Dominant or Recessive?

Inherited Traits Living things inherit traits, or characteristics/parents. Ex. – Eye color, hair color, flower color. Genes and Chromosomes Genes – Hereditary information. What else do genes do? Determine traits of an organism - Ex. Shape of ears, you have a backbone/legs, hair color Genotype and Phenotype Genotype – Genes passed to offspring. Phenotype – Physical appearance. Ex. Black hair Genotype determines Phenotype. Genes are located on Chromosomes. Chromosomes – Hold genetic info. 1 chromosome contains many different genes.

More on Genes and Chromosomes Cells in different kinds of organisms contain different numbers of chromosomes. Ex. – Cats – 38 / Dogs - 78 Human baby = 23 chromosomes from mom/23 from dad. Human body cells=46 chromosomes in 23 pairs. Each pair has a number from 1-23. Chromosome 1 from dad/mom have similar genetic information. This is true for the other 22 pairs.

Homologous Chromosomes Genes that determine a specific trait are in matching locations on paired, or homologous, chromosomes. Mom Dad Genes for ear shape are located in same place on 2 homologous chromosomes.

Dominant and Recessive Alleles Many traits are controlled by a single gene. Ex.- 1 gene = Earlobes attached 1 gene = Earlobes free Trait Trait Made By Dominant Allele Recessive Hair Type Curly or Wavy Straight Color Dark Light Earlobe Free Attached Dimples Present Not Different forms of same gene are called Alleles. Alleles will be either: Dominant = Stronger Trait Recessive = Weaker Trait Let’s look at the table to the right for examples of human traits.

Identifying Genotypes and Phenotypes Genotype for a trait is written as 2 letters. Capital letters = Dominant Alleles Lowercase letters = Recessive Alleles The allele that causes free earlobes is dominant over the allele for attached earlobes. So F is used for free earlobe gene. What do you think is used for attached earlobe gene? Lowercase f

Let’s Stop and Answer Some Questions 1. What do living things inherit and from where? 2. What are some things you can inherit from mom/dad? 3. What are genes? 4. What else do genes do? Give some examples. 5. What do the terms genotype and phenotype mean? 6. Genotype determines ___________________. 7. Where are genes located? 8. What is the job of chromosomes? 9. One chromosome contains many different _____________. 10. How many chromosomes do we receive from mom/dad? For a total of? 11. What makes males and females different at the chromosome level? 12. How many pairs of chromosomes does each human cell have? 13. Describe how the chromosome pairs are numbered and how the genetic information is arranged. 14. What are homologous chromosomes? 15. What are alleles? 16. What is meant by the terms dominant and recessive? 17. Give some dominant and recessive traits. 18. How do you distinguish between dominant and recessive traits when written?

More on Genotypes and Phenotypes Offspring receive 2 copies of each gene-1 from each parent. 3 possible genotypes : FF, ff, or Ff. FF and ff = Homozygous Ff = Heterozygous “Homo” means “the same.” Homozygous genotype – Made up of 2 dominant or 2 recessive alleles. Ex.- FF or ff “Hetero” means “different.” Heterozygous genotype – Made up of 1 dominant and 1 recessive allele. Ex.- Ff

Do your ears hang low? If an organism inherits a dominant allele, the dominant trait is expressed. Allele for free earlobes = dominant. So, how would we write the genotype? FF and Ff ___________________________ How then would we write the genotype for attached earlobes? ff ___________________________

Using Punnett Squares Used to predict results of genetic crosses. Cross – Mating of 2 parent organisms Punnett Squares are used to calculate probability of genotypes/phenotypes in offspring.

Let’s make a Punnett Square with the information below. Task – Predict outcome of crossing tall pea plant with short pea plant. First, I must know the genotype of each parent plant. There are 3 possible genotypes : TT, Tt, and tt Genotype of pure tall plant : TT <---- It has 2 dominant alleles Genotype of pure short plant : tt <--- It has 2 recessive alleles. To make a Punnett Square, 1st separate the parent alleles. Place 1 pair across top of square, and other pair down the left side. t t t t T Tt Tt T tall tall Tt Tt T T tall tall Genotype - Genes Phenotypes - physical Dominant Gene always 1st in genotype

Sex Chromosomes In humans, females have 2 “X” chromosomes. So, each egg contains one “X” chromosome. Males have both an “X” and a “Y” chromosome. Each sperm cell contains either an “X” or a “Y” chromosome. XX = Female XY = Male

Let’s consider a cross between 2 plants with heterozygous genotypes : Tt x Tt Probability of tall plants? TT Tt T Tall Tall 3 out of 4, or 75%. Probability of short plants? tt Tt t Tall Short 1 out of 4, or 25%. How many possible genotypes here? 3: TT, Tt, tt How many phenotypes? Tall , Short

We’re done! Let’s answer some questions. 1. 2 different forms of the same gene are called A. phenotypes. C. dominant traits B. genotypes. D. alleles 2. An organism’s expressed traits make up its A. recessive traits C. phenotype B. genotype D. alleles 3. A pea plant that is homozygous dominant for seed color is crossed with a pea plant that is homozygous recessive for seed color. Since yellow is the dominant color, the letters Y and y represent the genes for seed color. What cross represents these 2 plants? A. Yy x Yy C. YY x yy B. YY x Yy D. Yy x yy 4. You meet a person and notice that she has dimples. What can you say for sure about the phenotypes of her parents? A. At least 1 of her parents has dimples. C. Neither parent has dimples. B. Both of her parents have dimples. D. 1 of her parents does not have dimples.