http://www.athro.com/evo/gen/punnett.html http://www.kidshealth.org/kid/talk/qa/what_is_gene.html http://brookings.k12.sd.us/biology/ch%2011%20genetics/punnettpractice.ppt#1 http://www.usoe.k12.ut.us/CURR/Science/sciber00/7th/genetics/sciber/punnett.htm http://www.biotechnologyonline.gov.au/images/contentpages/karyotype.jpg

The study of genetics began with observations made by Gregor Mendel. After noticing that the flowers of his pea plants were either violet or white, Mendel began to study the segregation of heritable traits. Between 1856 and 1863 he cultivated and tested at least 28,000 pea plants. Remember that Mendel worked almost 150 years ago when nobody knew about genes or even the structures (chromosomes) that carry genes.

A gene carries information that determines your traits. Traits are characteristics you inherit from your parents. Genes are located in chromosomes. Chromosomes come in pairs and there are thousands of genes in one chromosome. Chromosome

There is a X and Y chromosome. What do you notice? Chromosomes are structures in the nucleus of cells that consist of DNA. X There is a X and Y chromosome. What do you notice?

In humans, a cell’s nucleus contains 46 individual chromosomes or 23 pairs of chromosomes. Half of the chromosomes come from one parent and half come from the other parent. This is a human karyotype representing the 23 pairs of chromosomes in a male

A gene controls the trait Examples of traits are hair color, eye color, and fingerprints. What fingerprint do you have? Everyone is different, even twins! If you lose the skin on your fingertip, it grows back with the same print. Rub a pencil over your fingertip and touch it to your paper.

Allele- discrete version of the same gene Heredity- is the passing of traits to offspring (from its parent or ancestors). The process by which an offspring cell or organism becomes predisposed to the characteristics of its parent. Allele- discrete version of the same gene Genotype- the genes of an organism for one specific trait Phenotype- the physical appearance of a trait in an organism

Dominant trait refers to a genetic feature that “hides” the recessive trait in the phenotype of an individual. The term “recessive” describes a trait that is covered over (or dominated) by another form of that trait and seems to disappear. Homozygous = 2 of the same alleles for a trait (Pure) Heterozygous = two different alleles for a trait (Hybrid)

A pedigree chart is a chart that shows all of the known phenotypes for an organism and its ancestors So, it shows us how traits were passed down and why we look the way we do!

Pedigree Chart – Dominant Disease Four puppies are born to parents where the mother is affected with a dominant disease that causes her to have an extra tail. This would result in 2 of the puppies born having the same dominant disease with extra tails and the other 2 of the puppies being unaffected by the trait.

Pedigree Chart – Recessive Disease If four puppies are born to a couple where one of the parents has a dominant gene and it carries a disease, it is great probability that two children will inherit the abnormal gene and two other children won’t. Puppies who do not inherit the abnormal gene will not be carriers of abnormal gene in the future. But none of the puppies are affected because they do not have rr genes where the disease would be in full affect.

The standard way of working out what the possible offspring of two parents will be. It is a helpful tool to show allelic combinations and predict offspring ratios.

We begin by constructing a grid of two perpendicular lines.

B B b Next, put the genotype of one parent across the top and the other along the left side. For this example lets consider a genotype of BB crossed with bb. B B Notice only one letter goes above each box It does not matter which parent’s genotype goes on either side. b

Next, fill in the boxes by copying the column and row head-letters down and across into the empty spaces. B B b B b B b b B b B b

Now that we have learned the basics of genetics lets walk through some examples using Punnett Squares.

W w W W W W w w W w w w Parents in this cross are heterozygous (Ww) Usually write the capital letter first W W W W w w W w w w Parents in this cross are heterozygous (Ww) Note: Make sure I can tell your capital letters from lowercase letters. What percentage of the offspring will have violet flowers? ANSWER: 25% (homozygous recessive)

Red hair (R) is dominant over blond hair (r) Red hair (R) is dominant over blond hair (r). Make a cross between a heterozygous red head and a blond. R r r Rr rr 50% What percentage of the offspring will have red hair?

Tt tt T t t Let’s try some more… Construct a Punnett In pea plants, tall pea plants (T) are dominant over short pea plants (t). Construct a Punnett Square for a heterozygous tall pea plant and a short pea plant. T t What are the percentage of phenotypes? Tt tt t 50% tall 50% short

Black eyes (R) are dominant over red eyes (r) in rats Black eyes (R) are dominant over red eyes (r) in rats. Make a cross between a homozygous rat with black eyes and a rat with red eyes. R R Rr r What is the possibility of a red eye off springs? Discuss with students other possible answers 0% 