1. Genetics
Genetic Dominance

2. Gregor Mendel
Austrian Monk, studied pea plant traits in the mid-1800’s
Considered ‘Father of Genetics’
Things Mendel discovered (his laws of genetics):
Law of dominance—some alleles are ‘stronger’ than others
Law of segregation—you get two alleles (one from each parent). When your body makes gametes, those two alleles are separated (each gamete only gets one of your alleles for each of your traits)
Law of independent assortment—your alleles divide independently of each other (genes for different traits are not ‘stuck’ to each other)

3. A trait is a characteristic of an organism ex: hair color
Your genes (codes on your DNA) create your traits
You get two genes for each trait on your chromosomes (one from mom and one from dad)
gene from mom for breast cancer
gene from dad for breast cancer
gene from mom for freckles
gene from dad for freckles

4. Alleles-different forms of a gene/trait
Alleles-different forms of a gene/trait. trait: eye color alleles: brown, green, gray, blue, hazel, etc trait: freckles alleles: having freckles, not having freckles trait: hairline alleles: straight, peaked

5. Some alleles are dominant and some alleles are recessive
Some alleles are dominant and some alleles are recessive. For most genes, if a person inherits a dominant allele and a recessive allele for a trait, only the dominant allele will be exhibited.
Example: the allele for wet earwax is dominant to the allele for dry earwax. If your mom gives you the allele for wet earwax on her chromosome and your dad gives you the allele for dry earwax on his chromosome, you will have wet earwax.

6. The dominant allele for a gene is represented by a CAPITAL letter.
We represent different alleles of the same trait with the same letters.
The dominant allele for a gene is represented by a CAPITAL letter.
Ex: G
The recessive allele for the gene is represented by a lower case letter.
Ex: g
**Try not to use letters that look alike…Oo, Ww, Yy, Uu, Pp, Ss, Jj, Kk, Ll, Zz, Xx, Cc, Vv, !
(Cross your hands)

7. Left or Right - Thumbed
Left Dominance Right Dominance
The allele for left dominance is dominant and the allele for right dominance is recessive.
**Note-we have recently learned that there is more to this trait than simple genetics, but for now we will use this as an example

8. If you got an allele for right dominance from your mom and an allele for left dominance from your dad, how will the trait be expressed?
You will be left thumb dominant because your dominant allele will ‘turn off’ your recessive allele

9. Genotype-The alleles you get for a trait
Homozygous Dominant-two of the same dominant alleles AA
Heterozygous-one dominant allele and one recessive allele Aa
Homozygous Recessive-two of the same recessive alleles aa

10. Phenotype-The way your alleles are actually expressed (often, what you look like)
If you have an allele for tongue rolling and an allele for not being able to roll your tongue, your genotype is heterozygous and your phenotype is that you can roll your tongue.
**Note-we have recently learned that there is more to this trait than simple genetics, but for now we will use this as an example

11. Even though we can’t ‘see’ that recessive allele in your phenotype, it is still part of your genotype. If you are heterozygous for a trait, when your body makes gametes, half will get the dominant allele and half will get the recessive allele. This is called allele segregation.

12. Probability and Punnett squares

13. Probability is the likelihood that an event will occur
Probability is the likelihood that an event will occur. We use information about parents’ genetics to calculate probabilities for their children’s genetics.
We use a Punnett Square to calculate probability for genetic crosses.

