3.4 INHERITANCE Flashcards
Dominant
allele that is expressed in the heterozygous
Recessive
allele that is not expressed in the heterozygous
Gametes
haploid sex cells formed by the process of meiosis
male → sperm
female → ova
zygotes
when the male and female gametes fuse during fertilisation (contains two alleles for each gene)
Heterozygous
when the allele in the genotype are not the same
Homozygous
when the allele in the genotype are the same
AA
Homozygous Dominant
Aa
Heterozygous
aa
Homozygous Recessive
Genotype
the combination of alleles of a gene carried by an organism
Phenotype
the expression of alleles of a gene carried by an organism
Codominant alleles
alleles that are both expressed equally in the phenotype of a heterozygous individual
They therefore have an altered phenotype as the alleles are having a joint effect
A and B blood Groups
co-dominant and each modify the structure of the antigen to produce different variants
O blood group
recessive and does not modify the basic antigenic structure
Type A
Anti-B Antibody
Cannot have B or AB Blood
Can have A or O blood
Type B
Anti-A Antibody
Cannot have A or AB Blood
Can have B or O blood
Type AB
Neither antibody
Can have any type of blood
Type O
Both Antibodies
Can only have O blood
Genetics disease
diseases caused by a gene
Carriers
Heterozygous individuals will possess one copy of the faulty allele but not develop disease symptoms
Autosomal recessive genetic disease
will only occur if both allele are faulty
Autosomal dominant genetic disease
only requires one copy of a faulty allele to cause a disorder
Sex linkage
when a gene controlling a characteristic is located on a sex chromosome
Cystic Fibrosis
Autosomal recessive disorder
Mutation in chromosome 7
Produce mucus unusually sticky and thick
This mucus clogs the airway and secretory ducts of the digestive system → respiratory failure
Huntington’s Disease
Autosomal dominant disorder
Mutation in chromosome 4
The HTT gene posses a repeating trinucleotide sequence (CAG) that is usually present in low amounts
+28 CAG repeats → unstable
+40 → the huntingtin protein will misfold and cause neurodegeneration
Symptoms →dementia and uncontrollable spasmodic movements
PKU
a mis-sense mutation in the gene that produces tyrosine hydroxylase
phenylalanine cannot be converted to tyrosine so it builds up
resulting in brain developmental problems and seizures
Dairy, breastmilk, nuts are avoided since they are rich in phenylalanine
Colour-blindness
an individual fails to discriminante between red and green hues
caused by a mutation to the red or green retinal photoreceptors, located in X-chromosome
XA → unaffected
Xa → affected
Haemophilia
when the body’s ability yo control blood clotting is impaired
The formation of a blood clot is controlled by a cascade of coagulation factors whose genes are located on the X chromosome
When one of these factors becomes defective, fibrin formation is prevented - meaning bleeding continues for a long time
XH → unaffected
Xh → affected
