Hereditary Flashcards
p21
- Tumor suppressor gene
- inhibits cyclin dependent kinase (CDK) activity —> decreases the frequency of cell division (CDK stimulates cell division; p21 inhibits phosphorylation activity in order to decrease excessive cell division)
- Haplosufficient
- Important gene in regulating cancer by regulating cell division
Which chromosome are the majority of sex-linked disorders passed down through?
Due to the size difference, the majority of sex-linked disorders are passed down through X-chromosome linkage
Down syndrome
trisomy at chromosome 21
a result of nondisjunction at chromosome 21, producing a zygote with 2n+1 (47) chromosomes
it is a trisomy that is non-fatal —> the altered chromosomes does not kill the embryo
Haplotype
A group of genes that are located so close to each other on a chromosome that they tend to be inherited together
Because the genes are clustered together, they tend to not be split via crossing over (recombination event) and are often found in offspring
p53
A tumor suppressor gene
Plays numerous roles in cancer prevention
upregulated (increase in its protein production) in response to cell stress
One loss-of-function mutation in p53 would result in what?
No effect
Loss-of-function in both copies of the genes are required for cancer causing, null tumor suppressor alleles
Pleiotropy
When one gene affect many different traits
Ex: cystic fibrosis
A single gene will lead to the expression of cystic fibrosis, a disease that cause the expression of different symptoms in different tissues
Epistasis
An interaction between genes where one gene affects the expression of different genes
Ex: hair varieties
Heterozygous organisms
Organisms that posses a dominant allele on one of their homologous chromosomes (homolog) and a recessive allele (for the same gene) on the other homolog
Heterozygous organism
Organisms that posses a dominant allele on one of their homologous chromosomes (homologs) and a recessive allele (for the same gene) on the other homolog
During crossing over, what structures do homologous chromosomes form when they physically join together?
Form a tetrad (or bivalent)
Occurs doing prophase of meiosis I
Allele
Variance of a gene that has different forms
Found on the same loci on both chromosomes in a homologous pair
Ex: various color alleles at the eye color gene locus, such as brown eyes or blue eyes
Oncogenes
Genes that can transform a normal cell into a cancerous cell
Test cross
Used t determine an unknown parental genotype, based on the phenotypes seen in the offspring generations
One parents of an unknown genotype will be bred with a parent that is phenotypically recessive with genotype homozygous recessive
Turner syndrome
- X chromosome monosomy that only affects females
- A female will have one X chromosome (deletion of one X chromosome), leading to 2n-1 (45) chromosomes
- Usually does not cause any intellectual disability’s but it does lead to physical abnormalities and sterility- short stature, gonadal dysgenesis, heart defects, kidney abnormalities
- XO genotype
Proto-oncogenes
Genes involved with control and regulation of cell division and can become oncogenes (cancer-causing genes) due to gain-of-function mutation
Follow the one-hit-hypothesis
One-hit-hypothesis
A gain-of-function mutation in one copy of the gene is enough to produce a mutant phenotype (turns into an oncogene)
Proto-oncogene + gain-of-function mutation = oncogene
Gain-of-function mutations
Can cause too much protein to be made which results in over expression of a gene or production of an over-active protein which results in an increase in gene product activity, cancerous growth occurs as a result
Two-hit hypothesis
Loss-of-function mutations in both copies of the gene are needed to produce a mutant phenotype (cancer causing)
Haploinsufficiency
When one copy of the gene is lost or nonfunctional and the expression of the remaining copy is not sufficient enough to result in a normal phenotype- it can result in an intermediate phenotype
The normal trait requires two functional gene copies to produce enough protein to show the trait
Haplosufficiency
One copy of the gene is sufficient enough to achieve a normal phenotype because it produces enough protein to show the trait
The normal trains only requires one functional copy
During DNA methylation, where are the methyl groups added to the genome?
to the nitrogenous bases on a DNA strand
what is the function of DNA methylation?
