1. Notes: The Genetics Unit
Biology I S409
Notes: The Genetics Unit
Name: Hour: Date:
Chapter 10.2: Mendelian Genetics (Pgs )
Chapter 11: Complex Inheritance and Human Heredity (Pgs )

2. How Genetics Began
T: 1, 2a
Heredity- the passing of traits from parent to offspring (the next generation)
Genetics – is the science of heredity
The Father of Genetics: Gregor Mendel
An Austrian monk & plant breeder in 1866)
Studied pea plants (a “true-breeding” simple, predictable plant; consistently produce offspring with only one form of a trait = complete dominance)
Kept precise records of 7 traits
Seed shape and color
Flower color and position
Pod color and shape
Plant height
the_history_of_gene_testin.htm

3. The Inheritance of Traits
2 different plants crossed. (P1) “cross pollinate”
Tall plant X short plant x
Results (offspring): F1 generation
Found all were tall (Same for all 7 traits)
One trait “masks the other”
F1 was allowed to “self pollinate” to produce F2
Results: Majority tall and some short
Found ¾ tall : ¼ short
3:1 ratio for all 7 traits
Must be a pair of factors (genes)
one gene from each parent

4. Genes & Dominance Genes are represented by letters of the alphabet
T: 2 f, g, h
Genes & Dominance
Genes are represented by letters of the alphabet
Good letters  = Aa, Bb, Rr
Bad Letters  = Cc, Oo, Ww (look too similar! )
Genes represented in pairs (1 individual has 2 letters)
One from mom, one from dad
Principle of Dominance
One gene masks the other from being expressed
A gene that “masks” is Dominant = R
A gene that gets “masked” is Recessive = r
Two identical genes are homozygous (purebred)
RR = homozygous dominant (shows dominant trait)
rr = homozygous recessive (shows recessive trait)
One of each gene is heterozygous (hybrid)
Rr = heterozygous (shows dominant trait)

5. Vocabulary Summary
T: 2 b-i
Allele – different forms of the same gene; tall/short, brown/blue (represented by letters)
Chromosome- DNA containing structure that carries genetic material from one generation to another
Gene- functional unit that controls inherited trait expression that is passed from one generation to another; section of DNA found on a chromosome; i.e. the gene for eye color
Genotype – an organism’s allele pairs (letters)
Phenotype – observable characteristic; what organism looks like (words)
Homozygous – an organism with two of the same alleles for a particular trait (RR or rr)
Heterozygous – an organism with 2 different alleles (Rr) ; called hybrids
Dominant- allele that will mask a recessive gene (R)
Recessive- allele that is masked (r)

6. Probability & Genetics
Probability = likelihood an event occurs
Example: coin flip
Either heads or tails
There is a 1 out of 2 chance it is heads
½ or 50% probability
Each flip is independent of other
What if you flip a coin 3 times?
The probability of all heads ½ X ½ X ½ = 1/8
You can use this to predict genetic cross outcomes

7. Punnett Squares (Dr. Reginald Punnett)
Used to predict & compare results of a cross
Types of gametes (sex cells) produced are shown along the top and left side of the square
Possible combinations of the offspring appear in the boxes (zygotes; a.k.a. fertilized egg)
Consider one of Mendel’s Experiments: Tall plants are considered dominant to short plants regarding pea plant height. If two pea plants heterozygous for height are crossed, the following genotypes and phenotypes may be determined regarding the possible offspring.

8. One Trait is being considered: plant height (T, t)
Key: TT = tall Tt = tall tt = short P1: Tt x Tt Punnett Square: Genotype: (letters) 1 TT: 2 Tt : 1 tt Phenotype: (words) 3 Tall Pea Plants: 1 Short Pea Plant T t TT Tt tt

9. Probability & Segregation
In the previous example the results of the cross were…
Genotype
¼ TT ; 2/4 or ½ Tt; ¼ tt
Phenotype
¾ tall; ¼ short
75% tall; 25% short
Remember these are predictions;
They hold true for large #s
Not necessarily for individual/small events

10. Complete Dominance Cross (4 Boxes 1 trait)
T: 3a
When looking at the shape of peas on pea plants, round peas are dominant to wrinkled peas. Using a Punnett Square, determine the genotype and phenotype of the possible offspring when you cross a plant that is heterozygous for pea shape WITH a homozygous recessive plant for the same trait.
Trait: shape (R, r) Key: R R = round R r = round r r = wrinkled P1 R r X r r Punnett Square: Genotype: (letters) 2 Rr : 2 rr Phenotype: (words) 2 Round Peas: 2 Wrinkled Peas R r Rr rr

