PROBABILTY

P= number of ways that a given outcome can occur total number of possible outcomes

Gene InteractionsThere are three main types of gene interactions:

1) Multiple AllelesThere are many traits that are controlled by more than two alleles for example, eye colour in Drosophila is controlled by four possible alleles.The following phenotypes and dominance hierarchy is possible:

wild type (red) > apricot > honey > white

Multiple Alleles

Wild type- the most commonly seen trait Mutant- non-wild-type traits

When dealing with multiple alleles, it is no longer necessary to use upper & lower case letters both letters & upper case numbers are used.

phenotype genotypewild type E1

Apricot E2 honey E3

white E4

Predict the genotypes and phenotypes of the F1 generation from the mating of wild type (E1E4) with apricot (E2E3).

Predict the genotypes and phenotypes of the F1 generation from the mating of wild type (E1E4) with apricot (E2E3).

E1E2 E2E4

E1E3 E3E4

E1 E4

E2

E3

In the F1 generation ½ are wild type; ¼ apricot; ¼ honey

Do Now

phenotype genotype

wild type E1

Apricot E2

honey E3

white E4

With the above information, make two heterozygous crosses what phenotypes do you get?

2) Incomplete Dominance

In some heterozygotes, both alleles of a pair are expressed in the phenotype. These alleles are said to be equally dominant. This lack of dominance is known as incomplete dominance.eg. P1 Black White

F1 Grey

P2 Grey × Grey F2

wwWW Ww

Ex. Snapdragons

An interaction between the alleles in the heterozygote shows an intermediate

phenotype.

3) Codominance

A form of incomplete dominance where two alleles are expressed in such a way that the effect of each is noticed separately in the phenotype.

Both parental phenotypes can be distinguished in the heterozygote offspring.

The expression of one allele does not mask the expression of another.

Ex. A red bull crossed with a white cow = roan calf (calf has intermingled white & red hair)

Roan cattle and horses have both coloured and white hair.

Strawberry RoanBlue Roan

The ABO blood group system is another example.

Inheritance of blood groups is determined by the gene “I” which has three different alleles, only two of which can occur at the locus at once. The alleles are responsible for producing antigens on the surface of the red blood cells, which determines the blood group.

Alleles A and B are co-dominant so that when they are both present, both A and B antigens are produced. Both A and B are dominant to O.

Blood Types (A, B, O, AB)

Allele IA – formation of blood factor A (antigen A)Allele IB – formation of blood factor B (antigen B)Allele I – no factors result

Genotype Blood TypeIAIA or IAi AIBIB or IBi Bii OIAIB AB

IA an IB are codominant and i is recessive.

Rh antigens are straight dominant vs. recessive.

Type A Type B Type AB Type O

Blood types of North America

Blood types of North America with RH.

Example: A mother with blood type A has a child with Blood type O. The father is blood type B. Indicate the genotypes of the parents.Father can be IBIB or IBi and mother can be IAIA or IAi. To have a child that is type O (ii) both mother and father must contribute the i allele, therefore the father must be IBi and the mother is IAi

Case Study

Page 611: A Mystery of Blood Types

Pedigrees• A chart or register showing a line of ancestors

• Circles represent females, squares represent males, solid circles & squares represent those who have the trait being studied.

•Horizontal lines between circles and squares represent mating between male and female.

• A vertical line joins parents and children.

• Pedigrees are often used to study sex-linked traits such as color-blindness and hemophilia

PEDIGREE SUMMARY

This will help you determine a trait in a pedigree as with autosomal or X-linked:

Autosomal Dominant must be in each generation affected individuals transmit to minimum ½ of their offspring males and females are equally affected cannot have carriers, they will all be affected!

Autosomal Recessive may skip a generation affected offspring generally have normal (but heterozygous) parents male and female are equally affected

X-linked Dominant very likely to be observed in each generation females pass on to half of either sex no transmission from father to son (only daughters)

X-linked Recessive affect males more than females no transmission from father to son daughters of males are carriers females pass onto ½ sons affected females have affected fathers and carrier mothers

Pedigree analysis

Probability

• Probability is the likelihood of an event happening.

• Probability can be expressed by the following formula:

Probability = # of chances for an event

# of possible combinations

Therefore, when a coin is tossed, there are two possibilities – heads or tails.

What are the chances of getting heads?

What is the probability of two coins being tossed and getting heads?Coin 1 –Coin 2 –

1 head/2 head/tail = 50 % chance

½ = 50 % chance

½ = 50 % chance

The Rule of Independent Events –

Product of the probabilities of two separate events:

The Product Rule –½ × ½ = ¼ therefore a 25% chance

The probability of two or more independent events occurring together is the product of the individual probabilities if each individual event occurs separately.