14. Step 1: assign letters to the alleles of the trait you are examining
Step 1: assign letters to the alleles of the trait you are examining. Remember to use letters for which the lower case looks different from upper case. Give the dominant trait the capital letter and the recessive trait the lower case letter.
Example:
Wet earwax is dominant to dry earwax.
E=wet earwax
e= dry earwax

15. Dad=Ee (the problem tells us this)
Step 2: Use the information available to determine the genotype of each parent and use the letters to show the genotypes of each parent.
Example:
Mom has dry earwax and Dad is heterozygous for earwax. What is the probability that their children will have dry earwax?
Mom=ee (she can’t have a E because she would have wet earwax if she did)
Dad=Ee (the problem tells us this)
Think about it: What is Dad’s PHENOTYPE? (it is wet earwax)

16. Remember that your two alleles get separated when you make gametes (sperm/egg). So, your child gets one of your two alleles and one of your spouse’s two alleles. The Punnett square shows the possible combinations of the alleles from one sperm and one egg.
Step 3: Label the top of the Punnett square with one parent and show the alleles for that parent. Do the same for the other parent on the other side. Put the alleles into the boxes as shown by the arrows.

17. Example:
e e
Mom E e E e e E e e
Dad

18. What is the probability for the genotypes of their children?
Homozygous dominant (EE)=0/4
Heterozygous (Ee)=2/4=1/2
Homozygous recessive(ee)=2/4=1/2
Mom
e e E e E e e E e e
Dad

19. What is the probability for the phenotypes of their children?
Wet earwax=2/4=1/2
Dry earwax=2/4=1/2
e e
Mom E e E e e E e e
Dad

20. Mom and Dad have three children who all have dry earwax
Mom and Dad have three children who all have dry earwax. They are expecting their fourth child. What is the probability that this child will have wet earwax?
This child has a 50% probability of wet earwax

21. Practice Problem #1
In pea plants, yellow peas are dominant over green peas. Use a Punnett square to predict the phenotypic and genotypic outcome (offspring) of a cross between a plant heterozygous/hybrid for yellow peas and a plant homozygous/purebred for green peas.

22. In pea plants, yellow peas are dominant over green peas.
Practice Problem #2
In pea plants, yellow peas are dominant over green peas.  
Use a Punnett square to predict the phenotypic and genotypic outcome (offspring) of a cross between two plants heterozygous for yellow peas.

23. Practice Problem #3
In pea plants, round peas are dominant over wrinkled peas. Use a Punnett square to predict the phenotypic and genotypic outcome (offspring) of a cross between a plant homozygous for round peas and a plant homozygous for wrinkled peas.

24. Practice Problem #4
In pea plants, round peas are dominant over wrinkled peas.  Use a Punnett square to predict the phenotypic and genotypic outcome (offspring) of a cross between two plants heterozygous for round peas.

25. Complex Inheritance

26. Sex-linked traits are located on the sex chromosomes, so boys only get one allele (instead of two) for any genes located on these chromosomes.
Incomplete dominance-the dominant allele is not completely dominant to the recessive, so a heterozygous individual has a blended phenotype.
Codominance-there is more than one dominant allele and they are equally dominant, so a heterozygous individual shows BOTH in the phenotype.
Polygenic-have many places in the DNA that code for polygenic traits, so the phenotype is a blending of all of the genes’ results.

27. Sex-Linked Traits
The 23rd pair of chromosomes determine gender. The traits located on these chromosomes are called sex-linked traits.
Girls (XX) have two homologous sex chromosomes (same types of genes, one chromosome from each parent)
Boys (XY) have one X chromosome from mom and one Y chromosome from dad
These chromosomes do NOT have the same types of traits, so boys only get ONE allele for these traits.

28. Sex-Linked Traits Girls are XX Boys are XY
Sex chromosomes are the 23rd pair. This is the karyotype of a boy.

29. Practice Problem #1
Hemophilia is a sex-linked recessive blood disorder. A heterozygous (carrier) female is crossed with a male who does not have the disorder. What percent of their males and females will have hemophilia?

30. Practice Problem #2
Color-blindness in humans is a sex-linked recessive trait. A woman with normal vision (she had a color-blind father) marries a color-blind man. What is the probability of the following?
_____% Color-blind Offspring
_____% Normal-vision boys
_____% Normal-vision girls

31. Practice Problem #3
Can a normal son have a color-blind father? Can a normal daughter have a color-blind father? Can a color-blind brother and sister have a brother who is normal-visioned?