11. Trait: Flower color (R, r)
Incomplete Dominance Cross
T: 3b
In four o’clock plants, the alleles for red and white flowers show incomplete dominance. When alleles are mixed, pink flowers result. If a red flower is crossed with a white flower, the following genotypes and phenotypes may be determined regarding the possible offspring.
Trait: Flower color (R, r)
Key: RR = red Rr = pink rr = white P1: RR x rr Punnett Square: Genotype: (letters) 4 Rr Phenotype: (words) 4 Pink (All Pink) R r Rr

12. Co-Dominance Cross Trait: fur color (R, r)
T: 3b
In cows, the alleles for fur color show co-dominance. Fur color may be red or white in cows, however, when alleles are mixed fur will have red and white spots. If a red cow is crossed with a white cow, the following genotypes and phenotypes may be determined regarding the possible offspring.
Trait: fur color (R, r)
Key: RR = red fur Rr = red & white spots rr = white fur P1: RR x rr Punnett Square: Genotype: (letters) 4 Rr Phenotype: (words) 4 (All) red & white spots R r Rr

13. Co-Dominance Cross Trait: attitude (L, l)
T: 3b
In cats, the alleles for attitude show co-dominance. Cats can have attitudes that are snotty or lazy, however, when alleles are mixed a cat with a snotty & lazy attitude results. If two heterozygous cats are crossed, what are the genotypes and phenotypes of the possible offspring?
Trait: attitude (L, l)
Key: LL = snotty cat Ll = snotty & lazy cat ll = lazy cat P1: Ll x Ll Punnett Square: Genotype: (letters) 1 LL : 2 Ll : 1 ll Phenotype: (words) 1 snotty : 2 snotty & lazy: 1 lazy L l LL Ll ll

14. Trait: eye color (E, eR, er)
Multiple Alleles Cross
T: 3d
Set of 3 or more alleles determine 1 trait (2 ways to do this…)
In fruit flies, there are multiple alleles for eye color. 3 alleles produce different eye colors. Red eyes are dominant to purple and white eyes, however, purple eyes are dominant to white eyes. If you cross a heterozygous red eye fly that carries the white eye allele with a heterozygous purple eye fly will the offspring be?
Trait: eye color (E, eR, er)
P1: Eer x eRer
Key: EE = red eyes EeR = red eyes Eer = red eyes eReR = purple eyes eRer = purple eyes erer = white eyes Genotype: (letters) 1 EeR: 1 Eer: 1 eRer : 1 erer Phenotype: (words) 2 red eye : 1 purple eye : 1 white eye
Punnett Square: E er eR
EeR
eR er
Eer
erer

15. Trait: ear length (E, eL, el)
Multiple Alleles Cross
T: 3d
In bunnies, there are multiple alleles for ear length. Different combinations of 3 alleles produce ear lengths. Long ears are dominant to floppy ears and short ears, however, floppy ears are dominant to short ears. If you cross a heterozygous long ear bunny that carries the floppy ears allele with a short ear bunny what offspring will result?
Trait: ear length (E, eL, el)
P1: EeL x elel
Key: EE = Long ears EeL = Long ears Eel = Long ears eLeL = Floppy ears eLel = Floppy ears elel = short ears Genotype: (letters) 2 Eel: 2 eLel Phenotype: (words) 2 long ears : 2 floppy ears
Punnett Square: E eL el
Eel
eL el
eLel

16. Multiple Alleles Cross
T: 3d
More than two genes control a particular trait.
The most common example of this is blood type.
There are 3 alleles and 4 blood types (phenotypes).
The alleles are:
A B O
A and B are both dominant over O, but A and B are not dominant over each other.
GENOTYPE PHENOTYPE
IAIA AA Type A Blood
IAi AO Type A Blood
IAIB AB Type AB Blood
IBIB BB Type B Blood
Ibi BO Type B Blood
ii OO Type O Blood

17. Trait: blood type (A, B, O)
Multiple Alleles Cross
T: 3d
Mr. Wiggles is trying to prove that he is not the father of 500 bunnies. He has a blood type of O. 50% of the bunnies have blood type A and 50% of the bunnies have blood type AB. Can Mr. Wiggles be the father of these bunnies?
Trait: blood type (A, B, O)
Key: AA = A Blood Type AO = A Blood Type BB = B Blood type BO = B Blood Type AB = AB Blood type OO = O Blood type Genotype: (letters) 2 AA: 2 AB Phenotype: (words) 2 Blood type A: 2 Blood type AB
P1: x
Punnett Square: B A AA AB
NO, HE COULD NOT BE THE FATHER!

