Punnett Squares

Introduction Gregor Mendel, a priest was very curious about how traits were passed from one generation to another. He experimented with peas (29,000 plants!) for seven years and used mathematical principles to figure it all out. Mendel determined that traits aren't blended but are instead passed on, intact, from parent to child. He found that everyone got two genes for each trait — one from the mom and one from the dad. He also concluded that some traits are dominant and some are recessive. Mendel took a tall pea plant and crossed it with a short one. He expected medium pea plants, but what he got was all tall pea plants! Mendel then crossed these tall babies (he called them the F1 generation) and he got three tall plants and one short plant.

Dominant traits- always shows up even if there a different gene for the same trait Recessive trait –trait that doesn’t show up if there is a dominant gene. Example: if you have a gene for attached ear lobe and a gene for detached ear lobe, you will have attached ear lobes as it is a dominant trait. Phenotype -The way you look on the outside Genotype- the way you really are deep down in your genes.Homozygous-When Alleles for a characteristic are same, the organism is homozygous for that characteristic.Heterozygous- When the alleles are different for a characteristic, then the organism is heterozygous for that characteristic. Alleles- Different versions of the same gene. Allele-One version of the pair of genes that appear at a particular location on a particular chromosome and control the same characteristics like eye color.

Punnett Square Identify the trait that is to be studied assign a letter to represent the trait. Don’t use letters where the capital and the lowercase look similar, like S,O and W. Then draw the square. Since you are only investigating one trait and each trait has two genes, then the Punnett square should have four boxes. It should look like this: Place each parent's genes on the outside of each square B B b B- Dominant Brown eye color b b- recessive blue eye color Bb

monohybrid cross is used to determine the dominance relationship between two alleles. The cross begins with the parental (P1 or P) generation. One parent is homozygous for one allele, and the other parent is homozygous for the other allele. The offspring make up the first filial (F1) generation. Cross that looks at one trait Originally, we know one parent is tall and its genotype is TT (remember, we're talking about what you look like in your genes, and you have two alleles, or gene options, for each trait), so we put those letters on one side of the square. The other parent is short and its genotype is tt, so we put those letters on the other side. Every baby plant gets an allele from each of them. All the pea kids are all tall because, in peas, tall is dominant. Genotype-heterozygous (half tall and half short) Phenotype- Tall (short trait is hidden) F1 Generation T t Tt

Crossing the F1 generation tall plants (Tt) will give F2 generation plants consisting of 3 tall plants and 1 short plant. The short trait which was missing in F1 generation appears in F2 generation. The trait did not disappear, it was hidden as it was a recessive trait. Genotype (1:2:1) 1 Homozygous dominant 2 Heterozygous 1 Homozygous recessive Phenotype (3:1) 3 tall, 1 short F2 Generation T t TT Tt tt

F1 generation F2 generation Pea plant with purple flowers (P) and another Pea plant with white flowers (w) Purple color(P)-Dominant gene White color(w)-recessive gene F1 generation will have all purple flowers as purple is the dominant gene. Genotype-heterozygous; Phenotype-Purple F2 generation ¾ will have purple flowers and the ¼ will have white flowers (which skipped a generation). Genotype (1:2:1) 1 Homozygous dominant 2 Heterozygous 1 Homozygous recessive Phenotype (3:1) 3 purple, 1 white F1 generation F2 generation P w Pw P w PP Pw ww

In pea plants, spherical seeds (S) are dominant to dented seeds (s) In pea plants, spherical seeds (S) are dominant to dented seeds (s). In a genetic cross of two plants that are heterozygous for the seed shape trait, what fraction of the offspring should have spherical seeds? A. None B. 1/4 C. 1/2 D. 3/4 E. All

A genetic cross between two F1-hybrid pea plants having yellow seeds will yield what percent green-seeded plants in the F2 generation? Yellow seeds are dominant to green. A. 0% B. 25% C. 50% D. 75% E. 100%

References http://www.mensaforkids.org/teach/lesson-plans/peas-in-a-pod-genetics/ http://www.biology.arizona.edu/mendelian_genetics/problem_sets/monohybrid_cros s/01q.html http://www.ducksters.com/science/biology/hereditary_patterns.php https://www.youtube.com/watch?v=Mehz7tCxjSE https://www.youtube.com/watch?v=cWt1RFnWNzk https://www.youtube.com/watch?v=Lsj-Ij53CkA&t=181s http://www.biology-pages.info/M/Mendel.html