32. Incomplete dominance
Incomplete dominance: neither of the alleles is dominant, so heterozygous phenotype is a mix between the two alleles
Example: In snapdragons, flower color is a case of incomplete dominance.
RR=red
Rr=pink
rr=white

33. Incomplete Dominance Cross a red snapdragon with a white snapdragon.
Practice #1
Genotypic ratios:
Phenotypic ratios:
Cross a red snapdragon with a white snapdragon.

34. Incomplete Dominance Cross a pink snapdragon with a pink snapdragon.
Practice #2
Genotypic ratios:
Phenotypic ratios:
Cross a pink snapdragon with a pink snapdragon.

35. Codominance
Codominance: two dominant alleles are equally dominant, so the heterozygote individual’s phenotype shows BOTH
Since both alleles are dominant, use two different letters and make them both capital (A and B). Another option is to use the prine mark (A and A’)

36. Codominance Example: In horses, coat color shows codominance.
RR = red coat
WW = white coat
RW = roan coat (some hairs are red and some are white)

37. Codominance Cross two roan horses Genotypic ratios: Phenotypic ratios:
Practice #1
Genotypic ratios:
Phenotypic ratios:
Cross two roan horses

38. Codominance Cross a red horse with a roan horse. Genotypic ratios:
Practice Problem #2
Genotypic ratios:
Phenotypic ratios:
Cross a red horse with a roan horse.

39. Codominance—blood types
Human blood type is codominant. The alleles for blood type are as follows:
A=dominant
B=dominant
O=recessive
A and B are codominant, so if you get an A and a B allele, your blood type is AB. The only way to have O blood type is if you get two recessive O alleles.

40. Blood Types AA A blood Ao BB B blood Bo AB AB blood oo O blood
Genotype
Phenotype AA
A blood Ao BB
B blood Bo AB
AB blood oo
O blood

41. Blood Types
A woman heterozygous for Type A and a man with type O marry. What are the possible blood types for their children?
Genotypes:
Phenotypes:

42. Blood Type (phenotype)
Baby Mix-up
Ms. Johnston, Ms. Johnson, and Ms. Johnstone all entered the same hospital, gave birth to baby girls on the same day, and all three babies were taken to the nursery to receive care. Someone later claimed that the hospital mixed up the babies. As a hospital administrator, it is your job to make sure that each pair of parents has the correct baby, so you order blood typing to be done on all the parents and all the babies.
Person
Blood Type (phenotype)
Mrs. Johnston A+
Mr. Johnston B+
Mrs. Johnson B-
Mr. Johnson O+
Mrs. Johnstone
Mr. Johnstone A-
Baby A
Baby B
AB-
Baby C

43. Which baby belongs to which couple?
Person
Blood Type (phenotype)
Mrs. Johnston A+
Mr. Johnston B+
Mrs. Johnson B-
Mr. Johnson O+
Mrs. Johnstone
Mr. Johnstone A-
Baby A
Baby B
AB-
Baby C

44. Polygenic Traits Polygenic traits: traits determined by multiple genes
The phenotype is a blending of the multiple genotypes
These traits can be influenced by the environment
Examples: height (400/700), hair color, eye color (2/16), skin color in humans

45. Dihybrid Crosses

46. Dihybrid Cross
Instead of the probability of ONE trait, what is the probability of a combination of TWO traits—for example:
What is the chance for offspring with red hair and brown eyes?
What is the chance for offspring with curly and white fur?
What is the chance for offspring with smooth and green peas?

47. How do we set up the Punnett square?
In dihybrid crosses, there is one more step to include…
To find the possible gametes of the parents, you must “FOIL” (just like in math when you factor).
FOIL stands for
First
Outer
Inner
Last

48. Dihybrid Example: S=brown fur s=white fur B=short tail b=long tail
Mom and dad both have brown fur and short tails. What are the chances of offspring with white fur and a long tail?

49. Pedigrees