1. GENETICS

2. Genetics Video Clips
Learn about Heredity
What are genes?
Where do genes come from?

3. Terms
Gene: a segment of DNA with coded information for a particular trait or characteristic.
Because animals are diploid (have two sets of chromosomes) there are 2 genes for each trait…one inherited from each parent.

4. Terms
Allele: Actual DNA “letters” found in the chromosome
One allele is inherited from each parent for each genetic trait

5. terms
Dominant allele: alleles which hide or mask the information carried by recessive alleles.
Dominant allele = capital letters
Dominant alleles takes over when there are 2 dominant alleles or a dominant and recessive allele are present.
Examples: RR or Rr

6. terms
Recessive allele: alleles that only show up as a trait in someone when NOT paired with a dominant allele
Recessive alleles = lower case letters
Recessive traits only show up in people when there are 2 copies present.
Example: rr

7. Genotype: the 2 alleles inherited for each genetic trait the actual genetic info (represented by letters). Like RR, hh, Rr, etc.
Homozygous: 2 copies of the same allele for a trait. Ex: RR or rr
Heterozygous: 2 different alleles for a trait
Ex: Rr

8. Terms con’t
Phenotype: physical appearance of the trait which can be seen.
Examples: if a person has brown hair or blond hair or if they have a disease or not

9. What is a phenotype?

10. Let’s Review
Homozygous or heterozygous?
Homozygous

11. Let’s Review
Homozygous or heterozygous?
heterozygous

12. Let’s Review
What is this flower’s genotype?
Ff (heterozygous)

13. Let’s Review
What is this flower’s phenotype?
purple

14. Let’s Review
Is this flower homozygous or heterozygous?
heterozygous

15. Let’s Review
What is this flower’s phenotype?.
white

16. Let’s Review
What is this flower’s genotype? ff

17. Homozygous versus Heterozygous Practice
Genotype versus Phenotype Practice

18. Cracking The Code Of Heredity

19. The study of heredity, how traits are passed from parent to offspring
Genetics
The study of heredity, how traits are passed from parent to offspring or x = or

20. Mendel & Heredity
Heredity was a mystery for a long time
It was thought that parents’ traits blended in the next generation…like red and white blend to make pink
But in reality traits are NOT always inherited this way

21. Gregor Mendel
Austrian monk
“The Father of Genetics”
The first person to start unraveling the mystery of heredity in the 1800s

22. Mendel’s experiments
Modern genetics began with Gregor Mendel’s experiments with pea plants
Mendel crossed pea plants that differed in certain characteristics and traced the traits from generation to generation

23. Mendel’s law of segregation
Parents have two alleles for every trait, but only give one allele to a gamete (sex cell)
In the offspring, one allele comes from each parent

24. GENETIC CROSSES (ONE TRAIT)

25. The inheritance of many human traits follows Mendel’s principles and the rules of probability

26. Punnett squares
Punnett square: a box like diagram used to predict all possible genotypes that result from a cross
Punnett Square Quick Tips:
Find out which alleles are dominant or recessive
Write each parent’s genotype
Fill in Mom’s genotype on the top of the punnett square and the Dad’s along the side of the punnett square
Complete boxes to see all the possible genetic cross outcomes or kids’ genotypes

27. LAYOUT OF PUNNETT SQUARES
Kids’
Genotypes
Punnett square basics clip:
Dad's genotypes
Mom's Genotypes

28. PUNNETT SQUARES:
Monohybrid crosses-- A cross between organisms that involves only ONE pair of traits
Example 1: Having freckles is dominant trait. What is the chance that a child will have freckles if DAD is homozygous for freckles and MOM does not have freckles?
4/4 f f
Gene Notation Symbols
F = freckles
f = no freckles Ff Ff F
Parent Genotypes:
MOM: ff
DAD: FF F Ff Ff

29. Monohybrid CROSSES cont…
Example 2: Widow’s peak is a dominant trait. What is the chance that a child will have a straight hairline if DAD is heterozygous for widow’s peak and MOM has a straight hairline?
2/4 p p
Gene Notation Symbols
P = widow’s peak
p = straight hairline Pp Pp P
Parent Genotypes:
MOM: pp
DAD: Pp p pp pp

30. Law of Independent Assortment
Allele pairs separate independently of each other during gamete formation (meiosis)
Which means….
Different traits appear to be inherited separately

