L17- genotype, phenotype and inheritance Flashcards
central dogma
genotype
our set of genes
phenotype
our traits- proteins
what factors influence our phenotype
- e.g. Genetic disorders like CF (genetic mechanism)
- infection (environment)
- non commiunicable disease (genotype and environment)
what is a gene
A sequence of DNA found at a specific location within chromosomes, which codes for a protein.
an allele is a
form of a gene
how many genes do we have
25,000
- all indiviudals have two copies of each given gene ( one maternala nd one paternal)
many alleles of a gene
within a population e.g. why we have different hair and eye colours
- gene codes of hair colour
- allele codes for the specific colour
homozygous
tow alleles of a gene are the same
heterozygous
two alleles of a gene are different
hemizygous
only one allele of a gene on the X chromosome (male only)
dominant
a dominant alleles in a heterozygote determines phenotype (Aa – would have A phenotype)
recessive
the non-dominant allele in a heterozygote is called recessive.
co- dominance
where both alleles have equal contribution to phenotype e.g. ABO blood types
co-dominance and ABO blood groups
Human isoglutamin gene codes for glycoproteins on the surface of RBC.
Three alleles for blood type:
- A or I^A
- B or I^B
- O or I^O
We have 2 alleles each
- Allele A is dominant over O
- Allele B is dominant over allele O
- Neither A or B is dominant over the other= Co-dominant
in a pedigree each line represents
a separate generation
oldest sibling on the pedigree will be
furthest to the left
how to draw a pedigree- reminder of symbols
describe III.17
youngest of 8 children, married with no children
in autosomal recessive disorders, heteozygotes will be
unaffected
in autososmal recessive disorders males and females
equally affects
in autososmal recessive disorders, if both parents are heterozygotes
Two heterozygotes have 25% chance of having affected offspring
with autosomal recessive disordrrs, 2 affected homozygous individuals will have
affected offspring only
heterozygous pedigree characteristic
isease comes out of nowhere (disease skip generations). Both parents of the affected must be heterozygous ‘carriers’ e.g. CF
in autosomal domiannt disorders heterozygotes will be
affected
in autosomal dominant disorders male and females are
equally affected
autosomal domiannt disorders are rarely found
in homozygous state
- if you see individual with disease, assume they are heterozygous
every individual with autosomal dominant disorder in heterozygous form
has a 50% chance of haveing affected off spring
e.g. huntingtons disease
characteristic of autosomal domiannt pedigree
will not skip generations
- every affected indiivudal will have at lest one affected parent
who are affected with X-linked recessive disorders
Hemizygous men and homozygous females are affected.
X-linked recessive disorders always more common in
males
heterozygous female carrier has a
50% chance of havign an affected son
man with x-linekd recessive disorder cannot
cannot give trait to sons (only get Y chromosomes from dad)
E.g. Haemophilia
x-linked recessive pedigree
Son is hemizygous recessive
Every affected male will have a heterozygous carrier mother
Every affected female will have an affected father and a carrier mother
show an x-linked recessive punnet square example for haemophilia
no H gene on the Y chromosome
in X-linked dominant disorders men and women
affected
- hemizyous males
- heterozygous females
in x-linked dominant diseases females have a ….. chance of havign affected offspring
50%
in X-linked dominant disroders, affecrted males cannot give traits to sons, but will
give it to all their daughters e.g. fragile X syndrome
Y linked disorders only occur in
males
- appearin all sons of males who exhibit that trait
- absent in daughters of trait carriers (pehnotypically normal)
e. g. male infertility
mitochondrial inhertiance occurs due to
mitochodria having separate DNA (mDNA)
mDNA is inherited from
mother due to sperm mitochondria not entering the egg.
polygenic/ complex or multifactorial inheritance shows that
- give an example
More than one gene can be involved in producing a phenotype
e.g. albinism
Albinism is inherited in a recessive manner- monogenic or polygenic?
- monogenic
(Albinisms is inherited in a recessive manor)
One gene: Gene A: Two alleles: A, a
You would expect all offspring to be albino…. HOWEVER in real life non of the offspring are affected.
Albinism is inherited in a recessive manner- monogenic or polygenic?
- polygenic
Two genes: Gene A1 (A1,a1) and A2 (A2, a2)
genes on the same chromosome are said to be
linked
genes on different chormsosmes are said to be
not linked
linked genes do not show
independent assortment at meiosis
what can occur to linked chromosomes
crossing over
linked chromsosmes can show corssinging over in prophase, producing
new combinations of zygotes
recombination frequency in linked chromosomes depens on
the distance between the two linked genes
- Genes closely together are ‘tightly linked’
- Genes far apart on the same chromosome behave as unlinked genes
which linked genes are more likely to cross over
e. g. A and E much more likely to cross over than A and D or E and D.
- closer together
