Activity 5 Genes and Traits

1. Activity 5Genes and Traits

2. Early Breeding Practices • Farmers realized thousands of years ago that if you only breed parent plants & animals that have the best characteristics you could produced offspring that also had those favorable characteristics. • This practice is referred to as selective breeding…sound familiar? • Selective breeding practices have led to the production of thousands of varieties of potatoes that differ in size, color, and how long they can be stored.

3. Genetics • the study of inheritance or heredity; the process by which characteristics or traits are passed down from parent to offspring Challenge: What can we infer about genes and traits based on heredity patterns?

5. What we know & understand about inheritance is based on the work of Gregor Mendel and his experiments with pea plants. He performed controlled experiments and kept detailed records. Mendel & Genetics

6. Mendel’s Work • 1860’s • Austrian monk with a background in biology, math & physics • Used pea plants to make lots (I mean LOTS!) of observations and predictions about heredity

7. FYI -Personal History • 1843 – Mendel, at age 21, entered a monastery in Austria in order to study to become a teacher; he flunked the teacher exam...  • 1851 – Was sent to the University of Vienna to work on his studies; he came to enjoy studying science and math; tried to take the teacher exam again & failed...  • Few years later - he returned to the Austrian monastery; used his knowledge of science & math to study biological patterns & occurrences in nature… 

8. Pea Plant Traits • Mendel chose pea plants because they were easy to grow & had 7 different, easily observable, traits . • Each trait has only 2 distinct forms – no in betweens. • What do we call “in betweens”??????? (Think pink rose from red & white roses…)

9. The Actual Experiments • First time, he crossed a pure-bred tall plant (What does pure-bred mean?) with a pure-bred short plant. • Genotypes of these plants? • He ended up with all tall plants in this F1 generation. • What is F1 you ask?

10. In the next experiment… • Mendel allowed the hybrid (what is this?) to self-fertilize. • So what will these genotypes look like? • He ended up with 3 tall plants for every 1 short plant produced in the F2 generation. • Gee, where have you seen this ratio before? • Mendel repeated this with multiple other traits and guess what? • You got it, he got the same ratio every time!!!

11. Mendel’s Data: WHAT IS UP WITH THIS 3:1 Ratio?!?!?!

12. Mendel’s 3 Principles of Heredity • A dominant trait, if present, will always appear in the individual. The trait that seems to be “hidden” is the recessive trait. • Every plant has 2 versions, alleles, of the gene for each trait. • Every offspring receives 1allele for each trait fromeachparent.

13. Traits, Genes & Alleles • Traits are characteristics that can be passed on from parents to offspring (e.g. hair & eye color) and are controlled by GENES. • Each gene has different forms or versions called alleles. (e.g. trait=eye color, alleles=brown & blue)

14. Sexual Reproduction • Involves 2 parents • Each parent produces gametes • Males produce sperm • Females produce eggs • Each gamete carries 1 allele for each gene • Fertilization=1 sperm cell fuses with 1 egg cell to produce a zygote • Offspring that develops from that zygote has a unique combination of genes passed to them from both parents

15. Example: • Purple corn kernels are dominant over yellow corn kernels • What is the genotype of corn w/purple kernels? • PP or Pp • What is the genotype of corn w/yellow kernels? • ff • If the genotype is Ff it is referred to as… • Heterozygous • If both alleles are the same? • homozygous

16. Terminology to Know: • Cross – breeding combination; TT x Tt • Parent generation (P)- the two plants selected to cross for a breeding experiment • First Filial generation (F1)- all the offspring produced by crossing the two (P) individuals. • Second Filial generation (F2)- all the offspring produced by crossing two of the F1 individuals. • True Breedingor Purebred- refers to a plant that passes on the same trait from one generation to the next. (HmD or HmR) • Hybrid– refers to a plant that passes on different traits from one generation to the next. (Ht)

17. Exceptions to simple dominance… • Incomplete dominance= when neither allele is dominant • Heterozygous individuals show a phenotype in between the other two • Example: hair texture in humans • Curly hair=HH • Straight hair=hh • Wavy hair=Hh

18. Exceptions to simple dominance… • Codominance=more than one allele is dominant, both are expressed equally • Ex. blood types in humans • There are actually 3 alleles for the blood type trait in humans (A, B, and O) • If a child has type O blood, what blood types might his or her parents have?

21. Few more exceptions… • Some traits are polygenic, meaning that the phenotype of the individual is determined by several genes. • Ex. Eye color and Hair color • Many traits are determined not just by the genes you inherit, but also environmental conditions • Ex. skin pigmentation

22. Analysis Questions • Explain the difference between an organism’s phenotype and its genotype. Include an example in your answer. • An organism’s genotype refers to the actual alleles that the organism inherits for the gene. • An organism’s phenotype refers to the physical appearance of that trait. Genotype: TT or Tt Phenotype: regular thumb Genotype: tt Phenotype: Hitchhiker’s thumb

23. Analysis Questions • Explain the difference between simple dominance, incomplete dominance, and codominance. • Simple dominance refers to one allele being completely dominant over another. Example: in pea plants purple is dominant over white for flower color; as long as the purple allele is present it will be expressed • Incomplete Dominance means that neither allele is dominant over the other • Codominance refers to both alleles are dominant and are both expressed

24. Think back to the Bt corn you considered in Activity 1. When an organism is genetically modified, which of the following is changed: genotype, phenotype, both or neither? Explain. • When an organism is genetically modified its genes are being changed so that means that the genotype would be altered. If the genotype is altered then the phenotype would also be altered. The phenotype is determined by the genotype.

25. AQ #4-What type of inheritance is being exhibited by each example? codominance Simple dominance Incomplete dominance