Human bio mutations and evolution and genes and stuff Flashcards
Define mutation
A change in a gene or a chromosome leading to new characteristics in an organism
What are two types of mutations
Gene mutations
- changes in a single gene so that the trait normally produced by that gene are changed or destroyed and occurs during replication of DNA before cell division
Chromosomal mutations
- mutations in which all or part of a chromosome is affected
What are causes of mutations
Induced mutations
- mutation caused by a mutagenic agent
Spontaneous mutation
- mutation that occurs due to error in natural biological processes
What are effects of mutations
Missense mutations
Caused by change in the amino acid, and therefore in the protein produced
Nonsense mutations
Changes the base sequence to the code to stop, this means the synthesis of the protein will stop, and so a shorter protein is produced that is unlikely to fulfil its function
Neutral mutations
Causes a change in an amino acid; howerever, the amino acid is of the same type and does not change the structure of the protein enough to change its function
Silent mutations
Does not cause any changes in the amino acid and therefore in the protein produced. This is possible as most amino acids are coded for by more than one base sequence
Describe point mutations
Point mutations occur to due changes in a single nucleotide, which may be due to the nucleotide being:
Inserted - a new nucleotide is added to the DNA strand
Substituted - an existing nucleotide is replaced with another once, with a different base
Deleted - a nucleotide is removed from the DNA strand
Frameshift - a mutation involving an insertion or deletion of that results in a change in the way a sequence is read
What can cause chromosomal mutations?
Duplication - a section of chromosome occurs twice
Deletion - a piece of DNA is removed
Inversion - breaks occur in a chromosome and the broken piece joins back in, but the wrong way around
Translocation - part of a chromosome breaks off and is re-joined to the wrong chromosome
Nondisjunction - during meiosis, a chromosome pair does not separate and so one daughter cell has an extra chromosome and one daughter cell has one less than the normal number.
What is a lethal recessive and an example
A recessive allele that, inherited in the homozygous condition, results in the death of the embryo, foetus or child
Example: Tay-Sachs disease
Describe Tay-Sachs disease
It is a lethal recessive condition caused by a mutation in the HEXA gene that codes for the enzyme beta-hexosaminidase
This enzyme responsible for breaking down toxic substances, including fatty substance called GM2 ganglioside, in the brain and spinal cord
The missing enzyme results in the accumulation of GM2 ganglioside in the nervous system, destroying neurons
Intellectual + physical disabilities for baby, death usually occurs in early childhood
What is variation
Difference in characteristics such as height, weight, skin colour, eye colour
How can variation occur
Mutations, epigenetic factors, sexual selection, random fertilisation, meiosis (nondisjunction, crossing over, independent assortment)
How does random assortment occur?
At fertilization, zygote chromosomes get one set of chromosomes from mother (maternal) and one from father (paternal)
Chromosomes exist in homologous pairs
1st stage of meiosis, homologous pair separate randomly
How does crossing over occur?
1st division of meiosis, chromosomes may get tangled = crossing over
Chromatids may break and reattach = recombination
How does non-disjunction occur
1st division of meiosis, chromosomes pair then separate
One or more of the chromatids may fail to separate
Daughter cells may then lack or gain a chromosome
Monosomy (missing a chromosomes) / trisomy (extra chromosome)
Trisomy 21 = down syndrome
