9A- Inheritance and variation Lesson 3: Basic Genetics

Learning Objectives Describe the work of Mendel in discovering the basics of genetics dominant and recessive genes

Selective Breeding Historically people have selectively bred plants and animals for specific traits (variations) Cows- milk and meat Chickens-eggs and meat Horses/camels- speed and stamina Corn/grain/vegetables- flavour and hardiness Dogs- working and show Flowers- beauty

Inheritance How are traits passed from parents to offspring? Old theory- offspring a mixture of parents but this didn’t explain why some traits disappeared and then reappeared

Gregor Mendel (1866) selectively bred pea plants over years he always found the same ratios when breeding pure strains of discontinuous characteristics Flower colour (purple or white) Stem length (long or short) Seed shape (round or wrinkled) Seed colour (yellow or green) Pod colour (yellow or green)

Dominant and Recessive He found that when he crossed a yellow pea plant with a green pea plant all the new plants were yellow pea plants. BUT when he crossed these first generation yellow peas the next generation had the green pea return in a 3:1 ratio What was going on?

Principles of inheritance Traits are determined by “units” of inheritance (genes) An individual inherits one unit (allele) from each parent for each trait The trait may not show up in an individual but can be passed on to the next generation (carrier) Dominant alleles will mask a Recessive allele Genes pairs are assigned letters Capital (W ) for dominant lower case (w) for recessive

Three possible combinations WW- homozygous dominant Ww- heterozygous ww- homozygous recessive WW and Ww will show the dominant trait ww will show the recessive trait

Basic genetics the pair of genes (alleles) of each parent separate and only one allele passes from each parent on to the offspring. new combinations of genes from the parents occur randomly- creates variation

Punnett Square- predicting crosses

Punnett Square

Make three of your own

Task: Booklet Reference: textbook p.9 Worksheets: Mendel, 1.23, 9Ab-7,9Ab-9 Reference: textbook p.9