Genetics and Heredity

Genetics LT 3.3 Ask questions to clarify relationships about the role of DNA and chromosomes in coding the instructions for characteristic traits passed from parents to offspring. 

Hook Put the strip in your mouth. Did you taste something or not?

Hook Try to roll your tong. Can you?

Why do you share some but not all characteristics of each parent Why do you share some but not all characteristics of each parent? What are the rules of this sharing game?

Genes and Traits Genetics is the study of how traits are passed from parent to offspring. Traits are physical characteristics and they are determined by the genes on the chromosomes. A gene is a segment of DNA that determines a trait.

Think What is the relationship between genes and traits?

J-TPS Which set of fruit flies are most likely the offspring’s parents J-TPS Which set of fruit flies are most likely the offspring’s parents? WHY? Offspring B or D Parents A Parents C Parents D Parents B

J-TPS (Justify –Think Pair Share)

Discussion questions What traits does the offspring have? Dominant genes will always present themselves in the offspring, and recessive genes only present themselves if dominant genes are not present. What might be the dominant and recessive genes of parents B? What might be the dominant and recessive genes of Parents D? Parents B: Since only one parent has white eyes, black bottom, and short wings, then those traits are dominant. Since both parents have tan bodies, then that trait could be recessive. Offspring Parents A Parents C Parents D Parents B

What do the words dominant and recessive mean? http://www.youtube.com/watch?v=EIy8AzwKFZE

Dominant vs. Recessive Genes DOMINANT GENE: Genes that prevents the other gene from “showing” upper case letter – T) RECESSIVE GENE: Gene that does NOT “show” even though it is present (lower case letter – t)

You do Straight thumb is dominant to hitchhiker thumb. How can you express this concept in genetics?

(Always use the same letter for the same alleles— 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”

Genotype vs. Phenotype GENOTYPE: combination of genes an organism Ex: TT, Tt, tt PHENOTYPE: Physical appearance resulting from gene make-up Ex: hitchhiker’s thumb or straight thumb

Interpreting diagrams: Phenotype vs Genotype

Homozygous vs. Heterozygous Homozygous – Term used to refer to an organism that has two identical alleles for a particular trait (TT or tt) Heterozygous - Term used to refer to an organism that has two different alleles for the same trait (Tt)

Interpreting diagrams (SEP4): Phenotype vs Genotype

Interpreting diagrams: Phenotype vs Genotype

Check your understanding The following alleles AA are Dominant Recessive Heterozygous Homozygous dominant

Check your understanding Heredity is The study of how people reproduce The study of germ cells The study of how people inherit traits The study of peas

Check your understanding A trait is A different form of a gene A special gene A physical characteristic None of above

Check your understanding If you look at someone you will be able to see his or her genotype True False

Check your understanding Let’s assume you have brown eyes. Is it possible that you are carrying the gene for blue eyes? No, otherwise I would have blue eyes No, I only carry one allele for that trait Yes, the allele for brown eyes is dominant Yes, the allele for blue eyes is dominant None of above

Are dominant alleles better than recessive alleles? Why or why not? Scenario: In rock pocket mice fur color is controlled mainly by a single gene. The gene codes for a protein that makes dark pigment. Some rock pocket mice have dark fur, and some have light fur. The dark-fur allele is dominant, and the light-fur allele is recessive. Using the given scenario write a scientific explanation why dominant alleles are or are not better than recessive alleles (SEP6). When mice live in a habitat filled with dark rocks, dark fur is “better” because it makes the mice less visible to predators. But when mice live in a habitat filled with light rocks and sand, light fur is “better.” It’s the environment that matters, not whether the allele is dominant or recessive.  

Tapping into prior knowledge We talked about heterozygous and homozygous genes. Why are we considering two genes (two letters) and not just one? LT 3.1

Tapping into prior knowledge We talked about heterozygous and homozygous genes. Why are we considering two genes (two letters) and not just one? How many of you got this question right?

Genetics song http://www.youtube.com/watch?v=54wxJ6E_2K8

Punnett Square Diagram showing the gene combinations that might result from a genetic cross Used to calculate the probability of inheriting a particular trait What is probability?

Punnett Square Diagram showing the gene combinations that might result from a genetic cross Used to calculate the probability of inheriting a particular trait Probability – The chance that a given event will occur What is probability?

Look at this Punnet Square and interpret it

Look at this Punnet Square and interpret it Parent Offspring Parent

How to Complete a Punnett Square

You do! Give the genotype and phenotype for the following cross: TT x tt (T = Tall and t = Short)

TT x tt Step One: Set Up Punnett Square (put one parent on the top and the other along the side) T T t

TT x tt Step Two: Complete the Punnett Square T T t Tt

TT x tt Tt t Genotype: 4 - Tt Phenotype: 100% Tall Step Three: Write the genotype and phenotype T T t Genotype: 4 - Tt Phenotype: 100% Tall Tt Remember: Each box is 25%

You Try It Now! Give the genotype and phenotype for the following cross: Tt x tt

Tt x tt Step One: Set Up Punnett Square (put one parent on the top and the other along the side) T t t

Tt x tt Step Two: Complete the Punnett Square T t t Tt tt

Tt x tt t Tt tt Genotype: Tt - 2 (50%) tt - 2 (50%) Phenotype: Step Two: Complete the Punnett Square T t t Genotype: Tt - 2 (50%) tt - 2 (50%) Phenotype: 50% Tall 50% Short Tt tt Remember: Each box is 25%

You do 1. If you crossed a true-breeding black rabbit with a true-breeding white rabbit, all of the offspring would be black. Which trait is dominant in rabbits: black fur or white fur? 2. Which trait is recessive?

Answer Black Rabbit (BB) The trait for black fur is dominant over the trait for white fur. The white fur trait is recessive. White Rabbit (bb)   (Bb)   (Bb) http://www.buckeyevalleyfarms.freeservers.com/photo.html

Problem: Justify Think-Pair-Share How can you tell if an organism is homozygous or heterozygous for one specific allele? FF or Ff??

J-TPS (Justify –Think Pair Share)

Would any of these crosses be useful? Why? X X

Testcross A testcross is a cross between an organism with an unknown genotype (FF or Ff) and an organism with the recessive phenotype (ff) ? ?

Testcross A testcross is a cross between an organism with an unknown genotype (FF or Ff) and an organism with the recessive phenotype (ff) F f

Problem – Justify Think-Pair-Share Omar, a healthy man, marries Jen, a healthy woman. Their son has a genetic disease. In order to have this desease their son has to be homozygous recessive. How is it possible that Omar and Jen do not have the disease? Why they do not show any symptom?

Autosomal genetic disorders (dominant) A person can be a heterozygous carrier for a disorder A carrier does not have the disorder but it can pass it on to offspring What are autosomes?

What is this diagram telling you?

Genes located on sex chromosomes (sex-linked genes) Why is it important to study sex-linked genes?

Check for understanding A person who is heterozygous for a disorder caused by recessive alleles is a carrier of the disorder. A carrier is a person who does not have the disorder but can pass it on to offspring can develop the disorder later in life but cannot pass it on has a dominant normal allele that has been inactivated passes the disorder to offspring on the Y chromosome only.

Check for understanding Genes that are located on sex chromosomes are called Alleles Recessive XY sex-linked

True or False If an allele is dominant on the other, the offspring will show the dominant trait. Only homozygous recessive offsprings will show the recessive trait