Cystic fibrosis, Polydactyly, Embryo Screening, Family trees, Inheritance of Sex Flashcards
What is polydactyly
People with polydactyly have extra fingers or toes
What is polydactyly caused by
Polydactyly is caused by a dominant allele
Polydactyly is caused by a dominant allele
This means that a person with one copy of the polydactyly allele and one copy of the normal allele will have polydactyly
What cant you be of the polydactyly allele
You cannot be a carrier of the polydactyly allele
That is true of any dominant allele (disorder)
If you have a dominant allele, then you will have the characteristic
Polydactyly
Male - heterozygous for the polydactyly allele
Female - homozygous for the normal allele
work out genotype and phenotype for the offspring
as well as the percentages and ratios
50% of the offspring are heterozygous for the polydactyly allele. Because this polydactyly allele is dominant, these people will have polydactyly
The other 50% are homozygous recessive. They are unaffected by polydactyly.
They do not have the polydactyly allele
Ratio: 1:1
polydactyly to not affected
A solution to inherited disorders
Embryo screening
What happens in embryo screening
In embryo screening, embryos are tested to see if they have the alleles for the inherited disorders.
Embryos which do not have the defective alleles are implanted into the woman. These can then be developed into healthy offspring
Issues around embryo screening
Embryo screening is expensive. Some people think that the money should be spent elsewhere in the Health Service
Often a large number of embryos are created but only a small number are implanted. That means that some healthy embryos are destroyed and some people think that this is unethical
In the future, we may be able to screen embryos to produce offspring with desirable features e.g. taller of more intelligent offspring. Many people find this unethical
What is gene therapy
In the future, scientists may be able to correct faulty alleles and use this to treat inherited disorders.
This is called gene therapy. At the moment this is still experimental
How can a person get cystic fibrosis
A person with cystic fibrosis must inherit the faulty allele from both parents
How can a person get polydactyly
A person only has to inherit the faulty allele from one parent, in order to develop polydactyly
What do family trees show
Family trees only show the phenotype and not the genotype
Using the family tree, give one piece of evidence that cystic fibrosis is caused by a recessive allele
https://www.youtube.com/watch?v=wky7R3zYtTQ&list=PL9IouNCPbCxWt28Bifo2jK9xn-ym956sf&index=11
Person 11 has cystic fibrosis
However, neither of their parents have cystic fibrosis (persons 7 and 8)
Persons 7 and 8 must be carriers and the cystic fibrosis allele must be recessive
If cystic fibrosis was dominant, then at least one of the parents would have to have cystic fibrosis, in order to pass the allele on to person 11
What is the genotype of person 3 explain your answer
https://www.youtube.com/watch?v=wky7R3zYtTQ&list=PL9IouNCPbCxWt28Bifo2jK9xn-ym956sf&index=11
In this case, person 3 must have the genotype Pp, - they are heterozygous
Because they have polydactyly, we know that person 3 has to have at least one copy of the polydactyly allele
However person 3 cannot have inherited the polydactyly allele from person 1.
That is because person 1 cannot have polydactyly, so person 1 cannot have a copy of the polydactyly allele.
So person 3 must have inherited their polydactyly allele from person 2
Using the family tree, give one piece of evidence that polydactyly is caused by a dominant allele
https://www.youtube.com/watch?v=wky7R3zYtTQ&list=PL9IouNCPbCxWt28Bifo2jK9xn-ym956sf&index=11
If two unaffected have a child, child will be unaffected.
This shows it is caused by a dominant allele. Because in other families, at least one person in the family has it for one of the offspring to have it
If polydactyly was dominant, then at least one of the parents would have to have polydactyly, in order to pass the allele on
