Week 3: Genetics Flashcards
What does DNA contain?
the basic genetic information in a cell
Define nucleotide
molecules that contain a deoxyribose sugar, phosphate and a base
What are the bases? How do they pair in complementary base pairing (include # of hydrogen bonds)?
Thymine, Cytosine, adenine, guanine
Adenine + Thymine: 2 hydrogen bonds
Guanine + Cytosine: 3 hydrogen bonds
How is single-stranded DNA formed?
formed between the sugars and phosphates of the nucleotides
What is the sugar phosphate backbone?
structural framework of nucleic acids
- How is double-stranded DNA formed?
2. What is the ultimate structure double-stranded DNA forms?
- formed as hydrogen bonds form between bases between two strands of DNA
- double-helix
How are DNA strands oriented?
5’ to 3’ orientation, strands are arranged in opposite directions
How is DNA organized in the nucleus and when is this structure visible in the cell?
Organized in chromosomes, visible during the cell cycle
How are histones used?
DNA is wrapped around histones to consolidate and organize the genetic information
How is chromatin formed?
Chromatin formed when DNA associates with histones
What is the genome?
the haploid set of chromosomes in a gamete or microorganism, or in each cell of a multicellular organism
What is a karyotype?
evaluation of the number and content of chromosomes
Where (1) and how (2) does DNA replication occur (3 main steps)?
- the nucleus
- DNA polymerase makes a copy of the genetic information in each chromosome
- DNA replication begins at specific sites in the DNA and proceeds in a 5’ to 3’ direction
- Molecule is unwound to create a replication fork where complementary base pairing is done by polymerase – base paring ensures DNA information is copied faithfully
Define mitosis & cytokinesis
Mitosis: division of the nucleus
Cytokinesis: division of the cell
Explain the basic functions of DNA with regard to replication and translation
Replication: performed to maintain the genetic information in a cell
Translation: process by which RNA translates DNA into a form that can be used for protein synthesis
Define semi-conservative replication (1) and explain the value of this process to health and disease (2)
- DNA is semi-conservative: each resulting DNA molecule contains one original strand and one newly synthesized strand
- Ensures mistakes or mutations can be fixed as the strand is marked with methyl groups that can be identified by DNA repair enzymes
How does semi-conservative replication relate to DNA repair?
Using the methyl markings, DNA repair enzymes detect any mismatches between bases and fix the mistake in the new strand by using the original information as a template
Describe what is meant by the term “genetic code” (1) and generally how a genetic mutation can alter protein structure and function (2)?
- Genetic code = groups of 3 nucleotides that specify an amino acid to be created
- Mutations can result in an aberrant protein sequence which can alter protein structure and function
Define mutation, silent mutation, missense mutation, nonsense mutation.
mutation: errors in the DNA sequence
silent mutation: mutations that do not change the amino acid
missense mutation: mutation that alters the amino acid but may or may not alter protein structure and function
nonsense mutation: mutation that introduces a stop to protein synthesis
How is genetic information from DNA transferred through complementary base pairing?
Complementary base pairing between the mRNA codon and tRNA anticodon specify a strict association between the genetic information and amino acid sequence
Define and distinguish between somatic and germline mutations.
Mutations in germline cells (gametes) can be inherited whereas mutations in somatic cells are not inherited
How is human genetics used for disease diagnosis?
Genetic changes can be markers of disease – predict disease risk or likelihood of response to certain treatments
Define mitosis and meiosis. What cells do they occur in?
mitosis: division of the nucleus in somatic cells
meiosis: division of the nucleus in gametes
What is the name of the type of division associated with meiosis?
reduction division
How many chromosomes does a diploid cell have? A haploid cell? Which processes (mitosis or meiosis) creates a diploid cell or a haploid cell?
Diploid - 46 chromosomes, maintained by mitosis
Haploid - 23 chromosomes, maintained by meiosis
Define sex chromosome
chromosomes that determine sex of the human – XX/XY
Define autosome
all chromosomes except sex chromosomes
Define homologues
sequences on chromosome pairs are similar, but not identical as one of each allele is inherited from each parent
Define sister chromatids
copies of chromosomes made during cell replication
Phases of mitosis (4)
- Prophase: Nuclear membrane dissolves and two copies of each chromosome (sister chromatids) attach at the centromere
- Metaphase: Chromosomes line up on the equatorial plane of the cell
- Anaphase: Sister chromatids separate and chromosomes are pulled apart
- Telophase: Nuclear membrane forms around the two sets of chromosomes
Phases of meiosis (2)
Meiosis I: reduction division stage that results in the formation of two haploid cells per diploid cell, homologous chromosomes separate but sister chromatids remain together. Results in two individual cells with 23 chromosomes.
Meiosis II: further separate each of the sister chromatids to generate four cells – each contains a copy of 23 homologous chromosomes
What happens more specifically during meiosis I? (5)
- Homologous chromosomes line up in the middle of the cell
- Separate to opposite sides of the cell
- Random shuffling of maternal and paternal chromosomes occurs
- Crossing over or exchange between homologous segments of the sister chromatids that make up each homologous chromosome occurs
- Results in genetic recombination, which ensures that genetic information in the offspring is unique
How do two haploid cells create one diploid cell during fertilization?
