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Terms in this set (97)
human cells can be organized in to ______ cells and ____ (gametes)
somatic; germ cells
Each somatic cell has __ chromosomes in __ pairs, these are known as ____ cells
46; 23; diploid
gametes are _____ cells; they only have 1 member of each chromosome pair, for a total of __ chromosomes
What are produced during mitosis?
2 diploid somatic cells
What are produced during meiosis?
4 haploid germ cells
If a mutation occurs in a germ cell that is subsequently involved in fertilization, how will the somatic and germ cells of the new individual be affected?
the mutation will be reproduced in ALL of the somatic cells and approximately HALF of the germ cells of the new individual
a metacentric centromere is in the
a sub-metacentric centromere is
somewhat off center
an acrocentric centromere is locateed
very close to the end of short arm
During DNA replication, what is actually binding the old and new strands together?
What is transcription?
-RNA is synthesized from the DNA template
-RNA polymerase binds to promoter site
What does transcription result in?
What is translation
In translation, RNA directs the synthesis of a polypeptide interacting with tRNA
The composition of genes at a given locus is known as the
The outward appearance of an individual, which is the result of both the genotype and environment, is the
Check levels of ___ to determine whether or not a gene is active in a cell
DNA sequence can produce dramatically different phenotypes because of chemical modifications that alter the EXPRESSION of genes. These modifications are called
What is DNA methylation
-an important example of epigenetic
-the attachment of a methyl group to a cytosine base that is followed by a guanine base in the DNA sequence
-CpG islands --> gene becomes transcriptionally inactive
What are 3 other types of epigenetics
-acetylation of histones coiling the DNA
-mRNA regulation of translation
This is the process by which RNA directs the synthesis of polypeptides. This takes place in the ribosomes.
What happens in translation?
tRNA with an amino acid matches with a triad of nucleotides on mRNA to form a polypeptide chain
_____ are different forms genes located at the same locus on a chromosome
different alleles produce variation in ______ ________
A single allele for each locus is inherited from ____ _____
What is a mutation?
any inherited alteration of genetic material
One type of mutation is base pair substitution. What is this?
one base pair replaces another, many of these have no consequence
Another type is frameshift mutation, What is this?
The insertion or deletion of one or more base pairs. These mutations change the entire "reading frame". They greatly alter the amino acid sequence
What are mutagens
agents that increase the frequency of mutations
What is a karyotype?
an ordered display of chromosomes
What are the leading known cause of mental retardation and miscarriage?
What are euploid cells?
cells with a multiple of the normal number of chromosomes; haploid and diploid cells are this form
When is a cell considered to be a polyploid cell?
when a euploid cell has more than the diploid number
What is triploidy?
a zygote having three copies of each chromosome (69)
What is tetraploidy?
when a zygote has four copies of each chromosome (92)
are triploid/tetraploid fetuses able to survive?
What is aneuploidy?
a somatic cell that does not contain a multiple of 23 chromosomes
What is trisomy?
a somatic cell containing three copies of ONE chromosome
What is monosomy?
the presence of only one copy of any chromosome
Is it better to be trisomic or monosomic?
trisomic, it is better to have extra than less, monosomy is often lethal
What is disjunction?
the normal separation of chromosomes during cell division
Aneuploidy is usually the result of _______
What is nondisjunction?
An error in which homologous chromosomes or sister chromatids fail to separate normally during meiosis or mitosis
What is the best known example of aneuploidy?
What does trisomy 21 cause?
What increases the risk of giving birth to a baby with trisomy 21?
maternal age greater than 35
Describe children with downs
-low nasal bridge
-poor muscle tone
How common are babies with down syndrome?
1:800 live births
What is one of the most common trisomies?
What causes trisomy X?
a female with three X chromosomes, 47, XXX
Females with only one X chromosome (45,X) have what?
Who is the X chromosome USUALLY inherited from
What constitutes Klinefelter Syndrome?
male karyotype with more than one X
some individuals can be XXY and XXXY
How common is Klinefelter Syndrome?
