Genetics Flashcards
Define locus
The position of a gene on a chromosome
Why are some genes said to be linked?
Genes with loci on the same chromosome are linked; bc this means they’ll stay together during independent assortment + their alleles passed onto offspring together
- Closer together loci = more close linkage
What is sex-linked characteristic?
When the locus of the allele coding for it is on a sex chromosome
Why are males more likely to show recessive phenotypes for sex-linked genes?
- Y chromosome is smaller than the X + carries fewer genes
- as males have only one X chromosome, often have one allele for sex linked genes, meaning they express the alleles characteristic even if it’s recessive
- also more likely to express disorders caused by faulty genes on X chromosomes called X-linked disorders
Define autosomal
Describes all chromosomes excluding sex chromosomes
Define stem cell
An undifferentiated cell which can divide to become other cell types
Define the three types of stem cells
Multipotent = can give rise to many different cell types
Pluripotent = able to give rise to many types of specialised cells but not placental cells
Totipotent = can give rise to all/any types of specialised cells including placental cells
What are the two sources of stem cells and which type are they?
- Embryonic stem cells (totipotent) or adult stem cells (pluripotent)
Give examples of sources for adult stem cells
- bone marrow
- skin
- brain
- umbilical cord blood
What are the positives and negatives of stem cell use?
+ Can be used to treat diseases or replace damaged tissue, could improve quality of life of people
- Adult stem cells can have permission from donor
— Unethical - people may object to killing of embryos in embryonic stem cell extraction, often use IVF embryos
- Also a risk of infection when cells are transported
Name the process by which cells become specialised
Differential gene expression
Describe the process of cells becoming specialised
~ Stimulus acts on unspecialised cells
~ Activator + repressor molecules bind to promoter regions on DNA sequence
~ Some genes become switched on and are active whilst others are switched off
~ Active genes are transcribed to produce RNA
~ mRNA is then translated on ribosomes + used to produce proteins
~ Protein is able to change structure + function of cells
What are operons?
Section of DNA including:
- group of structural genes transcribed together
- control elements —> promoter region (where RNA polymerase binds to) + operator region (where transcription factors bind)
- regulatory genes coding for repressor/activator proteins
What are regulatory molecules + 3 types?
- Molecules affecting expression of operons
~ repressors = proteins which suppress transcription of gene in response to external stimulus
~ activators = proteins which increase transcription of genes in response to external stimulus
~ inducers = small molecules activating or repressing transcription depending on needs of cell + substrate availability
Describe the lac operon and how it is involved in gene expression
• Operon containing genes necessary to acquire + process lactose from environment
• used in E. coli as it can use lactose for energy when glucose is low
• when glucose is absent but lactose present, catabolise activator protein CAP binds to operator to activate transcription
• if lactose is absent, repressor binds to operator to prevent transcription
Define phenotype
Characteristics of an organism, resulted from the interaction of genes of organism with its environment
Describe the two types of variation in phenotype
Continuous = When individuals in a population vary within a range e.g. height, mass
Discontinuous = When there are distinct categories e.g. sex, shoe size
Which characteristics tend to fall under discontinuous and continuous variation?
Monogenic —> coded for by one gene; tend to show discontinuous variation (e.g. blood type)
Polygenic —> coded for nu multiple genes on different loci; tend to show continuous variation
What are epigenetic modifications?
Changes in DNA which alter expression of genes but do not change the base sequence
How does DNA methylation result in epigenetic changes?
- Methyl groups are added to DNA, modifying the function of the DNA
- Typically suppresses gene transcription (turns genes off), preventing cell from converting back into stem cell or another cell type
-Can be removed through demethylation
How does histone modification result in epigenetic changes?
- DNA wraps around proteins called histones
- when histones are tightly packed, proteins reading the gene cannot access DNA, so gene is turned off
- when loosely packed, genes turned on
- acetylation (addition of acetyl group) results in loose packing of nucleosomes, allowing transcription
How does non coding RNA result in epigenetic changes?
Non coding RNA controls gene expression by attaching to coding RNA (creates proteins) to break it down so it cannot create proteins
Define codominance
When both alleles are expressed in the phenotype; occurs when heterozygous for a trait
