3.4 inheritance Flashcards
what did GREGOR JOHANN MENDEL discover
the basic underlying principles of heredity (thru work on garden pea plants)
define Mendel’s Laws
3 fundamental laws of inheritance
that apply to sexually reproducing species
state the 3 mendels laws
law of segregation
law of independent assortment
law of dominance
what is the law of segregation
each gamete has only 1 allele for each gene!!! –>
2 alleles (on 2 chromosomes) seperated during meiosis (anaphase 1)
- HENCE alleles are passed generation to the next as distinct units
exceptions to law of segregation
alleles in sex chromosomes and mitochondrial DNA
what is the law of independent assortment
allele inherited for one trait DOES NOT AFFECT the allele inherited for another trait
+
gamete has one copy of each gene – result of random orientation of homologous chromosomes (metaphase I)
exception to law of independent assortment
linked genes
what is the law of dominance
when 2 diff alleles:
dominant determines trait, recessive in unexpressed
exception to law of dominance
co-dominance
diploid organiams carry ___ copies of each gene
two
how are gametes haploid
- diploid orgs carry 2 copies of each gene – one on each homologous chromosome
- alleles are segregated during meiosis
when sperm and ovum fuse in fertilisation they form a?
single diploid cell – zygote
homozygous vs heterozygous definition
homo: sperm and egg carry same allele for particular gene
hetero: different alleles
phenotype of an individual is determined by?
genotype
define phenotype
an organisms observable characteristics/traits
- including morphology and biochemical properties
define genotype in individuals
two alleles present in an organism for a particular gene
what is a carrier (genotypes)
an individual with a recessive allele of a gene with no effect on phenotype
define gene
a piece of DNA containing information about a particular trait
define allele
a particular version of a gene
define dominant allele
allele that has the same effect on the phenotype whether 1 or 2 copies are present
In heterozygous state: will mask presence of recessive allele
define recessive allele
allele that only has an effect on the phenotype when two copies are present (in a homozygous state)
define co-dominant alleles
Alleles that jointly affect the phenotype when present together in a heterozygote
define locus
the particular position on homologous chromosomes of a gene
what does this mean:
P
F1
F2
P = Parental generation
F1 = first filial (offspring) generation
F2: second filial generation – offspring, cross of F1 gen
define autosomal genes
genes on autosomes (non sex chromosomes)
sex linked genes
genes on sex chromosomes (X and Y)
what is complete dominance?
when the dominant allele masks the recessive allele
(in context of genetic diseases) distinguish between rare and recessive alleles
recessive: interaction of allele in diploid state, only affect phenotype when heterozygous
rare: frequency of allele – how many individuals carry it
what is a mutagen
any agent that causes or increases the frequency of mutations by triggering changes in the genetic material of an organism
examples of mutagens
radiation, chemicals (Eg from cigarette smoke)
mutagens vs carcingogens
carcinogens are mutagens that can lead to cancer!
what is radiation
higher level radiation (ionising radiation) can break bonds between atoms incl DNA = mutations
when does ARS occur
when person is exposed to large dose of ionising radiation
what were the consequences of the nuclear bombing of Hiroshima
over 100k ppl died from fires, explosive shockwave, and Acute Radiation Syndrome (ARS)
effects of lower vs larger vs very high doses of radiation
low: nausea, headache
larger: seizures, fever
very high: death
incr risk of cancer
what was the chernobyl accident 1986?
accidental nuclear core explosion at chernobyl power station in ukraine
how did the radiation from chernobyl lead to an increased rate of thyroid cancer in children 3
- a radioactive isotope released was iodine-131
- thyroid gland incorporates iodine into some hormones it produces
- radioactive iodine incorporated into thyroid hormones = incr rate of mutation
how was the radiation of the chernobyl site limited
concrete cover
(new cover needed in 2016)
what kind of genetic disease is cystic fibrosis
autosomal recessive
how does the recessive allele in cystic fibrosis cause it
mutation in cystic fibrosis transmembrane conductance regulatory gene (CFTR) (a gene in chormosome 7)
which codes for a chloride channel in mucous membranes
effects of cystic fibrosis
altered mucus buildup in lungs = dangerous infections + damage to lung tissue
+ mucus builds up in liver and pancreas =affects digestion
what kind of genetic disease is sickle cell anemia
autosomal co-dominant
how is the sickle cell anemia genotype presented in diagram
Hb^aHb^s = carrier
what kind of genetic disease is Huntington’s disease
autosomal dominant
what is huntington’s disease
neurodegenerative disorder that manifests ppl 30-50 of age
what is huntington’s disease caused by
dominant allele is mutation of Huntingtin (HTT) gene on chromosome 4
symptoms of Huntington’s disease
loss of muscle coordination, cognitive delcine, psychiatric problems
how many years life expectancy after huntingtons disease symptoms are observed
10 years
how common is the gene for huntingtons disease
1 in 10 000
how are blood group alleles presented
I^A
I^B
i
genotype for B blood
I^BI^B or I^Bi
alleles I^A and I^B are __________
codominant
what does the I in the alleles of blood. groups stand for
isoagglutinogen
whats the difference between IA and IB and i (blood groups)
same base molecule BUT different additions to the molecule by A and B
additions: antigens
A: N-acetylegalactosamine
B: galactose
how are linked genes shown (Eg on X and Y)
as a superscript to the letter
what is haemophilia
genetic disorder where blood clotting is impaired
(formation of blood clot controlled by cascade of coagulation factors whose genes are located on X chromosome)
what component in blood clotting is affected by haemophilia
fibrin formation is prevented
how are haemophilia alleles presented
Xᴴ = unaffected
Xʰ = haemophilia
what is red green colourblindness
individual fails to differentiate red and green
what is red green colour blindness caused by
mutation to red/green retinal photoreceptors – located on X chromosome
how is red-green colour blindess diagnosed
ishihara colour test
how are alleles for colour blindness presented
Xᴬ = unaffected
Xᵃ = colour blindness
what is a test cross
testing a suspected heterozygote plant/animal by crossing it with a KNOWN HOMOZYGOUS RECESSIVE
how to calculate probability of 2 independent events occuring
multiply
how to calculate probility that one event or another occurs
add
the larger the sample size, the ______ the difference between observed and expected outcomes
smaller
what are pedigree charts used for (those circle square family tree things)
demonstrate a particular type of inheritance, deduce pattern of genetic disease inheritance
how to identify autosomal dominant when analysing a pedigree
every affected individual has at least 1 affected parent
both males and females affected
every generation
how to identify autosomal recessive when analysing a pedigree
both m and f affected
2 unaffected can have affected child
skips generations
how to identify sex-linkage in pedigree charts
usually only males affected
sometimes females affected only when father is affected