31. Monohybrid Cross Practice 1—do together as a class
Monohybrid Cross Practice 2—do on your own

32. Genetics Drama #1 Monohybrid
How Could Our Baby Be Albino??
Monohybrid quiz tomorrow!!

33. INCOMPLETE DOMINANCE, CODOMINANCE AND SEX-LINKED TRAITS

34. VARIATIONS ON MENDEL’S PRINCIPLES
The inheritance of some traits is more complex than Mendel’s principles can explain

35. Incomplete dominance
Sometimes the 2 alleles for a trait BLEND together creating an intermediate phenotype = incomplete dominance
NEITHER ALLELE IS DOMINANT
Red RR
White rr R r
Pink Rr
1/2 R
1/2 r
1/2 R
1/2 R
Eggs
Sperm
Red RR
1/2 r
1/2 r
Pink Rr
Pink rR
White rr
F2 GENERATION
Figure 9.12A

36. Incomplete dominance cont…
Heterozygotes (Rr) show an intermediate phenotype
RR = red flowers
rr = white flowers
Rr = PINK flowers

37. Codominance
Codominance is when both traits are fully and separately expressed
Both alleles show up
Example: white and red flower crossed makes a flower that shows both red and white on its petals

38. Looking at blood types can show some examples of codominance…
Human A, B, AB, & O blood types are determined by 3 alleles in the human gene pool: A, B, or O
The alleles for A and B blood types are both dominant (codominant)
The O allele is recessive = o
This means that there are two dominant alleles and one recessive allele, but if the two dominant alleles are together, then they are both expressed (A + B = AB blood type)

39. Blood types Phenotype Genotype Type A Blood AA or Ao Type B Blood
BB or Bo
Type AB Blood AB
Type O Blood oo
See blood type punnett square examples at:

40. Type A = AA or Ao Type B = BB or Bo Type O = oo Codominance cont…
Example 1: List all the possible blood genotypes and phenotypes and their ratios for children conceived from a male heterozygous for type A blood (Ao) with a woman with homozygous type B blood (BB).
Type A = AA or Ao
Type B = BB or Bo
Type O = oo
Parents’ genotypes
MOM = BB
DAD = Ao

41. Codominance practice

42. Genetics Drama #2 Codominance
Were the Babies Switched??

43. SEX-LINKED TRAITS XX A human female = A human male =
Chromosomes determine sex (gender) in many species XX
A human female =
A human male =
A baby’s gender depends on whether Dad’s sperm delivers a X or Y chromosome
So, should Henry the 8th have executed all of his wives for not giving him sons? XY

44. Genes on sex chromosomes
Y chromosome = Sex-regulation gene
master gene for maleness & male hormones
X chromosome = other traits beyond sex determination
Duchenne muscular dystrophy affects one in 3,500 males born in the United States.
Affected individuals rarely live past their early 20s.
This disorder is due to the absence of an X-linked gene for a key muscle protein, called dystrophin.
The disease is characterized by a progressive weakening of the muscles and loss of coordination.

45. Sex-linked traits have genes on the X chromosome
Human X chromosome
Sex-linked traits have genes on the X chromosome
more than 60 diseases are traced to genes on X chromosome, including:
Hemophilia
Duchenne muscular dystrophy
color-blindness

46. Sex-linked traits
All genes that are carried on the X chromosome are considered to be sex-linked
In many organisms, the X chromosome carries many genes unrelated to gender
Fruit fly eye color is a sex-linked characteristic

47. Connection:
Sex-linked disorders affect mostly males
Most sex-linked human disorders are due to recessive alleles
Examples: hemophilia, red-green color blindness
A male receives a single X-linked allele from his mother, and will have the disorder, while a female has to receive the recessive X allele from both parents to be affected

48. Color Blindness Test A B C D

49. E F

50. Sex-linked traits cont…
Example 1: Color-blindness is a sex-linked trait. Jim is not colorblind and neither is his wife, Mary. However, because Mary’s dad WAS colorblind, she is heterozygous for red-green colorblindness. What are the chances that a daughter will be colorblind? What about a son? What are the chances that a daughter will be a carrier?
Gene Notation Symbols
XBXB = female non-carrier
XBXb = female carrier
XbXb = female colorblind
XBY = male normal
XbY = male colorblind
Parents’ genotypes
MOM = XBXb
DAD = XBY

51. Sex-linked traits, example 1 cont…
1st generation phenotypes:
½ females will be normal,
½ females will be carriers, ½ males will be normal,
½ males will be colorblind
The chance of having a colorblind child is ¼. XB Xb XB
XBXB
XBXb
XBY
XbY Y

52. I Don’t’ Want To Have Colorblind Daughters!!
Genetics Drama #3
I Don’t’ Want To Have Colorblind Daughters!!
Later…
Punnett Square practice on all types of crosses