Genetics Unit Review Guide Answers
1. Describe protein synthesis.
Transcription: Occurs in the nucleus; DNA is converted into mRNA
Translation: Occurs at the ribosome; mRNA code is read and tRNA picks
up correct amino acids in cytoplasm and brings them to the
ribosome where they are assembled in the correct order to
form the required protein
2. List the differences between DNA & RNA
DNA
Made of 2 strands
Found only in nucleus
Contains deoxyribose sugar
Contains thymine (nitrogen base)
RNA
Made of 1 strand or less
Travels throughout the cell
Contains ribose sugar
Contains uracil (nitrogen base)
3. Define the following:
nucleotide – 1 unit of DNA (sugar, base, phosphate)
replication – DNA makes an exact copy of itself before mitosis
codon – a group of 3 nitrogen bases that code for a specific amino acid
hydrogen bond – holds base pairs together in DNA molecules (weak)
amino acid – building block of protein
uracil – nitrogen base found only in RNA; binds with adenine
4. What are homologous chromosomes? What is crossing over? When
does it occur? Why does it occur?
Homologous chromosomes are chromosomes that carry the same genetic
information (ex: Chromosome pair #1 might contain the genes that control
traits such as height or blood type) – they are a matching pair of
chromosomes
Crossing over is the exchange of genetic material between homologous
chromosomes – it occurs during meiosis and its purpose is to allow for the
formation of genetically different gametes
5. List two types of haploid cells and two types of diploid cells. What
process produces diploid cells? Haploid? What is the big difference
between a haploid cell and a diploid cell? Give an example.
Haploid cells = sperm & egg; Diploid cells = all other body cells such as
skin, bone, blood, or muscle
Diploid cells are produced by mitosis, haploid cells are produced by
meiosis.
Haploid cells have one set of chromosomes (half the normal amount) and
diploid cells have two sets of chromosomes (-di = two)
Example: In humans, haploid cells have 23 chromosomes & diploid cells
have 46 chromosomes.
6. Draw a diagram to show how the following are related: DNA,
chromosome, gene
Gene = small piece of DNA that codes for a specific protein
Chromosomes are large structures composed of DNA – each
chromosome contains many genes
7. What is a mutation? List 3 different causes of mutations. Describe 2
different types of mutations.
Mutation = permanent change in the DNA
Causes of mutations (mutagens) include: radiation, UV light, cigarette
smoke, pesticides, extreme heat, etc.
Examples of mutations: Point mutation – 1 base is substituted which may
change the amino acid; Frameshift mutation – a base is added or removed
which changes all amino acids added after that point; Monosomy – a type
of nondisjunction in which an entire chromosome is missing - there are
many others
8. Genetic Vocabulary – Answers to crossword puzzle listed below
Across
2. crossing over
5. genotype
6. gamete
9. dominant
10. phenotype
13. homozygous
15. meiosis
16. allele
Down
1. Mendel
3. recessive
4. heterozygous
7. gene
8. haploid
11. XY
12. mutation
14. diploid
15. male
9. How do breeders of dogs and horses use inbreeding to their advantage?
Give a specific example of how this could have a negative effect.
Advantage = good traits such as speed, agility, protectiveness, hunting
instincts, etc. stay in the bloodlines
Disadvantage = negative recessive traits such as hip dysplasia,
temperament problems, eye disorders, etc. may become
magnified (more prevalent)
10. Blood Type Genetics – see lab handouts & jeopardy review sheet
11. Genetic Diseases – see handouts & jeopardy review sheet
12. Pedigrees – see handouts & jeopardy review sheet
13. Explain why sex-linked diseases are more common in males than in
females.
Males only receive one X chromosome (from their mother – dad gives Y)
and therefore, they only have one chance to obtain a dominant normal
gene. Since females get 2 X chromosomes, they have an extra chance to
cover up a bad gene.
14. Genetic Problems – See handouts & sample problems below.
-----------------------------------------------------------------------------------------------------------SAMPLE GENETIC PROBLEMS
1. A couple brought their newborn son home from the hospital. They
suspect they were given the wrong baby. Upon checking the blood
types, it was found that the father had AB blood, and the mother was
Type O. The baby’s blood was type B. On the basis of this evidence,
could you say whether or not the couple was given the wrong baby?
