Genetics

Vocabulary Segregation Trait Gametes Genes Alleles True breeding Hybrids Homozygous Heterozygous Phenotype Genotype

Traits

Traits are qualities, features or other things that distinguish the organism. Traits can include things like hair color, tooth shape, beak shape, bone size, or muscle structure.

Traits come in two varieties: acquired and inherited.

Acquired Traits Animals can acquire usesful abilities. These acquired traits can not be passed on

genetically. You can't inherit your uncle's knowledge, skills, ideas or memories and it doesnt' work that way with other organisms either.

Acquired traits include things such as calluses on fingers, larger muscle size from exercise or from avoiding predators.

Behaviors that help an organism survive would also be considered acquired characteristics most of the time. Things like where to hide, what animals to hide from.

Inherited Traits In organisms, inherited traits must come from a

parent or other ancestor. A trait may seem to skip a generation or even two

or three, but if a trait shows up it must have been present in an ancestor.

Inherited traits include things such as hair color, eye color, muscle structure, bone structure, and even features like the shape of a nose.

Inheritable traits are traits that get passed down from generation to the next generation. This might include things like passing red hair down in a family.

The basics…

Gregor Mendel: "father of genetics" Blending Theory of Inheritance - offspring of two

parents "blend" the traits of both parentsParticulate Theory of Inheritance - traits are inherited as "particles", offspring receive a "particle" from each parent.

Evidence for Particulate Theory of Inheritance: A plant with purple flowers is crossed with another plant that has purple flowers. Some of the offspring have white flowers (wow!). Mendel set out to discover how this could happen.

Mendel

parents were farmers he became ordained as a priest studied science and mathemathics at the University

of Vienna Mendel's Experiments - chose pea plants as his

experimental subjects, mainly because they were easy to cross and showed a variety of contrasting traits (purple vs white flowers, tall vs short stems, round vs wrinkled seeds)

1. _______________ was the father of genetics.

a. Charles Darwin b. Gregor Mendelc. Charles Watson2. What did he use in his research?a. Corn b. Fruit fliesc. Peas3. Hidden characteristics show up

in_________ of the second generation.a. One half b. One quarterc. One third d. All of them

Mendel’s Procedure

1. Mendel chose true-breeding lines of each plant/trait he studied (true breeding lines always produced offspring of the same type)

2. He crossed a true breeding plant with a plant of the opposite trait (purple x white). He called this the Parental (P) generation.

3. He recorded data on the offspring of this cross (First Filial, F1)

4. He self pollinated the F1 offspring5. He recorded data on the offspring of the second

generation, calling it the Second Filial generation (F2)

Mendel’s Analysis

The F1 generation always displayed one trait (he later called this the dominant trait)

The F1 generation must have within it the trait from the original parents - the white trait

The F2 generation displayed the hidden trait, 1/4 of the F2 generation had it (he later called this hidden trait the recessive trait)

Each individual has two "factors" that determine what external appearance the offspring will have. (We now call these factors genes or alleles)

Mendel’s Conclusion Mendel established three principles (or Laws) from

his research 1. The Principle of Dominance and

Recessiveness - one trait is masked or covered up by another trait

2. Principle of Segregation - the two factors (alleles) for a trait separate during gamete formation

3. Principle of Independent Assortment - factors of a trait separate independently of one another during gamete formation; another way to look at this is, whether a flower is purple has nothing to do with the length of the plants stems - each trait is independently inherited

2. True or False – Principle of Dominance states that one factor in a pair may prevent the other factor from appearing.

3. True or False – the recessive factor is kept from appearing by the dominant factor

1. True or False – each trait is controlled by 3 factors.

2. The principle of dominance states that one factor in a pair may prevent another factor from appearing.

3. The _____________ factor is kept from appearing by the ______________ factor.

a. Dominant, recessiveb. Recessive, dominant

4. If a dominant and recessive trait combine only ___________ will be displayed.

a. Dominantb. Recessive

5. True or False The recessive trait disappears and will never appear again.

The Law of Segregation The Law of Segregation:

two alleles separate during gamete formation (a Tt parent can produce both T sperm, and t sperm)

A punnet square is a representation of this law, showing how gametes separate and then come together during fertilization

A simpler look at Mendel’s generations

Modern Genetics

Mendel's factors are now called ALLELES. For every trait a person has, two alleles determine how that trait is expressed.

We use letters to denote alleles, since every gene has two alleles, all genes can be represented by a pair of letters.

