What’s the difference between a phenotype and a genotype?

Agenda for Friday Jan 30th 1. Go over HW (Dihybrid)2. Incomplete and codominance

Complete Dominance

Purebred red snapdragons were crossed with purebred white snapdragons all offspring were pink

Incomplete Dominance• one allele for a trait is not completely dominant

over the other allele

• Combined (blended) phenotype

R = allele for red flowers W = allele for white flowers red x white ---> pink RR x WW ---> 100% RW

Co-dominance• In COdominance, both traits appear together in

the phenotype of hybrid (heterozygous)

WHITE RED

ROAN

PracticeSet up genotypes for the phenotypes listed in each

set. Remember that the "medium" trait is always heterozygous.

a) Birds can be blue, white, or white with blue-tipped feathers.

b) Flowers can be white, pink, or red.c) A Hoo can have curly hair, spiked hair, or a mix of

both curly and spiked.

1. Write the genotypes for the pictured phenotypes

2. Show the cross between a star-eyed and a circle eyed. What are the phenotypes of the offspring? What are the genotypes?

3. Show the cross between a circle-star eyed, and a circle eyed.How many of the offspring are circle-eyed? How many of the offspring are circle-star eyed?Write the genotypic and phenotypic ratios.

4. Show the cross between two circle-star eyed. How many of the offspring are circle-eyed? How many of the offspring are circle-star eyed? How many are star eyed?

Agenda for Monday Feb 2nd 1. Go over Incomplete/codominance wkst2. Sex linked traits

In humans, straight hair and curly hair are incompletely dominant traits that result in hybrids that have wavy hair. Cross a straight hair with a wavy hair.

What are the chances of having a curly haired child?What are the chances of having a straight hair child?

Sex Determination

• Thomas Hunt Morgan – studied fruit flies in the early 1900’s

Sex Determination

• Observed that one pair of chromosomes was different between males and females

– Large one named “X” chromosome

– Smaller one named “Y” chromosome

– XX = female; XY = male

Sex Linkage

• Sex Linkage: the presence of a gene on a sex chromosome (X or Y)

• X-linked genes: genes found on the X chromosome– X chromosome carries more genes

• Y-linked genes: genes found on the Y chromosome

Fruit Fly Eye Color

• Fruit flies normally have red eyes– Red is dominant; white is recessive

• A few males have white eyes

Morgan’s Fruit Fly Experiments

• Red-eyed female (XRXR) x White-eyed male (XrY)

XR XR

Xr

Y

XRXr XRXr

XRY XRY

RESULTS:

F1 generation – all red-eyed

Morgan’s Fruit Fly Experiments

• Red-eyed female (XRXr) x Red-eyed male (XRY)

XR Xr

XR

Y

XRXR XRXr

XRY XrY

RESULTS:

F2 generation – 3 red-eyed and 1 white-eyed

** all white-eyed where males…why?

Morgan’s Conclusions

• Gene for eye color is carried on the X chromosome = eye color is an X-linked trait

• Y chromosome does not carry a gene for eye color

• Red-eyed = XRXR, XRXr , XRY• White-eyed = XrXr, XrY

In humans colorblindness (b) is an example of a sex-linked recessive trait. A male without colorblindness marries a female who isn’t colorblind but carries the allele.

1. How many females will be colorblind?2. What sex will any colorblind children be?3. What percent will be male and colorblind?

In fruit flies red eye color (R) is dominant to white eyes (r) and is a sex linked trait.

A heterozygous red eye female mates with a red eye male.

1. How many will have red eyes?2. What percent will have white eyes?3. How many will be female and red eyed?

In fruit flies red eye color (R) is dominant to white eyes (r) and is a sex linked trait.

A homozygous red eye female mates with a white eye male.

How many males will have white eyes?

In humans colorblindness (b) is an example of a sex-linked recessive trait. A male with colorblindness marries a female who isn’t colorblind and does not carry the allele.

What is the chance they will have a child that is colorblind?

In humans colorblindness is an example of a sex-linked recessive trait. A male with colorblindness marries a female who is a carrier. What is the chance they will have a child that is colorblind?

Agenda for Wednesday Feb 4th 1. Disorder project

What is meant by a sex-linked trait?

Agenda for Thursday Feb 5th 1. Go over HW2. Multiple alleles

Quiz tomorrow

Projects due Monday

Multiple Alleles• Multiple alleles – traits

determined by more than 2 alleles– Increases possible number of

genotypes & phenotypes– Blood groups

Blood Types• A,B,O blood types• A and B are dominant over O

– Co-dominant to each other• O blood type is recessive

GENOTYPEIAIA IAi

RESULTING PHENOTYPES Type A Type A

IBIB IBi

Type B Type B

IAIB Type AB ii Type O

• More alleles means more combinations• 6 different genotypes & 4 different phenotypes

• 2 genotypes for both "A" & "B" blood --- either homozygous (IAIA or IBIB) or heterozygous with one recessive allele for "O" (IAi or IBi).

• The only genotype for "O" blood is homozygous recessive (ii).

• And lastly, what's the deal with "AB" blood? The "A" trait & the "B" trait appear together in the phenotype. What is this an example of?

Problems• A woman with Type O blood and a man who is Type

AB have are expecting a child. What are the possible blood types of the kid?

• What are the possible blood types of a child who's parents are both heterozygous for "B" blood type?

One More

• What are the chances of a woman with Type AB and a man with Type A having a child with Type O?

Complete dominance - 2 traitsBB Bb bb**Homozygous dominant same as heterozygousIncomplete Dominance – 2 different lettersRR WW RW ** heterozygous is a blend of other 2 traitsCo-dominance - 2 different letters GG TT GT **heterozygous see both of the other 2 traitsSex Linked Traits – use X’s and Y’s **no gene on YMultiple alleles – blood type, use I’s

What are the chances of a woman with Type AB and a man with Type O having a child with Type O?

Agenda for Friday Feb 6th 1. Quiz2. Finish notes3. Disorders

Epistasis• Epistasis – one allele hides/suppresses another allele

Polygenic• Phenotype depends on alleles in multiple

genes– Skin color, height, eye color– Continuous progression in expression of traits

Another example of a polygenic trait:

• Hair Color– Hair color is controlled by alleles on chromosomes 3,

6, 10, and 18. – The more dominant alleles that appear in the

genotype, the darker the hair!

Eye Color

• Has to do with the amount of melanin– More melanin = darker eyes

• Multiple genes determine how much melanin– More dominant genes = more melanin

• Heterochromia = different color eyes– uneven distribution of melanin

Environmental Influences

• Inherit tendency of getting heart diseases– Diet/exercise can also

influence

• Water/ temperature/ sunlight effect plants

Agenda for Tuesday April 29th 1. Sex Linked traits (go over HW)2. Multiple alleles3. Epistasis/polygenic4. Talk about disorder project

In fruit flies red eye color (R) is dominant to white eyes (r) and is a sex linked trait. Cross a heterozygous female with a white eye male.

How many will be red eye and male?