Genetics and Heredity

Heredity The passing of traits from parent to offspring.

Heredity Genes on chromosomes control the traits that show up in an organism. The different forms of a trait that a gene may have are alleles (corresponding pairs of genes located on the chromosomes).

Heredity During meiosis a pair of chromosomes separates and the alleles move into separate cells. Each chromosome now contains one gene for each trait.

Heredity The study of how traits are inherited is called genetics.

B. Gregor Mendel Known as the father of genetics Austrian monk Studied mathematics and science Began experimenting with garden peas in 1856 _ The patterns he observed became known as Mendel’s Laws of Heredity

B. Gregor Mendel Mendel was the first to use the mathematics of probability to explain heredity and to trace one trait for several generations.

C. Hybrid A hybrid receives different genetic information for a trait from each parent. Dominant allele- covers up or dominates the other trait. Recessive allele- trait that seems to disappear.

D. Probability Probability helps you predict the chance that something will happen.

E. Punnett Square A Punnett square can help you predict what an offspring will look like. Uppercase letters stand for dominant alleles. (Dominant alleles are “in control”.) Lowercase letters stand for recessive alleles.

F. Genotype The genetic makeup of an organism (internal) Homozygous- an organism with two alleles for one trait that are the same (Ex. Written TT, or tt) *Mendel would have called it purebred* Heterozygous- an organism with two alleles for one trait that are different (ex. Written Tt) *Mendel would have called it hybrid*

G. Phenotype The way an organism looks or behaves is a result of its genotype (physical).

Punnett Practice This animated Punnett square shows a cross between a homozygous brown-eyed father (BB) and a homozygous blue-eyed mother (bb). All of the children will be heterozygous for Brown eyes (Bb).

Punnett Practice The orange bird has two dominant A genes. We put two A s along the top of the square. The blue bird has two recessive a genes. We put two a s down along the left side of the square. All the offspring have the genes Aa. They will all have orange feathers, but will carry a recessive gene for blue feathers. This is called the F1 generation.

Punnett Practice Now suppose that two individuals from the F1 generation become parents. The baby birds (offspring) are called the F2 generation. You can see how their genes work out.-- The offspring are coded in the squares. One bird will be orange with two AA genes. Two birds will be orange with genes coded Aa. One bird will be blue and will have two recessive aa genes. Individual nests of birds may not turn out exactly like this, but if there are many baby birds, they will work out genetically with the ratios 1:2:1.