Welcome to Class

Cross a homozygous dominant green plant with a heterozygous green plant. What are the genotypic and phenotypic

ratios.

Agenda

• Complex patterns of inheritance– Incomplete and Co-dominance

Incomplete Dominance• Organism is heterozygous its phenotype will

show the dominant trait

• When red snapdragons (RR) were crossed with white snapdragons (rr) offspring were pink (Rr)

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

over the other allele

• Combined phenotype (blended)

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

Co-dominance• In COdominance, the "recessive" & "dominant"

traits appear together in the phenotype of hybrid (heterozygous) organisms

PracticeSet up genotypes for the phenotypes listed in each

set. Remember that the "medium" trait is always be 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.D) A Sneech can be tall, medium, or short.

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?

Welcome

In humans, straight hair (ss) and curly hair (cc) are co-dominant traits that result in hybrids that have wavy hair (sc). Cross a Straight hair female with a wavy haired male.

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

Agenda

• Quiz• Sex Linked Traits

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

XY XX

X Y X X

X X

X

Y

XX

Female

XX

Female

XY

Male

XY

Male

50% Female; 50% Male

Sex Linkage

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

Sex Linkage

• 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

• A few males have white eyes

• Red is dominant; white is recessive

Welcome to Class

What is sex linkage?

Agenda

• Finish sex linked traits notes– worksheet

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 with colorblindness marries a female who is not colorblind but carries the (b) allele.

Using a Punnett square, determine the genotypic and phenotypic probabilities for their potential offspring.

In fruit flies red eye color (R) is dominant to white eyes (r). In a cross between two flies, 50% of the male and 50% of the female offspring had red eyes. The other half of the males and females had white eyes.

What are the phenotype, and all possible genotypes, of the offspring?

Welcome to Class

In fruit flies red eye color (R) is dominant to white eyes (r). Cross a heterozygous female with a white eye male. What are the phenotypic and

genotypic ratios?

Agenda

• Review Sex linked traits

• Multiple Alleles

Epistasis• Epistasis – when one allele hides another

• Labrador Coat Color– 2 alleles– Dominant allele E determines pigment

• ee will have no pigment

– Dominant allele B determines how dark the pigment• EEbb or Eebb = chocolate brown• eebb, eeBb, or eeBB will be yellow because e masks effects

of dominant B allele

Multiple Alleles• Multiple alleles – traits that are determined by

more than 2 alleles– We have only 2 alleles (1 from mom, 1 from dad)– Blood groups (ABO)– O is recessive (i allele)

ALLELE IA IB i

CODES FOR Type "A" Blood Type "B" Blood Type "O" Blood

GENOTYPES IAIA IAi

RESULTING PHENOTYPES Type A Type A

IBIB IBi

Type B Type B

IAIB Type AB

ii Type O

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

for blood type

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

• Note too that the only genotype for "O" blood is homozygous recessive (ii).

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

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?