PP = purple, Pp = purple, pp = white

Important Terms Homozogyous: when the alleles are the same, the

individual is said to be homozygous, or true breeding. Letters designating a homozgyous individual could be capital or lowercase, as long as they are the same. Ex. AA, bb, EE, dd

Heterozygous: when the alleles are different, in this case the DOMINANT allele is expressed. Ex. Pp, Aa

Monohybrid cross = a cross involving one pair of contrasting traits. Ex. Pp x Pp

Punnet Square: used to determine the PROBABILITY of having a certain type of offspring given the alleles of the parents

Homozygous vs. Heterozygous

Homozygous involves traits where both alleles are the same , either dominant or recessive. If we were talking about round or wrinkeled seeds we could use the letter R. RR would be homozygous dominant and rr would be homozygous recessive

Heterozygous involves traits where one inherited allele is dominant and the other is recessive such as Rr

Indicate whether the following are homozygous dominant, homozygous recessive or heterozygous1. HH _________________2. Hh3. hh4. Rr5. rr6. RR

In this picture the two "hot dog" shapes represent a pair of homologous chromosomes.  Homologous chromosomes are the same size & have the same genetic info (genes).  Each letter in the diagram stands for an allele (form of a gene).  What's important to notice is that the letters can be in different forms (capital or lowercase) --- that is what we mean by allele --- and that the letters are lined-up in the same order along each hot dog --- homologous chromosome. The "a-forms" are in corresponding positions, so are the "B-forms", the "c" alleles, the "d" alleles, etc. etc. Reread that "allele" definition again & study the picture.

back to our abbreviations, we could use a "C" for the curly allele, and a "c" for the straight allele.  A person's genotype with respect to hair texture has three possiblilties: CC, Cc, or cc.  So to review some vocab, homozygous means having two of the same allele in the genotype (2 big or 2 little letters --- CC or cc).  Heterozygous means one of each allele in the genotype (ex: Cc).

Genotype vs. Phenotype

Genotype: letters used to denote alleles (BB, Pp, etc.)

Phenotype: what an organism looks like (brown, purple..) It’s physical appearance.

If we donate PP for purple flowers and p for pink flowers, fill in the genotype and phenotype of a …

1. homozygous dominant flower2. homozygous recessive flower3. heterozygous flower

Answers…

1. Homozygous dominant flowergenotype - PPphenotype – purple

2. Homozygous recessive flowergenotype – ppphenotype – pink

Heterozygous flowergenotype – Ppphenotype - purple

PUNNETT SQUARES

In pea plants, round seeds are dominant to wrinkled. The genotypes and phenotypes are:

RR = roundRr = roundrr = wrinkled

Punnett Squares: Monohybrid cross

Punnett Squares: Monohybrid cross

Punnett Squares: Monohybrid cross PARENTS: One is tall TT (homozygous) and one

is short tt (homozygous)

Tt Tt

Tt Tt

T T

t

t

All offspring are tall!

Punnett Squares: Monohybrid cross In the previous slide the two homozygous parents

had all tall children who were heterozygous. Now we cross the offspring Tt x Tt

TT Tt

Tt tt

TT t

TT

tNow the probability of having a tall child is lowerIt is 3:1, because three are tall one one is short

How to make a punnett square

1. Determine the genotypes (letters) of the parents. Bb x Bb2. Set up the punnett square with one parent on each side.3. Fill out the Punnett square middle4. Analyze the number of offspring of each type.

In pea plants, round seeds are dominant to wrinkled. The genotypes and phenotypes are:RR = roundRr = roundrr = wrinkled

If you get stuck make a "key". Sometimes the problems won't give you obvious information. Example: In radishes, a bent root is a dominant trait, though some roots are straight (which is recessive). If a straight rooted plant is crossed with a heterozyous bent root plant, how many of the offspring will have straight roots?

Say what? First of all, this problem doesn't make it easy. Start by assigning genotypes and phenotypes. Pick the letter of the dominant trait. B for bent

BB = bentBb = bentbb = straightNow use the key to figure out your parents. In this case you have a straight root plant (bb) crossed with a heterozyous bent plant (Bb). Once you've figured that out, the cross is simple!

Incomplete dominance

Some alleles are neither dominant nor recessive, and many traits are controlled by mulitple alleles or multiple genes

Incomplete dominance is when one allele is not completely dominant over another – results in blended traits

Incomplete Dominance

There is no dominant or recessive, the heterozygous condition results in a "blending" of the two traits. Example: Snapdragons can be red, white, or pink (heterozygous)

R = allele for red flowers W = allele for white flowers

red x white ---> pink RR x WW ---> 100% RW

Now you try… 1. A cross between a blue blahblah bird & a

white blahblah bird produces offspring that are silver.  The color of blahblah birds is determined by just two alleles. a) What are the genotypes of the parent blahblah birds in the original cross? b) What is/are the genotype(s) of the silver offspring? c) What would be the phenotypic ratios of offspring produced by two silver blahblah birds?

