man and a woman
plan to marry and wish to know the probability of their having any albino children. What would you tell
them if:
a) both of them are normally pigmented but each has one albino parent.
b) the man is albino, the woman is normal but her father is an albino.
c) the man in an albino, and there has never been any albinism in the woman's family.
8. Tall plants are dominant over dwarf ones in pea plants. A homozygous tall plant is crossed with a
plant homozygous for dwarf.
a) What will be the appearance (phenotype) of the F1?
b) What will be the phenotype of the F2?
c) What will be the genotypic ratios of a cross between an F1 and its tall parent?
d) What will be the genotypic ratios of a cross between an F1 and its dwarf parent?
9. (harder) In cattle, the polled or hornless condition, P, is dominant over horned cattle, p. A certain
polled bull is bred to 3 cows. As a result of the breeding of this bull to cow A, a horned cow, a calf is born
that is polled. The bull bred to cow B, also a horned cow, results in a calf with horns. And finally, the bull
bred to cow C, which is a polled cow, results in a calf which has horns.
a) What are the genotypes of the bull and each of the three cows?
b) What further types of offspring in what proportions, would you expect from each of these three
matings?
CO-DOMINANCE, INCOMPLETE DOMINANCE AND BLOOD TYPING
10. In Andalusian fowl, B is the gene for black plumage and W is the gene for white plumage. The
genes show codominance. The heterozygous condition results in blue plumage. List the genotypic and
phenotypic ratios expected from these crosses:
a) black x blue
b) blue x blue
c) blue x white
11. What is the probable genotypic ration among children born to a mother who is AO, and a father who
is AB?
12. A mother with type A blood has two children, one with type O and the other with type B. What must
have been the genotype and phenotype of the father, mother and children?
13. A family of four children have the following blood types: A, B, O, AB. Give the genotype and
phenotypes of the parents.
14. List the possible blood types of the children that would result form the following crosses:
a) type A x type O
b) type B x type O
c) type A x type A
d) type AB x type O
e) type A x type AB
f) type B x type B
15. Suppose two newborn babies were accidentally mixed up in the hospital and there was a question of
which baby belonged to which parents. From the following blood types, determine which baby belongs to
who. Also what is the genotype of each of the six persons?
baby 1
type O
baby 2
type A
Mrs. Brown type B
Mr. Brown
type AB
Mrs. Smith type B
Mr. Smith
type B
16. One parent has type A blood and the other has type B blood. What are their genotypes if they
produced a large number of children whose blood types were
a) all AB
b) 1/2 AB and 1/2 B
c) 1/2 AB and 1/2 A
d) 1/4 AB, 1/4 A, 1/4 B, 1/4 O
MULTIPLE ALLELES
17. In rabbits agouti coat is dominant over chinchilla, chinchilla is dominant over himalayan and
himalayan is dominant over albino. This is a case of multiple alleles. Show the possible genotypes that
produce the following coat colors.
a) agouti
b) chinchilla
c) himilayan
d) albino
18. Is it possible to cross two agouti rabbits and produce both a chinchilla and a himalayan progeny?
19. A series of rabbit matings between a chinchilla x himalayan produced a progeny ratio of 1 himalayan,
2 chinchilla and 1 albino. What were the parental genotypes?
SEX-LINKED TRAITS
20. In fruit flies, red eyes is dominant, R, over white eyes, w, and are sex-linked. Determine the probable
genotypic and phenotypic ratios expected from these crosses:
a) heterozygous female and a red-eyed male
b) heterozygous female and a white-eyed male
c) homozygous dominant female and a red-eyed male
d) homozygous dominant female and a white-eyed male
21. In humans the gene, h, for hemophelia is sex-linked and recessive to the gene H, for normal clotting.
Diagram on the chromosomes the genotypes of the parents of the following crosses and summarize the
expected phenotypic ratios resulting from the crosses.
a) hemophiliac woman x normal man
b) normal heterozygous woman x hemophiliac man
c) normal homozygous woman x hemophiliac man
22. In humans the gene for normal blood clotting, H, is dominant to the gene for hemophilia, h. The trait
is sex-linked. A woman with normal blood clotting has four children. They are a normal son, a
hemophiliac son, and two normal daughters. The father has normal blood clotting. None of the grand
parents were hemophiliacs. What is the probable genotype of each member of the family? What is the
probability of the daughters will be carriers of the disease (but not show it?)
SEX INFLUENCED TRAITS
23. (extra) The dominant autosomal gene, B, for premature baldness in man is considered to be sexinfluenced. If a man with the genotype ,Bb, married a woman with the genotype, Bb, what proportion of
their (a) male and their (b) female children might be expected to become bald prematurely?