Gametes fuse together during fertilization to form diploid zygote
Define genotype and phenotype
Genotype: genetic makeup of an organism
Phenotype: observable characteristics of an organism produced by the interaction between genotype and environment
Define allele, dominant allele, recessive allele, heterozygous and homozygous
Allele: alternatives for each trait
Dominant allele: variation that will produce a phenotype
Recessive allele: an allele that is masked phenotypically by a dominant allele
Homozygous: both gene copies are the same at a specific allele
Heterozygous: gene copies are different at a specific allele
What would be the likelihood of parents who are heterozygous for an autosomal recessive trait (like cystic fibrosis) to have an affected child? A carrier child? A wild-type child?
Affected child: 25%
Carrier child: 50%
Wild-type child: 25%
What tool can be used to determine likelihood of allele inheritance in offspring?
Punnett square
What would be the likelihood of parents who are heterozygous for an autosomal dominant trait (like Huntington disease) to have an affected child? A carrier child? A wild-type child?
Affected child: 75%
Carrier child: 0%
Wild-type child: 25%
Define Mendel’s first law of the principle of segregation
two members of a gene pair segregate from each other in the formation of the gametes
half of the gametes carries one allele; the other half carries the other allele
Define Mendel’s second law of the principle of independent assortment
genes for different traits assort independently of one another in gamete production
Genes controlling different individual loci are not transmitted together to the progeny but rather are inherited independently of one another
Define single-gene disorders
caused by mutations in individual genes, may be present on one or both alleles
Define chromosomal disorders
caused by an excess or deficiency of genes contained within a whole chromosome or chromosomal segment
Define multifactorial disorders
caused by a combination of variations in a number of genes that together produce or predispose an individual to a serious defect, often in concert with environmental factors
Most genetic disorders associated with human disease are considered ______, ______ or ______.
- complex
- multifactorial
- polygenic
Define mitochondrial disorders (1)
What is the inheritance pattern? (2)
What are the s/sx of mitochondrial disorders? (3)
- alterations in the mitochondrial genome
- inherited exclusively from mother to child
- can affect single organ or multiple organs depending on severity of the mutation – sx include poor growth, loss of muscle coordination, muscle weakness
Define genomic imprinting
phenotype depends on whether mutation was obtained from the mother or father
Define triple repeat patterns
mutations in genes that involve the expansion of three nucleotides, change is atypical if it is on the X chromosome
What is the inheritance pattern for an autosomal recessive trait? (1)
Examples of diseases (2)
Parents must be heterozygous or homozygous recessive
Examples: Cystic fibrosis, sickle cell anemia
What is the inheritance pattern for an autosomal dominant trait? (1)
Examples of diseases (2)
Parents can be heterozygous or homozygous dominant
Examples: Achondroplasia (dwarfism), Marfan syndrome (connective tissue defects)
What is the inheritance pattern for an X-linked recessive trait? (1)
Examples of diseases (2)
Single-locus genetic disorder
Examples: Duchenne muscular dystrophy, hemophilia A
Define polyploidy, aneuploidy.
Give an example of a disease associated with aneuploid
Polyploidy: complete sets of extra chromosomes
Aneuploid: chromosome number that is not 23
- Example: Down syndrome - Trisomy 21
What kind of chromosomal abnormality can result from nondisjunction?
Aneuploid
Define chromosome inversion, deletion and translocation.
What is an example of translocation?
Chromosomal inversion: segment of a chromosome is reversed
Chromosomal deletion: segment of a chromosome is removed
Chromosomal translocation: segment of a chromosome breaks off and switches with a segment from another
- Example: Philadelphia chromosome which can give rise to chronic myeloid leukemia
Turner syndrome:
What is the chromosomal change?
What are the major s/sx?
absence of all or part of the X chromosome
Short stature and lack ovaries – lack of development of secondary sexual characteristics
Klinefelter syndrome:
What is the chromosomal change?
What are the major s/sx?
one or more additional X chromosomes with a normal male composition (XY)
testicular dysgenesis, enlarged breasts, small testes, inability to produce sperm, typically see changes occur during puberty
Marfan syndrome:
What is the patho?
Major s/sx?
Patho: mutation of FBN1 gene which encodes the CT protein fibrillin-1, a component of the ECM including formation and maintenance of elastic fibers. 75% of cases are inherited autosomal dominant, 25% arise from new mutation
S/sx: unusually tall with long limbs and digits, cardiovascular changes can be life threatening
Hemophilia A:
What is the patho?
Major s/sx?
Treatment?
Patho: inherited X-linked recessive trait with the defective gene located on the X chromosome
S/sx: bleeding and easy bruising
Tx: replace factor VIII, desmopressin
Down Syndrome:
What is the patho?
Major s/sx?
Patho: often due to nondisjunction and is associated with advanced maternal age
S/Sx: slower physical development, developmental delays
DNA damage can also occur due to ______or exposure to ______and ______. _______ can often be repaired by ______.
- environmental exposures
- chemicals
- radiation
- mutations
- DNA repair mechanisms
