Noadswood Science, 2012

Mendel’s Experiments  To be able to explain Mendel’s experiments and why he is deemed the ‘father of genetics’ Saturday, January 23, 2016

Inherited  Children usually look a little like their father, and a little like their mother, but they will not be identical to either of their parents  Why is this?  Offspring get half of their inherited features from each parent  During fertilisation, the nucleus from the sperm cell joins with the nucleus in the egg cell, and a new nucleus is formed with all the genetic information needed

Inherited  Some variations are inherited, whilst other variations are due to environmental factors  Inherited variation is a characteristic you have got from your parents - what can you inherit? Gender Eye colour Hair colour Skin colour Lobed or lobeless ears Lobed (left) & lobeless (right) ears

Alleles  Some characteristics, such as eye colour and the shape of the earlobe, are controlled by a single gene – these genes may have different forms which are called alleles (one form of a gene)  The gene for eye colour has an allele for blue eye colour and an allele for brown eye colour  Alleles can be dominant (expressed) or recessive (masked or suppressed when in the presence of a dominant allele)

Alleles  The characteristic controlled by a dominant allele develops if the allele is present on one or both chromosomes in a pair  The characteristic controlled by a recessive allele develops only if the allele is present on both chromosomes in a pair  The allele for brown eyes is dominant, while the allele for blue eyes is recessive  An individual who inherits one or two alleles for brown eyes will have brown eyes  An individual will only have blue eyes if they inherit two copies of the allele for blue eyes Individuals A and B have brown eyes - only individual C has blue eyes

Mendel  Gregor Mendel ( ) studied the inheritance of different characteristics in pea plants  He found that when he bred red-flowered plants with white-flowered plants, all the offspring produced red flowers  If he bred these plants with each other, most of the offspring had red flowers, but some had white – this was because the allele for red flowers is dominant, and the allele for white flowers is recessive…

Genetic Diagrams  Genetic diagrams show all of the possible alleles for a particular characteristic  There will be two alleles from one parent, and two from the other parent, making four altogether  Lines show all the possible ways that these alleles could be paired in the offspring  There will be four possible ways, but some or all of them could be repeated  In genetic diagrams, the dominant allele is shown as a capital letter, while the recessive allele is shown as a lower-case letter

Genotype & Phenotype  The allele pair for each characteristic is called the genotype  The physical expression of an allele pair is the phenotype  What are the phenotypes of these genotypes? rrRRRr

Mendel’s Experiment  Mendel took 2 plants – one which is pure-bred for tallness and one pure-bred for shortness  He then crossed them: -

Mendel’s Experiment Two of these plants were then crossed… All the plants produced were tall 3 out of every 4 plants were tall Mendel hypothesised that for every characteristic there must be two determiners

Genetic Diagrams  Mendel’s first cross – all the offspring have red flowers, even though they carry the recessive allele for white flowers

Genetic Diagrams  Mendel’s second cross – three-quarters of the offspring have red flowers and a quarter have white flowers

Mendel  Unfortunately, nobody knew about chromosomes or genes when Mendel published his findings so no one believed him until many years after his death (when more powerful microscopes were available)