Introduction to Genetics A look at inheritance

Key Vocabulary Words-Rate what you know… On a separate sheet of paper make a chart with the following words down one side of the paper. Across the top of the page write “Can define,” “Have heard of it,” “Have never heard of it.” 1. Inheritance 2. DNA 3. Chromosomes 4. Genes 5. Alleles 6. Traits 7. Dominant 8. Recessive 9. Heterozygous 10. Homozygous NOW RATE HOW WELL YOU KNOW THESE WORDS BY PLACING A CHECK IN THE COLUMN THAT BEST DESCRIBES YOUR KNOWLEDGE OF THE WORD.

What is inheritance? Every living thing-plants, animals, bacteria, humans-has a set of characteristics inherited from its parent or parents.

How do we get the characteristics we inherit? All of the instructions that make you YOU are coded for in your DNA. Did you know that you have approximately 6 feet of DNA in each cell?

What is a chromosome? Chromosomes within the nucleus contain the genetic information that is passed from one generation of cells to the next. FLASHBACK: How many chromosomes do YOU have? How many pairs of homologous chromosomes do YOU have? Where did you get these chromosomes?

We have two copies of all of our chromosomes Why?

These are homologous chromosomes!                                                                                        

What is a gene? How is it different from a trait? A gene is the sequence of DNA that codes for a protein and thus determines a trait. A trait is a specific characteristic that varies from one individual to another.

What is an allele? An allele is one of different forms of a gene.

Summarize So, chromosomes are made of DNA, which has all the information that makes you YOU! On each chromosome are genes that code for specific traits. Alleles are variations of genes. Now, turn to the people at your table and teach each other the definition of these words.

The Origins of Genetics Gregor Mendel (1822-1884) “Father of Genetics” Cross pollinated over 30,000 pea plants to see the outcomes He looked at seven different TRAITS of the plants and recorded his findings. Gregor's life story

Genetics Pre-Mendel Theory = BLENDING Pre Mendel, theory of inheritance = qualities of the parents blended to form the qualities of the child Ex: tall and short parent = medium height child Theory did NOT explain examples like: two brown-eyed parents giving birth to a blue-eyed baby Because of Mendel's work there became a consistent theory of heredity = GENETICS

Mendel’s Experiments Mendel crossed plants with contrasting traits (ie-purple flowers v white flowers) and studied their offspring. The parent generation is referred to as P and the offspring he called F1 (for “filial” in Latin, which means “son.”) The offspring of crosses between parents with different traits he called “hybrids.” THINK ABOUT IT: What do you think he saw in the F1 generation if he crossed purple and white flowers? Do you think he saw a BLENDING of traits? What would a blending of purple and white flowers look like?

Mendel Crossed Purple Flowers with White Flowers and the results were…

In the P (parent generation) he crossed purple with white and got ALL purple flowers in the F1 generation! What does this mean? Was there blending?

Next he crossed the F1 generation and found…. Generation 2 F1 x F1 = Mostly purple, some white (P2 Parents) (F2) That’s a 3:1 ATIO! Out of 929 flowers, 705 = purple,W224 = white THAT IS A 3:1 RATIO!

Look at the trend. When Mendel crossed True-breeding TALL plants with TRUE breeding SHORT plants, all the F1 generation were tall. But, in the F2 generation the ratio was 3 tall to 1 short.

Mendel’s Conclusion “Each organism has 2 factors that control each of its traits” (now factors called alleles = types of a gene) Dominant Trait A trait that dominates (masks/covers up) a recessive one; written w/ Capital letter Example: Purple Flower= P Recessive Trait Can’t be expressed (seen) if a dominant trait is present; written w/ lower case letter Example: White Flower = p

The Principle of Dominance states that some unit characters (genes) can mask the expression of others.

For every trait… There are 2 alleles (types of genes) One from female parent, one from male parent Process of meiosis allows for this. The Principle of Segregation states that each unit character (gene) separates into a different sex cell. Because you get one allele from each parent, you can either inherit the same “homo” or different “hetero” alleles. If you inherit the SAME alleles, you are HOMOZYGOUS. If you inherit DIFFERENT alleles, you are HETEROZYGOUS. Look at how we write this: Purple flower = PP HOMOZYGOUS DOMINANT = pure dominant White flower = pp HOMOZYGOUS RECESSIVE = pure recessive What about Pp? HETEROZYGOUS “Hybrid”; carrier

Genotype vs. Phenotype What do these terms mean? The GENOTYPE is the genes you have- one from each parent (the TYPE of GENES). The PHENOTYPE is what is the physical trait that is shown- it is what we SEE. If you wanted to tell the phenotype of a dog, how would you do that?

What Mendel Saw… How did he know which were dominant & which were recessive?

How can we anticipate what alleles are passed down How can we anticipate what alleles are passed down? One way is through a Punnett Square. The first step is to write down the GENOTYPE of each parent. For example, if the parent plant is heterozygous tall, we write that as Tt. If the other plant is heterozygous, we write that as Tt. Each allele/letter gets its own box.

Now we have to determine the possible genotypes and phenotypes. GENOTYPE could be HOMOZYGOUS DOMINANT= TT or HETEROZYGOUS= Tt or HOMOZYGOUS RECESSIVE= tt HD________: HETERO___________: HR________________. The phenotype will either be tall (DOMINANT) or short (recessive). D_____: R_________. G ratio - ____:____:____ HwD Het HR P ratio - _____ : _____ D R

Now you practice. What would happen if you crossed a heterozygous purple flower with a homozygous recessive white flower. 1. Determine and write the genotypes of these two plants. 2. Make your Punnett square. 3. List the alleles for one plant across the top and the other down the side. 4. Cross the possible alleles and record in box. 5. Figure out genotype and phenotype of next generation.

Practice makes perfect… In pea plants round is dominant to wrinkled. What would happen if you crossed a HOMOZYGOUS DOMINANT round plant with a HOMOZYGOUS RECESSIVE wrinkled plant. 1. Determine and write the genotypes of these two plants. 2. Make your Punnett square. 3. List the alleles for one plant across the top and the other down the side. 4. Cross the possible alleles and record in box. 5. Figure out genotype and phenotype of next generation.

Actually, perfect practice makes perfect. Try again… In humans unattached earlobes are dominant to recessive. Write the genotype of a Heterozygous unattached earlobe father. Write the genotype of a homozygous dominant unattached mother. Cross these two on a Punnett Square. 1. Determine and write the genotypes of these two plants. 2. Make your Punnett square. 3. List the alleles for one plant across the top and the other down the side. 4. Cross the possible alleles and record in box. 5. Figure out genotype and phenotype of next generation.

For Homework: Do the practice sheet you picked up on the way in the class. Turn in for a grade tomorrow. Study for quiz tomorrow! Look over all your notes. The quiz will be over vocabulary words and Punnett Square.