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2 tightly wound pieces of DNA
how many chromosomes do humans have
23 pair/46 total
2 found in each chromosome (humans have 92)
a protein that holds the 2 chromatids together
- having 2 of each chromosome/cell
- humans have a maternal homolog and a paternal homolog
- non-sex chromosomes
- 22 pair
1 pair determining sex
3 ways to identify chromosomes
- 1) size
- 2) centromere location
- 3) staining
centromere is located int he middle
centromere is located a little off center
centromere is located at the end/tip
- found on acrocentric chromosomes
- a bulge of DNA on the tip of the chromatid
- forms part of the nucleus
- chromosomes grouped into 7 categories based on size and centromere location
- displayed as a karyotype
- possible to identify changes in chromosome # and major changes in structure
Paris conference system
- identifies chromosome by unique banding pattern
- possible to see fairly small deletions, additions, or re-arranements of chromosomes
international system of human chromosome nomenclature
- each chromosome is #ed
- identified by idiogram
- chromosome ends are named p and q
- banding regions are numbered away from the centromere (subdivided into bands)
why is the international system of human chromosome nomenclature useful?
reveals major and minor deletions, duplications and larger re-arrangements (inversions) and translocations
how is a specific location named using the international system of human chromosome nomenclature?
list # of chromosomes, sex chromosomes, chromosome #, arm, region, and band
banding patterns of a chromosome
are banding patterns genes??
having a complete set of chromosomes
having one complete set of chromosomes (23)
having 2 complete sets of chromosomes (46)
1 missing/additional chromosome
- type of aneuploidy
- missing 1 chromosome
- all considered non-viable
- type of aneuploidy
- 1 extra chromosome
what is the karyotype abbreviation for Down's?
what is the live birth incidence of downs?
1 in 800
what are the distinct features of Down's
- oblique palpebral fissures with epicanthic folds
- mental retardation
what accounts for 1/3 of moderate/severe mental retardation in kids?
most common way to diagnose downs?
translucency of nuchal area on ultrasound
is there a recurrent risk for women who are under 40?
yes, about 1%
what causes an aneuploidy?
failures during meitotic separation (non-dysjunction during anaphase 1 and 2)
- partial monosomy
- a piece of the chromosome is removed
deletion on paternal chromosome 15
deletion on maternal chromosome 15
Cri Du Chat
deletion on chromosome 5
- partial trisomy
- part of a chromosome is repeated
a piece of a chromosome is flipped around
two chromosomes break and exchange pieces
- 5% of Down's cases
- exchange b/t chromosomes 21 and 14
what would be the outcome from 1 normal parent and 1 translocation downs carrier??
- 25% normal offspring
- 25% translocation Down's carriers
- 25% monosomy 21 (non-viable)
- 25% translocation Down's
Chronic Myelogenous leukemia
frequency of live births with a chromosomal abnormality?
1 in 200
what % of recognizable pregnancies abort?
15% (up to 50%)
what % of abortions are of normal fetuses?
are chromosomal defects common?
how do you measure chromosomal disease rate?
pregnancy rate- miscarrage (so if all abnormalities are miscarried...no disease rate!)
what are repeated miscarrages suggestive of?
a chromosomal problem with one or both parents
steps of meiosis
- telophase (repeat last 4 twice for meiosis 2)
- chromatin visable- DNA doubles
- chromosomes appear and condense
- pairs align and crossing-over occurs
- pairs line up and attach to spindle apparatus
- random assortment occurs
dysjunction occurs- separation of homologous pairs (non-dysjunction could also occur)
nucleus reforms, cytoplasm separates (cytokenesis)
if pairs of chromosomes/chromotids dont separate (how trisomy 21 occurs)
recoiling of chromosomes
chromosomes line up and attach to spindle apparatus
spearation of chromatids (dysjunction)
reconstruction, chromatids uncoil to chatin
4 haploid daughter cells are made from 1 parent cell
gametic cell division
what important thing occur during meiosis?
- formation fo gametes
- reduction of chromosome number
- random assortment
- crossing over
main part of meiosis 1?
separating of pairs of chromosomes
main part of meiosis 2?
separating of chromatids
meiosis is critical for?
- chromosomal basis of sexual reproduction
- patterns of inheritance
- generating diversity
- chromosomal defects
- are a nucleotide coding sequence for a protein, molecular component or trait
- they are the smallest unit of biological instruction
the entire genetic constitution of humans
how many genes are in the human genome?
25,000 (99% are non-coding)
the location of a given gene on a chromosome
different forms of a gene
alleles with signicicant variation
alleles which are very similar
the process of nucleotide change (how alleles are made)
the most common form, produces expected outcome, dominant
the variant form, doesnt produce normal outcome, recessive
- small, 1 or 2 changes
- may or may not cause a change in the final peptide
2 reasons a point mutation would not have an effect?
- the genetic code is degenerative
- a change in a non-coding segment doesnt matter
the pair of genes a person has
the outward expression of a persons genotype
genotype + environment
in heterozygote, neither allele is fully expressed, you get a combination (red + white = pink)
caused by a single gene mutation
involve the inheritance of traits that follow predictable patterns
involves multiple mutations and environmental factors
and change in genetic material
what causes mutations?
- no one knows! but...
- an altered polypeptide product fails to fold correctly causing it to fail at its cellular function
sickle cell anemia
caused by a single base point subsitution in beta blobin gene on chromosome 11
progression of sickle cell
point mutation --> single amino acid substitution--> abnormal hemoglobin--> sickling erythrocytes
outcomes of sickle cell
- tower skull and long bones (anemia)
- poor physical development (anemia)
- impaired mental function (anemia)
- weakness and lassitude (anemia)
- heart failure
- abdominal pain
- renal failure
types of radiation causing mutation
- cosmic rays
- radioactive decay
types of chemicals causing mutations
- polycyclic aromatic hydrocarbons
- oxidative agents
- 1. loss of function (recessive)
- 2. gain of function (dominant)
- 3. dominant negative (dominant or co-dominant)
- 4. lethal
the mutational load of a person in their lifetime