Essay Question Practice Flashcards
Describe how meiosis and different types of mutation contribute to genetic variation and the role of this variation in natural selection
Meiosis :
- crossing over of chromatids of homologous chromosomes takes place in prophase 1
- points at which chromatid crossover is called chiasmata
- Genetic material is exchanged between is exchanged between maternal and paternal chromosomes
- random arrangement of chromosomes occurs during metaphase 1
- Separation occurs in a random independent manner
- resulting in new combinations of genetic material
Mutations
- A gene mutation occurs
- as a result of change in sequence of nitrogen base in DNA
- A chromosome mutation occurs
- as result of change in structure of chromosome or number of chromosomes during meiosis
- mutations that occur in sex cells
- are passed on to new generations
- creating new characteristics
Natural selection
- Organisms in specific species show great deal of variation
- some individuals have characteristics that are favourable (example)
- others may have characteristics that are unfavourable (example)
- competition or environmental conditions occur / selectivepressure
- organisms with favourable characteristics survive
- pass this trait onto their offspring
- other organisms with unfavourable characteristics will die out
- over time the entire population will have the favourable trait
Describe the process of protein synthesis and the way in which this process would be affected by a gene mutation
Transcription
- Double stranded DNA unwinds and unzips when weak hydrogen bonds break
- this is controlled by enzymes
- one strand is used as a template
- to form mRNA
- using free RNA nucleotides from the nucleoplasm
- The mRNA is complimentary to the DNA
- mRNA now has the coded message for protein synthesis
Translation
- mRNA moves from the nucleus to ribosome
- each tRNA carries the amino acid to the ribosome
- when anticodon on the rRNA matches the codon on the mRNA
- Amino acids become attached in the sequence determined by the mRNA by peptide bonds
- to form the required protein
Effects of a mutation
- A gene mutation affects arrangement type of the nitrogen bases /nucleotides
- This changes the code on the DNA
- which changes the code on the RNA
- A different amino acid may be coded for which causes a change in the amino acid sequence in the protein
- leading to the formation of a different protein
Fossils of the bipedal primates Ardipithecus, Australopithecus and early homo species are used to support the “Out of Africa” hypothesis
state the “out of Africa” hypothesis. Describe the evidence that supports the ‘Out of Africa” hypothesis and the evidence that shows that the three primate genera mentioned above, were all bipedal
Hypothesis
-All modern humans/Homo sapiens/ originated in Africa and migrated to other parts of the world.
Fossil evidence
- Ardipithecus fossils were only found in Africa (Rift valley Ethiopia and south Africa )
- Australopithecus fossils were found only in Africa (Rift valley Ethiopia and South Africa)
- The homo Habilis fossils were only found in Africa
- The oldest fossils of homo Erectus were found in Africa
- The oldest fossils of Homo sapiens were found in Africa
Genetic evidence
- Mitochondrail DNA is inherited only from maternal line
- Analysis of mutations on this mitochondrial DNA shows that the oldest female ancestor were located in Africa and that all humans descended from her/mitochondrial Eve
- The Y chromosomes shows paternal line
Cultural evidence
-The oldest artefacts(tools , cutlery and art) were found in Africa
Bipedalism
- The foramen magnum is located in a more forward position
- the pelvis is wider and shorter
- the spine is S-shaped
