Download What you absolutely need to know for the Regents Exam

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Genetics
I.
Chromosomes:
A) Humans have 46 chromosomes, or 23 homologous pairs.
1. Homologous: chromosomes with the same size, shape and genes.
B) Chromosome pairs carry genes for the same traits. We all have 2 alleles for each gene.
1. Most organisms have two genes for each trait - 1 from each parent, 1 on each member
of the homologous pair.
C) Sex chromosomes – In humans, females are XX and males are XY
1. The Y chromosome is much smaller than the X, so it is missing many genes. This means
many genes on the X chromosome do not have a “partner” so:
 If a male has a recessive trait on the X chromosome, the Y chromosome will not be
able to “hide” it with a dominant gene, so...
 This makes males more likely to have some traits (like color blindness). These are
called sex linked traits.
D) Autosomes the 22 chromosome pairs that are not sex chromosomes.
E) Common mistake: “Humans have 23 chromosomes (or 46 pairs of chromosomes, or some
other incorrect number).” Wrong! These numbers are often confused. You must
memorize them correctly.
F) We have 23 pairs, 46 total!
II. Chromosomes and Genes
A) Each chromosome has hundreds or thousands of genes.
B) Each gene codes for a particular protein.
1. Common mistake: “Genes/DNA are made from protein.”
Genes carry the instructions to make protein. The genes themselves are made from
nucleic acids.
2. While genes determine our traits, the environment can affect expression of genes. (
Identical twins with different freckle patterns.)
III. DNA
A) DNA is the chemical that makes up your genes and chromosomes.
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B)
C)
D)
E)
1. Analogy: If your genes and chromosomes are the “instruction manual” for your body,
DNA would be the paper it is printed on.
The shape of a DNA molecule is a double helix, which resembles a twisted ladder.
The shape of DNA allows it to replicate (copy) itself almost perfectly.
DNA is made up of many nucleotides. Each nucleotide contains a phosphate, a
deoxyribose sugar, and a nitrogen base.
DNA is made of 4 nitrogen bases: A, T, C and G
1. Base pairs: A - T and C- G
 in RNA the pairs are A - U and C- G
DNA – Always Tired, Constantly Grumpy
RNA- Always Ugly, Constantly Grumpy
IV. Protein Synthesis: This is how genes control your body:
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A) A codon is a sequence of three bases in DNA.
 Each codon represents a specific amino acid.
 Ribosomes assemble amino acids in the same order that they are listed in the DNA
codons.
 The amino acids will make a protein.
 The order of the amino acids (determined by the DNA sequence) determines the
shape of the protein.
 The shape of a protein determines its function.
 Therefore: The sequence of bases in DNA will determine the functions of all the
proteins in the body.
 The proteins build and run the body.
B) RNA carries the genetic code to ribosomes.
1. m RNA gets copied in the nucleus.
2. m RNA moves from the nucleus into the cytolplasm, and then to the ribosome.
3. t RNA transfers the amino acid to the m RNA where protein synthesis occurs (in the
ribosome)
The order of DNA bases in your genes determines the order of amino acids in your proteins, which determines the
proteins’ shape, which determines the proteins’ function, and the proteins build and run your body.
Therefore: How your body functions depends on the order of the bases in your genes!
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V. Mutations: Any change in the genetic material of an organism.
A) Can only be passed on if they occur in reproductive cells (sperm or egg).
B) Common mutagenic agents include radiation, chemicals and viruses.
1. Mutagenic agent: Any environmental factor that causes a mutation.
C) Gene mutations may cause a change in a gene which can change the shape of a protein.
This will have an effect on the way the protein works (if it still works at all).
1. Gene mutations are caused when DNA bases are in some way changed.
D) Chromosome mutations are usually caused when a person inherits too many or too few
chromosomes.
1. Chromosome mutations affect many genes at once. Most are lethal
2. Down’s Syndrome: Non lethal mutation, caused by inheritance of an extra copy of
chromosome 21. (Note – only chromosome 21 can cause Down Syndrome).
