Exam One Flashcards
Human Genome
23 Chromosome pairs
- 22 pairs of autosomes
- 1 pair of sex chromosomes.
- Humans are Diploid 2N
Chromosome Structure
- p arm: short arm
- q arm: long arm
- centromere and telemores
- microtubules are important for positioning
Centromere
- metacentric= center
- submetacentric= slightly off to one side
- acrocentric=
- telocentric= at the tip
- MSAT
Eukaryotic Cells
- Histone: proteins that associate with one another. The DNA wraps around the histone.
- Nucleosome: DNA wrapped around histone protein
- Chromatin: DNA complexed with histone proteins .
The Central Dogma
DNA–>[transcription]–> RNA–>[translation]–>protein
Genes
inherited DNA sequences that control biochemical and physiological traits of an organism by directing synthesis of proteins.
Genome
the ENTIRE COLLECTION of all genetic material (both genes and nonprotein coding DNA) in the cells of an organism: entire genetic blueprint.
Cell Division Goals
Mitosis: make two GENETICALLY IDENTICAL
Meiosis: make HAPLOID gametes. Germ cells specialized for reproduction. Have only one copy of the gene.
Cell Cycle
Interphase (cell growth) -G1: committed to dividing -S :DNA replication -G2: cell prepares for mitosis Mitosis -Prophase -Metaphase -Anaphase -Telophase Cytokinesis *Checkpoints are important to make sure things are happening properly.
Interphase
- nuclear envelope/ membrane is present
- relaxed chromatin
- no dyads
Prophase
- chromosome condense
- sister chromatids
- spindle fiber (microtubule) formation
- nuclear membrane disintegrates
- spindle fibers attach
- become visible as dyads
Metaphase
- chromosome align on metaphase plate (equatorial plate)
- aligned at the center so that the sister chromatids will go to different poles
Anaphase
- sister chromatids separate and move toward opposite poles.
- when they separate you then can refer to them as chromosomes.
Telophase
- chromosomes arrive at poles
- nuclear membrane reforms
- chromatin begins to relax
- cleavage furrow forms
Mitosis (Function)
- used for division of somatic cells
- development and replacement
Cell Division and Cell Death
balance between:
- mitosis(cell division): produces two somatic cells from one
- apoptosis(PCD): precise genetically-programmed sequence…eliminating different cells
Programmed Cell Death (proper development)
- formation of fetal fingers and toes
- menstruation
- synapse formation in the brain
- sunburn
Programmed Cell Death (organism integrity)
- Cells infected with viruses (done by themselves or immune system)
- Cells with DNA damage (problems with genome)
- Cancer cells (radiation & chemicals induce apoptosis in some type of cancer cells)
- Cells of the immune system: defects in apoptosis are associated with autoimmune diseases.
Apoptosis
highly choreographed processes
Somatic cells (body)
two copies of the genome and perform body functions
DIPLOID 2N
Germ cells (sperm & egg)
one copy of the genome and are specialized for reproduction
HAPLOID N
Zygote
cell differentiates into a female or male
Stem Cells
- present throughout life and provide for growth and repair
- self renewal
- ability to differentiate into multiple cell types
Stem Cells (in Healthcare)
-discovery and development of drugs
-observing the earliest sign of disease
-treatment of disease via implants and transplants
ex/
Chord Blood Banking
Bone Marrow Transplants
Sources of human stem cells
- embryonic stem cells
- induced pluripotent stem (tips) cells
- adult stem cells
Genetic Significance of Meiosis
- conservation of chromosome number
- variability in gametes due to independent alignments
- new combinations of hereditary traits due to recombination
Meiosis 1
- 2 standard divisions
- PAIRING OF HOMOLOGOUS CHROMOSOMES
- sister chromatids remain attached all thru MI
Meiosis 1 Prophase
- Chromosomes condense
- Dyads visible
- CROSSING OVER between homologous chromosome
Crossing Over
-produces genetic variation
Meiosis 1 Metaphase 1
- Homologous pairs line along the metaphase plate
- maternally derived faces one pole, paternally derived faces another
Random Distribution/ Independent Alignment
-produces genetic variation
Meiosis 1 Anaphase 1
- homologous pairs separate and move toward opposite poles
- sister chromatids remain attached to the centromere.
