Heredity

What would you do if you opened your eggs and saw that some of them were blue or green?

Selective Breeding in Agriculture For thousands of years farmers have selective bread animals to get the traits they want. Farmers mate one animal with qualities they want with another with qualities they want hoping to get animals with both qualities. This the earliest form of Heredity. –Heredity is the passing of traits from parents to offspring.

Gregor Mendel 1822 Mendel was a monk from Austria He grew up on a farm so he grew crops in the monastery garden He was the first to use plants to learn how traits are passed from one generation to another.

Why peas? Peas grow relatively quickly Pease come in many varieties Pease are self-pollinating –Self-pollinating= contains both male and female reproductive structures and can fertilize itself or another plant.

Mendel’s First Experiment Round crossed with Wrinkled The results:100% Round Does this surprise you? What happened to the trait for wrinkled seeds?

Mendel repeated this for other traits… Mendel had similar results from the other crosses he made One trait always appeared, then the other trait seemed to vanish.

What happened to the wrinkled seeds? Mendel allowed the first generation from each of the seven crosses to self-pollinate. He crossed two of the offspring In this second generation the trait that disappeared reappeared. 3 of the offspring were Round and 1 was wrinkled.

Mendel’s Brilliant Idea Mendel concluded each plant had two sets of instructions for each characteristic. The fertilized egg would then have two forms of the same GENE for every trait- -one from each parent. The two forms of a gene are known as ALLELES. –Homozygous – two identical alelles(HH) –Heterzygous – two different alelles(Hh)

But what about the wrinkled ones? Traits can be expressed as dominant or recessive. Dominant alleles mask the expression of recessive alleles. –They are written with a capital letter. Recessive alleles are only expressed when there they are by themselves. –-They are written with a lower case letter.

Peas, For Example, Round is dominant to wrinkled If an plant gets an allele for round from its mother and an allele for wrinkled from its father then the plant will be round. If the dominant is present it masks the expression of the recessive.

The Punnett Square A punnett square is used to visualize all the possible combinations of alleles from the parents. Dominant alleles are symbolized with capitol letters and recessive with lowercase letters. Like algebra, you can use any letter to symbolize a trait.

Birdie Example Blue bird crossed with a red bird. Each box represents a potential offspring. Remember meiosis? Half from mom, half from dad? Mom only has A and Dad only has a to give. All offspring in this case will be red because the A masks the expression of the a.

Genotype vs Phenotype The inherited combination of alleles is known as the offspring’s genotype (the letters). –The genotype of the offspring is Aa. They physical appearance of the offspring would be RED as this is the dominant allele.

What are the chances? Probability- the mathematical chance that an event will occur Probability is usually expressed as a percentage or fraction. Punnett square: –4 boxes –1 box blue –3 boxes red –3/4= red, 75% –1/4= blue, 25%

New Ideas… New ideas are often rejected. In 1865 Mendel published his findings but was ignored by the scientific community. 30 years after his death Mendel finally got eh recognition he deserved: Father of Genetics

Practice: Male or Female What is the percent chance that the offspring will be male?

Practice: Peas What is the percent chance that the flower will be white? What % of the offspring will be heterozygote?