Mendelian Genetics Mendel’s Principle of Dominance and Punnett Squares

Standards: BI2. c. Students know how random chromosome segregation explains the probability that a particular allele will be in a gamete. BI2. g. Students know how to predict possible combinations of alleles in a zygote from the genetic makeup of the parents. BI3. a. Students know how to predict the probable outcome of phenotypes in a genetic cross from the genotypes of the parents and mode of inheritance (autosomal or X-linked, dominant or recessive). BI3. b. Students know the genetic basis for Mendel’s laws of segregation and independent assortment.

Objectives: SWBAT explain the genetic factors that influence the way we look. recognize that DNA contains the genetic information that determines the way we look. explain the structure and function of DNA. predict the physical characteristics of an organism based on its genetic make up.

Mendel’s Principle of Dominance Some alleles (diff. forms of gene) are dominant and some are recessive Organisms with dominant alleles will always show that form of the trait (YY, Yy) Organisms with recessive alleles will only show that form of the trait when there are no dominant alleles present (yy)

Allele Combinations Homozygotes- two identical alleles for a certain trait (YY,yy) Heterozygotes- two different alleles for the same trait (Yy)

What are Punnett Squares? Punnett Squares are… a grid system for predicting all possible genotypes resulting from a cross. The sides of the square represent the possible gamete genotypes of each parent. Shows all possible genotypes of offspring

Punnett Squares

What’s actually happening?

What is probability? Probability-the likelihood that an event will occur P= # of ways an event can occur ________________________ # of total possible outcomes