Genetics: Punnett Square Notes First…some vocab!

Let’s Review… What is heredity? What is a gene? What is an allele? The passing of traits to offspring What is a gene? A specific section on a strand of DNA that codes for a certain trait What is an allele? Different versions of a gene

Vocab: Trait- physical characteristic that we see Dominant- expressed allele (overpowers and covers up recessive allele, if present) Recessive- unexpressed allele (covered up by dominant gene)

Phenotype- the physical appearance of a trait in an organism Genotype- the genes of an organism; for one specific trait we use two letters to represent the genotype. Uppercase letter= dominant allele Lowercase letter= recessive allele. Phenotype- the physical appearance of a trait in an organism

Homozygous- two same alleles (2 dominant or 2 recessive) [purebred] Heterozygous- two different alleles- 1 dominant and 1 recessive [hybrid]

Tt QQ Ff rr Yy hh mm Ss GG PP Ll Bb dd Underline the following that are homozygous and circle the ones that are heterozygous: Tt QQ Ff rr Yy hh mm Ss GG PP Ll Bb dd

B= brown eyes b= blue eyes What would the genotype be for an individual who is heterozygous? ______ What would be the phenotype be for an individual who is heterozygous? _________   If a person has blue eyes, what must their genotype be? _______ Bb Brown eyes bb

Punnett Square What is it? A diagram used to predict the probability of traits being passed from parents to offspring. What do I need to know before doing a Punnett Square? Both parents’ genotypes for that trait (Tt x tt) Does the Punnett Square guarantee anything?? No! It just predicts the probability of traits being passed on to offspring.

Important Note! Probability is NOT influenced by previous results Each offspring has the exact same chance of getting a trait as previous offspring Ex: every time a baby is born, there is a 50% chance of being a boy or a girl.

Step-by-Step Punnett square review 1st. Draw your square   Parental Cross: Tt x tt

2nd. Then place the parent’s genotypes on the outside 2nd. Then place the parent’s genotypes on the outside. Each allele goes next to its own box!! Parental Cross: Tt x tt  

T t t t 3rd. Complete the square. (“Drag & Drop”) Parental Cross: Tt x tt 3rd. Complete the square. (“Drag & Drop”) T t   t t

Genotypes (letters): Phenotypes (physical appearance): 4th. Summarize your results, using percentages.

Sample Problem #1 1. An elephant with large ears (EE) is crossed with an elephant with small ears (ee). What are the expected offspring?

Sample Problem #2 2. A heterozygous white chicken, which is the dominant allele, is crossed with a red chicken (recessive). What is the probability of having a red chicken?

Now it is your turn! Refer to vocab list as you work You must show a completed Punnett Square for each problem. Answer Key will be posted on screen in a few minutes

Answer Key- check yourself! 1. BB x bb G: 100% Bb P: 100% Black bulls 2. Pp x pp G: 50% Pp, 50% pp P: 50% horned, 50% polled 3. Ss x Ss G: 25%SS, 50%Ss, 25%ss P: 75% Large, 25% Small First Generation- SS x ss G: 100% Ss P: 100% Long hair Second Generation- Ss x Ss G: 25%SS, 50%Ss, 25%ss P: 75% Long, 25% short “Genetic Problem Solving” wkst is due TOMORROW.