Dominance: Co-Dominance, Incomplete Dominance and Blood Types

Lesson Objectives

• Minds ON• Yesterday’s Recap • Dominances and Blood Types• Blood Typing Lab• Success Criteria• Homework Take Up • New homework

Minds ON

Two rabbits are heterozygous. Brown fur (B) is dominant to white fur (b). Dwarf (small) ears (D) are dominant to floppy ears (d). Draw a Punnett square showing the possibilities.

We’ll do it together on the board once you’ve tried it.

Yesterday’s RecapDihybrid Crosses

• Refers to the crossing of two individuals who are both heterozygous for TWO traits (e.g. PpTt x PpTt)

• Assumes that these traits are on different genes and can occur at the same time.

• E.g. Pod colourand seed colour

Dihybrid Crosses

• Parent 1 genotype is: AaBb

• Parent 2 genotype is: AaBb

Dominances

So far, we have been looking at situations where a dominant trait completely masks the allele

Bb/BB = dominant for purple colour

Incomplete Dominance

Occurs when:- Neither gene is dominant or recessive- The gene effect is mixed - We use 2 different letters for the homologous

pair since neither is dominant.

An Example of Incomplete Dominance

With red and white snapdragons, the dominant allele that codes for the colour red is not completely dominant over the recessive allele that produces the white colour. The result is a pink flower.

Using a Punnett Square

Red Flower – RR White Flower – WW

R

= 100% Pink Offspring

x W W

R RW RWR RW RW

Co-Dominance

Occurs when:- Neither gene is dominant or recessive- Gene effects are NOT mixed- Therefore, both genes are expressed at the

same time!- Examples: Roan cow or Camelia flower

An Example of Co-Dominance

Write C (for co-dominance) and a super script (R=Red, W=white)• Red haired = CRCR• White haired = CWCW• Red and White (Roan) =CRCW

Using a Punnett Square

Red haired = CRCRWhite haired = CWCWRed and White (Roan) =CRCW

= 100% RoanX

Blood Types – A Special Case • There are three alleles:• IA (Type A), IB (Type B) and i (Type O)

– A and B are co-dominant– O is recessive

• +/- is the Rh (Rhesus) factor (if the Rh blood antigen is present, the person is Rh+; if not, they are

Rh-)

Predict offspring bloodtypes for: Heterozygous type A mother, type O father

Using A Punnett Square

X i

i i ii

i i ii

IA (Type A), IB (Type B) and i (Type O)-A and B are co-dominant-O is recessive

50% = A5-% = O

Blood Types

Types Distribution Ratios

O+ 1 person in 3 38.4%

O- 1 person in 15 7.7%

A+ 1 person in 3 32.3%

A- 1 person in 16 6.5%

B+ 1 person in 12 9.4%

B- 1 person in 67 1.7%

AB+ 1 person in 29 3.2%

AB- 1 person in 167 0.7%

AB universal plasma donors

AB+ universal recipients

O+ blood most needed

O- universal RBC donor

Rhesus Disease• An individual either has, or does

not have, the "Rhesus factor" on the surface of their red blood cells.

• The status is usually indicated by Rh positive (Rh+ does have the D antigen) or Rh negative (Rh− does not have the D antigen) suffix to the ABO blood type.

• Rhesus Disease occurs when there is incompatibility between blood types of mother and fetus.

• Untreated, the result can cause death of the child.

• Occurs in second and later pregnancies

Murder Mystery Lab

“I THINK THERE’S BEEN…(sunglasses on)..AN ACCIDENT!” (with emphasis)https://www.youtube.com/watch?v=mznsEcZlM2I&noredirect=1

The Jim Carrey shows us…https://www.youtube.com/watch?v=HJSqkwyL1Zo

Lab

There’s been a murder. Hortatio needs your help! You have to find out who did it. • Agglutination: refers to the clumping effect of

blood when it is mixed with Anti-A , Anti-B or Rh serum .

• Go around to each station and sample the blood to find out the blood type and Rh factor to determine who killed One-Eyed Earl!