Unit 8 - GeneticsProbability - The likelihood of a particular event

occurring. - The chance of something happening - It can be expressed as a Fraction ( ¼ ),

Percent ( 25 % ), or Decimal ( .25 ) - Probability is a mathematical way of making

a prediction

How to Determine or Calculate Probability

# of Desired OutcomesProbability = # of All Possibilities

To determine the odds of rolling an even # on a die:

# of Even Numbers (3) # of All Numbers (6) = ½ or 50% or .50

Rules of Probability1) Probability suggests what is Likely to happen, NOT

what will Definitely happen. Ex Not all females have half male and half female

kids

2) Previous outcomes DO NOT affect future outcome Ex A coin will not come up heads just because it was

tails the time before

3) In order for Probability to be accurate, the sample size must be large.

Ex This class is not 50% male and 50% female, but the school population is

Calculating Probability for Multiple Events• Multiply the probability of each event by each other Ex The odds of flipping 3 coins & they all land

tails up. ½ x ½ x ½ = 1/8 .50 x .50 x .50 = .125 50% x 50% x 50% =12.5% Ex The odds of rolling a 6 three times in a row 1/6 x 1/6 x 1/6 = 1/216 .166 x .166 x .166 = .0045 or 0.45%

Probabilities Role in Genetics• Each parent has two sets of DNA• Only one set can be passed to the offspring.• What are the odds certain traits being passed

on based on the combinations.

Ex MOM DAD set “A” set “B” set “A” set “B” 1-23 1-23 1-23 1-23 Mom A & Dad A or Mom A & Dad B or Mom B & Dad A or Mom B & Dad B

Mother’s DNA Strand # 11 Gene

2 Gene

3 Gene

4 Gene

Father’s DNA Strand # 2PurebredHomozygousDominant

R R

PurebredHomozygousRecessivec c

PurebredHomozygousRecessivep p

HybridHeterozygoust T

PH-Roll

PH-NO

PH-5

PH- Medium

TongueRolling

TRAITS

Cleft

Polydactyl

Height

PurebredHomozygousRecessive

r r

PurebredHomozygousRecessive

c c

HybridHeterozygousP p

PurebredHomozygousDominant

T T

PH-NO

PH-NO

PH-6

PH- Tall

• Each parent possesses 2 strands of 23 different types of DNA

• 1 strand came from their Mom & 1 strand came from their Dad

• Each parent can only give one strand to their child• Each strand has hundred/thousands of segments

called Genes• Each gene is the information needed to develop a

Trait or Characterisitic• Some traits have many different types or forms that

can show up called Alleles Ex Trait: Eye Color Alleles: Gray Brown Blue Green

Unit 8 – Genetics• The basic rules of Heredity were first discovered by

Gregor Mendel, who conducted his experiments on garden peas (pg 256)

• He was the first to determine that genes (factors) are the carriers of traits and that it takes two genes to cause a characteristic to develop

Guidelines Used By Mendel1)Concentrated on one trait at a time2)Used large numbers organisms (trails)3)Used rules of probability to check his work

• The original Parents (P1) were Purebred Tall crossed with Purebred Short

• The 1st generation offspring (F1) were all Tall

• The 2nd generation offspring (F2) had some tall and some short plants

Law of Dominance**When two different alleles are crossed and one

masks over the otherDominant - The allele that is expressed in a hybrid - Symbolized by a Capitol LetterRecessive - The allele that is masked over in a hybrid - Symbolized by a lower case letterPurebred Dominant x Purebred Recessive = Hybrid RR x rr = Rr

• Parents Phenotype Tall & Short• Parents Genotype TT & tt• Cross parents (find all

the possible offspring genotypes & phenotypes by using a Punnett Square)

• 1st generation offspring phenotype Tall

• Genotype Tt

Indicate whether it is heterozygous or homozygous:

AA ______ dd _______Bb ______ EE _______Cc ______ Ff _______For each genotype below determine the

phenotype:(purple is dominant to white)PP ______Pp ______pp ______

B = Blue b = gold Genotype

PhenotypeHomozygous dominant Purebred recessiveHeterozgousHybridHomozygous recessive

1. A tall plant (TT) is crossed with a short plant (tt). Show the cross. What % will be tall?

2. A Tt plant is crossed with a Tt plant. What is the phenotypic and genotypic ratio?

3. A heterozygous round seeded plant is crossed with a homozygous round seeded plant. Round is dominant to wrinkled.

Show the cross. (Use letter R)

Unit 8 - Genetics• Each individual has two alleles/genes for each trait,

but only has the ability to pass on one of them to its offspring

Law of Segregation - The random passing of only one of an organism’s

two alleles to its offspring** The alleles/genes segregate or separate because of

Synapsis in Anaphase I of Meiosis I**The new offspring must also have 2 alleles for each

trait and it will receive only one from each parent. This results in 4 diff. possible combinations instead of 2

Pedigree Charts**A chart that is used in human genetics to analyze

Mendelian inheritance of certain traits, especially diseases.

