Understanding Genetics: Traits, Alleles, and Inheritance

BELL WORK: 1. Take out piece of paper and pen/pencil. 2. Put all notes away.

1. What do we call different forms a gene may have for a trait? 2. What height of pea plant (tall or short) did Mendel find to be dominant? 3. How are dominant and recessive traits represented? (upper or lower case) Give an example!

Heredity : the passing of traits from parent to offspring Traits are controlled by genes, SO what is GENETICS? Genetics: The study of how traits are inherited.

GREGOR MENDEL • First known geneticist and “father of genetics” • Was an Austrian monk and was born in 1822 • Did most of his genetic studies on pea plants

He performed cross-pollination • He became the pollinator himself • He controlled which plants mixed. • Some traits Mendel worked with were shape of pea and it’s pod, color and shape of seeds, plant height, flower position and flower color.

WHAT ARE ALLELES? • Are ONE FORM of a gene (there can be more than one form) • Sex cells have one form of a gene on their chromosomes • Body cells have two forms or ALLELES for a single gene (you got one from Mom and one from Dad) • One may be dominant over another. If this happens, the dominant gene is the one expressed. If not, the recessive trait is expressed.

DOMINANT AND RECESSIVE • A Dominant trait: will always be expressed and will “mask” a recessive trait • A recessive trait can only be expressed if there are nodominant alleles present.

Example: Eyecolor—Brown color is dominant and blue is recessive. A person can have a brown allele and a blue allele but still have brown eyes because the brown allele is dominant and “hides” the blue allele.

Example:R= dominant r = recessive • Generally, dominant alleles are represented with a capital letter, and recessive alleles are represented with a lower case letter.

Each organism is represented by TWOletters, one for each allele.

“Purebred” species have two alleles of the same trait • Represented by two of the same letters. This is called homozygous. For instance: BB or bb. • Species with two different alleles or two different forms of the gene would be “hybrid” • Represented by two different “letters” and by called “heterozygous”. For instance: Bb • The alleles present in the organism are referred to as its genotype. For instance, BB, Bb, or bb.

The PHYSICAL trait that shows, regardless of genotype is called a PHENOTYPE. • For instance, Blue or Brown Eyes.

Genetics by Brainpop Mom has blue eyes (bb) Dad has brown eyes (BB or Bb) Therefore, Dad must have the Bb genotype, because he must have given her the “b” allele. His “b” allele is masked by his “B”/dominant allele. Daughter has blue eyes (bb)

PROBABILITY • Helps predict the chance that something will happen • Example: the probability of throwing heads or tails on a coin is 50% (1/2 chances) • Your predictions become more accurate with the more trials you run!

Using a Punnett Square… • Used to help predict Mendelian genetics

Steps for using the Punnett square: • One parent’s alleles (genotype) go along the top • The other parent’s alleles go down the side. • You fill in the squares like doing the communicative property of multiplication. B b B BB Bb b Bb bb

Steps for using the Punnett square: Let’s say the parents are Bb and Bb (the same genotype). What would be their phenotype? Brown Eyes B b So you would predict: ¼offspring to be BB, or Brown Eyes 2/4 or 1/2 to be Bb, or Brown Eyes and ¼to be bb or Blue eyes B BB Bb b Bb bb

So, if Miss Hemphill had children with her husband to be …what color eyes would they have? Mr. Ellinger Blue eyes (bb) Miss Hemphill Blue eyes (bb) b b b b All of their kids would have blue eyes!

Using a Punnett Square Clip

Let’s try some practice problems…

Practice Problem #1 • Predict the fur color of the offspring of a brown heterozygoushamsters and a white homozygoushamster. Brown is dominant. White is recessive. • Use any letter you like.

Practice Problem #1 B b b b

Practice Problem #2 • Predict the offspring of 2 white homozygouscows. Black is dominant over white. • Use any letter you like.

Practice Problem #2 b b b b

Practice Problem #3 • Predict the offspring of 2 Grey Heterozygousrats. Gray is dominant over white, which is recessive. • Use any letter you like.

Practice Problem #3 G g G g

Practice Problem #4 • Predict the pea shape of the offspring of one HeterozygousRound Pea plant and one homozygouswrinkled pea plant. Round is dominant over wrinkled. • Use any letter you like.

Practice Problem #4 R r r r

Practice Problem #5you don’t have to write this one down… • What are the chances of having a boy or a girl? • How would you solve this one?

Practice Problem #5 X Y X X

Heredity by Brainpop • Heredity by Brainpop • What do we call different forms a gene may have for a trait? • What height of pea plant (tall or short) did Mendel find to be dominant? • Which kind of trait can’t be passed from parent to child? • )Eye color b) height c) broken arm

Understanding Genetics: Traits, Alleles, and Inheritance