Meiosis 1 Telophase 1
- chromosomes are at opposite poles
- cleavage furrow
- NO NEW DNA SYNTHESIS before meiosis II
Meiosis II
products are not genetically identical in the cell due to recombination and random assignment
Meiosis II Prophase II
sister chromatids are attached at centromeres
Meiosis II Metaphase II
chromosomes (attached sister chromatids) line up INDIVIDUALLY along the metaphase plate
Meiosis II Anaphase II
sister chromatids separate for the first & only time in meiosis
Meiosis II Telophase II
chromosomes at opposite poles
Spermatogenesis
continual process in males; each meiosis produces 4 mature gametes (sperm cells)
Oogenesis
-discontinuous
-arrested in prophase I until puberty
-meiosis I after ovulation
meiosis II after fertilization
- one mature gamete (egg)
-omy
individual chromosomes
-ploid
one or more complete sets of chromosomes
Chromosomal Rearrangements
- Duplications
- Deletions
- Inversions
- Translocations
aneuploidy
individual chromosomes
polyploidy
entire sets of chromosomes
unbalanced gened dosage
leads to altered characteristics
can be detrimental if it is a gene that is important in the early developmental stage
chromosome inversion
- order of alleles change
- may lead to an alteration in gene function and regulation
translocation
-movement of genetic material between nonhomologous chromosomes
Types:
1. Reciprocal 2. Nonreciprocal 3. Robertsonian
Non-disjunction
the failure of homologous chromosomes to properly segregate.
*monosomy & trisomy almost always lethal
Non-disjunction of Autosomes
Trisomy 13: Patau Syndrome
Trisomy 18: Edward Syndrome
Trisomy 21: Down’s Syndrome
Non-disjunction of sex chromosomes
imbalance in sex chromosomes is less damaging than imbalance in autosome
Klinefelter Syndrome
XXY
2n+1
Turner’s Syndrome
XO
2n-1
Random X-inactivation
only one X is in an active state; all others are inactive & condensed into Barr Bodies
Nondisjunction of Sex Chromosomes
- easy assay is Barr body
- # Barr Bodies= #supernumerary x chromosomes
Nondisjunction of Meiosis I
All 4 gametes are abnormal
- [2]Trisomic (2n+1)
- [2]Monsomic (2n-1)
Nondisjunction of Meiosis II
2 normal gametes, 2 abnormal gametes
- [2] Normal diploid (2n)
- [1] Trisomic (2n+1)
- [1] Monosomic (2n-1)
Uniparental Disomy
both homologs from one parent; attempt to correct aneuploidy
Problem of having both homologs from one parent
- HOMOZYGOSITY for any detrimental alleles
- IMPRINTING
- small number of humans genes expression occurs by parental origin
- only one parental allele (maternal or paternal) is expressed in some cells
- the other allele is repressed
Mendel’s Principle
- Principle of Segregation
- Principle of Independent Assortment
Principle of Segregation
each individual possesses 2 alleles that segregate when gametes are formed
(occurs in anaphase; happens if crossing over occurs or not)
[separation of homologous]
Phenotype
characteristics you can see
- Dominant
- Recessive
Genotype
genetic makeup
*Homozygous
Dominant
Recessive
*HeterozygousMonohybrid Cross
- one characteristic
* both are heterozygous
Probability “and”
multiplication
Probability “or”
addition
Dihybrid Cross
-two characteristics
Principle of Independent Assortment
- alleles at different loci segregates independently of one another
- Phenotypic Ratio 9:3:3:1
Simple Mendelian Inheritance
-Complete dominance (AA=Aa in phenotype)
-both parents contribute equally
-trait is controlled by one gene
-inheritance is governed by Principles of Segregation & Independent Assortment
[most phenotypes don’t exhibit patterns of simple Mendelian inheritance]
Lethal alleles
- cause death usually in development
- can alter phenotypic ratios
- can be dominant or recessive
Recessive lethal
2 copies required for death
ex. cystic fibrosis, sickle cell anemia
(Homozygous recessive is missing or dies)
Dominant lethal
1 copy required for death
ex/ huntington disease
(Heterozygotes and homozygous dominant are typically very severely affected and often die early in development
Dominant
- interaction between alleles at the same locus
* *heterozygote is same as one parent
Incomplete (partial) dominance
-interaction between alleles at the same locus
heterozygote is intermediate
ex/ hypercholesterolemia (FH)
Codominance
Heterozygote exhibits both phenotypes
