genetics test HL BIO
Gregor Mendel
He used pea plants to explain the inhertiance of genetics. considered the father of modern genetics.
Artificial Pollination
Using a paint brush and transferring pollen of one plant to the stigma of another and then it will fertilize an egg. The anthers on the fertilized plant will be removed to prevent self-ferilization. Flower must then be enclosed in a paper bag. This creates less genetic diversity.
When u cross two different purebred varieties,
the result is NOT a blend, rather only one feature would be expressed.
When mendel self-fertilizwd offspring, the resulting progeny expressed
two different trains in a 3:1 ratio
Law of segregation
when gametes form, alleles are seperated so that each gamete carries only one allele for each gene.
Law of independent assortment
The segregation of alleles for one gene occurs independently to that of any other gene
Principle of dominance
Recessive aleles will be masked by dominant alleles
Genotype
symbolic representation of a pair of alleles possesed by an organism. ex. GG, Bb, tt
Phenotype
The characteristic or traits of an organism. ex. colour blindness, type O blood, five fingers on each hand
Dominant ALlele
has the same effect on the phenotype whether it is paired with the same allele (homozygous) or a different one (heterozygous). Always expressed in the phenotype. ex. Aa give the dominant A trait cuz the a allele is masked (the a allele is not transcribed and translated during protein synthesis).
Recessive allele
An allele that only has an effect in the phenotype when present in the homozygous state. ex. aa gives rise to the recessive trait because there is no dominant allele there to mask it
Homozygous
If maternal and paternal alleles are the same. ex. AA, aa
Heterozygous
If maternal and paternal alleles are different. ex. Aa
Carrier
An individual who has a recessive trait of a gene but doesn't show up in their phenotype. Heterozygous.
Pure-breeding
Individuals of the same phenotype that, when crossed, will have offspring of the same. Homozygous.
Test Cross
Testnig a suspected heterozygous organism by crossing it with a known homozygous recessive (aa). Since the recessive allele can be masked, it is often impossible to tell whether the organism is AA or Aa until crossed.
Locus
The particular position on homologous chromosomes of a gene.
Factors that affect phenotypes
Genotype only: DNA (ABO blood typem eye-colour, genetic diseases like Huntington's)
Environment interacting with Genotype: Height, skin colour, cancer
Environment only: learned behaviour (languages), acquired characteristics (scars from surgery)
Phenotype plasticity
The ability to express a phenotype in response to an environmental change...
Physiology: birds can produve more of a digestive enzyme maltase when fewer insects are available and they have to eat more grain
Morphology: plants can deactivate genese that produce growth hormones to make thicker leaves when theres more light
Behaviour: Bird migration
Phenology: flowering of plants in response to seasons
Phenylketonuria (PKU)
caused by a recessive allele of the PAH gene on chromosome 12. results in low level of phenylalanine hydroxylase (converts amino acid phenylalanine into tyrosine). can impair brain development in children. If both parents are carries, kid has a 25% chance.
Huntington's Disease
Caused by the dominant allele of the HTT gene on chromosome 4. repeating trinucleotide sequence (CAG).
Incomplete Dominance
When neither allele for a gene completely conceals the presence of the other. Both alleles are equally dominant producing a new phenotype (homogynous mix) that looks like a blend. (red and white will make pink).
Codominant alleles
when both alleles for a trait are dominant. both alleles are expressed in the heterozygous individual (not a new phenotype).
Single Nucleotide Polymorphism (SNP)
These are positions in a genome where some individuals have one nucleotide and other have a different nucleotide. If one occurs in a coding part of a gene ir could lead to an altered protein and give rise to a new allele.
Bloody Typing: multiple alleles
antibodies are specific to antigens. THe immune system recognizes foreign antigens and produces antibodies in response, so if you are given the wrong blood type, the antibodies could cause the blood to clot. Type O is universal donot as it has no antigens. Type AB is universal recipient as it has no antibodies which will react to AB antigens.