18. Trait: blood type (IA, IB, i)
Multiple Alleles Cross – another way
T: 3d
Mr. Wiggles is trying to prove that he is not the father of 500 bunnies. He has a blood type of O. 50% of the bunnies have blood type A and 50% of the bunnies have blood type AB. Can Mr. Wiggles be the father of these bunnies?
Trait: blood type (IA, IB, i)
Key: IAIA= A Blood Type IAi = A Blood Type IBIB = B Blood type IBi = B Blood Type IAIB= AB Blood type ii = O Blood type Genotype: (letters) 2 IAIA: 2 IAIB Phenotype: (words) 2 Blood type A: 2 Blood type AB
P1: x
Punnett Square: IB IA
IAIA
IAIB

19. Sex-Linked Traits Sex chromosomes (gametes) are called: X & Y
Each cell in your body, except your gametes, contains 46 chromosomes (23 from mom, 23 from dad)
22 pairs of chromosomes are called autosomes
1 pair of chromosomes is called your sex chromosomes (determines gender)
Sex chromosomes (gametes) are called: X & Y
Males = XY Females = XX
Thomas Hunt Morgan (Early 1900’s) discovered sex-linked genes in Drosophila. (Fruit flies)
Most Sex-linked genes are on the X, not the Y.
Why? The X chromosome is physically larger!
Most sex-linked genes are recessive
One gene, from mom, gives males mutant trait.
Two genes, from each parent, are needed to give a female offspring the mutant trait (that’s why there are fewer females with sex-linked traits)

20. Examples of Sex-linked Traits
T: 3e
Again, females are less likely to express a recessive X-linked trait because the other X chromosome may mask the effect of the trait!
Red-green color blindness (~8% of males in US)
Hemophilia (inability to clot blood)

21. XR = female sex chromosome w/ normal dominant gene for red eyes
T: 3e
Sex-Linked Cross
In fruit flies, eye color is sex-linked. Normal eye color is red, and recessive eye color is white. If you cross a white-eyed male with a normal red-eyed female what offspring result?
XR = female sex chromosome w/ normal dominant gene for red eyes
Xr = female sex chromosome w/ mutant recessive gene for white eyes
Y = male sex chromosome

22. Trait: eye color (XR, Xr, Y)
Key: XRXR = Normal Female, Red Eyes XRXr = Carrier Female, Red Eyes XrXr = Mutant Female, White Eyes XRY = Normal Male, Red Eyes XrY = Mutant Male, White Eyes P1: XrY x XRXR Punnett Square: Genotype: (letters) 2 XRXr: 2 XRY Phenotype: (words) 2 Carrier Females, red eyes : 2 Normal Males, red eyes XR Xr
XR Xr Y
XR Y

23. T: 3e
Sex-Linked Cross
Hemophilia is a disease that results from the bloods inability to clot. This disease has been found to be a sex-linked trait in humans. The hemophilia allele is recessive to the normal allele. If you cross a female carrier with a normal male what offspring result?

24. Trait: blood’s ability to clot (XB, Xb, Y)
T: 3e
Trait: blood’s ability to clot (XB, Xb, Y)
Key: XBXB = Normal Female; Can Clot XBXb = Carrier Female; Can Clot XbXb = Mutant Female, hemophiliac XBY = Normal Male; Can Clot XbY = Mutant Male, hemophiliac P1: XBY x XBXb Punnette Square: Genotype: (letters) 1XBXB: 1XBXb : 1XBY : 1XbY Phenotype: (words) 1 Normal Female Can Clot : 1 Carrier Female Can Clot:1 Normal Male Can Clot: 1 Mutant Male, hemophiliac . XB Xb
XB XB
XB Xb Y
XB Y
Xb Y

25. Dihybrid Cross Two Traits (16 Boxes)
T: 3c
Dihybrid Cross Two Traits (16 Boxes)
Principle of Independent Assortment
States that genes for different traits segregate (separate) independently during gamete formation
This holds true for more than one trait 
Plant height and flower color are being studied. Tall plants are dominant to short plants and red flowers are dominant to white. A white plant heterozygous for height is crossed with a short plant heterozygous for flower color. Using this cross, the following genotypes and phenotypes may be determined regarding the possible offspring.

