Study Guide
Genetics
Exam 1
Chapter 1:
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Difference between Genetics and Biochemistry
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The use of model organisms in genetics
o Quick generation time
o Studied in the lab
o Mice, C. elegans, D. melanogaster, A. aegypti etc – good to know names
 Should be able to do genetics with them!!!
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Germ plasm theory
o Contemporary idea of how we have gametes
o Sexual reproduction
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Mendelian inheritance
o Know Mendel and his importance to the field of Genetics
o Rediscovery in the early 20th century
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The gene is the fundamental unit of heredity
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Genes come in multiple forms called alleles
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Genes and their alleles determine the phenotype
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Genes are encoded in DNA
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Genes are located on chromosomes
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Central Dogma: genetic information is transferred from DNA to RNA to Protein
Central Dogma of Molecular Biology
DNA  RNA  Protein
Genes are transcribed from DNA into RNA and translated into
Proteins.
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Mutations are permanent changes in genes – important in evolution
o UV Radiation
o Errors in Replication
Chapter 2:
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Differences between Prokaryotic and Eukaryotic cells
o Prokaryotic: Bacteria and Archaea
o Eukaryotic: Humans, Plants, Yeast (single celled organism) etc.
o Eukaryotic cells aren’t always multicellular (such as yeast)
o Know structural differences (ex. Prok. doesn’t have a nuclear membrane,
Eukaryotic cells do)
Prokaryotic cell division
o Used to reproduce (replicate)
Eukaryotic cell cycle – Know the phases.
Basic structure of a chromosome
Diploid vs haploid
o Diploid – two sets of homologous chromosomes (2n; zygote)
o Haploid – one set of chromosomes (1n; example: gametes)
Cell division in prokaryotes is called binary fission; (usually) only one circular
chromosome to replicate.
What is the function of cell division in prokaryotes? Reproduction.
Cell Cycle
o G1 phase - growth
o G0 phase (quiescence) – post mitotic cells.
 Can maintain in this phase for extended periods of time
o S Phase – replication of DNA
o G2 Phase – growing and preparation of mitosis
o M Phase - Mitosis
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Mitosis
o All the stages
 At what stage do DNA molecules double?
 In S phase DNA content doubles, but the actual molecules
do not separate until anaphase (which is then the doubling of
the DNA molecules because there are now two)
o What the purpose of Mitosis is? Cell Division
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From prophase to cytokinesis:
o Prophase - centrioles go to the poles of the cell, the nuclear envelope
disintegrates, chromosomes condense, mitotic spindles begin to form
o Prometaphase - spindles attach to the kinetochores (protein structure)
which formed on the centromere (DNA region)
o Metaphase – alignment of the chromosomes at the metaphase plate.
o Anaphase – Sister chromatids  >:< 
o Telophase – reformation of nuclear envelope, disintegration of
centrioles.
o Telophase ≠Cytokinesis
o Cytokinesis – division of cytoplasmic contents O|O
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Structure of Eukaryotic Chromosome
o Telomeres – the ends of linear DNA
o Centromere –where the kinetochore forms and the spindle fibers attach
o All chromosomes have chromatin (form of gene regulation)
 Euchromatin – genes more likely to be expressed
 Heterochromatin – genes less likely to be expressed
Meiosis
o Why? To increase genetic variety, to form a gamete. Organelles (Mitochondrial
DNA is almost all from your mother). Male mitochondria is used to power the
movement of the sperm it is not included in the embryo (this is just a fun fact)
o Prophase I – crossing over occurs; linking homologous chromosomes together.
Results in
 Synaptonemal Complex – structure that form during Crossing over
 Chiasmata – links homologous chromosomes together
o Metaphase I – homologous chromosomes align at metaphase plate.
o Anaphase I – What separates? Separation of homologous chromosomes; Still
diploid
 Independent assortment happens here.
o Telophase I – reformation nuclear envelope, arrival of Homologous
chromosomes at the poles. Cleavage occurs.
o Interkinesis – time between meiosis I and II. May or may not happen
o Prophase II – chromosomes condense, basically the same in mitosis.
o Metaphase II – Sister chromatids align horizontally in the center of the cell.
o Anaphase II – Sister chromatids (mixed up because of recombination) separate;
o Telophase II – Reformation of nuclear envelope and going to the pole
o Cells differentiate into gametes! Sperm and Egg
***Be able to visually recognize the different stages in meiosis and mitosis***
Differences between mitosis and meiosis
o Mitosis end result two identical cells. Same exact DNA content
o Meiosis you’re looking to make multiple Haploid cells that aren’t all the
same
o Meiosis is fundamental to genetics
Chapter 3:
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Mendel’s laws
o Principle of segregation – alleles of the same gene separate randomly
 Alleles for the same gene.
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o Principle of independent assortment – different genes are inherited
independently of each other.
 Distance from each other on the chromosome determines how they
are going to assort (used for gene mapping).