Blood Typing Test
mix your blood sample with antibodies that attack types A and B blood to see how it reacts. if ur blood clumps together (agglutination) when mixes anti-B antibodies, you have type B blood. then the sample will be mixed with an anti-Rh serum. if blood clumps, it means u have Rh positive blood.
ABO blood type
classification system that uses presence or absence of certain antigen on red blood cells to catogorize blood into four typs (A, B, AB, O).
A: antigen A, antibody B
B: antigen B, antibody A
AB: antigen A+B, no antibody
O: no antigen, antibody A+B (recessive)
ABO gene alleles
i: O alleles (no antigen)
I^A: A allele (A antigen)
I^B: B allele (B antigen)
ABO gene allele combination
Type O: ii (no antigen produces)
Type A: I^AI^A & I^Ai (type A antigen)
Type B: I^BI^B & I^Bi (type B antigen)
Type AB: I^AI^B (type A+B antigens)
Sex chromosomes
the first 22 pairs of chromosomes are homolgous and are called autosomes. The sex chromsomes (chromosomes 23) are non-homologous. Females are XX, makes are XY. When women produce gametes, each egg will contain an X. When men produce gametes, half the sperm will be X and the other half will be Y. As a result, all offspring will get an X from their mom and will either get X or Y from dad. X chromosome is longer than Y.
Sex determination
first appearance of gonads is the same in both sexes (can either become testies or ovaries). SRY gene (if present) encodes for TDF protein, which binds to DNA and acts as a transcription factor promoting the expression of other genes. the testis produces MIF hormone which causes degeneration of gemale organs. Testis also produces testosterone. In the presence of TDF, gonads become testis. In absence, gonads become ovaries.
Morgan's discovery of sex linkage
he experimented with the fruit fly. he noticed that there was a white eyed fly as opposed to the red eyes ones. he mated it with a red eyed one and noticed the offspring all had red eyes except for three males. He also noticed in the next generation that there where three red-eyed flies for every white eyed fly. All white eyed flies were male. gene for eye colour is on X chromosome. x-linked traits are exhibited more often in males.
sex-linkage
traits carried on x chromosome in non-homologous region. ex. hemophilia and colour blindness.
colour blindness (sex linkage)
red-green gene is carried at locus Xq28. This locus is in the non-homologous region so there is no corresponding allele/gene on the Y chromosome. normal vision is dominant over colour-blindness. genes found at locus Xq28 are responsible for producing photoreceptive pigments in the cone cells in the eye. if one of the genes is mutant, pigments aren't produces and u get red-green colour blindness.
Hemophilia (sex linkage)
blood clotting. a series of enzyme-controlled biochemical reactions. it requires globular proteins called clotting factors. a recessive x-linkes mutation in hemophiliacs results in one of these factors not being produces and therefore the clotting response to injury doesn't work and the patient can bleed to death.
Autosomal Dominant vs Recessive
Dominant: both parents affected and an offspring isn't (parents are both heterozygous). all affected individuals must have at least one affected parent (homozygous recessive).
Recessive: both parents are unaffected and an offspring is affected (both parents are carriers). if both parents show a trait, all offspring must also (homozygous recessive).
X-linked Dominant vs Recessive
Dominant: if a male shows a trait, all daughters and mother must also. an unaffected mother must have all sons and father also unaffected. more common in females.
Recessive: if a female shows a trait, all sons and father must also. an unaffected mother CAN have affected sons if she's a carrier. more common in males.
Type of variation
Discrete: when individuals fall into a number of distinct categories. no in-between categories.
Continuous: phenotypes vary gradually from one extreme to another (skin colour, height). Polygenic inheritance involves two or more genes influencing the expression of one trait. each allele of a polygenic character often contributes only a small amount to the overall phenotype.
Mendel's Law od Independent Assortment
states that the presence of an alleles of one of the genes in a gamete has no influence over which allele of another gene is present. ONLY HOLDS TRUE FOR UNLINKED GENES.
