Introduction to Genetics Life Science

Traits survey Why causes these differences?

Genetics- The study of heredity (how traits are passed on) x = or

The study of heredity started with the work of Gregor Mendel and his pea plant garden Mendel was an Austrian Monk that lived in the mid 1800’s

Mendel noted that the size of pea plants varied. He cross-bred these pea plants to find some surprising results.

Mendel’s cross between tall pea plants yielded all tall pea plants. X =

His cross between small pea plants yielded all small pea plants. X =

Mendels’ cross between tall pea plants and small pea plants yielded all tall pea plants. x =

Mendel then crossed these second generation tall pea plants and ended up with 1 out 4 being small. x =

Mendel’s work led him to the understanding that traits such as plant height are carried in pairs of information not by single sets of information. Hereditary information (DNA) is carried in Chromosomes!

DNA DNA is found in all living cells –It controls all functions inside a cell –DNA stores all the genetic information for a living organism –Single cell like an amoeba –Multi cell like a human

Genetics Small sections of DNA are responsible for a “trait”. These small sections are called “Genes”. –Gene - A segment of DNA that codes for a specific trait –Trait - A characteristic an organism can pass on to it’s offspring through DNA Gene

Genes There are two main kinds of genes: –Dominant - A gene that is ALWAYS expressed and hides others –Recessive - A gene that is only expressed when a dominant gene isn’t present (hidden)

Dominant and Recessive Genes A dominant gene will hide a recessive gene! Example: A “widows peak” is dominant, not having a widows peak is recessive. If one parent contributes a gene for a widows peak, and the other parent doesn’t, the off- spring will have a widows peak. Widows Peak

Alleles All organisms have two copies of each gene (one from female, one from male) Homozygous- Two copies of the same gene Heterozygous - Two different genes

Example: A Widows Peak, dominant trait, would be symbolized with a capital “W”, while no widows peak, recessive trait, would be symbolized with a lower case “w”. Father - No Widows Peak - w Mother - Has a Widows Peak - W

Example: For the widows peak: WW - has a widows peak Homozygous dominant Ww - has a widows peak Heterozygous ww - no widows peak Homozygous recessive

Genotype vs Phenotype Genotype- Genes you have Ex: WW, Ww, or ww Phenotype- physical features SHOWN Ex: WW  Widows peak Ww  Widows peak ww  NO widows peak

Example: Since Herman has no widows peak, he must be ______, since Lilly has a widows peak she could be EITHER ______ or ______. wwWW or Ww

Punnett Square Punnett Square - A tool we use for predicting the traits of an offspring –Letters used as symbols to represent genes –Capital letters= dominant genes –Lower case letters= recessive genes –Genes always exist in pairs

Punnett Squares We can use a “Punnet Square” to determine what pairs of genes Lilly has Wwww Wwww w w Ww Assume Lilly is heterozygous Assume Herman is homozygous recessive ww A Punnet Square begins with a box 2 x 2 One gene is called an “allele” One parents pair is split into alleles on top, the other along the side Each allele is crossed with the other allele to predict the traits of the offspring Ww

Punnett Squares Notice that when Lilly is crossed with Herman, we would predict that half the offspring would be “Ww”, the other half would be “ww” Half “Ww”, Heterozygous, and will have a widows peak Half “ww”, Homozygous, and will not have a widows peak Wwww Wwww w w Ww

Try it yourself! Create a punnett square assuming Lilly is homozygous dominant (WW) w w WW What is the chance of the offspring having a widows peak?

Try it yourself! All of the offspring will have a widows peak! Ww w w WW 100%

Genetics Recall that Herman and Lilly had another offspring, Marylin. She had NO widows peak.

Genetics So which is true? Is Lilly homozygous dominant (WW) or is she heterozygous (Ww)? Ww w w WW ww Wwww w w Ww

Genetics Ww w w WW ww Wwww w w Ww If Lilly were heterozygous, then 1 / 2 of their offspring should have a widows peak, 1 / 2 shouldn’t If Lilly were homozygous, all of their children will have a widows peak