-full & independent phenotypic expressions of both alleles
Monohybrid genotypic & phenotypic ratio (1:2:1)
ex. blood
Incomplete dominance ratios
in a monohybrid cross the phenotypic and genotypic ratios mirror each other
(1:2:1)
Epistasis
one gene hides/ masks the effect of another gene at a different locus
ex/ Bombay Blood (can’t make the H compound)
Gene Interaction
genes at multiple loci determines a single phenotype
Cystic Fibrosis
single gene responsible for a variety of traits
- recessive genetic disease
- > 10 million are (symptomless) carriers
Pleiotropy
single gene impacts many characteristics
Sex-linked
genes on x and y chromosome
Sex-influenced
genes on autosomes more readily expressed in one sex
ex/ facial hair
Sex-limited
autosomal genes expressed only in one sex
ex/ females have a uterus
Genomic imprinting
genes whose expressions is influenced by sex of transmitting parent
genes on sex chromosomes
- addition of sex as a phenotype is an extension of simple Mendelian inheritance
- genes on sex chromosome can affect other traits than sex
X & Y pairing meiosis I
- Pseudoautosomal regions (Par 1 (p) & Par 2 (q))
- PAR has the ability to cross over
SRY
- turns on/off other genes
- destroys female structures
- male structures are stimulated
- Y-linked traits involve infertility and are not transmitted
Genomic Imprinting (epigenetic silencing)
- silencing maintained in somatic cells
- modification: adding a methyl group to silence
- X-inactivation turns off the entire chromosomes
- Imprinting turns off specific genes
- male& female balance each other {ex/ placenta size}
Genomic Imprinting disease
- chromosome 15: neuromuscular defects. mental retardation
- Prader-Willi syndrome: inherited from father
- Angelman syndrome: inherited from mother.
Phenotypes are often modified by environmental effects
ex/ bunnies that are genetically identical , but pigment differs with temperature
Multifactoral
polygenic and influenced by the environment
(many overlapping phenotypes)
ex/ human height
Penetrance
PERCENTAGE of individuals with a particular genotype that expresses the expected phenotype
(what we expect to see is what we actually see)
Incomplete Penetrance
Genotype does not produce expected phenotype
Expressivity
Degree to which a character is expressed
once you see it then you can talk about how much you actually see it
Incomplete Penetrance & Variable Expressivity
alteration or suppresion of the effects of a particular gene due to the effects of other genes and environmental factors ex/ human polydactyly; penetrance is 90%
Multiple Alleles: the Rule
- individual carries two alleles for each autosomal gene
- gene can have multiple alleles in the human population
- different allele combinations can produce variations in the phenotype
Investigate characteristics in human
- Twin studies: examine concordance of a trait between members of a twin pair.
- Adoption studies: comparisons of adopted persons with their adoptive parents and their biological parents.
- Pedigrees: pictorial representation of a family history.
Magnitude of genetic risk
determines a family’s decision about future pregnancies
Tay-Sachs disease
autosomal recessive
Pedigree analysis
- specific disease or characteristic
- initiated by a probing
- symbols represent individuals in the family
Proband
doesn’t have to be the first person impacted by the characteristic. They are the ones that seek help
Pedigree analysis patterns
- Dominant or Recessive
- Autosomal, sex-linked, or mitochondrial
- confirm chosen mode of inheritance works for all individuals
Testcross
with homozygous recessive
features of sex-linked inheritance
- must include sex as a phenotype
- heterozygote is phenotypically normal carrier
- Y has no gene (or alleles) for this trait, so HOMOZYGOUS males display recessive X linked trait more frequently
Dominant Phenotype
- generally appears in every generation
- affected individuals have at least one affected parent
Recessive Phenotype
- can skip generations
- affected individuals can be born from unaffected parents
Autosomal
approx equal frequency in both sexes
Sex-linked
- appears more in one sex
- Y-linked: fathers to all
- Sons are hemizygous and inherit X from mom
Mitochondrial
maternal lineage not paternal
