genetics Flashcards
applications:
crop breeding.
medical.
forensic.
chromosomes- structural types:
metacentric, submetacentric, acrocentric, telocentric.
changes in chromosome number can derive from chromosome fusion or fission. in chromosome fusion, 2 telomeres and 1 centromere lose function. in a chromosome splitting, a new centromere must develop, and telomeres must be added at the new ends.
ideogram:
each gene has a specific location, in specific chromosome and cytoband.
duplicated genes:
Duplicated genes can develop different functions over time, resulting in gene and protein families. Alpha and beta globin gene families are derived from a single ancestral globin gene. Humans have 3 protein coding genes at the alpha locus and 5 at the beta locus, plus pseudogenes that have lost function. The coding genes have specialised functions and times of expression.
functional divergence:
functional divergence can occur when different family members are expressed in different tissues.
The hedgehog family encodes signalling molecules, important for development, that are expressed in different tissues.
Sonic, desert and Indian are paralogs (related copies of a gene in a single species). Orthologs are genes in different species that are derived from a common ancestor (sonic, desert and Indian are orthologs of drosophila hedgehog).
Homologs are inferred from sequence similarity and are descended from a common ancestor.
duplicated genes
when genes are duplicated, evolutionary pressure is reduced as there is a spare gene copy- this is why functional divergence can occur.
Mutations can then reduce or eliminate function in some copies without detriment to the organisms- pseudogenes (non functional gene remnants).
ploidy:
Refers to the number of sets of chromosomes in a cell.
One set = n chromosomes
n monoploid
2n diploid (gametes n – haploid) in humans n = 23
3n triploid, 4n tetraploid etc incompatible with life in humans
extra or missing chromosomes from a set e.g 2n+1, 2n-1 are aneuploid (an – not, eu – true, + ploidy, i.e. not composed of full sets
monohybrid cross (punnett square):
used to determine phenotype and genotype of offspring.
Phenotype- physical (colour, shape appearance).
Genotype- gene or allele (Aa, AA, aa). Dominant- trait always displayed (AA, Aa). Recessive- trait always masked, only expressed when homozygous (aa). Co dominance- all traits are dominant (no recessive lowercase alleles), both traits are exposed.
co dominance and blood typing:
all traits are dominant. both traits are expressed.
There are 4 possible blood groups- A, B, O, AB.
If AB, neither parents will be group O. if O, neither parents will be group AB.
ABO blood groups:
One locus, 3 alleles IA , IB , i
IAIA or IAi = group A
IBIB or IBi= group B
ii= group O
IAIB= group AB. alleles are CODOMINANT
The alleles IA and IB code for enzymes which
attach sugar residues to red blood cell surfaces
incomplete dominance:
all traits are dominant (no recessive). traits blend together.
sex linked traits, x linked traits:
affects the sex chromosomes (pair 23). Most sex linked traits affect the X chromosome. Males are more affected by sex linked traits because they have 1 X chromosome.
Females are often carriers because they have 2 X chromosomes.
meiosis:
makes gametes (sex cells). Divides adult chromosome number in half (haploid), so that parents only pass 23 chromosomes to offspring.
events in meiosis:
crossing over- occurs in prophase 1, where the chromosomes break, and exchange genetic material, why organisms look different than parents.
Non disjunction- failure of chromosomes to separate properly, causing organism to have extra chromosome (trisomy 21).
karyotypes and genetic disorder:
karyotypes are mapping of human chromosomes. A normal human karyotype has 46 chromosomes (diploid), and 23 pair (haploid).
Chromosomes 1-22 are called autosomes. The sex chromosomes are the 23rd pair. Males are XY and females are XX.
sex determination:
all diploid human cells have 22 pairs of autosomes (44A). females have 2 copies of the X chromosome (44A XX). Males have 1 x and 1 Y chromosome (44A XY). All children inherit an X from their mum and either X or Y from their dad.
human aneuploids:
single sex chromosome- XO= turner.
