revision - inheritance Flashcards
what is the genome
the entire DNA of an organism
what is a gene
a section of a molecule of DNA that codes for a specific protein
where are genes located
in chromosomes, which are contained in the nucleus of a cell
describe the structure of a DNA molecule
two strands coiled to form a double helix
DNA made up of nucleotides, which contains a deoxyribose sugar, a phosphate and a base.
the strands are linked by paired bases (adenine - A - with thymine - T - and
cytosine - C - with guanine - G -)
how is an RNA molecule different to a DNA molecule
it is single stranded, and contains uracil (U) instead of thymine (T)
describe the process of transcription (protein synthesis pt1)
- the hydrogen bonds between the DNA strands are broken (double helix separated)
- free RNA nucleotides (hydrogen) bond to the template strand (one u want to copy) of the exposed DNA
- RNA polymerase joins the RNA bases together, to form a mRNA molecule
- The (hydrogen) bonds between the DNA template strand and the mRNA break
- The mRNA leaves the nucleus, moves towards then attaches to a ribosome
describe the process of translation (protein synthesis pt2)
- A tRNA molecule, with the anticodon complementary to the first codon of the mRNA strand brings the first amino acid to the ribosome.
- The ribosome catalyses a reaction between the 2 amino acids which attaches to the two adjacent tRNA molecules, forming a polypeptide chain
- This process continues until a stop codon is reached
- The polypeptide chain folds to form a functional protein
what is a mutation
a rare, random change in genetic material, that can be inherited
how does a change in DNA affect the phenotype
If nucleotides are missed out, swapped, reversed or an extra one is added, this alters the sequence of the amino acids and changes the phenotype
what are the effects of genetic mutations and why
most genetic mutations have no effect on the phenotype some have a small effect and rarely do they have a significant effect. This is because the change in base may still code for the same protein, it could still result in a functional protein, or could affect a recessive allele, so is not expressed in the phenotype
how can the incidence of genetic mutations be increased
by exposure to ionising radiation and some chemical mutagens (e.g. chemicals in tobacco)
number of chromosomes in a human diploid cell
46
number of chromosomes in a human haploid cell
23
what can cause variation within a species
can be genetic (eye colour) , environmental (hair length) or a mixture of both (strength)
what is an allele and what do they lead to
alleles are different forms of genes, and they gives rise to differences in inherited characteristics.
what is polygenic inheritance
Inherited characteristics which are controlled by 2 or more genes
what are most phenotypic features controlled by
mostly polygenic inheritance, but sometimes single genes
how can we describe/predict probabilities of monohybrid inheritance
with a punnet square
how are males and females represented on pedigree diagrams
males - squares
females - circles
what is sex of a person controlled by
one pair of chromosomes
XY - male
XX - female
what is codominance and common examples
when both alleles are expressed in the phenotype of an individual. AB blood type, roan cows, pink snapdragons
general structure for a natural selection question
- random mutation meant…
- selective pressure introduced
- those individuals have selective advantage, more likely to survive, more likely to reproduce
- pass on their advantageous alleles
- over time, other type outcompeted/more mutated ones than non
evidence for Darwin’s natural selection theory
- Galapagos finches
- fossil records
- peppered moth
- homologous bones in mammals
