Mendel's Laws

Question 1

Mendels first law - Law of segregation
and where it fits into meiosis

Answer 1

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

Question 2

Mendel’s second law - Independent assortment

Answer 2

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

Question 3

Mendel’s law of dominance

Answer 3

in a heterozygote, one trait will conceal the presence of another trait for the same characteristic

Question 4

def of point mutation and 3 types

Answer 4

Mutation causing change of a single base pair

Silent
Nonsense
Missence

Question 5

what is a silent/synonymous mutation

Answer 5

change in base pair that doesnt have a change in the amino acid formed
basically does nothing

Question 6

what is a nonsense mutation

Answer 6

change in DNA makes a stop codon

get shorter protein than normal

Question 7

what is a missence mutation

Answer 7

change in codon leads to change in amino acid of protein

Question 8

what is the difference between a conservative and non-conservative mutation

Answer 8

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

Question 9

what is a wild type protein

Answer 9

functional protein

Question 10

what type of protein do most mutations give rise to?

Answer 10

Loss of function (LOF)
if it’s non-synonymous ofc

Question 11

what is another type of protein that a mutation could lead to?

Answer 11

gain-of-function

much less common

Question 12

what is the phenotype shown if the genotype has one wild type and one loss of function allele?

Answer 12

wild type is shown as pehnotype

so the LOF gene is recessive (this isnt an absolute rule)

Question 13

what is the phenotype shown if the genotype has one wild type and one gain of function allele?

Answer 13

GOF allele shown as phenotype

so GOF is dominant

Question 14

what is incomplete dominance

Answer 14

the heterzygote phenotype is intermediate between the 2 homozygote phenotypes

dont get regular 3:1 ratio according to mendel

Question 15

how can cholesterol be used as an example of incomplete dominance?

Answer 15

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

Question 16

co - dominance

Answer 16

heterozygots show phenotype of both alleles

Question 17

how is human ABO blood groups an example of co-dominance?

Answer 17

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

Question 18

how many alleles was medel aware of and why was he wrong

Answer 18

he said 2
there can be more than 2
as seen in blood group example duh

Question 19

how might dominance change when more than one allele is involved

Answer 19

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)

Question 20

what is pleiotropy

Answer 20

one gene can affect more than one trait

Question 21

what is PCD and how does it affect cilia and flagella

Answer 21

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

Question 22

how else can PCD affect humans (situs inversus)

Answer 22

situs inversus

major organs are reversed

vry rare
but 50% of people w/ PCD have it

Question 23

how does situs inversus occur

Answer 23

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

Question 24

what are lethal alleles

Answer 24

when a particular combo of alleles is set, it can be lethal

Question 25

how can lethal alleles affect phentoypic ratios (mouse example)

Answer 25

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

Question 26

what is achondroplasia and how is it an example of lethal alleles

Answer 26

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

Question 27

what is penetrance

Answer 27

the percentage of individuals w/ a genotype that show the expected phenotype (simply whether or not it shows, only yes or no)

Question 28

what is expressivity

Answer 28

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

Question 29

what does BRCA gene control

Answer 29

breast/ovarian cancer

Question 30

how are tumor supressor genes expressed

Answer 30

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

Question 31

3 examples of cancers that lack of tumour supressor genes could lead to

Answer 31

neurofibromatosis type 1 (in peripheral nervous system)

retinoblastoma (retina)

BRCA1/2 ( breast/ovary )

Question 32

are mutations in tumour supression gene in somatic cells or no?

Answer 32

somatic
so not carried on in germline

Question 33

neurofibromatosis type 1 (NF1)

Answer 33

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)

Question 34

why are pearson twins (with NF1) so diff in appearance

Answer 34

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

Question 35

see onenote for combining probabilities

Answer 35

:)