6.1 dna and inheritance Flashcards
(25 cards)
genes definition
a short sequence of dna that codes for a specific sequence of amino acids to make a protein responsible for a specific characteristic
4 bases
adenine
thymine
cytosine
guanine
mutations
changes in the sequence of bases in the dna
silent mutation—no effect, a change in dna base sequence means the the new triplet still codes for the same amino acid
dramatic effect - a change in DNA base sequence codes for a different amino acid—shale of protein is different, e.g. active site is no longer complementary to substrate
protein synthesis
when a particular protein is required, the section of the dna forming the gene is copied by making a mRNA copy
as only the code for one gene and not the whole dna has been copied it is small enough to tracel out of the nucleus
it binds to a ribosome which is where the protein eill be made
the order of bases on the mRNA is ‘read’ in groups of 3 letters by rhe ribosomes. each triplet is then used by the ribosome to guide the correct amino acids into place
The amino acids are carried to the ribosome by a carrier molecule called transfer RNA (tRNA). Each tRNA carries only one specific amino acid.
The amino acids join together to form a protein, which then folds to form a unique 3D shape that allows it to carry out its particular function e.g. it may fold to form the active site of an enzyme, the specific shape of a hormone or form long fibres in structural proteins such as collagen.
how does each gene determine a different characteristic about you
each gene controls the production of a protein which is responsible for the characteristics that a cell/organism possesses
genome
genome of an organism is its entire genetic material, including all the chromosomes in its nucleus and in its mitochondria
in plants there is also dna in the chloroplasts
Human Genome Project
started in 1990
aimed to identify all the genes in the human chromosomes and sequencing the 3 billion base pairs which make up the human DNA
discovered that not all parts of DNA code for proteins. Non-coding parts of DNA can switch genes on and off, so variations in these areas of DNA may affect how genes are expressed
applications of the human genome project
identify genes linked to non-communicable disease, e.g. cancer—early diagnosis due to genetic screening, personalised medicine
identify genes linked to inherited disease, e.g. cystic fibrosis—screening of newborns
trace human migration patterns from the past—test us more about our ancestors and histroy
identify differences in gene sequences between individuals—crime scene investigations, paternity testing
mendel
Mendel was an Austrian monk who carried out hundreds of breeding experiments with plants at his monastery
bred peas
looked for characteristics, e.g. wrinkly/round seeds, tall/short plants, pod colour, shape of pea
mendel crossed a pure breeding green and a pure breeding yellow plant, and the offspiring turned out all yellow
then he crossed two of the offspring—75% were yellow, and 25 were green
mendel called ‘units’/‘factors’ what we now call genes
mendel’s work wasn’t recognised until after his death as there was no mechanism as there was no knowledge of DNA
homologous pairs
pairs of chromosomes, one maternal, one paternal
alleles
different versions of the same gene
homozygous
both alleles in the genotype are the same
heterozygous
the alleles in the genotype are different
dominant
the allele that if present in the genotype will always be expressed in the phenotype
(written with capital letter)
recessive
the allele that is only expressed in the phenotype if there is no dominant allele present in the genotype
(lower case)
genotype
the alleles an individual possesses
phenotype
the physical characteristic, e.g. eye colour
this is due to genotype, but also can be due to environment in some cases
cross between two heterozygours pea plants (Yy and Yy) why are some of the offspring green, when both parents are yellow? 3 marker
both parents are heterozygous Yy
both parents will pass on the recessive green allele
the offspring genotype is homozygous recessive and therefore the phenotype is green
inherited genetic disorders
some disorders are inherited—caused by inheritance of certain alleles
some diseases are the result of change in the base sequences of our genes (mutation) and can be then inherited
for example:
cystic fibrosis
poludactyly
cystic fibrosis
caused by recessive allele
a disorder of cell membranes that means they are unable to transport certain substances
mucus secretions become very thick and sticky
organs become clogged up which stop them from working properly
symptoms particularly evident in lungs, pancreas, reproductive system
polydactyly
caused by dominant allele
having extra fingers and toes
can be passed on by only one parent who has the disorder
gamete
reproductive cell
male gamete = sperm
fermal gamete = ovum, pl. ova
chromosome
a long structure made of DNA found in the nucleus
contains many genes
screening for genetic diseases
first obtain cells from the developing individual to screen an embryo/foetus
these cells can either be extracted from the amniotic fluid or from the placenta
procedure usually takes place between 10-16 weeks of pregnancy
small risk of miscarriage
if IVF, embryo can be genetically screened before being implanted in the mother = preimplantation genetic diagnosis
