GENETIC TEST REVIEW PACKET
1. What is a Punnet square and what is it used for? A Punnet square is a tool used by
geneticist to predict offspring from a particular cross.
2. Make a Punnet square to show a cross between a homozygous dominant trait and a
heterozygous trait.
H
H
H HH
HH
h Hh
Hh
3. What are the possible phenotypes of the offspring in this cross? All will have the
dominant phenotype.
4. What are the possible genotypes of the offspring in this cross? The possible
genotypes from this cross will be either HH, or Hh.
5. What if you cross two heterozygous organisms. What would the possible
phenotypes and genotypes be?
H
h
H
HH
Hh
h
Hh
hh
Phenotypes: 75% chance dominant trait, 25% recessive trait
Genotypes: 25% chance dominant homozygous, 50% chance heterozygous, 25% chance
homozygous recessive.
6. Draw a Punnett square to show a cross between a white rat (WW) and a black rat
(ww). What is the probability that the offspring will have black fur?
W
W
w
Ww
Ww
w
Ww
Ww
There is a 0% probability that there will be a rat with black fur, 100% of them will have
white fur.
Define the following terms:
7. Allele- one of a pair of genes that determine a specific trait.
8. Phenotype- the physical appearance of an organism.
9. Genotype- the set of genes carried by an organism (the alleles).
10.Heterozygous- has one of each allele, one dominant, one recessive.
11.Homozygous- has two of the same allele; either 2 dominant alleles or 2 recessive
alleles.
12.Genes- segment of DNA found on the chromosome, that determines the
inheritance of a particular trait.
13.Mutation- a random change in a gene.
14.Sex –linked traits- carried on or transmitted by a sex chromosome. Color blindness
is an example of a sex-linked trait.
15.Heredity- passing of traits from one generation to another (from parent to
offspring).
16.Dominant- in a pair of alleles, the one that, if present, determines the trait of the
offspring.
17.Recessive – in a pair of alleles, the one that is masked if a dominant allele is
present.
18.Hybrid – an organism that carries both a dominant and a recessive allele for the
same trait (for example Tt).
19.Purebred – an organism that carries two of the same alleles for a trait, either two
dominant alleles, or two recessive alleles.
20.Probability – the likelihood that a particular event will occur.
21.CoDominance – a condition in which neither of 2 alleles of a gene is dominant nor
recessive. If the gene is present it will show (like blood types).
22. Gametes – sex cells; sperm and eggs.
23.Genetic Code – the sequence of nucleotides in DNA and RNA that determines the
structure of amino acids in a protein.
24.Trait – a characteristic or condition that is determined by one’s genes.
25.Who was Gregor Mendel and what did he study? Gregor Mendel is known as the
father of genetics and he studied pea plants.
26.What does DNA stand for?Deoxyribonucleic Acid
27.What cells contain DNA?All cells with a nucleus contain DNA.
28.Who shares the same DNA?Only identical twins and clones share the same DNA.
29.How many total chromosomes are in a human cell? 46 How many pairs of
chromosomes are in a human cell? 23
30.What are the amino acids in DNA?Adenine, Thymine, Cytosine, Guanine.
31.Which amino acids pair with each other? Adenine with Thymine; Cytosine with
Guanine.
32.How is cancer related to cell growth? Cancer is uncontrolled cell growth.
33. What does the notation HH mean to geneticists? This notation means homozygous
dominant or a purebred for the dominant trait.