Chance has no memory. This means that previous events will not affect future events. Ex. If you tossed two heads in a row, the probability of tossing heads again will still be ½.

Dihybrid Crosses

Mendel also studied two separate traits with a single cross by using the same procedure he had used for studying single traits.

Mendel crossed a purebred yellow round pea with a purebred green wrinkled pea. Pure breeding round = RRPure breeding wrinkled = rr

Pure breeding yellow = YY Pure breeding green = yy

Genotype for the yellow, round parent is RRYY Genotype for the green, wrinkled parent is rryy

P1 YYRR x yyrrPurebred yellow round × Purebred green wrinkled

YR YR YR YR

yr YyRr YyRr YyRr YyRr

yr YyRr YyRr YyRr YyRr

yr YyRr YyRr YyRr YyRr

yr YyRr YyRr YyRr YyRr

F1

Male gametes

Female gametes

The entire F1 generation has the genotype: YyRr

and is phenotypically yellow round!

Now let’s cross the F1 generations with one another and see what we get…

9/16 Yellow Round

3/16 Yellow wrinkled

3/16 green Round

1/16 green wrinkled

The phenotypic ratio 9:3:3:1 is the ratio you will find in all heterozygous dihybrid crosses!

Example:In summer squash, white fruit color is dominant “W” and yellow fruit color is recessive “w”. Another allele produces disc shaped fruit “S” while its recessive allele “s” yields sphere-shaped fruit. If a pure breeding white disc variety is crossed with a homozygous yellow sphere variety, the F1 are all white disc hybrids. If the F1 generation is allowed to mate, what would be the expected phenotypic ratio in the F2 generation?

Try this!

P1 WWSS x wwss

F1 All offspring will be WwSs

P2 WwSs x WwSs WS

Ws wS ws

WS

WWSS WWSs WwSS WwSs

Ws WWSs WWss WwSs Wwss

wS WwSS WwSs wwSS wwSs

ws WwSs Wwss wwSs wwss

F2

Rhesus Factor & Birth

P1 : Female Rh- × Male Rh+

Baby is Rh+ because father is. Mother’s blood produces antibodies upon birth, (since blood mixes at birth). First baby is okay.

Second pregnancy- mom’s antibodies can now move across the placenta and cause baby’s RBC’s to clump (agglutinate) if second baby is also Rh+. This decreases oxygen delivery in the baby – “blue baby.”

What can be done? Mom can be given an injection of a drug that inhibits antibody production immediately after delivery.What happens if this is undetected?

Baby could be given a blood transfusion while in the womb. Fairly uncommon.

Blood Types & Rhesus Factor Question

R – dominant allele (Rh+)r – recessive allele (Rh-)

Example: A woman homozygous for blood type A and heterozygous for the rhesus allele, Rh+, has a child with a man with type O blood who is Rh-. What is the probability that their child will have blood type A, Rh+? There will be a

50% chance.

Do Now

Biology creatures have many strange traits. Blinking eyes “B” is dominant and burning eyes are recessive “b”. Another allele produces pleasant smelling pheromones “P” while its recessive allele “p” yields rotting fruit pheromones. If a pure breed blinking pleasant smelling biology creature is crossed with a heterozygous blinking pleasant smelling biology creature, what would be the expected phenotypic ratio?

Techniques used in order to produce the genotype or phenotype that you want:

Selective Breeding: the crossing of desired traits from plants or animals to produce offspring with both characteristics

Inbreeding: the process by which breeding stock is drawn from a limited number of individuals possessing desirable phenotypes.

Hybridization: Blending of desirable but different traits.

Gene Interaction1) Many traits studied by Mendel were controlled by one gene.

2) Some traits are regulated by more than one gene; many of your characteristics are determined by several pairs of independent genes – polygenic.eg.) skin color, eye color and height, feather colour in parakeets

3) One trait controlled by more than one allele (multiple alleles).Eg. Blood types, Drosophilia eye colour

4) Genes that interfere with the expression of other genes are called epistatic.

Example:-allele B produces a black coat color in dog- b produces a brown coat color -A second gene, W prevents the formation of pigment - w does not prevent color

- genotype wwBb would be black- genotype WwBb would appear white-W allele masks the effect of the B color gene- If wwBb is crossed with a WwBb, state the phenotypes produced.

8/16 = white

6/16 = black

2/16 = brown

5) Complementary Interaction occurs when two different genotypes interact to produce a phenotype that neither is capable of producing by itself.

Example:-Allele R produces a rose comb in chickens -Allele P (on a different chromosome) produces a pea comb. - R and P alleles both present = walnut comb- The absence of rose and pea alleles results in an individual with a single comb