Understanding Genetics: Genes, Alleles, and Punnett Squares Explained

1. Genetics Terms

2. Target #8- I can define gene • Gene: a piece of DNA that provides a set of instruction to a cell to make a certain protein • Each gene has a locus (location) on a chromosome

3. Target #9- I can define allele • Allele: any of the alternative forms of a gene that may occur at a specific locus • Cells have two alleles for each gene

4. Target #10- I can differentiate between homozygous & heterozygous • Homozygous: two of the same allele at a specific locus • Ex: If B = tall in size, then a homozygous allele is BB • Heterozygous: two different alleles at a specific locus • Ex: if B = tall b= short, then a heterozygous allele is Bb

5. Checking for understanding • PP • Gg • tt • QQ • Ww • Homozygous or heterozygous?

6. Target #11- I can define genome • Genome: all of an organism’s genetic material • Determines all traits of an individual

7. Target #12- I can differentiate between genotype & phenotype • Genotype: the genetic make-up of a set of genes • Trait not seen outwardly • Phenotype: the physical characteristics displayed by the genes • What is expressed physically

8. Punnet Squares & Monohybrid Crosses

9. Target #13- I can differentiate between dominant and recessive alleles • Dominant: an allele that is expressed when two different alleles or two dominant alleles are present • Ex: if B = tall and b = short, an organism with Bb or BB will be tall because the capital letter represents the dominant trait • Recessive: an allele that is only expressed when two copies are present • Ex: if B = tall and b= short, an organism will only be short with a bb because the lower case letters represent the recessive trait

10. Checking for Understanding • Dominant or recessive? • Q • H • n • y • A

11. Checking for understanding- combining concepts • Lets use the letter A for practice • Homozygous dominant • Homozygous recessive • Heterozygous

12. Target #14- I can explain what a punnett Square is used for • Punnett Square: a grid system for predicting all possible genotypes resulting from a cross • The axis represent the possible gamete genotypes of each parent • Show the possible genotypes of each offspring • By counting the number of squares of each offspring genotype, the ratio of genotypes can be determined • The ratio of phenotypes can be determined also

13. Target #15- I can determine the ratio of genotype and phenotype of offspring produced in a monohybrid cross • Monohybrid cross: a cross that examines one trait • Ex: Suppose you cross a pea plant that is homozygous dominant (PP) for purple flowers with a pea plant that is homozygous recessive for white flowers (pp) • F1 generation • Genotype: Pp • Heterozygous • Phenotype • Purple Flowers

14. Target #15- cont. • A homozygous tall plant (TT) is crossed with a heterozygous plant (Tt). • What are the genotypes of the offspring? What is the ratio of genotypes? • What are the phenotypes of the offspring? What is the ratio of phenotypes? • A man with hitchhiker’s thumb (Hh) and his wife who also has hitchhiker’s thumb (Hh) are expecting a child. • What are the genotypes of the offspring? What is the ratio of genotypes? • What are the phenotypes of the offspring? What is the ratio of phenotypes? • What is the probability that the child will also have hitchhiker’s thumb?

15. Dihybrid Crosses

16. Target #16- I can determine the ratio of genotype and phenotype of offspring in a dihybrid cross • Dihybrid Cross: crosses that examine the inheritance of two different traits • The grid for dihybrid crosses is similar to monohybrid • Ex: Supposed you cross two plants with yellow, round peas that are heterozygous for both traits (YyRr) • F2 Generation • Genotypes? • Phenotypes?

17. Target #16- cont. • A woman has the genotype eegg (no hitchhikers thumb and no widow’s peak. A man has the genotype EeGg (hitchhikers thumb and widow’s peak) • Diagram the Punnett square for the offspring between the man and the woman above. What are the genotypes and phenotypes • A man has the genotype BbDd (brown hair and brown eyes). His wife has blonde hair and blue eyes (bbdd). • What are the genotypes and phenotypes of the offspring? Draw a Punnett square