Inheritance and evolution. DNA, genes and chromosomes; how meiosis makes every gamete different; predicting offspring with Punnett squares; then variation in a population and natural selection. Concept tutorials with a zoom from body to gene, a live cross board and a beetle population that evolves.
DNA, genes and chromosomes, meiosis, and patterns of inheritance (AC9S10U01).
DNA carries the instructions for an organism. It is coiled into chromosomes in the nucleus; a gene is a section of DNA that codes for a protein. Alleles are different versions of the same gene.
Meiosis makes gametes. The chromosome pairs separate and each gamete gets one chromosome from each pair, chosen at random, so it has half the number and a different combination. With 23 pairs there are over 8 million combinations.
A Punnett square shows every way two parents' gametes can combine for one gene. It gives the probability of each genotype and phenotype (such as 3 in 4 showing the dominant trait for Pp × Pp), not a guaranteed count.
A few quick questions on mitosis, how fertilisation and meiosis give variation among siblings, and sex-linked inheritance. Taught in class; use this to check yourself.
Variation in a population and natural selection (AC9S10U02).
Individuals in a population vary. Measuring one characteristic across a population gives a spread of values, often most near the middle. Some variation is inherited (genes) and some comes from the environment; inherited variation is what natural selection acts on.
Natural selection: individuals vary; more are born than survive; those best suited to the environment are more likely to survive and reproduce, passing on their alleles. Over generations the population changes. Individuals don't change to suit the environment.
A few quick questions on the evidence for evolution, how new species form and die out, and evolution happening now. Taught in class; use this to check yourself.
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