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 embryonic 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 (multipotent)
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 like leukaemia or replace damaged tissue, could improve quality of life of people
- May be able to grow organs from stem cells in future, helping those in need of organ donors
- 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
~ Within cells certain genes are activated (turned ‘on’) and others inactivated (turned ‘off’)
~ only activated genes are transcribed into mRNA, which is translated into a protein
~ proteins formed modify cells structure and cellular processes —> these changes cause the cell to become specialised
What are transcription factors?
Proteins which carry out activation and deactivation of genes
Describe the two types of transcription factors
Activators = activate genes; bind to promoter region (beginning of gene) and help RNA polymerase bind and transcribe the gene Repressors = deactivate genes; bind to the gene, blocking RNA polymerase from binding
What are operons and describe their structures
The area where transcription factors bind to (in prokaryotes); contain:
- structural genes —> code for useful proteins e.g. enzymes
- control elements —> contain a promoter region where RNA polymerase binds to + an operator region where TFs can bind
- regulatory genes —> code for transcription factors
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 by 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 proteins involved in transcription from binding
-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 chromatins, allowing transcription
Define codominance
When both alleles are expressed in the phenotype; occurs when heterozygous for a trait
Describe role of the lac operon in E. coli bacteria
- found in E. coli which feed on glucose —> when glucose not present, can digest lactose
- genes which produce enzymes to digest lactose are found on the lac operon
- when lactose is absent, a regulatory gene produces a lac repressor protein; this binds to the operator region, blocking RNA polymerase from binding so structural genes aren’t transcribed
- when lactose is present, lactose binds to the repressor, changing its shape so it no longer binds to the operator region —> allows RNA polymerase to bind to the promoter region, transcribing the structural genes which code for proteins allowing E. coli to respire lactose