1 in 500 males
What is translocation?
interchange of genetic material between nonhomologous chromosomes
When does reciprocal translocation occur?
when two chromosomes break and the segments are rejoined in an abnormal arrangement
robertsonian translocation only occurs with ________ chromosomes
What are the two mechanisms that cause trisomy 21 which then causes down syndrome?
-meiotic non-disjunction (95% of cases)
-robertsonian translocation (3-5% of cases)
What is a "fragile site"
areas on chromosomes that develop breaks or gaps when cells are cultured or stained
Fragile X syndrome is more common in females/males
males because they only have one X chromosome
Explain autosomal dominant inheritance
-one allele required for observable effect
-50% chance of recurrence in offspring
-males and females affected equally
-vertical transmission in pedigree
What is incomplete penetrance?
individuals who have the disease causing genotype may not exhibit the disease phenotype at all, even though the genotype and associated disease may be transmitted to the next generation
What are the two triple repeat mutations?
What repeats in fragile X syndrome?
CGG repeats FMR1 gene
Mutation > 200-4,000 repeats
What repeats in huntington disease?
CAG repeats in HD gene
Huntington disease is a disorder of what 3 things?
mood, mentation, and movement
What is the percentage of penetrance in huntington disease?
When is the onset of huntington disease?
middle adult years
When it comes to autosomal recessive inheritance, affected individuals have mutations in one/both of the alleles of the gene pair
When it comes to autosomal recessive inheritance, carriers of the mutation have a mutation in one/both of the alleles
True or False: The trait skips a generation in autosomal recessive inheritance
Ashkenazi Jews are often carriers of (2)
tay sachs & panel
African Americans are often carriers of (2)
sickle cell and thalassemia
Northern Europeans are often carriers of
Mediterraneans are often carriers of
What is Tay Sachs?
build up of GM2 ganglioside in neuronal lysosomes
How is Tay Sachs characterized?
-loss of developmental milestones
-seizures, blindness, deafness
-Death by 4 or 5 years
What mutation is involved in sickle cell disease
A to T point mutation in beta-globin gene
How often is it that a heterozygote gets sickle cell disease?
1 in 12 among african americans
How often is it that a homozygote gets sickle cell disease
homozygotes have increased frequency of infectious disease, chronic anemia, and painful sickle crises
What is deficient in phenylketonuria?
deficiency of phenylalanine hydroxlase due to mutations in PAH gene
Patients with phenylketonuria are unable to what?
convert phenylalanine to tyrosine, their blood phenylalanine is >20mg/dL
most sex-linked traits are located on the __ chromosome
Sex-linked disorders are usually expressed by males, why is this?
because females have another X chromosome to mask the abnormal gene
Most X-linked disorders are dominant/recessive
True or False: Fragile-X is recessive
false, Fragile-X is dominant
Who does Duchenne Muscular Dystrophy usually occur in?
What causes Duchenne Muscular Dystrophy?
X-linked; mutations in dystrophin gene (alterations/deletions of dystrophin protein, actin fibers in muscles tear apart)
Duchenne muscular dystrophy causes a _____ _____ in the dystrophin gene leaving a 'one-ended' protein whereas Becker's MD causes an __-____ deletion
What is a polygenic trait?
traits that result from several genes acting together
What is a multifactorial trait?
when environmental factors influence the expression of the trait.
What are quantitative traits?
traits that are measured on a continuous numeric scale
What is genomics?
the study of all of the genes in the human genome including their interactions with each other and the environment
What are some diseases that are related to both genetics and the environment
What would make you genetically susceptible to CAD
-2 or more close relatives with CAD
-female relatives with CAD
-diabetes, hypertension or prothrombin mutation in family
What is pharmacogenomics?
the study of how an individual's genetic make-up affects the body's response to drugs.
what is gene therapy?
the treatment of human genetic disease by adding exogenous wild-type genes to correct the defective function of mutation
What are the limitations to gene therapy
-viral vectors for gene insertion (not replacing defective gene but MASKING it)
-not possible for genetic defects that express in all somatic cells
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