1. WARM UP
January 3, 2011

2. Warm Up
If you are acquainted with your birth parents, list 4 physical traits you share, and from which parent you acquired that trait from.
If you are not acquainted with your birth parents, think of one of your friends that is, and pick out 4 traits he or she shares with them.

3. Introduction to Genetics

4. Genetics Terms to know:
Gamete
Gene
Allele
Dominant
Recessive
Heterozygous
Homozygous
Hybrid
Genotype
Phenotype

5. What is genetics? Genetics: The study of heredity
All things seem to inherit traits from their “parents”
Trait: a characteristic based on heredity
i.e. hair color, plant flower color, number of wings on a fly…

6. Understanding Heredity
For centuries humans have known that offspring inherit traits from their parents.
However it is the work of a monk, named Gregor Mendel that greatly increased knowledge of genetics!

7. Watch this clip about Mendel
“Thread of life”: Gregor Mendel’s experiments
23 and me: “What is a gene?”

8. Go Go Gregor cont.. The monastery had several true-breeding pea plants
meaning that they only self-pollinate
One stock of true breeding plants only bred tall plants
One stock of true breeding plants only bred short plants every time
Tall
Short

9. Go Go Gregor cont..
So Gregor decided to cross pollinate the tall plants with the short plants, and do you know what he got?
All tall plants!!!

10. Go Go Gregor cont..
So he crossed the offspring of the first cross (the two new tall plants) and what did he get?
About ¾ tall and ¼ short!

11. So what did this mean?
Mendel drew a couple of conclusions from his experiments.
1st conclusion: Biological inheritance is determined by factors passed from one generation to the next. (We call these factors GENES)
The different forms of a gene are called alleles.
Example: tall pea plant allele and short pea plant allele
Every organism that reproduces sexually gets two alleles (genes) for each trait, one from each parent. So every organism has two alleles for a certain trait, one from each parent.

12. So what did this mean? Cont.
2nd conclusion: THE PRINCIPLE OF DOMINANCE
This means that alleles can come in a dominant or recessive form. Dominant traits mask recessive traits when they are expressed.
Example: tall is dominant over short pea plants. Yellow seeds is dominant over green seeds, etc… etc..
Letter size signifies dominant (CAPITAL) or recessive (lower case)
T = tall height
t = short height
TT, Tt, tt ? Are these tall or short?

13. Phenotype Vs. Genotype
Phenotype – outward physical appearance Example: Tall pea plant or blue eyes
Pheno-physical!!!!
Genotype – genetic composition (what alleles are in DNA) Hh or bb

14. Wow! what are some dominant and recessive traits in humans?
Tongue rolling is dominant of non tongue rolling
Widow’s peak is dominant

15. Wow! what are some dominant and recessive traits in humans
Free earlobe is dominant over attached earlobe

16. Alleles and Punnett squares
Homozygous – individuals that have 2 identical alleles for a given trait. Example genotypes: HH (homozygous dominant) or hh (homozygous recessive).
Heterozygous – individuals with 2 different alleles for a given trait. Example genotype: Hh

17. Go Go Gregor cont..
Mendel did this with several other true breeding traits as well.

18. Review
dominant – only one copy of the allele is present for the trait to be “shown”
recessive – absence of a dominant allele required (2 copies of recessive allele) to “show” trait