1. A cross between a blue blahblah bird & a white blahblah bird produces offspring that are silver.  The color of blahblah birds is determined by just two alleles. a) What are the genotypes of the parent blahblah birds in the original cross?

  Since there are only 2 alleles & three phenotypes (blue, white, & silver), we must be dealing with incomplete dominance.  So the blue parent is homozygous blue (BB) & the white parent is homozygous white (WW).

b) What is/are the genotype(s) of the silver offspring? 

The silver offspring are hybrids (BW), one blue allele & one white allele, neither one dominating the other.  Instead, we get a blending of blue & white, i.e. silver. c) What would be the phenotypic ratios of offspring produced by two silver blahblah birds?    silver x silver = BW x BW

The p-square would look like what you see here.

As you can see, 25% (1/4) of the offspring are homozygous white (WW), 25% (1/4) are homozygous blue (BB), & 50% (2/4) are hybrid & therefor have

the silver phenotype.

Codominance

Both alleles attribute to the phenotype Trait is not blended (as in the pink

snapdragons) rather they are both expressed – example would be spotted coats

R = allele for red flowers W = allele for white flowers red x white ---> red & white spotted RR x WW ---> 100% RW

Now you try…

1. A cross between a black cat & a tan cat produces a tabby pattern (black & tan fur together). a) What pattern of inheritence does this illustrate? b) What percent of kittens would have tan fur if a tabby cat is crossed with a black cat?

a) What pattern of inheritence does this illustrate?  Codominance, two phenotypes together at the same time

b) What percent of kittens would have tan fur if a tabby cat is crossed with a black cat?   Tabby cats are the hybrids (because they have both colors) & a black cat must be homozygous black.  So the cross for this problem is BB (black) x BT (tabby).

The results show that 50% of the offspring will be BB (black) & 50% will be tabby (BT).  So to answer the question, 0% of the kittens will be tan.

Multiple Alleles Genes which have more

than two alleles – does not mean that the individual has more than two, just means that more than two possiblities exist in the population. Examples include different color coats, blood types in humans

Blood type in humans is controlled by three alleles: A, B, and O

Phenotype Genotype

A AA or AOB BB or BOAB AB onlyO OO only

Examples of Blood type crosses

Polygenic Traits Traits controlled by two or more genes Wide variety of phenotypes Example – skin color in humans

Punnett Squares: Dihybrid cross Monohybrid

crosses are used to determine only ONE trait.

Dihybrid crosses involve TWO traits

Dihybrid crosses Crosses that involve

2 traits For these crosses

your punnet square needs to be 4x4

In any case where the parents are heterozygous for both traits (AaBb x AaBb) you will get a 9:3:3:1 ratio.

Now you try…

If you cross other combinations, you will need to do a square.

Try RrYy x rryy

Meiosis Warm Up #1 pg. 43 HonorsPg. 41 regulars1. What is the main goal of meiosis?2. What is a gamete?3. How many cells are produced through

mitosis?4. How many cells are produced through

meiosis?5. 2n=30, what is the haploid number?

GRAB YOUR CLICKERS!

Did you know? A group of ravens is called a murder. A group of bears is called a sleuth. Twelve or more cows is called a flink. A baby oyster is called a spat. A group of unicorns is called a blessing. A group of kangaroos is called a mob.

Did you know? By some

unknown means, an iguana can end its own life.

Did you know? It was discovered on a

space mission that a frog can throw up. The frog throws up it’s stomach first, so the stomach is dangling out of it’s mouth. Then the frog uses it’s forearms to dig out all of the stomach’s contents and then swallows the stomach back down again.

Did you know? The woodland frog is the only animal able to

survive being completely frozen. These frogs live north of the arctic circle and can be frozen for weeks: their cells don’t freeze but the water outside their cells does. The heart can also stop, but once the temperature rises they “come back to life”

Did you know? The bagpipe was originally

made from the whole skin of a sheep.

Did you know? More people are killed annually by donkeys

than in airplane crashes.

Did you know? When a horned toad is angry, it squirts blood

from its eyes.

Did you know? The average garden-variety caterpillar has

248 muscles in its head.

Chapter 14 – Human Genome