inhibiting gene expression by two mechanisms:
1) blocking transcription from occurring by preventing transcription proteins from binding to the DNA strand
2) DNA that has been methylated can wrap tightly around histones through the recruitment of specific proteins, preventing access to methylated DNA
what is DNA demethylation?
the removal of the methyl group on the nitrogenous base which results in increased gene expression (gene upregulation)
opposite of DNA methylation which upregulats
what is histone acetylation?
the addition of an acetyl group to the amino acid lysine found in the histone tails that protrude from one histone core
what is the result of histone acetylation?
causes DNA to wrap less tightly around histones, leading to an increase in gene expression –> weakens the electrostatic affinity/interaction between DNA and histone proteins due to histones becoming less positive
*associated with euchromatin
what epigenetic regulation is present in the inactive X chromosome of females compared to the active X chromosome?
DNA methylation: the inactive X chromosome is heavily methylated compared to the active DNA regions –> this is known as the barr body (located on the periphery of the ell nucleus)
prader-willi syndrom
- occurs due to genomic imprinting
- a set of genes on chromosome 15 inherited from the mother are inactivated, while the same genes on the copy of chromosome 15 inherited from the father are left active
- occurs when the genes on the paternal copy of the chromosome are deleted or mutated and the child does not have active gene expression from either chromosome
what is genomic imprinting?
- the alteration in expression of a gene is dependent on which parent the gene was inherited from
- only one allele of the gene is expressed –> the genes on a chromosome from one parent are imprinted (silenced via DNA methylation) while genes on the chromosome from the other parent are expressed (activated via histone acetylation)
histones
- positively charged, basic proteins
- organize and condense DNA
- bond between (+) histones and (-) DNA is an ionic bond
transcriptome
- the entire set of mRNA expressed by a cell
proteome
- entire set of proteins expressed by a cell
sanger sequencing
- amplification of DNA and use of fluorescence to determine the order of the genetic sequence
cri du chat
caused by deletion on chromosome 5
klinefelter’s syndrom
- caused form an extra X chromosome leading to an XXY genotype
how can a fetus be tested for genetic disorders?
- amniocentesis or
- chorionic villus sampling (CSV)
what are 3 sex-linked recessive conditions?
- hemophilia
- color blindness
- Duchenne’s muscular systrophy
hemophilia
- sex-linked recessive condition
- causes abnormal blood clotting
color blindness
- sex-linked recessive disorder
- primarily observed in males
duchenne’s muscular dystophy
- sex-linked recessive disorder
- progressive loss of muscle
phenylketonuria (PKU)
- autosomal recessive disorder
- inability to produce the proper enzymes for phenylalanine breakdown
- causes degradation product, phenylpyruvic acid to accumulate
cystic fibrosis
- autosomal recessive disorder
- causes fluid builduo in respiratory tract
tay-sachs
- autosomal recessive disorder
- lysosome defect in which cells can’t breakdown lipids for normal brain function
huntington’s disease
- autosomal dominant disorder
- nervous system degeneration
achondroplasia
- autosomal dominant disorder
- causes dwarfism
hypercholesterolemia
- autosomal dominant disorder
- excess cholesterol in blood that progresses into theart disease
viroids
- smaller than viruses
- circular RNA molecules that infect plants
- they do not encode for proteins, they replicate in host plant cells via host enzymes
- cause errors in the regulatory system of plant growth
prions
- not virus or cell
- infectious, mis-folded versions of proteins in the brain
- cause normal versions of proteins to become mis-folded
- fatal
- implicated in diseases like mad cow, kuru, scrapie the sheep and creutzfeldt-jakob disease
retrovirus
- single-stranded RNA virus
- uses reverse transcriptase to make complement DNA from their RNA by hijacking the host cells replicating machinery
- the RNA is then used to manufacture mRNA or enter the lysogenic cycle (encorperated into host cell)
- ex: HIV
