Genes SL Flashcards
Define “gene”
A gene is a length of DNA that codes for a polypeptide
Define locus (plural: loci)
A locus is the specific position of a gene on a chromosome.
the gene for a particular characteristic is always found at the same position on a particular chromosome, known as the locus.
What is the number of genes in humans? Name 2 other species, one with more genes than a human and one with less.
Humans have about 20,000 genes.
DOGS have around 19,000
Rice plants have around 41,500
List the number of genes of any plant, and any bacterium
Rice plants have around 41,500
e.coli bacteria have around 4,300
Water flees have around 31,000 genes.
What are alleles?
Alternative forms of a gene
A: What are homologous pairs of chromosomes?
B: What does it mean when an allele is homozygous or heterozygous?
A:
Homologous pairs are two copies of each chromosome, one copy inherited from each parent. This means that cells have 2 copies of every gene.
Homologous chromosomes have the same genes on the same loci, and are the same size. But may not be genetically identical since each one may contain different alleles of the same gene.
B:
Homozygous alleles are when 2 alleles at the same locus on 1 homologous pair of chromosomes are the same/identical
Heterozygous alleles are when 2 alleles at the same locus on 1 homologous pair of chromosomes are the different
Define gene mutation
It is a change in the sequence of base pairs in a DNA molecule, which may result in a new allele, which may affect the phenotype
When is it most likely for a mutation to occur? Explain why
During the S phase in interphase, because that is when DNA is replicated, so copying errors may occur.
Are mutations harmful?
Are mutations inherited? and why?
Most mutations are harmful or have no effect, but some can be beneficial
Mutations in normal body cells are not inherited, and are usually gone when those cells die
However, mutations in gametes are inherited and usually result in genetic diseases.
Outline substitution mutation
Substitution mutation is when a base in the DNA sequence is substituted for another, which results in the formation of another amino acid.
What is a disease that is caused by a substitution mutation?
What is the mutation that occurs exactly in detail?
Sickle cell anaemia
It is caused by a single base substitution mutation within the gene (Hb) that codes for the alpha-globin polypeptide in haemoglobin. The normal allele is HbA
Within the hemoglobin gene, the base adenineis substituted with the base thymine, which leads to the DNA triplet mutating to GTG insead of GAG
The mutated gene GTG is transcribed into GUG now, which results in the amino acid valine (val) instead of glutamic acid (glu)
The allele for the mutation is HbS
What are the effects of the sickle cell anaemia mutation and disease?
The protein haemoglobin S is produced instead of haemoglobin A. Which results in sickle shaped red blood cells.
Sickle shaped red blood cells have:
- limited oxygen carrying capacity
- Blocking capillaries because sickle cells have trouble traveling through capillaries
- People with sickle cell anaemia suffer from acute pain, fatigue and anaemia
What is a genome and what does it include?
It is the total of all genetic information in an organism, it also includes non coding DNA, as well as mitochondrial and chloroplast DNA
What is DNA like in prokaryotes?
Naked DNA, in one single circular chromosome known as nucleoid. Plasmids are small circular DNA around the cytoplasm that contain some info about genes.
Describe the general structure of Eukaryotic chromosomes
2 chromatids joined by a centromere which makes them into one chromosome. Each chromatid is made up of long kengths of DNA that is warpped around proteins called histones. The structure in which the DNA is wrapped round histones is called chromatin.
