Genotype, Phenotype And Inheritance Flashcards
What is genotype?
Is the alleles present
What is the phenotype?
Observable characteristics
What effects genotype and phenotype?
Genotype can be effected by the environment - e.g. radiation, mutagens, chemicals that alter DNA
Phenotype is effected by genotype and can be the environment - e.g. diet, lifestyle,smoking
You may be more likely genetically to get cancer and then increase risk by smoking
What is the difference between a gene and an allele ?
A gene is a section of DNA that codes for a protein. So everyone had the same genes. Alleles are version of the same genes. So there are many alleles for one gene. Each individual has 2 alleles of the same gene (one from each parent)
What does homozygous mean?
The 2 alleles are the same
What is someone who is homozygous for a gene called?
A homozygote
What does heterozygous mean?
Two alleles of a gene are different
What does hemigzygous mean ?
In males only, when there is only one allele of a gene on the X chromosome because is it not on the Y chromosome.
What is it called when someone has only one allele of a gene on the X chromosome?
Hemizygous
What does dominant mean?
The allele is always expressed
What does recessive mean ?
The allele is only expressed when homozygous
What is it is called when 2 alleles are both expressed ?
Co-dominance
What are the human blood groups ?
3 alleles A,B,O. A and B are co-dominant and o is recessive. Blood groups are A, B, AB, O. Blood group O has no antigen.
What are the potential genotypes of the phenotype blood group A
Could be IAIA or IAIO
In pedigree trees what do the following mean; White/black Square/circle Half coloured Diamond Line through the shape
White=uneffected Black=effected Square=male Circle=female Half coloured=carrier Diamond=unknown sex Line through=dead
Describe autosomal recessive
Single gene where you must have 2 of the allele to be effected. Make and females equally effected Disease can skip generations Both parents of affected are carriers E.g. cystic fibrosis
Draw a punette square to show mating of 2 carriers for a recessive condition. What are offspring phenotype and genotypes
AA normal
Aa normal
aA normal (can write this the other way round)
aa affected
Describe autosomal dominant
Need only 1 allele copy to be effected.
Makes and females affected equally
Not normally homozygous (as normally killed so if it says its dominant and the person has it presume they are heterozygous)
E.g. Huntington’s disease
Effected individual will have at least one affected parent
Will not skip a generation
Describe X linked recessive inheritance
Hemizygous makes and homozygous females are affected.
More common in makes (only get one X chromosome so that x will always be expressed)
Males cannot give trait to sons- because passed on the X gene and male alleles only have a Y chromosome
Male and female are unequally effected (sex linked)
E.g. haemophilia
Find out what the genotype and phenotype of the offspring of an affected male and carrier female.
1 carrier female
1 affected female
1 healthy male
1 affected male
Where is mitochondrial DNA inherited from?
Mother only
Can inheritance be of more than one gene?
Yes it’s called polygenic inheritance
Describe polygenic inheritance
Sometimes several genes are involved in the production of a phenotype. One gene could produce a substrate that needs several enzymes to transform it into the product. These enzymes require other genes to code for them.
You should always assume when working with inheritance that it is v complicated polygenic inheritance.
True or false
No always use the most simple single gene inheritance model first (monogenic)
If working with the inheritance of 2 genes and a parent has the genotype aaBB what are the gametes
aB as the gametes need one allele of each gene
Explain and describe linked genes.
Genes on the same chromosome are linked. Genes on different chromosomes are not linked.
Linked genes do not independently assort at meiosis (so they’re inherited together).
How does recombination frequency relate to linked genes?
The further the distance between the genes the less tightly linked and so the less likely they are to be inherited together
