Genetics Flashcards
What is a gene?
A heritable factor that consist of a length of DNA and influences a specific characteristic
What do most genes code for?
A polypeptide
What is the gene locus?
The specific position that the gene occupies on a specific chromosome
List the few trends for gene numbers
- Prokaryotes have fewer genes than eukaryotes
- Some animals have fewer genes than humans, others more
- Some plants have fewer genes than humans, but many have more
What are alleles?
Alternative forms of the same gene that differ in just one or very few bases.
What do alleles occupy?
The same gene locus and influence the same characteristic
What are the alleles for blood group?
IA, IB and i
How are new alleles formed?
By mutation and thus are a source of genetic variation necessary for evolution
What are mutations?
Random changes to the base sequence of a gene/DNA
What is base substitution?
A mutation which replaces one base with another
What can most mutations be classified as?
Harmful or neutral
What can mutations cause?
Cancer
If a harmful mutation occurs in a cell that will develop into a gamete, it will be passed on to offspring and may cause genetic disease
What can cause mutations?
They are RANDOM
- can be caused by errors made by DNA polymerase during DNA replication
- Mutagens that affect bases/nucleotides. Mutagens include high energy radiation and mutagenic chemicals
What are mutagens?
Factors that increase the mutation rate
What is sickle cell anemia?
A genetic disease that demonstrates how a single base substitution mutation can have significant consequences for the individual
Describe what people without sickle cell anaemia have
- Have the allele HBA which codes for the alpha globin polypeptide of haemoglobin
- 6th triplet is GAG
- mRNA has a codon of GAG
- glutamic acid is produced
Normal red blood cells, normal haemoglobin, efficient transport of oxygen, affected by malaria
Describe what people with sickle cell aneamia
- Base substitution mutation in the 6th triplet changes DNA from GAG to GTG
- Allele becomes HBS
- mRNA has a codon of GUG
- different tRNA minds to the codon and the 6th amino acid is valine
Sickle-shaped red blood cells, abnormal, less soluble haemoglobin, anaemia, resistant to malaria
What is the genome?
The whole of the genetic information of an organism
What is the genome size?
Total amount of DNA of an organism measured in millions of base pairs
What does the genome consist of in animals?
All the chromosomes in the nucleus and the mitochondria
What does the genome consist of in plants?
Chromosomes in the nucleus, mitochondria and chloroplasts
What does the genome consist of in prokaryotes?
The single chromosome plus any plasmids
What are the differences between prokaryotic and eukaryotic chromosomes?
Prokaryotes have circular DNA molecule whereas eukaryotes have a linear DNA molecule
Prokaryotes have naked chromosomes whereas eukaryotes have chromosomes associated with histones
Prokaryotes have one chromosome only whereas eukaryotes have two or more different chromosomes
What are the differences between prokaryotic and eukaryotic genomes?
- Prokaryotes have chromosomes with circular DNA, Eukaryotes have chromosomes with linear DNA.
- Prokaryotes have chromosomal DNA that is naked, Eukaryotes have chromosomal DNA associated with proteins called histones
- Prokaryotes have one chromosome only, eukaryotes have two or more
- Prokaryotes have plasmids present eukaryotes do not
- Prokaryotes have no mitochondrial or chloroplast DNA whereas eukaryotes have mitochondrial DNA and sometimes chloroplast DNA
- Prokaryotes have a smaller genome whereas eukaryotes have a larger genome
- Prokaryotes have a haploid genome whereas eukaryotes have a diploid genome