VI. Genetic technology:
A) Selective breeding: Breeding organisms to produce offspring with desired traits. (disease
resistance, larger fruit, more meat or milk, specific colors)
1. Inbreeding – Breeds organisms with the same traits ( ex: beagle x beagle)
2. Outbreeding – Breeds organisms with different traits ( ex: horse x donkey = mule)
3. Cannot be used to breed completely unrelated species.
B) Genetic engineering: Inserts a gene from one organism into the DNA of a different
organism.
1. Restriction enzymes are used to cut the DNA segments.
2. Organism that receives the new gene will begin to make the protein coded for by that
gene.
3. The new protein/enzyme/hormone will be exactly the same as the one produced by
the original organism.
4. Bacteria are often used because they are cheap, simple, and reproduce quickly.
5. The example of gene splicing you MUST know:
 Bacteria have been engineered to make insulin for diabetics.
 Bacteria have been engineered to make human growth hormone.
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
In both cases the engineered hormones are safe to use because they are identical
to normal human hormones.
C) New technologies (karyotyping, DNA fingerprinting) are making it easier to diagnose and
treat genetic disease, though we cannot yet cure them.
1. Karyotype: A photograph of an organism’s chromosomes.
 Can determine if a person has a chromosome disorder such as Down Syndrome.
2. DNA finerprinting, or gel electrophoresis, creates banded patterns based on a person’s
DNA base sequence.
 Each fingerprint is unique, so it can be used to identify people.
 Fingerprints of relatives are similar to each other, so can be used to determine
genetic relationships between two people, or even two groups of organisms.
D) Genetic research has posed many ethical problems (ie right and wrong) that science alone
cannot answer.
1. Ethics: Study of what is morally right or wrong.
A karyotype shows all 23 pairs of human chromosomes. Note the last pair
identifies this as a male.
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Genetics Unit Review
These are the vocabulary words that you need to know for the genetics unit. You need to study
them and quiz yourself using the castlelearning flashcard assignment that is posted.
acquired characteristic
A characteristic developed during an
individuals lifetime. These are not
passed on to succeeding generations.
addition
The adding of DNA nucleotides to a
chromosome.
allele
A procedure that removes amniotic
fluid containing fetal cells for analysis
to determine the presence of genetic
defects.
artificial selection
A breeding practice by which
organisms are purposely mated to
produce offspring with specific
desirable traits.
One of the two or more possible genes autosomes
for a trait. They are always at the same
Chromosomes that are not sex
position (loci) on homologous
chromosomes.
chromosomes.
amino acid
The basic building block of proteins.
They contain an amine group and a
carboxyl group.
centromere
amniocentesis
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The region where the chromatids of a Inheritance in which both of the
double-stranded chromosome are held alleles are expressed. The hybrid is a
together.
blend of both.
chromatid
Codon
One of the two strands of a replicated
chromosome.
A sequence of three nitrogenous
bases in the messenger RNA
sequence that are specific for one
amino acid.
chromosomal mutation
Any change in the number or structure
common ancestors
of the chromosomes.
Organisms from which closely related
chromosome
organisms have evolved.
A structure found in the nucleus that is
complementary
made of DNA and protein. It contains
Being the complement of the other,
the hereditary information.
the result of specific pairing.
cloning
The production of genetically identical
organisms.
crossing-over
codominance
The equal exchange of genetic
material by homologous
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chromosomes during the synapsis of
meiosis.
deletion
environmentally influenced traits
Traits that are not expressed unless
the environmental conditions are
correct.
A chromosomal abnormality in which a
portion of the chromosome has been gametes
lost.
Monoploid sex cells produced in
gonads by meiotic cell division.
diploid
Sperm and egg.
The 2n number. The normal number of
chromosomes for a particular species. gel electrophoresis
The human diploid number is 46
A method used to separate DNA
DNA (deoxyribonucleic acid)
fragments on the basis of their size.
The nucleic acid that stores the
hereditary information, that is, the
genetic material.
gene
A section of DNA on a chromosome
that codes for a particular trait.
gene mutation
Any change in the sequence of bases
in DNA.
double helix
gene-chromosome theory
The shape of the DNA molecule, the
spiral shape formed by the parallel
strands.
The theory that states that genes are
arranged in a linear sequence in
definite locations (loci) on
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chromosomes. Genes for the same
trait are located at the same loci on
homologous chromosomes.
