1. Genetics and Heredity

2. 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. 

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

4. Hook
Try to roll your tong. Can you?

5. 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?

6. 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.

7. Think
What is the relationship between genes and traits?

8. 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

9. J-TPS (Justify –Think Pair Share)

10. 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

11. What do the words dominant and recessive mean?

12. 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)

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

14. (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”

16. 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

17. Interpreting diagrams: Phenotype vs Genotype

18. 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)

19. Interpreting diagrams (SEP4): Phenotype vs Genotype

20. Interpreting diagrams: Phenotype vs Genotype

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

22. 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

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

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

25. 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

26. 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.

27. 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

28. 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?

29. Genetics song

30. 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?

31. 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?

32. Look at this Punnet Square and interpret it

33. Look at this Punnet Square and interpret it
Parent
Offspring
Parent

34. How to Complete a Punnett Square

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

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

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

38. 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%

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

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

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

42. 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%

43. 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?

44. 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)

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

46. J-TPS (Justify –Think Pair Share)

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

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

49. 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

50. 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?

51. 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?

52. What is this diagram telling you?

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

54. 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.

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

56. 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