 If genes are far away from each other, for example on different
chromosome, they will assort independently
How Meiosis relates to Mendel’s laws
o Mendel’s Laws are made possible and function during meiosis
o Both of his laws occur during anaphase I of meiosis
Monohybrid crosses – need to know how to do this
o Understand ratios that would result from different crosses
The Punnett square
Probability in genetics
o The multiplication rule – keyword ‘and’ (and any words that denote ‘and’)
o The addition rule – keyword ‘or’ (and any words that denote ‘or’)
o When to use each rule
Dihybrid Crosses – need to know how to do this
o Understand the ratios that would result from different crosses
o More complicated version of monohybrid cross but the same rules apply
 Genotypic ratio: 1:2:2:4:1:1:2:2:1
 Phenotypic ratio: 9:3:3:1
o Different phenotypes:
 12 green
 4 yellow
 ratio of green to yellow (12:4)
 12 smooth
 4 wrinkled
 ratio of green to yellow (12:4)
Chi-Square Goodness of Fit test
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Dominant alleles vs Recessive alleles
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A
A
a
AA
Aa
a
Aa
aa
Genotypic ratio (AA: Aa: aa) - 1:2:1
Phenotypic ratio (Green: Yellow) - 3:1
A = Green peas – is dominant allele with not codominance or incomplete dominance
a = Yellow peas – recessive allele
Genotyptic ratio (AA: Aa: aa)
(Green: Yellow) – 4:0
AB
A
A
a
Aa
Aa
a
Aa
Aa
AaBb X AaBb
Ab
– 0:4:0 - Phenotypic ratio
aB
ab
AB
AABB
AABb
AaBB
AaBb
Ab
AABb
AAbb
AaBb
Aabb
aB
AaBB
AaBb
aaBB
aaBb
ab
AaBb
Aabb
aaBb
aabb
B = Smooth peas – is dominant allele with not codominance or incomplete dominance
b = wrinkled peas – recessive allele
Chapter 4:
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Sexual reproduction: from haploid to diploid and back again
o Understanding meiosis is key
o Meiosis makes sexual reproduction possible
Sex determination systems:
o XX-XO – amount of chromosomes determines sex
o XX-XY – type of chromosome determines sex
 Mammals
 The heterogametic sex is male.
o ZZ-ZW – type of chromosome determines sex
 Birds
 The heterogametic sex is female.
o Genic – touched upon in class. Understand the basic idea.
 No specific sex chromosome. Overall chromosomal set determines
the sex.
 Not completely understood.
o Environmental – understand the basic idea.
 Do not need to know how this happens.
Sex determination in Drosophila:
o X chromosome to Haploid set of Autosome ratio
 Ratio of sex chromosomes to autosomal chromosomes
Thomas Hunt Morgan and the X-linked white gene
o Father of fly genetics (Drosophila melanogaster)
o Research was useful in understanding how chromosomes work
o Led the way to the chromosomal theory of inheritance
o Figured out that there could be nondisjunction of chromosomes
Chromosomal theory of inheritance
Nondisjunction of chromosomes
Turner Syndrome
Klinefelter Syndrome
The role of the Y chromosome in mammals – sex determination
o If you have the Y chromosome, you’ll be a male, regardless of the number
of X’s you have.
 Testosterone is enough to make you male
 SRY Gene leads to the production of testosterone
 However, if you’re going to reproduce, you should have the correct
number of X’s
Barr Bodies and X inactivation
o All female mammals are essentially mosaic, because each of their cells
inactivates one of their X’s
 This happens at random
 It is normal and necessary (dosage compensation)
 Dosage compensation – Control dosage of genes on X
chromosome; too much or too little gene expression can lead to the
death of the organism
Chapter 5: More about Mendel
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Complete Dominance – dominant allele, you get the dominant phenotype
o Even if you’re heterozygous
Incomplete Dominance – Hybrid phenotype
Codominance – both alleles are expressed independently
Difference between penetrance and expressivity
o Penetrance – number of affected individuals
Number of people with phenotype
 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑝𝑒𝑜𝑝𝑙𝑒 𝑤𝑖𝑡ℎ 𝑡ℎ𝑒 𝑔𝑒𝑛𝑜𝑡𝑦𝑝𝑒
o Expressivity – degree to which the trait is expressed
 You either have an entire extra toe (high expressivity)
 Or a flap of skin but not yet an extra toe (low expressivity)
Interactions between multiple genes that determine a single phenotype
Recessive Epistasis – same concept as a regular recessive allele, but in this
case it is masking another gene
o Ex. Baldness
Dominant Epistasis – same concept as a regular recessive allele masking
o Ex. Different coat colors in dogs
The use of complementation testing
Sex-influenced characteristics – phenotype expressed influenced by the sex
Sex-limited characteristics – phenotype only present in a certain sex, regardless
of genotype
Cytoplasmic inheritance
Genetic maternal effect
Genomic imprinting
The concept of epigenetics
Histone modification and epigenetics
Anticipation and Huntington’s disease
Temperature-sensitive phenotypes
Continuous characteristics
Polygenic vs pleiotropic characteristics
o Polygenic: phenotype affected by many genes
o Pleiotropic: one gene can affect many characteristics
 Ex. hormones
Chapter 6:
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Symbols using in pedigrees
Pedigree analysis
Autosomal recessive pedigrees
Autosomal dominant pedigrees
X-linked pedigrees (dominant & recessive)
Y-linked pedigrees
Use of twin studies in genetics
Difference between monozygotic and dizygotic twins
Concordance
Genetic counseling
Genetic testing of the fetus
Amniocentesis vs cell-free DNA testing