Inheritance (Genetics, Mutations and Evolution) CHECK ALL Flashcards
What are alleles?
Variations of the same gene
We have two alleles of each gene, one in each chromosome within a chromome pair
Therefore, we have two alleles which control each characteristic
One comes from our mother, and one comes from our father
What is the phenotype of an organism?
The observable characteristics of the organism
What is the genotype of an organism?
The combination of alleles that controls each characteristics in an organism (what genes the organism has)
What is a dominant allele?
An allele which only needs to be inherited from one parent in order for the characteristic to show up in the phentotype
What is a recessive allele?
An allele which needs to be inherited from both parents in order for the characteristic to show up in the phenotype
What does homozygous (dominant and recessive) mean?
If an individual is homozygous for a gene, that means their two alleles of the gene are the same
If these two alleles are dominant, they are homozygous dominant, if these two alleles are recessive, they are homozygous recessive
What does heterozygous mean?
If an individual is homozygous for a gene, that means their two alleles of the gene are different
This means they have a dominant and a recessive allele for the gene
If height was controlled by two alleles, T and t, T being tall, and t being short, and T was dominant, what are all of the possible offspring if:
* One parent was homozygous dominant and the other was homozygous recessive
* Both parents were heterozygous
* One parent was homozygous recessive, and the other was heterozygous
* One parent was homozygous dominant, and the other was heterozygous
Tall, Tall, Tall, Tall
Tall, Tall, Tall, Short
Tall, Tall, Short, Short
Tall, Tall, Tall, Tall
What is codominance, using blood groups as an example?
When both alleles within a genotype are different but both expressed in the phenotype
For example, to determine blood group, there are 3 alleles instead of the usual 2
The A allele will produce the A antigen, the B allele will produce the B antigen and the O allele will produce no antigens
A and B and both dominant over the O allele, but are not dominant over eachother
Therefore, if an individual has both A and B, they will produce both antigens
What are polygenic characteristics?
Characteristics which are controlled by multiple genes
In reality, most characteristics are determined by polygenic inheritance, but for simplicity things have been earlier explained as monohybrid (there only being one gene controlling each characteristic)
Polygenic characteristics can therefore show a much wider range of different combinations
How is sex determined in humans?
The 23rd chromosome pair will either be two X chromosomes, or an X chromosome and a Y chromosome
XX is female, XY is male
As you can see, the mother will always pass on an X chromosome, but the father could pass on either an X or a Y - therefore the father is responsible for determining the sex in a human
As with all characteristics, it is 50/50 because, as a result of meoisis, half of all the male gametes (sperm) will contain the X chromosome, and the other half will contain the Y chromosome
What is a mutation?
A rare, random change in genetic material, specifically the sequence of bases
How does a mutation change the genetic material?
Insertions - a random base is added to the sequence of bases, changing the amino acid that would have been coded for in the triplet in which the mutations occurred, and having a knock on effect down the strand
Deletions - a random base is deleted from the sequence of bases, having similar (but logically different) effects to insertions
Subsitutions - A base in the DNA sequence is randomly changed for another base - unlike insertions and deletions, this will only affect the amino acid which the affected triplet codes for
How can mutations affect the phenotype of an organism?
Changing the sequence of amino acids can change the protein a gene codes for
It can lead to a significantly altered protein, or a completely new protein
For example, if the affected protein is an enzyme, the shape of the active site can change and therefore it cannot fit the substrate
On rare occasions, a mutation can make the gene into a completely different allele, drastically changing the phenotype of an organism
How often do mutations affect the phenotype of an organism and why?
Most mutations have no effect, with only some having a small effect and very rarely do they have a significant effect
This could be because:
* The changed bases could still code for the same amino acids
* The changed amino acids may not be relevant to the function of the protein
* The protein may still be fairly similar and therefore perform same function, therefore no there is no effect on the phenotype
* The gene changed could be a recessive allele
