Introduction To Genetics

Heredity & Genetics Heredity = the passing of traits from parent to offspring Traits are controlled by genes, so therefore, GENETICS is the study of how traits are inherited through the action of alleles

GREGOR MENDEL First known geneticist and “father of genetics” Was an Austrian monk who was born in 1822 Did most of his genetic studies on pea plants He made careful observations, and strictly adhered to the scientific method

He performed cross-pollination by becoming the pollinator himself, and controlling 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.

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 no dominant alleles present.

Example: Eyecolor—Brown color is dominant and blue is recessive 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. Example: R= dominant r = recessive

Each organism is represented by TWO letters, one for each allele.

“Purebred” species have two alleles of the same trait, and therefore would be 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 have two different “letters” and is 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.

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

Why is it that if a couple has 2 children, they don’t always have one boy and one girl? 2 is a really small trial #…so don’t always “see” the ratio! …we will investigate this more later on!

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. See Below:

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 So you would predict: ¼1/4 offspring to be BB, or Brown Eyes 2/4 or 1/2½ to be Bb, or Brown Eyes and ¼1/4 to be bb or Blue eyes B b B BB Bb b Bb bb

Little girl all grown up So, if the little girl (all grown up)marries and have children with a blue eyed man …what color eyes would they have? Her Husband Blue eyes (bb) Little girl all grown up Blue eyes (bb) b b bb b b All of our kids would have blue eyes!

Using a Punnett Square Clip

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

Let’s try some practice problems…

Practice Problem #1 Predict the fur color of the offspring of a brown heterozygous hamsters and a white homozygous hamster. Brown is dominant. White is recessive. Use any letter you like.

Practice Problem #1 B b Bb bb b

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

Practice Problem #2 b b bb b

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

Practice Problem #3 G g GG Gg gg G g

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

Practice Problem #4 R r Rr rr r

Practice Problem #5 you 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 XX XY X