3.17-3.21 development and inheritance (not definitions) unit 2

why is cell differentiation important

enables the formation of specialised tissues with specific functions e.g. muscle tissue

what are embryonic stem cells

stem cells found in very early embryos that are unspecialised and capable of differentiating into any cell type

what is the function of embryonic stem cells

enables the growth and development of tissues in human embryos

where can embryonic stem cells be collected from

• donor stem cells removed from embryos grown in vitro

• patient’s own stem cells removed from the umbilical blood before birth

what are adult stem cells

stem cells that can differentiate into a limited range of cell types e.g. bone marrow stem cells

describe the potential uses of stem cells in medicine

• treat disease e.g heart disease, type 1 diabetes

• used to repair damaged tissue e.g. brain damage

• used in scientific research

• growing organs for transplants

what are the ethical issues related to the use of stem cells in medicine

• the embryos used to provide stem cells are destroyed which is seem as unethical and a waste of potential human life

• could lead to the ‘farming’ of embryos for stem cells

• may lead to the reproductive cloning of humans

what is a pluripotent stem cell

a type of stem cell which can differentiate into any type of cell in the body

what is a totipotent stem cell

a type of stem cell which can differentiate into any type of cell in the body or into cells which make up extra embryonic tissues like the placenta

what is gene expression

the synthesis of active functional products through the transcription and translation of a gene

how is pre-mRNA coverted to mature mRNA

post transcriptional modifications and splicing alter the structure of the mRNA molecule to remove introns

how can one gene give rise to multiple polypeptides

through alternative splicing where different exons are joined together in different orders to produce different mRNA molecules

what are epigenetic modifications

modifications which cause changes in gene expression that are not due to alternations in the nucleotide base sequence of DNA

what are histones

proteins which help to package DNA tightly in the form of chromatin, the DNA coils around the histone protiens

describe two types of epigenetic modifications

DNA methylation - the addition of methyl groups to cytosine bases in DNA, this typically downregulates transcription

histone acetylation - the addition of acetyl groups to histone proteins which make them bind less tightly to DNA molecules and hence allow for increased transcription

describe briefly what happens to epigenetic modifications after cell division

many epigenetic modifications are lost during cell division, some specific epigenetic modifications are retained during the production of new histones, each new DNA strand gets a mix of old and new histones, which means that some modifications are retained

what is multiple allele inheritance

how multiple different versions of the same gene affect a trait

what type of variation does polygenic inheritance give rise to

continuous variation

what is continuous variation

• variation that cannot be categorised

• produces a continuous range (e.g. height, weight)

what is discontinuous variation

variation that can be categorised into distinct groups e.g. eye colour, blood group