Essential Question: How do organisms reproduce more organisms like themselves? All organisms are made out of cells The DNA inside of cells contains instructions to build proteins which determine the type of organism that will develop, how it will be built, and how it will function DNA is passed down from parents to offspring during reproduction In sexually reproducing organisms (ex. humans), the DNA comes from 2 parents and is passed down through special cells called gametes

NOTES – Genetics: Mendel & Heredity

What is genetics? Genetics – the study of heredity (how traits are passed from parents to offspring)

Trait – a characteristic of an organism that can be inherited (passed from parents to offspring) Traits are controlled by genes EX. Eye color in humans is a trait controlled by genes which are passed from parents to offspring

Alleles – Different versions of the same gene EX. A certain eye color gene in humans has two alleles: Pigmented iris (non-blue eyes) Non-pigmented iris (blue eyes)

Who was Gregor Mendel and why was he important? Gregor Mendel – Mendel was a Czechoslovakian monk who is considered the “father of genetics” for figuring out the basic rules of how traits are inherited by doing experiments with pea plants back in the 1850’s

Mendel’s Experiments Mendel did breeding experiments called test crosses A test cross is when you choose 2 parents (P1 generation) and use them to create offspring (F1 generation) to see how a specific trait(s) is passed down

Mendel Studied Pea Plants

Mendel’s Famous Experiment Mendel noticed that pea plants had either tall stems or short stems Mendel noticed that some tall plants, when self-fertilized, always produced tall offspring and he noticed the same about certain short plants He called these plants true-breeding Mendel took a true-breeding tall stem plant and crossed it with a true-breeding short stem plant

What happened? All the F1 offspring were tall – what happened to the short trait? Mendel then allowed the F1 offspring to cross-pollinate In the next generation (F2), 75% of the offspring were tall, but 25% of the offspring were short – the short trait reappeared How can you get short plants from tall plants?

What Mendel Figured Out The Principle of Unit Factors Sexually reproducing organisms have 2 copies of each gene One gene comes from the sperm cell and one gene comes from the egg cell The genes can have different versions called alleles EX. For stem length, a pea plant can have 2 tall alleles, 1 tall allele and 1 short allele, or 2 short alleles

What Mendel Figured Out The Principle of Dominance and Recessiveness When an organism has 2 different alleles (like 1 tall and 1 short), the trait that shows up is said to be dominant The allele that does not show up is said to be recessive

What Mendel Figured Out The Principle of Segregation The two alleles that an organism has for a particular trait separate during gamete formation (meiosis) A gamete contains 1 allele for each trait

How can we predict what traits will appear in the offspring of parents? Thanks to Mendel’s discoveries, we can predict what traits offspring are likely to have as long as we know the traits of the parents

Punnett Square Punnet Square – a chart used to predict the traits of offspring Capitol letters are used to represent dominant alleles EX. T for tall allele in pea plants Lower case letters are used to represent recessive alleles EX. t for short allele in pea plants

Phenotype – The trait the organism shows EX. tall pea plant or short pea plant Genotype – The 2 alleles present in the organism for a trait EX. T T or T t or t t

Genotypes can be homozygous or heterozygous Homozygous – The 2 alleles for a trait are the same EX. T T or t t Heterozygous – The 2 alleles for a trait are different EX. T t

Mendel’s Experiment Revisited Here is another look at Mendel’s experiment using some new terms Mendel examined the height gene in pea plants The height gene in pea plants has 2 alleles, tall (T) and short (t) The tall allele is dominant and the short allele is recessive

Mendel’s First Cross Mendel crossed a homozygous tall plant with a homozygous short plant P1 = T T x t t

Mendel crosses a homozygous tall plant (TT) with a homozygous short plant (tt)

The tall parent passes on either its first tall allele (T)…

…or its second tall allele (T) – either way, it always passes a tall allele

The short parent passes either its first short allele (t)…

…or its second short allele (t) – either way it always passes a short allele

Possible offspring 1 – the tall parent’s first tall allele with the short parent’s first short allele (T t)

Possible offspring 2 – the tall parent’s second tall allele with the short parent’s first short allele (T t)

Possible offspring 3 – the tall parent’s first tall allele with the short parent’s second short allele (T t)

Possible offspring 4 – the tall parent’s second tall allele with the short parent’s second short allele (T t)

Genotypic Percentage – 100% of the offspring are heterozygous (T t)

Phenotypic Percentage – 100% of the offspring are tall plants

Mendel’s First Cross Each parent only passes 1 of its alleles, so the tall parent always passed on a T and the short parent always passed on a t All the offspring had the genotype T t, because they received a T from the tall parent and a t from the short parent Because the tall allele is dominant, all the offspring were tall

Mendel’s Second Cross Mendel allowed the F1 generation, which were all heterozygous, to self-pollinate P2 = T t x T t

Mendel crosses a heterozygous tall plant (Tt) with a heterozygous tall plant (Tt)

The first tall parent passes on either a tall allele (T)…

…or a short allele (t)

The second tall parent passes on either a tall allele (T)…

…or a short allele (t)

Possible offspring 1 – the first tall parent’s tall allele with the second tall parent’s tall allele (T T)

Possible offspring 2 – the first tall parent’s short allele with the second tall parent’s tall allele (T t)

Possible offspring 3 – the first tall parent’s tall allele with the second tall parent’s short allele (T t)

Possible offspring 1 – the first tall parent’s short allele with the second tall parent’s short allele (t t)

Genotypic Percentage – 25% of the offspring are homozygous dominant (T T)

Genotypic Percentage – 50% of the offspring are heterozygous (T t)

Genotypic Percentage – 25% of the offspring are homozygous recessive (t t)

Phenotypic Percentage – 75% of the offspring are tall plants

Phenotypic Percentage – 25% of the offspring are short plants

Mendel’s Second Cross Each parent only passes 1 of its alleles, but because each parent has 1 of each type of allele, they can pass either a T or a t Some of the offspring received two T alleles, some received one T and one t, and some received two t alleles The plants with genotype T T were tall, the plants with genotype T t were tall, and the plants with genotype t t were short

Check for Understanding A one-eyed purple people eater is crossed with a two eyed purple people eater.  All of their offspring have two eyes.   Which trait is dominant? If you use the letter E for this gene. What is the genotype of the offspring?  Are these offspring the F1 or F2 generation? If you crossed the offspring with each other?  How many of the new offspring would you expect to have two eyes? Check for Understanding