Pedigree Chart Rules:Males: Are represented by a square shapeFemales: Are represented by a circle shapeHusband & Wife: Are represented by a line between a

square and a circleChildren: Are represented by lines

coming down from the line between husband & wife

Which color is dominant?

REDRED PINKPINK WHITEWHITE

Law of Incomplete Dominance Traits

Definition When neither of the two genes are dominant or recessive, there is a blending of the two traits where they meet in the middle

Example: When red colored petunias are crossed with white petunias some pink petunias show up in the offspring.

** We use the same capital letter for both since neither is dominant or recessive to each other. A prime ‘ or apostrophe is used to differentiate the letters.

Genotype Phenotype RR = red

R’R’ = white R’R or RR’ = pink

Parents: Red x White RR x R’R’

R’ R’

R

R

RR’ RR’

RR’ RR’

Results:100% Pink Phenotype100% RR’ Genotype

** Now do a cross between 2 pink flowers

Human Blood Types & Co-Dominance

• The human blood gene has three different alleles; 2 dominant & 1 recessive. More alleles mean more combinations, which results in more phenotypes.

• The three alleles are; IA , IB , and i• They result in four blood types: A, B, AB, & O

Law of Co-Dominance: Where two different alleles are paired and

BOTH are dominant. Both phenotypes show up independently without blending

• Both the IA and IB alleles are dominant over the i allele.

• Neither the IA nor the IB alleles are dominant over each other.

The blood gene cause Antigens (Protein Tags) to form on the red blood cells (RBC). The type of antigen determines the type of blood (phenotype).

• Allele IA produces A antigens, IB produces B antigens, and i does not produce any antigens.

• Chemicals called antibodies are also found in blood in the liquid plasma part. Antibodies react with antigens by clotting all RBC’s that have the improper antigen together.

• In blood transfusions we must consider the receivers antibodies & the donors antigens (do they conflict?)

According to the chart:Type A blood can receive blood from . . .Type B blood can receive blood from . . .Type AB blood can receive blood from . . .Type O blood can receive blood from . . .

Universal Donor = Type OUniversal Receiver = Type AB

IT TAKES ALL TYPES• The myth that, “my blood type is common, so there

are plenty of donors,” is just that, a myth. The more people there are in your blood group, the more that will need your donation. The reverse is also false. “My blood type is so rare, no one will need a donation.” The truth of the matter is, your community blood bank needs all types. From the most common O+’s to the rarest AB-’s. So help save a life today, give the gift of life, GIVE BLOOD!

O + . . . 37% O- . . . 7% A + . . . 33% A- . . . 6%

B + . . . 11% B- . . . 2% AB+ . . . 3.4% AB- . . . .6%

Blood Typing Problems1. Mom is heterozygous type A blood. Dad is

heterozygous type B blood. What % of their kids would be type A? Type B? Type AB? Type O?

2. Mom is genotype AB. Dad is genotype Ai. What % of their kids would be type A? Type B? Type AB? Type O?

3. Mom is heterozygous type B blood. She had a baby with type A blood. She thinks the father is Mr. Y. He is type AB. Could Mr. Y be the father?

4. A mom who is genotype Ai had a baby who is type A blood. What are the potential genotypes of the father?

Sex-Linked Traits

Are you Colorblind?

Sex-Linked TraitsDefinition A gene/trait that is found on the sex

chromosomes (X or Y)Example Hemophilia and Red-Green Colorblindness

are recessive traits found on the “X” chromosome

Male’sGenotype

Male’s Phenotype

Female’s Genotype

Female’s Phenotype

XY Normal XX NormalXCY Colorblind XCX Carrier (but

is normal

XcXc Colorblind

Sample Dad is colorblind and Mom is totally normal. What is the probability of having a colorblind child?

XC Y

X

X

XCX XY

XCX XY

Sample Mom is colorblind and Dad is totally normalA) What is the probability of having a colorblind child?B) What is the probability of their son being colorblind?C) What is the probability of their daughter being colorblind?

• In the recessive sex-linked traits females can be “carriers.” They do not have the trait, but they carry it on their X chromosome and can pass it on to their offspring.

• This is possible because females have two “X” chromosomes. The normal X chromosome is dominant to the defective X C or H chromosome and masks the defective trait.

• Males are more likely to get sex-linked traits because they either have the trait or they don’t. Males do not have another X chromosome to mask over the defective X C or H. Their other chromosome is the Y chromosome.

1) Mom is carrier for colorblindness and Dad is colorblind. What would be the phenotypic ratio of the offspring?

XC X

XC

Y

XCXC XCX

XCY XY

2 Colorblind : 2 Normal

2) Mom is a carrier for Hemophilia and Dad is normal. What are the chances of them having a child who is a Hemophiliac?

A male who is a Hemophiliac? A female who is a Hemophiiac?

Xh X

X

Y

XhX XX

XhY XY

25% Hemophilia

50% Male Hemophilia

0% Female Hemophilia