XYY= Klinefelter.
Trisomy 21= down syndrome. Trisomy 18= Edwards syndrome. Trisomy 13= pataus syndrome.
male XXY klinefelters syndrome:
males have an extra X chromosome.
Smaller genitals.
develops breasts.
47 chromosomes total.
female turner syndrome (XO):
45 chromosomes.
Missing an X chromosome.
Infertile, does not go through puberty due to non functioning reproductive organs.
cystic fibrosis:
thick mucus in the lungs and digestive tract. Mainly affects Caucasian population.
Caused by defective protein in cell membrane.
Treated with special diet and physical therapy.
tay-sachs disease:
caused by recessive trait.
An important enzyme (protein) is missing that breaks down lipids in the CNS.
Lipids accumulate in the CNS causing damage.
sickle cell anaemia:
primarily affects the African American community.
Red blood cells are crescent shaped.
Pain in the extremities.
Caused by point (substitution) mutation. Patients with SCA are immune to malaria.
glucose-6-phosphate dehydrogenase deficiency:
genetic disorder that occurs almost exclusively in males. This condition mainly affects RBCs, which carry O2 from the lungs to tissues throughout the body.
A defect in g6pd causes RBCs to break down prematurely. The most common medical problem associated with g6pd is haemolytic anaemia.
People with g6pd mutation may be partially protected against malaria. A reduction in the amount of functional g6pd appears to make it more difficult for mosquitos to invade RBCs.
g6pd inheritance:
This condition is inherited in an X-linked recessive pattern. The gene associated with this condition is located on the X chromosome
In males (who have only one X chromosome), one altered copy of the gene in each cell is sufficient to cause the condition
In females (who have two X chromosomes), a mutation would have to occur in both copies of the gene to cause the disorder
Because it is unlikely that females will have two altered copies of this gene, males are affected by X-linked recessive disorders much more frequently than females
A characteristic of X-linked inheritance is that fathers cannot pass X-linked traits to their sons
PKU:
recessive disorder. Missing an enzyme that converts the amino acid phenylalanine into tyrosine. Phenylalanine cant be broken down by the body and causes damage to the CNS. Patients treated with diet low in phenylalanine (found in many fizzy drinks).
alleles:
the location of a gene is called locus (loci). For autosomes, and X in female, there are 2 copies of each gene, one on each chromosome. If we have the same allele on each chromosome, we are homozygous for that gene. If we have different alleles on each chromosome, we are heterozygous for that gene. The male is hemizygous for genes on the X chromosome as he only has 1 copy of each.
PKU:
allele A is active, allele a is inactive.
2 alleles, 1 inherited from each parent.
AA and Aa can both make PAH- healthy phenotype.
Aa cant make PAH- has PKU, recessive disorder.
huntingtons disease:
degeneration of nerve cells (neurons), cognitive impairment, inability to focus, muscle rigidity, no treatment, when symptoms arise, death in 10-25 years. Neuron apoptosis (neurons die).
disorder of trinucleotide repeat CAG normally repeated 10-35 times. Huntington patients have a stretch of 36 to over 120 repeats. CAG-CAG-CAG. An increase in the size of the CAG segment leads to the production of an abnormally long version of the Huntington protein. The elongated protein is cut into smaller toxic fragments that bind together and accumulate in neurons, disrupting the normal functions of these cells.
huntingtons inheritance:
in an autosomal dominant pattern, which means 1 copy of the altered gene in each cell is sufficient to cause the disorder. An affected person usually inherits the altered gene from 1 affected parent. In rare cases and individual with huntingtons does not have a parent with the disorder. As the altered HTT gene is passed from 1 generation to the next, the size of the CAG trinucleotide repeat often increases in size. Individuals who have 27-35 repeats in the HTT gene do not develop huntington disease, but they are at risk of having children who will.