The study of DNA and how the
hereditary information is transmitted
from one generation to the next.
genetic
genotype
Pertaining to DNA, the hereditary
material.
The genetic makeup of an individual;
ex. hybrid tall.
genetic engineering
heredity
The process which transfers genes to
another organisms DNA resulting in
recombinant DNA.
The sum total of genetically inherited
characteristics which are passed from
parents to offspring.
heterozygous
genetic screening
The analysis of body fluids such as
blood or urine to detect the presence
of a genetic disease.
genetically
Having to do with the chromosomes
and how traits are inherited.
genetics
Hybrid. The pair of genes for a trait
are not alike; for example Tt.
homologous chromosomes
A pair of chromosomes of the same
size and shape that carry genes for
the same trait.
homozygous
Pure. The pair of genes are the same;
for example TT.
identical twins
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Two individuals formed from a single
fertilized egg. They have the same
genetic makeup.
independent assortment
Different traits that are carried on
different chromosomes are inherited
independently from one another.
inherited
Coming from ancestors.
insertion
at enlarged images of them arranged
on a grid according to size.
male
An organism that has XY sex
chromosomes or produces sperm
cells.
Mendel
A mathematician and monk who
developed the hereditary principles
of dominance, segregation, and
independent assortment.
A mutation that is caused by the
placement of a DNA nucleotide into an
existing gene.
messenger RNA
An RNA molecule with a specific code
for a polypeptide. This code is
A hormone produced by the Islands of
determined by the sequence of bases
Langerhans in the pancreas. It lowers
of the DNA molecule in the nucleus.
blood sugar levels.
mutagenic agents
karyotyping
Any substance that can change the
The process by which an individual’s
structure of the DNA, causing a
chromosomes are examined by looking
mutation.
Insulin
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mutation
recessive traits
A change in the genetic material.
Traits that do not appear if the
dominant gene is present.
nitrogenous bases
Adenine, thymine, uracil, cytosine and
guanine.
recombinant DNA
nucleotide
The DNA of an organism has been
changed usually by the addition of a
gene.
The basic unit of nucleic acids. It
consists of a 5-carbon sugar bonded to
a phosphate and a nitrogenous base. recombination
The formation of new combinations
of genes. This can be the result of
The appearance of an organism; how it
crossing over during meiosis.
looks.
replication
protein
The copying of the exact base
An organic compound made of amino
sequence of the DNA.
acids.
ribosome
protein synthesis
The organelle that is the site of
The making of a protein from amino
protein synthesis in the cell.
acids by matching the anticodon of the
transfer RNA to the codon of the
messenger RNA.
phenotype
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A group of organisms that can
interbreed and produce fertile
offspring.
sperm
selective breeding
The manipulation of reproductive
processes to produce offspring with
specialized traits; choosing mates or
crossing traits to produce offspring
that have desired traits. Methods of
selective breeding include inbreeding,
artificial selection, hydridization, and
vegetative propagation. For example,
dog breeds such as the Dalmatian are
the result of selective breeding.
sex chromosomes
The pair of genes that determines the
sex of the individual, with XX being
female and XY being male.
The male monoploid (n) gamete, sex
cell.
Tay-Sachs
A fatal recessive genetic disease
which is characterized by the
deterioration of nerve tissue due to
the accumulation of fatty material. It
is most frequent in Jews of Central
European descent.
Template
A guide for the assembly of products
to assure their uniformity.
sex determination
In humans, the male determines the
sex. XX is female XY is male.
species
Tetrad
The structure formed when the
homologous double stranded
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chromosomes (4 chromatids) come
together during the synapsis of
meiosis.
Trait
A characteristic of an organism.
transfer RNA
vegetative propagation
A form of asexual plant reproduction
that produces identical new plants as
undifferentiated tissue divides by
mitosis. The resulting cells specialize
providing the needed tissues.
The type of nucleic acid that contains
an anticodon three nucleotides long. It
carries a specific amino acid to the
Watson and Crick
mRNA at the ribosome during protein
The scientists who discovered the
synthesis.
structure of the DNA molecule.
tumor
An abnormal mass of cells.
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