Mendel's Laws Flashcards
Mendels first law - Law of segregation
and where it fits into meiosis
Alleles of a single gene segregate randomly and equally into gametes
During M 1 - homologous pairs line up
During M 2 - sister chromatids seperate
So each gamete inherits one of the 2 alleles for any gene
and this happens randomly
Mendel’s second law - Independent assortment
Alleles from different genes also segregate randomly into gametes due to random alignment in Met 1
e.g. AaBb
will split equally in the gametes to give
AB, Ab, aB and ab
Mendel’s law of dominance
in a heterozygote, one trait will conceal the presence of another trait for the same characteristic
def of point mutation and 3 types
Mutation causing change of a single base pair
Silent
Nonsense
Missence
what is a silent/synonymous mutation
change in base pair that doesnt have a change in the amino acid formed
basically does nothing
what is a nonsense mutation
change in DNA makes a stop codon
get shorter protein than normal
what is a missence mutation
change in codon leads to change in amino acid of protein
what is the difference between a conservative and non-conservative mutation
cpnservative = a change in amino acid, but the new AA is chemically and stucturally similar to the first (e.g. consider +ve or -ve charges etc)
has subtle effect
non-conservative = the opposite,
can have more drastic effect on structure and function
what is a wild type protein
functional protein
what type of protein do most mutations give rise to?
Loss of function (LOF)
if it’s non-synonymous ofc
what is another type of protein that a mutation could lead to?
gain-of-function
much less common
what is the phenotype shown if the genotype has one wild type and one loss of function allele?
wild type is shown as pehnotype
so the LOF gene is recessive (this isnt an absolute rule)
what is the phenotype shown if the genotype has one wild type and one gain of function allele?
GOF allele shown as phenotype
so GOF is dominant
what is incomplete dominance
the heterzygote phenotype is intermediate between the 2 homozygote phenotypes
dont get regular 3:1 ratio according to mendel
how can cholesterol be used as an example of incomplete dominance?
familial hypercholesterolaemia
- mutation in gene that encodes for LDL receptor
LDL receptor allows for LDL (which carries cholesterol) to be broken down
when HH = cell normal, lots of LDL rec, chol broken down
when hh = severe disease, no LDL rec, chol cant be broken down
when Hh = mild disease, few LDL rec
co - dominance
heterozygots show phenotype of both alleles
how is human ABO blood groups an example of co-dominance?
three possible alleles
A, B and O
can have AA or AO = type A
BB or BO = type B
AB = both phenotypes (the antigen on surface) is shown
OO = O
how many alleles was medel aware of and why was he wrong
he said 2
there can be more than 2
as seen in blood group example duh
how might dominance change when more than one allele is involved
may have a dominance series
the dominant allele is only dominant relative to what it’s next to
e.g. mouse colours (see diagram in onenote)
what is pleiotropy
one gene can affect more than one trait
what is PCD and how does it affect cilia and flagella
primary ciliary dyskinesia (PCD)
little hooks called dyenin arms (a protein) in cilia and glagella
allows them to move smoothly
but sometimes mutation = no dynein arms
thi causes failure to clear airways - bacterial infection
or infertility in males - sperm don’t have motlity
how else can PCD affect humans (situs inversus)
situs inversus
major organs are reversed
vry rare
but 50% of people w/ PCD have it
how does situs inversus occur
usually, in embryos the cause of our regular symmetry starts with the ‘node’ structure
but in PCD, the motiloe cilia in the node doesn’t flow properly and the sensory cilia cant pick it up
so
it basically randomly decides which orientation to put all the lungs
hence 50/50 chance
see onenote
what are lethal alleles
when a particular combo of alleles is set, it can be lethal
how can lethal alleles affect phentoypic ratios (mouse example)
can skew them
e.g. in mouse, the yellow allele is dominant for fur colour
however, when u cross 2 heterozygous yellow mouse
then u expect a 3:1 ratio
with one being not yellow
BUT
u end up w/ 2:1
cuz plot twist
when the yellow is hom recessive, it is lethal
rip
what is achondroplasia and how is it an example of lethal alleles
achondroplasia is growth defect
usually, cartilage grows to a certain length, then the FGFR3 protein replaces the cartilage with bone
but the mutant replaces cartilage with bone prematurely, hence shorter bones
but babies that are homozygous for the mutation are still born or die in early infance
cuz recessive lethal
what is penetrance
the percentage of individuals w/ a genotype that show the expected phenotype (simply whether or not it shows, only yes or no)
what is expressivity
measures the extent to which a genotype is expressed at phenotypic level (has varying levels)
variabilities could be caused by modifier genes, and the genes contorlling the phenotype being on multiple sites
what does BRCA gene control
breast/ovarian cancer
how are tumor supressor genes expressed
usually heterozygous, and has no effect on the cell
but sometimes a mutation may cause it to become homozygous, where tumour supressor gene inactivated on both alleles
leads to cancer
3 examples of cancers that lack of tumour supressor genes could lead to
neurofibromatosis type 1 (in peripheral nervous system)
retinoblastoma (retina)
BRCA1/2 ( breast/ovary )
are mutations in tumour supression gene in somatic cells or no?
somatic
so not carried on in germline
neurofibromatosis type 1 (NF1)
Dominant familial cancer syndrome
usually benign neurofibromas under the skin
characteristised by brow spots under skin
caused by LOF mutations in the NF1 gene
effects can vary, even when they carry same NF1 mutation (seen in Pearson twins)
why are pearson twins (with NF1) so diff in appearance
adam’s facial tissue, cells were HOMOZYGOUS for the NF1 gene
whereas Neil was heterozygous
loss of heterzygosity in adam occured in foetal development (2nd mutation)
also found in CT scan, that Neil had benign tumours in his abdomen whereas adam didn’t have any
see onenote for combining probabilities
:)
