Genetics TEKS 6F: Predict possible outcomes of various genetic combinations such as monohybrid crosses, dihybrid crosses, and non-Mendelian inheritance.

Gregor Mendel Father of Modern Genetics Performed experiments with pea plants Helped determined how traits are passed from one generation to the next.

How are offspring influenced by genetic combinations? Parents pass on units of information called genes. These genes produce traits, which are characteristics that make up an organism. Ex: height, hair color, blood type, intelligence. For each trait, an individual has two alleles (different forms of a gene). Alleles are represented as letters (ex: TT can stand for the trait of tallness). How are these passed along?

Where she get that booty from? She get it from her momma…and her daddy Traits are passed on from parents. You inherit ½ of your genes from your mom and the other ½ from your dad. These come from the sperm and the egg when an egg is fertilized.

Mendel’s principle of dominance FAQ’s Mendel’s principle of dominance states that some alleles are dominant and others are recessive. Dominant alleles are written with capital letters (ex: TT, Tt) Recessive alleles are always written in lower case letters (ex: tt) The recessive allele is exhibited only when the dominant allele is not present. How do I know if it’s dominant? If there is even one big letter, it is dominant. (TT and Tt) Why is Tt dominant if it has a small letter? Because there is a big letter next to it. Dominant will always overpower recessive! How do I know if it’s recessive? If it has two little letters, it is recessive. (tt)

Homozygous vs. Heterozygous FAQ’s When both alleles (letters) are the same, the individual is homozygous for that trait. This is also called true-breeding. When the alleles are different, the individual is heterozygous for the trait. This is also called hybrid. What if the letters are both big, like SS or TT? It is Homozygous. What if the letters are both little, like ss or tt? What if one letter is big and one letter is little, like Ss or Tt? It is Heterozygous because they are different sizes.

FAQ’s Genotype vs. Phenotype The genetic makeup of an organism is called its genotype. Write this as letters, like TT. The organism's physical traits are its phenotype. Write this as a description, like tall, red.. Is Aa a genotype or phenotype? Genotype! Because it’s just the letters. Are purple, tall, short, white, and round genotypes or phenotypes? Phenotypes! Because it’s a physical description. What is an organism’s genotype if it receives two recessive alleles for height (T=tall, t=short)? tt. Because little letters are recessive. The phenotype would be short.

How can you predict which traits will be expressed using monohybrid crosses? When doing a genetic cross, the parent organisms are the P, or parental generation. The offspring are called the F1, or first filial generation. A monohybrid cross is a cross in which there are two contrasting alleles for a single trait. A Punnett square is a diagram that helps predict combinations in genetic crosses. Punnett squares are easy to construct. Do this animation: http://www.siskiyous.edu/class/bio1/genetics/monohybrid_v2.html You can watch this for more practice and explanation: http://biology-animations.blogspot.com/2011/07/punnett-square-animation.html

Practice with monohybrid crosses on the whiteboard!

What if you are using more than one trait, like someone that has blue eyes and is short? You would use a dihybrid cross instead of a monohybrid cross. A dihybrid cross is a cross that shows the possible offspring for two traits.

How do you predict the outcomes of dihybrid crosses? Let’s do an example! Coat Texture: R: Rough r: Smooth Fur Color: B: Black b: White In this example, we will cross: A heterozygous black/heterozygous rough individual with another heterozygous black/heterozygous rough individual. Their genotypes will be: __________. BbRr x BbRr

How do you predict the outcomes of dihybrid crosses? BR, Br bR, br BR, Br bR, br BbRr x BbRr First, you must find ALL possible gametes that can be made from each parent. Remember, each gamete must have one B and one R.

How do you predict the outcomes of dihybrid crosses? BbRr x BbRr Possible gametes: BR Br bR br Next, arrange all possible gametes for one parent along the top of your Punnett Square, and all possible gametes for the other parent down the side of your Punnett Square…

How do you predict the outcomes of dihybrid crosses? BbRr x BbRr BR bR br Br Fur Color: B: Black b: White Coat Texture: R: Rough r: Smooth Then, find the possible genotypes of the offspring

How do you predict the outcomes of dihybrid crosses? BbRr x BbRr BR BBRR BBRr BbRR BbRr Fur Color: B: Black b: White Br BBRr BBrr BbRr Bbrr Coat Texture: R: Rough r: Smooth bR BbRR BbRr bbRR bbRr br BbRr Bbrr bbRr bbrr

How do you predict the outcomes of dihybrid crosses? How many of the offspring would have a black, rough coat? How many of the offspring would have a black, smooth coat? How many of the offspring would have a white, rough coat? How many of the offspring would have a white, smooth coat? bR br BR BBRR BBRr BbRR BbRr Br BBRr BBrr BbRr Bbrr bR BbRR BbRr bbRR bbRr br BbRr Bbrr bbRr bbrr Fur Color: B: Black b: White Coat Texture: R: Rough r: Smooth

How do you predict the outcomes of dihybrid crosses? How many of the offspring would have black, rough coat? How many of the offspring would have a black, smooth coat? How many of the offspring would have a white, rough coat? How many of the offspring would have a white, smooth coat? BR bR br Br BBRR BbRR BbRr BBRr BBrr Bbrr bbRR bbRr bbrr Phenotypic Ratio 9:3:3:1

More dihybrid practice.. In pea plants, yellow seeds (Y) are dominant over green seeds (y), and rounded peas (R) are dominant over wrinkled peas (r). Cross a plant that is heterozygous for both traits with a plant that is homozygous recessive for both traits. Draw a Punnett square to show all possible offspring, and determine the genotypic and phenotypic ratios.

YyRr X yyrr YR yR yr Yr YyRr yyRr yyrr Yyrr

Non-mendelian genetics: What are some other patterns of inheritance? Some forms of inheritance are distinctly non-Mendelian inheritance because they do not follow the principles described by Gregor Mendel. Incomplete Dominance and Codominance

Incomplete Dominance Neither allele is dominant, so the traits blend together. Phenotypes combine to create a separate trait. Example, red and white snapdragons = offspring pink snapdragons

You can use two different letters now! Incomplete Dominance You can use two different letters now! RR (red) X WW (white) R W RW pink 22

Incomplete Dominance Practice Cross of two purple flowers (what 2 colors make purple?) ____ X ____ What are the genotype ratios? 1RR : 2RB : 1BB What are the phenotype ratios? 1red : 2 purple : 1 blue Can you have a heterozygous red or hybrid blue flower? ___ RB RB R B RR RB R red purple http://www.gwu.edu/~darwin/BiSc150/One/rose.GIF BB RB B purple blue no

Expression of both alleles equally Codominance Expression of both alleles equally Phenotype of both traits are seen in heterozygous individuals Example black rooster and white chicken produce offspring with both black and white feathers. 24

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Punnett Square of Codominant cross Expressed as two separate traits in a Punnett Square Cross BB (black) X WW (white) B W BW (Black and white) 26