Explain.
No, AB x OO could give a child with heterozygous Type B blood.
2. A woman sues a man for the support of her child, claiming that he is the
biological father. She has Type AB blood and her child has Type AB
blood. The man is Type O. Could he be the father of the child?
No, the mother could give A or B and the man in question could only give
O – So the couple in question could only produce heterozygous Type A or
heterozygous Type B blood.
What blood type or types might the father have been? Type A, B, or AB
3. The proportion of Rh+ genes in the population is 6/10. What is the
probability of a person being homozygous for the Rh+ condition?
6/10 x 6/10 = 36/100 = 36%
4. Long wings in fruit flies are due to a dominant gene (V) and vestigial
wings to its recessive allele (v). A vestigial winged male is crossed with
a heterozygous long-winged female. What are the genotypes of the
parents?
vv X Vv
What are the phenotypic ratios among the offspring?
50% long; 50% vestigial
5. Skip
6. A tomato plant bearing red fruit is crossed with one bearing yellow fruit.
252 seeds are produced from this cross. When they are planted, 121 of
the resulting plants develop red fruit and 131 develop yellow fruit. What
are the probable genotypes of the parents?
Rr x rr – This is the combination that gives a 50% chance of red and 50%
chance of yellow offspring
7. In morning glories, flower color is determined by red (R) and yellow (Y)
genes. The heterozygous condition will produce orange flowers
because neither gene is completely dominant. What proportion of the
offspring will have orange flowers if two orange-flowered plants are
crossed?
RY x RY = 50% chance of having RY (orange flowers) and 25% chance
for RR (red) and 25% chance for YY (yellow)
8. What blood type is the universal donor?
O-
9. What blood type is the universal receiver? AB+
10. A person with A+ blood needs a transfusion. What blood types can be
given safely? A+, A-, O+, or O11. Can O+ blood be given to an O- person?
No, an O- person would develop antibodies to the Rh protein.
12. Under what conditions are Rh incompatible pregnancies dangerous?
Why?
Only if there is an Rh- mom pregnant with an Rh+ baby because if/when
their blood mixes, the mother will develop Rh antibodies. This is usually
not a problem during the first pregnancy because the baby is born before
the mother has prepared the antibodies but for every Rh+ pregnancy after
that, the antibodies in the mothers blood could destroy the baby’s red
blood cells = hemolytic disease of the newborn.
13. If two animals are heterozygous for a certain trait, how many of their
offspring would be expected to show the dominant trait? 75%
14. If one animal is heterozygous for a certain trait and is crossed with one
showing the recessive trait, what proportion of their offspring will show
the recessive trait? 50%
15. What blood type clumps in all three anti-sera?
AB+
16. If you are testing someone’s blood and it clumps in anti-A and anti-Rh
serum, what is that person’s blood type? A+
17. In watermelons, red fruit (R) is dominant over yellow fruit (r), and
striped skin (S) is dominant over solid-colored skin (s). A red, solid
colored watermelon is crossed with a yellow, striped one. ½ of the
offspring from this cross are red and striped and the other ½ are yellow
and striped. What are the genotypes of the parents?
R_ss x rrS_
= Rrss x rrSS
Extra
In humans, aniridia (a type of blindness) is due to a dominant gene (A).
Migraines (a headache condition) are the result of a different dominant
gene (M). A man with aniridia whose mother is not blind, marries a woman
who suffers from migraines, but whose father did not. Each of them is
normal for the other trait. What % of their children will not suffer from
either of these conditions?
Aamm x aaMm = 25%
In humans, muscular dystrophy (m) is a sex-linked recessive trait, with the
normal condition being dominant (M). A normal woman and a normal man
have a male child with muscular dystrophy. What are the probable
genotypes of the parents?
XMXm x XMY
In humans, hemophilia (h) is a sex-linked recessive trait, with the normal
condition being dominant (H). What are the chances that a homozygous
normal woman and a hemophiliac male will have children with hemophilia?
XHXH x XhY = 0% - sons will be normal and daughters will be carriers