Locus
the particular position on homologous chromosomes of a gene. Each gene is found at a specific plate on a specific pair of chromosomes
Human Chromosomes Nomenclature
7q22.1
7:Chromosomal number
q: arm (p or q)
first 2: region number
second 2: band number
1: sub-banc number
the centromere divides the chromosomes into short (p) or long (q) arms. the larger the sub-band number, the further from centromere it is.
Linked genes
pairs or groups of genes on the same chromosome and that tend to be inherited together.
linkage group
all of the genes on any one chromosome; tend to be inherited together
recombination
recombination of alleles occurs as a result of crossing over between non-sister chromatids. exchange of alleles gives new genotype of gametes.
gene linkage and recombination
the further apart a pair of alleles are on a chromosome, the more likely crossing over may occur between them, leading to recombination.
chi-squared test
used to determine whether the difference between an observed and expected frequency distribution is statistically significant. if observed frequencies don't conform to those expected of an unlinked dihybrid cross, this suggests either:
a)genes are linked and hence not independently assorted
b)the inheritance of the traits are not random, but rather are potentially being affected by natural selection.
chi-square test hypothesis
H0: there is no significant difference between observed and expected results.
H: there is a significant difference between observed and expected results.
statistical value equation
x^2= sum( ((O-E)^2) /E )
O= observed frequency
E= expected frequency
degrees of freedom
df = (m-1)(n-1)
m=number of rows
n=number of columns
a mathematical restriction that designates what range of values fall within each significance level
define CRISPR
found in prokaryotes and represents past infections from viruses. (Naturally found in bacteria). This can be used to treat genetic disorders like cystic fibrosis/sickle cell/etc. CRISPR can cut DNA at a specific location.
cas9 proteins
endonucleases that cut DNA
guide RNA
A guide RNA is inserted into the cas9 protein and is used to target a particular gene.
This is beneficial because the specificity prevents you from affecting other genes.
gene knockout
we have a library online of past knockout organisms (a database of all recorded knockout organisms). By looking at the change in an organism, we can see what the gene codes for.
condensed genes
genes with a similar sequence between species and one unchanged
Examples: genes associated with ribosomes DNA replication
theory 1
Functional requirements
Genes needed for basic functioning/reproduction need to be maintained/consistent (no mutations)
theory 2
Lower rates of mutation
Genes that are transcribed more tend to have lower mutation rates (probably cause they can have a higher proofreading rate)
LUCA
passed on conserved genes
PAM
allows guide RNA to bind to target DNA
SiRNA
double stranded RNA that interferes with gene expression by breaking mRNA transcripts before translation
Conserved Sequences
show minimal mutation over time
Highly conserved sequences
show no/almost no change
ex. genes involved in DNA replication
CRISPR-Cas9 is used in what??
gene therapy to modify defective genes
Binding and Cleaving
Binding: Cas9 binds to PAM, unwinds DNA, and matches target to guide
Cleaving: if match is perfect, Cas9 cuts the DNA and creates a double-stranded break
Targeting
Cas9 and guide RNA are combined and delivered (ex. by viruses)
CRISPR DNA repair
- CRISPR creates double stranded DNA breaks that are repaired via non-homologous joining (NHEJ - quick but error prone) or homology-directed repair (HDR - precise but slower)
- Cas9 repeated cutting and repair can deactivate genes
- HDR: provided repair template guides HDR to insert desired DNA sequence (cas9 must be deactivated after HDR to avoid further cutting)
- Prim Editing: combines Cas9 with a reverse transcriptase enzyme to directly write new genetic sequences
Benefits of CRISPR
treats genetic disorders, modifies mosquitoes to prevent diseases, enhances crops and livestock, etc.
Challenges and Risks of CRISPR
potential off-guard mutations can harm genome, high costs, ethical concern (embryo editing), etc.
homologous chromosomes have the same
type of genes