Genetics Genetics – study of how traits are passed from parent to offspring

Traits are determined by the genes on the chromosomes. A gene is a segment of DNA that determines a trait.

Chromosomes come in homologous pairs, thus genes come in pairs. Homologous pairs – “matching” genes – one from female parent and one from male parent Example: Humans have 46 chromosomes or 23 pairs. One set from dad – 23 in sperm One set from mom – 23 in egg

Gene for eye color (blue eyes) Gene for eye color (brown eyes) Homologous pair of chromosomes One pair of Homologous Chromosomes: Alleles – different genes (possibilities) for the same trait – ex: blue eyes or brown eyes

Genetics Notes Who is Gregor Mendel? Principle of Independent Assortment – Inheritance of one trait has no effect on the inheritance of another trait Principle of dominance – some traits “hide” other traits “Father of Genetics”

Results for One Trait

Dominant and Recessive Genes Gene that prevents the other gene from “showing” – dominant Gene that does NOT “show” even though it is present – recessive Symbol – Dominant gene – upper case letter – T Recessive gene – lower case letter – t Dominant color Recessiv e color

Example: Straight thumb is dominant to hitchhiker thumb T = straight thumb t = hitchhikers thumb (Always use the same letter for the same alleles— No S = straight, h = hitchhiker’s) Straight thumb = TT Straight thumb = Tt Hitchhikers thumb = tt * Must have 2 recessive alleles for a recessive trait to “show”

Both genes of a pair are the same – homozygous or purebred TT – homozygous dominant tt – homozygous recessive One dominant and one recessive gene – heterozygous or hybrid Tt – heterozygous BB – Black Bb – Black w/ white gene bb – White

Genotype and Phenotype Combination of genes an organism has (actual gene makeup) – genotype Ex: TT, Tt, tt Physical appearance resulting from gene make-up – phenotype Ex: hitchhiker’s thumb or straight thumb

White fur (b) Punnett Square and Probability Used to predict the possible gene makeup of offspring – Punnett Square Example: Black fur (B) is dominant to white fur (b) in mice 1.Cross a heterozygous male with a homozygous recessive female. Black fur (B) White fur (b) Heterozygous male White fur (b) Homozygous recessive female

Bb bb Write the ratios in the following orders: Genotypic ratio homozygous : heterozygous : homozygous dominant recessive Phenotypic ratio dominant : recessive b b b B Possible offspring – 2N Male gametes - N (One gene in sperm) Female gametes – N (One gene in egg) Male = Bb X Female = bb Genotypic ratio = 2 Bb : 2 bb 50% Bb : 50% bb Phenotypic ratio = 2 black : 2 white 50% black : 50% white

Sex Determination People – 46 chromosomes or 23 pairs 22 pairs are homologous (look alike) – called autosomes – determine body traits 1 pair is the sex chromosomes – determines sex (male or female) Females – sex chromosomes are homologous (look alike) – label XX Males – sex chromosomes are different – label XY

Try This…  When you are told, place the small piece of paper on your tongue.  What happened?  How many in the classroom can taste something?  How many cannot taste anything?

Traits  The ability to taste PTC is an inherited trait. There are two forms of the trait:  Let T = taster (dominant form)  Let t = non- taster (recessive form)  Traits are determined by genes. For each inherited trait, you get one form of the gene (an allele) from each of your parents.  Your phenotype is either taster or nontaster  Your genotype is TT or Tt if you are a taster, or tt if you are a nontaster.

BBBb bb Bb B Genotypic ratio = 1 BB : 2 Bb : 1 bb 25% BB : 50% Bb : 25% bb Phenotypic ratio = 3 black : 1 white 75% black : 25% white Cross 2 hybrid mice and give the genotypic ratio and phenotypic ratio. Black Fur (B) is dominant over white fur (b) Bb X Bb b

Incomplete dominance and Codominance When one allele is NOT completely dominant over another (they blend) – incomplete dominance Example: In carnations the color red (R) is incompletely dominant over white (W). The hybrid color is pink. Give the genotypic and phenotypic ratio from a cross between 2 pink flowers. RW X RW RRRW WW R WR W Genotypic = 1 RR : 2 RW : 1 WW Phenotypic = 1 red : 2 pink : 1 white

When both alleles are expressed – Codominance Example: In certain chickens black feathers are codominant with white feathers. Heterozygous chickens have black and white speckled feathers.

Sex – linked Traits Genes for these traits are located only on the X chromosome (NOT on the Y chromosome) X linked alleles always show up in males whether dominant or recessive because males have only one X chromosome

Examples of recessive sex-linked disorders: 1.colorblindness – inability to distinguish between certain colors Color blindness is the inability to distinguish the differences between certain colors. The most common type is red-green color blindness, where red and green are seen as the same color. You should see 58 (upper left), 18 (upper right), E (lower left) and 17 (lower right).

