Mendel’s Laws of Heredity Why we look the way we look...

What is genetics? Genetics is the study of heredity, how traits are passed from parent to offspring

The father of Genetics Gregor Mendel His most famous experiment was done with pea plants. Was an Austrian Monk that lived in the mid 1800s Mendel observed that the height of pea plants varied Mendel crossed different size plants to see if he could predict the height of the offspring

Mendel’s cross between tall pea plants yielded all tall pea plants Mendel’s cross between tall pea plants yielded all tall pea plants. His cross between small pea plants yielded all small pea plants. Mendels’ cross between tall pea plants and small pea plants yielded all tall pea plants. X = x

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

Lets Start heredity

These are my parents, who do I look like?

My dad?

My Mom?

What is heredity? The passing on of characteristics (traits) from parents to offspring Genetics is the study of heredity

Mendel used peas... They reproduce sexually They have two distinct, male and female, sex cells Their traits are easy to isolate

Mendel crossed them Fertilization - the uniting of male and female gametes Cross - combining gametes from parents with different traits

Questions What did Mendel cross? What are traits? What are gametes? What is fertilization? What is heredity? What is genetics?

Rule of Unit Factors Each organism has two alleles for each trait Alleles - different forms of the same gene Genes - located on chromosomes, they control how an organism develops

Rule of Dominance The trait that is observed in the offspring is the dominant trait (uppercase) The trait that disappears in the offspring is the recessive trait (lowercase)

Law of Segregation A parent randomly passes only one allele for each trait to each offspring

Questions... How many alleles are there for each trait? What is an allele? How many alleles does a parent pass on to each offspring for each trait

Questions... What do we call the trait that is observed? What case (upper or lower) is it written in? What about the one that disappears? What case is it written in?

Phenotype & Genotype Phenotype - the way an organism looks red hair or brown hair genotype - the gene combination of an organism AA or Aa or aa

Heterozygous & Homozygous Heterozygous - if the two alleles for a trait are different (Aa) Homozygous - if the two alleles for a trait are the same (AA or aa)

Monohybrid Monohybrid Cross - crossing parents who differ in only one trait (AA with aa)

Questions... What is the phenotype? What is the genotype? What is homozygous? What is heterozygous? What is monohybrid crossing?

Let’s Practice –Take a look at the genetics behind getting a widows peak Dominant and Recessive Genes A dominant gene will always mask a recessive gene. 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 This is lily Munster

Genetics All organisms have two copies of each gene, one contributed by the father, the other contributed by the mother. Homozygous - Two copies of the same gene Heterozygous - Two different genes

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

Genetics Since Herman has no widows peak, he must be “ww”, since Lilly has a widows peak she could be either “WW” or “Ww” Definitely ww Homozygous recessive Either Ww Heterozygous or WW Homozygous dominant

Genetics We can use a “Punnet Square” to determine what pairs of genes Lilly has 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 Assume Lilly is heterozygous Ww W w Assume Herman is homoozygous recessive ww w Ww ww w Ww ww

Genetics 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 W w w Ww ww w Ww ww

Genetics Another possibility is that Lilly might be “WW”, homozygous dominant. Assume Lilly is homozygous dominant WW W W Assume Herman is homoozygous ww Notice that all the offspring are heterozygous and will have a widows peak w Ww Ww w Ww Ww