Genetics Flashcards
Missense mutation
A missense mutation is a type of point mutation that results in a** single amino acid change in the protein sequence. **This happens when a single nucleotide change causes a codon to encode a different amino acid.
Sickle cell anemia is caused by a missense mutation in the HBB gene, where the amino acid glutamic acid is replaced by valine.
In frame mutation
deletion type
An in-frame mutation is a genetic mutation where the number of nucleotides inserted or deleted is a multiple of three (i.e., 3, 6, 9, etc.). **This ensures that the reading frame of the mRNA is not shifted, meaning the downstream codons (and thus the amino acids they code for) remain the same. However, some amino acids may be added or deleted depending on the mutation.
e.g. Cystic fibrosis can be caused by an in-frame deletion of three nucleotides in the CFTR gene, leading to the loss of a single amino acid (phenylalanine at position 508).
out of frame mutation
deletion type
An out-of-frame mutation (also known as a frameshift mutation) occurs when the insertion or deletion of nucleotides is not a multiple of three. This shifts the reading frame of the genetic code, changing the grouping of codons and often leading to the production of an* entirely different and nonfunctional protein.*
promotors
premature stop
promoter
the beginning of the gene
The starting point of a gene is determined by a promoter region, which is a repetitive non-coding sequence of nucleotides - for example, T A T A T A T A sequence is one very famous promoter, called the TATA box - that marks where to begin transcribing.
A few dozen proteins and enzymes come together to form what’s called a pre-initiation complex around the promoter, also featuring an enzyme called RNA polymerase.
GENETIC code that encodes for a stop codon
UAA
UAG
POINT MUTATIONS
single nucleotide base in the DNA sequence has changed.
could be insertion/deletion/substitution
- Silent mutations: The mutation does not change the amino acid due to the redundancy of the genetic code.
- Missense mutations: The mutation changes the amino acid in the protein sequence.
- Nonsense mutations: The mutation introduces a premature stop codon, truncating the protein.
purine
A / G
pyrimidine
C / T
how do you describe a mutation, where a stop codon has been introduced? (notation)
TER
or *
mosaicism
we all have some amount of mosaicism — The more frequently mosaicism is found in the body, the greater likelihood a person can develop a health condition because of it.
Mosaicism occurs when a person has two or more genetically different sets of cells in his or her body. If those abnormal cells begin to outnumber the normal cells, it can lead to disease that can be traced from the cellular level to affected tissue, like skin, the brain, or other organs.
It happens after the sperm fertilizes an egg, forming a zygote, which grows through a process of cells dividing over and over and over. When cells divide and multiply, they make an exact copy of their DNA, and then split the copies between each of the resulting two cells. If there is a mistake anywhere in this process—for example, a DNA copy that contains a mistake or DNA that is split unevenly, the resulting cells would be different. In some cases, the abnormal cell may simply die; but, if it survives, the result is mosaicism. If this occurs early in development, as many as 50% of a person’s cells could be abnormal, which would be a high level of mosaicism. If the mistake happens later, however, a smaller percentage of cells would be abnormal, resulting in a lower level of mosaicism. The impact of mosaicism is typically determined by the severity of the mistake in the DNA, as well as the degree of mosaicism.
–> Triple X syndrome. This condition is caused by an extra X chromosome in each of a woman’s cells. It can cause learning disabilities, delayed language skills, and problems with motor skills and muscles.
–> Trisomy 18. This condition can cause slow growth in the womb, heart defects, a small head, and other defects. Only a small number of children with this condition live past their first year.
–> Turner syndrome. This is a condition in women that causes short height, ovarian problems, lack of fertility, and heart defects.
most common cause of trisomy 21 (causing down syndrome)
non-disjunction of chromosomes 21 at meiosis (during anaphase II)
Frameshift mutation
a type of genetic mutation that occurs when nucleotides (the building blocks of DNA) are either inserted or deleted from a DNA sequence in numbers that are not multiples of three. This alters the reading frame of the genetic code, which has significant consequences for protein synthesis.