26. Traits: height (H, h) color (R, r)
T: 3c
Traits: height (H, h) color (R, r)
Key: HH = Tall Hh = Tall hh = Short RR = Red Rr = Red rr = White P1: Hhrr x hhRr

27. Traits: height (H, h) Cont. color (R, r)
P1: H h r r x h h R r Punnett Square: Genotype: (letters) 4 HhRr : 4 hhRr : 4 Hhrr : 4 hhrr Phenotype: (words) 4 Tall & Red : 4 short & red : 4Tall & white : 4 short & white Hr hr hR
HhRr
hhRr
Hhrr
hhrr

28. T: 3c
Dihybrid Cross
Number of spots and tail length are being studied in leopard. Even numbers of spots are dominant to odd numbers of spots and long tails are dominant to short tails. A leopard with a odd number of spots a short tail is crossed with a leopard who is heterozygous for both traits. Using this cross, the following genotypes and phenotypes may be determined regarding the possible offspring.

29. Traits: Number of spots (E, e) Tail length (L, l)
T: 3c
Traits: Number of spots (E, e) Tail length (L, l)
Key: EE = Even # Ee = Even # ee = Odd # LL = Long Tail Ll = Long Tail ll = Short Tail P1: eell x EeLl

30. Traits: Number of spots (E, e) Tail length (L, l)
T: 3c
Traits: Number of spots (E, e) Tail length (L, l)
P1: eell x EeLl Punnett Square: Genotype: (letters) 4 EeLl : 4 Eell : 4 eeLl : 4 eell Phenotype: (words) 4 Even #ed Spots & Long Tail : 4 Even #ed Spots & Short Tail : 4 Odd #ed Spots & Long Tail : 4 Odd #ed Spots & Short Tail el EL
EeLl El
Eell eL
eeLl
eell

31. 11.1: Basic Patterns of Human Inheritance
Recessive Genetic Disorders
Mendels work was ignored for about 30 years and “rediscovered” in the early 1900’s by Dr. Garrod & genetic studies now continue today…

32. 11.1: Basic Patterns of Human Inheritance
Dominant Genetic Disorders
Not all genetic disorders are caused by recessive inheritance. Some are caused by dominant alleles. That means those who do NOT have the disorder are homozygous recessive for the trait.

33. T: 3f
Pedigrees – Pg 299
Pedigrees can be used to track genetic information through generations of a family “family history”
Pedigrees have a few simple rules:
Men are shown as squares
Woman are shown as circles
Each generation is given a Roman Numeral (I, II, III, IV, V)
Each individual within a generation is given a number (1, 2, 3, 4, 5)
Shaded individuals have the trait being tracked in the pedigree

34. T:f
Pedigree Practice
Problem #1: The trait shown below is the ability to taste PTC (phenylthiocarbamide) paper. This trait is controlled by a dominant gene represented by T, and is transmitted by normal inheritance. Nontasters are, therefore, Homozygous for the recessive trait and are represented by tt. The shaded figures below are both homozygous recessives (tt) and are nontasters. All unshaded symbols have two possible genotypes: TT or Tt. Determine the genotypes of all the individuals in the pedigree below:
tt Tt
Tt Tt Tt Tt tt Tt/TT Tt

35. Pedigree Practice Problem #2
T: 3f
Pedigree Practice
Problem #2
Write the correct Roman numeral for each generation.
Write the correct number for each individual.
Assume the shaded symbols represent the recessive homozygous genotype rr. Which, individuals show the homozygous recessive trait?
In the spaces below each symbol, write as much of the genotype of each individual as can be determined from the information provided. I
1 Rr rr II
1 Rr 2 Rr 3 rr 4 Rr 5 Rr 6 rr
III
1 rr 2 Rr
3 Rr

36. T: 3f
Pedigree Practice
Problem #3 Colorblindness in humans is caused by a sex-linked recessive gene on the X-chromosome. In this pedigree chart, both of the first generation parents are colorblind. Assuming that none of the in-laws are colorblind or are carriers, what is the maximum number of descendants that could be colorblind? 3 4 5 12

37. 11.3: Chromosomes & Human Heredity
Karyotypes are a way of studying chromosomes
Used to identify genetic disorders.
You can not see changes in genes, but you can see changes in chromosome number.
There are 22 autosomes matched together with 1 pair of nonmatching sex chromosomes. (find X & Y)
Is this karyotype  from a male or female?

38. Nondisjunction
T: 4, 5
Nondisjunction: when sister chromatids fail to separate properly during cell division
Down syndrome: one of the earliest known human chromosomal disorders. It is usually the result of an extra chromosome 21; often called trisomy 21