Unit 4 Genetics – Review
Name______________________________Period___________
You should:

Know gametes are formed.

Know how a zygote is formed.

Know the purpose of meiosis.

Be able to identify the steps of meiosis.

Be able to describe what happens in each step of meiosis.

Be able to explain when and why crossing over occurs.

Be able to explain what independent assortment is and when it happens during meiosis.

Be able to explain some errors in meiosis.

Be able to describe Mendel’s research.

Be able to explain the difference between dominant and recessive traits.

Be able to carry out monohybrid and dihybrid crosses.

Be able to explain the following non-Mendelian processes: incomplete dominance,
codominance, epistasis, polygenic traits, sex-linked traits.

Be able to do Punnett squares showing incomplete dominance, codominance, & sex-linked
traits.

Be able to read a pedigree and determine whether it shows and autosomal or sex-linked
trait, and whether the trait is dominant or recessive.
1. Define the following:
a. Cell cycle – the growth and division life cycle of a cell
b. Interphase – 90% of the cell life cycle where cell is carrying out normal activities
c. Meiosis – the process that forms gametes
d. Gamete – haploid reproductive cells (e.g., sperm & eggs)
e. Fertilization – the joining of two gametes to form a diploid zygote
f.
Zygote – single-celled diploid cell formed during fertilization
g. Diploid – contains 2 copies of each chromosome
h. Haploid – contains ½ of the pairs chromosomes
i.
Prophase 1 – nucleus dissolves, chromatin condenses into chromosomes, spindle forms
and begins moving toward poles, synapsis occurs (tetrads form); crossing over may
occur; spindle fibers attach to centromeres on homologous chromosomes
j.
Metaphase 1 – homologous chromosomes line up in pairs on cell equator
k. Anaphase 1 – homologous chromosomes are separated and move toward poles
l.
Telophase 1 – nucleus begins to reform; spindle apparatus dissolves
m. Cytokinesis – cytoplasm divides; 2 haploid cells are formed
n. Prophase 2 – nucleus dissolves, chromatin condenses into chromosomes, spindle forms
and begins moving toward poles, spindle fibers attach to centromeres on homologous
chromosomes
o. Metaphase 2 – individual chromosomes line up on cell equator
p. Anaphase 2 – sister chromatids are pulled apart and move toward opposite poles
q. Telophase 2 -- nucleus begins to reform; chromosomes unwind into chromatin; spindle
apparatus dissolves
r.
Spindle apparatus – the protein structure that segregates chromosomes/chromatids
during mitosis & meiosis
s. Centromere – center protein structure on chromosomes
t.
Chromatids – the “legs” that contain copies of the same genes on a replicated
chromosome
u. Homologous chromosomes – pairs of chromosomes from each parent that carry the
same genes
v. Synapsis – pairing up of chromosomes that occurs during prophase 1
w. Tetrad – paired homologous chromosomes
x. Crossing over – when sections of homologous chromosomes are exchanged during
synapsis
y. Gene – a section of DNA that codes for a particular protein
z. Trait – the characteristic that a gene or set of genes code for
aa. Allele – a version of a particular gene; there can be many alleles for a particular gene
bb. Phenotype – the physical representation for a particular gene or set of genes; what an
organism looks like
cc. Genotype – the set of genes that an organism has
dd. Dominant/recessive – genes that “cover up” other genes (dominant) or gets “covered
up” (recessive)
ee. Monohybrid cross – a cross that looks at a single gene or trait
ff. Dihybrid cross – a cross that looks at 2 genes or traits
gg. Incomplete dominance – when two different alleles are “blended” in the phenotype;
e.g., red and white flowers make pink flowers
hh. Codominance – when two different alleles are expressed equally; e.g., red cow and
white cow makes a cow with red & white spots
ii. Epistasis – when the expression of a gene is dependent on other “modifier genes”; e.g.,
coat color in Labrador retrievers
jj. Polygeneic trait – a trait that is dependent on many different genes
kk. Sex-linked trait – a gene that is found on one of the sex chromosomes
ll. Pedigree – a diagram showing the inheritance of a particular trait
mm.
Autosomal – a non-sex chromosome
nn.
2. Draw the steps of Meiosis:
Interphase
3. At which state of meiosis does synapsis (the formation of tetrads) occur?
Prophase 1
4. At which stage of meiosis does crossing over occur?
Prophase 1
5. How does crossing over add to genetic variation?
Is allows for mixing of the genome of gametes, which contribute to zygotes that are genetically
different then their parents
6. At which stage of meiosis does independent assortment occur?
Meiosis 1
7. How does independent assortment occur?
When homologous chromosomes line up on the cell equator, they do so randomly. Each parent
chromosome has a 50/50 change of being on the left or right of the cell equator.
8. Purple flowers are dominant over white flowers. Carry out the following crosses and determine
the percentage of each phenotype.
a. A cross between 2 true breeding (homozygous) purple and white parents:
Phenotypes (%) 100% purple
b. A cross between 2 offspring of the cross in “a” above:
Phenotypes (%) 75% Purple, 25% white
9. A rare species of guinea pig comes in two colors, black (dominant) or white. This species also
exhibit another peculiar recessive trait: the homozygous-recessive individuals have a lust for
human blood (the vampire Guinea pig gene). Carry out a cross between two heterozygous black,
non-vampire Guinea pigs (BbVv).
Phenotypes (%) 56.25% Black Non-Vampire; 18.75% White Non-Vampire; 18.75% Black
Vampire; 6.25% White Vampire
How many vampire Guniea Pigs? 4 Blood-Sucking Guinea Pigs
10. Snapdragons exhibit incomplete dominance for flower color. Make a Punnett square showing a
cross between red and white parents, and then make another Punnett square crossing two
heterozygotes.
Phenotypes (%) 100 % pink
Phenotypes (%) 25% red; 50% Pink; 25%White
11. Hemophilia is a sex-linked trait that affects men more than women. Show a cross between a
normal father and a carrier mother.
Phenotypes (%) 50% Non-Hemophiliac Females; 25% NonHemophiliac Male; 25% Hemophiliac Male
How many male carriers are there? Zero
Can there ever be male carriers? Why? NO!!!! Males only get one
copy of an x-liked gene, so they cannot be carriers
(heterozygotes)
Examine the following pedigree:
12. Is this an autosomal or sex-linked trait?
sex-linked
13. Is this a dominant or recessive trait? recessive
14. How many children did Queen Victoria have? 9