Genetics basics Flashcards
(30 cards)
incomplete dominance
when a dominant allele does not completely mask the effects of a recessive allele and the resulting physical appearance shows a blending of both alleles
(ie. white and red flowers producing pink flowers)
codominance
both alleles are dominant and are expressed equally in the phenotype
(ie. AB blood type - A and B alleles are codominant)
autosome
any chromosome that is not a sex chromosome
name for pair of human chromosomes (XX) or (XY)
allosomes
epistasis
when one gene depends on another gene to be expressed
locus
position on a chromosome where a particular allele is found
monohybrid inheritance
inheritance of characteristics controlled by a single gene
normal GCSE punnett squares
X-linked and Y-linked
genes on the X chromosome
genes on the Y chromosome
sex-linked characteristic
when the allele that codes for the characteristic is on the X or Y chromosome
gene pool
complete range of alleles present in a population
genetic disorder
disorder caused by an abnormal gene or chromosome
dihybrid inheritance
inheritance of two different characteristics simultaneously
4x4 punnett square
autosomal linkage
genes located on the same chromosome (but cannot be sex chromosomes)
Hardy-Weinberg equation
mathematical model which can be used to predict the allele frequencies within a population.
Fault to Hardy-Weinberg equation
It assumes that there will be no change in the allele frequency between generations within a population (e.g. no deaths, births or migration), so it is not perfectly accurate.
aneuploidy
abnormal number of chromosomes present in the cell (for example a human having 47 rather than 46)
cause of Down’s syndrome
inherited 3 copies of chromosome 21 rather than 2
in punnett squares what goes along the top and what goes along the side?
XX along top (then below the alleles)
XY along side (then to right the alleles
THEN do the matching up or whatever
What are telomeres ?
A form of junk DNA
Repeats of the same six base pairs, TTAGGG that stretch for around 10 000 base pairs on the end of each of our chromosomes
How do telomeres allow the chromosome to be replicated properly during cell division?
Every time a cell carries out DNA replication the chromosomes are shortened by about 25-200 bases.
However because the ends are protected by telomeres the only part of the chromosome that is lost is the telomeres so the actual DNA is left u damaged.
Without telomeres important DNA would be lost every time a cell divides and so eventually the whole genome would be lost.
As we age, telomeres shorten. What factors can be attributed to this?
1) the end replication problem accounts for the loss of about 20 base pairs during cell division
2) oxidative stress accounts for the loss of 50-100 base pairs per cell division (amount of oxidative stress thought to be affected by lifestyle eg. Smoking)
What is the end replication hypothesis?
X
The ends of linear DNA cannot be replicated completely during lagging strand DNA synthesis.
What happens when a telomere becomes too short?
It reaches a ‘critical length’ and can no longer be replicated. The critical length triggers cell apoptosis.
How is telomere length maintained?
Telomerase is an enzyme that adds TTAGGG sequences to the end air the chromosome.
Telomerase is found in low concentrations in somatic cells. Because these cells don’t regularly use telomerase they age and this leads to a reduction in normal function.
Telomerase is found in high levels in egg and sperm cells and stem cells. In these cells telomere length is maintained after DNA replication so cells do not show signs of ageing.
