1. Activity 60 Genes 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. Mendel & Genetics
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.

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.

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. WHAT IS UP WITH THIS 3:1 Ratio?!?!?!
Mendel’s Data:
Characteristic
Dominant
Recessive
Ratio (Dom:Rec)
Flower Color
Purple
White
705: 224  3.15:1
3:1
Seed Color
Yellow
Green
6,022: 2,001  3.01:1
Seed Surface
Smooth
Wrinkled
5,474: 1,850  2.96:1
Pod Color
428: 152  2.82:1
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 1 allele for each trait from each parent.

13. Vocabulary
Trait- is the expression of genes in an observable way. (ex. eye color, hair color, wrinkled pea pods)
Gene- A specific sequence of DNA that codes for a specific trait
Allele-is one of a number of alternative forms of the same gene(Orange (t) or Blue (T) for critter tails)

14. 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)

15. Vocabulary
Homozygous- an organism that has identical alleles present for a gene on both homologous chromosomes (Ex TT or tt)
Heterozygous-an organism that has different alleles present for a gene on homologous chromosomes (Ex. Tt).

16. Vocabulary
Genotype-The genetic make up of an organism. The genotype is the alleles on the gene. (IF asked what the genotype of offspring are you always answer in letters ex. TT, Tt, or tt) Phenotype- This is the physical/observable condition of allele the offspring possesses. ( Ex. Brown, Tall, Round, Blue)

17. 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

18. Example: Purple corn kernels are dominant over yellow corn kernels
What is the genotype of corn w/purple kernels?
What is the genotype of corn w/yellow kernels?
If the genotype is Ff it is referred to as…
If both alleles are the same?

19. 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 Breeding or 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)

20. Simple Dominance
So far everything we have talked about is an example of Simple Dominance.
There are some exceptions to simple dominance

21. 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?

24. Punnett Squares

25. Punnett Square

26. Punnett Squares

27. Punnett Squares