2. hemophilia – blood won’t clot

XNXNXNXN XNXnXNXn XNYXNYXnYXnY XNXN XnXn XNXN Y Phenotype: 2 normal vision females 1 normal vision male 1 colorblind male Example: A female that has normal vision but is a carrier for colorblindness marries a male with normal vision. Give the expected phenotypes of their children. N = normal vision n = colorblindness X N X n X X N Y

Crazy Traits  The alleles you inherit from each parent are determined by chance.  In this investigation, you will play a game that will help you learn about inheritance.

Your creature’s gender  Find the egg coin (x on both sides)  Find the sperm coin (x on one side, y on the other)  Flip the coins together to determine the gender of your creature.  Record this in the table provided – see next slide for example

Determining trait genotypes for your creature  Members of this species have the following traits: main body, foot, leg, skin, arms, hands, beak, eyes, eyebrows, ears, wings, antenna.  You will flip sperm and egg coins to determine the allele for each trait your creature inherits from each parent.

Determining trait genotypes for your creature  In this activity, we will assume that both parents have the same genotype for all traits (Tt).  The genotype of each parent could be Tt, TT, or tt. We are choosing to have parents with the Tt genotype for each trait.

Determining the genotype for each trait  You will need the blue egg coin with a capital T on one side and a lower case t on the other side.  You will also need the green sperm coin with a capital T on one side and a lower case t on the other side.

Determining the genotype for a trait  The first trait you will roll for is skin color.  Place the egg and sperm coins in the cup.  Shake the cup and toss the two coins onto the lab table.  The side that lands up on each coin represents the sperm and egg that unite during fertilization.

Determining the genotype  Record the allele from each parent and genotype in columns 2, 3, and 4 of the first row of Table 1.  Repeat this procedure for traits 2 through 13.  See the next slide for an example.

Stop and Think a. What information do the letters on the sperm and egg coins indicate: alleles, genotype, or phenotype? Alleles. Both alleles together represent the genotype.

Stop and Think b. For the sperm coin, what are the chances of getting a T or getting a t? State your answer as a fraction or a percent. 1/2 or 50%.

Stop and Think c. For the egg coin, what are the chances of getting a T or getting a t? State your answer as a fraction or a percent. 1/2 or 50%.

Stop and Think d. When both coins are flipped at once, what are your chances of getting each of the following combinations: TT, Tt, or tt? State your answer for each as a fraction and a percent.

Building your creature  Once you have completed columns 2 through 4 of Table 1, use Table 2 (next page) to look up the phenotype for each trait. Record the phenotype for each trait in column 5 of Table 1.

Building your creature  Once you have completed Table 1, select the correct body parts to build your creature. See parts list on next slide.

Creature Building Tips 1. Orient the body for either male or female (which orientation do you think is male? Female?) 2. Place the skin on the smooth side of the body. 3. Attach the head. 4. Attach the leg. 5. Place foot on the stand. 6. Insert the leg into the foot and stand. 7. Attach the rest of the body parts.

Thinking about what you observed a. Examine the creatures. Do any of them look exactly alike? Why or why not?  Some look similar, but no two are alike. For two to look exactly alike, every single flip of all three coins would have to be the same for both creatures. That seems very unlikely.

Thinking about what you observed b. How does this investigation explain why siblings may resemble each other, but never look exactly alike (unless they are identical twins)?  Since siblings share the same parents they will likely share many of the same traits. With the huge amounts of traits possible for humans the probability of all of them matching from sibling to sibling is very small.

Thinking about what you observed c. Count the number of males and number of females. Does the number of each match the chances of getting a male or female in the game? Why or why not?  Not exactly because the sample is small. Larger samples yield results that are closer to the average.

Thinking about what you observed d. Which trait(s) are examples of complete dominance?  Eyebrows, beak, ears, leg, foot, arms, hands, antennae, antenna shape, wings, and gender. e. Which trait(s) are examples of incomplete dominance?  Skin color and tail. f. Which trait(s) are examples of codominance?  Eye color.

Adaptation Survivor 1. Environment Cards will be displayed on this screen. For each card, your creature can: thrive (+1 point); be pushed closer to extinction (-1 point); or have no effect (0). 2. Watch out for Catastrophe Cards! 3. When you earn a score of -3, you become extinct! 4. Play until there is one survivor left.

YOUR BRIGHT PURPLE SKIN IS NOTICABLE TO PREDATORS IN YOUR ENVIRONMENT! YOUR BRIGHT PURPLE SKIN IS NOTICABLE TO PREDATORS IN YOUR ENVIRONMENT! Purple skin -1 Purple skin -1

There is a food shortage on land. Those with webbed feet are able to swim to catch food. There is a food shortage on land. Those with webbed feet are able to swim to catch food. (If you have webbed feet +1, talons -1) (If you have webbed feet +1, talons -1)