Objective: 1) Provide an example for codominance, incomplete dominance, and multiple alleles. 2) Define karyotype.

SOME TRAITS THAT ARE DOMINANT INCLUDE:

HITCHHIKER’S THUMB, ALMOND-SHAPED EYES, THICK LIPS, HAIR ON MIDDLE SECTION OF FINGER.

.

Human Traits:  autosomal1. Shape of face (probably polygenic)

Oval dominant, square recessive

2. Cleft in chin No cleft dominant, cleft recessive

3. Hair curl (probably polygenic)    Assume incomplete dominance

Curly:  homozygousWavy:  heterozygousStraight: homozygous

4. Hairline Widow peak dominant, straight hairline recessive

5. Eyebrow size Broad dominant, slender recessive

6. Eyebrow shape Separated dominant, joined recessive

7. Eyelash length Long dominant, short recessive

8. Dimples Dimples dominant, no dimples recessive

9. Earlobes Free lobe dominant, attached recessive

10. Eye shape  Almond dominant, round recessive

11. Freckles  Freckles dominant, no freckles recessive

12. Tongue rolling  Roller dominant, nonroller recessive

13. Tongue folding  Inability dominant, ability recessive

14. Finger mid-digital hair   Hair dominant, no hair recessive

15. Hitch-hiker's thumb Straight thumb dominant, hitch-hiker thumbrecessive

16. Bent little finger Bent dominant, straight recessive

17. Interlaced fingers Left thumb over right dominant, right over left recessive

18. Hair on back of hand Hair dominant, no hair recessive

19. Tendons of Palmar Muscle Two tendons dominant, three tendons recessive

Return to Menu

 

INCOMPLETE DOMINANCE: THE PHENOTYPE OF THE HETEROZYGOUS CONDITION IS A CROSS BETWEEN THE DOMINANT AND RECESSIVE TRAITS.

EXAMPLE: IN CARNATIONS, R=REDr=WHITE

RR= RED CARNATION

Rr= PINK CARNATION

rr= WHITE CARNATION

CODOMINANCE: THE PHENOTYPES OF BOTH ALLELES ARE EXPRESSED IN A HETEROZYGOUS INDIVIDUAL.

EXAMPLE:

IN CHICKENS, B= BLACK FEATHERS, W= WHITE FEATHERS

BB = BLACK FEATHERS

BW = BLACK AND WHITE FEATHERS

WW = WHITE FEATHERS

MULTIPLE ALLELES: SOMETIMES MORE THAN 2 ALLELES CONTROL A TRAIT.

3 ALLELES DETERMINE PIGEON FEATHER COLOR

Occurs when one gene controls the expression of a second gene.

In mice, one gene controls whether the mouse will have coloration (dominant) or albinism/white (recessive). IF coloration is dominant, THEN a second gene will determine if the mouse will be brown or black.

Pleiotropy is a condition that occurs when 1 gene controls many phenotypes.

A classic example of pleiotropy is the human disease PKU (phenylketonuria). This disease can cause mental retardation and reduced hair and skin pigmentation, and can be caused by a mutation in a single gene that codes for an enzyme (phenylalanine hydroxylase) that converts the amino acid phenylalanine to tyrosine, another amino acid.

One trait or phenotype is controlled by many genes.

For example between 4 to 10 genes control human height.

Genes linked to human height: ZBTB38, HHIP, CDK6, HMGA2, GPR126, ADAMTSL3, GDF5, LCORL, EFEMP1, and HIST1H1D

AUTOSOMES: THERE ARE 22 PAIRS OF HOMOLOGOUS CHROMOSOMES (TOTAL CHROMOSOMES =44)

SEX CHROMOSOMES: 1 PAIR OF CHROMSOMES THAT DETERMINE THE SEX OF AN ORGNANISM. SOME TRAITS ARE CONTROLLED BY GENES LOCATED ONLY ON THE SEX CHROMOSOMES (EXAMPLE: COLOR BLINDNES AND HEMOPHILIA).

YOUR CHROMOSOMES DURING METAPHASE

YOUR CHROMOSOMES ORGANIZED AS A KARYOTYPE (CHROMOSOME MAP)

SEX-LINKED TRAITS: TRAITS CONTROLLED BY GENES LOCATED ON THR SEX CHROMOSOMES.

X = FEMALE SEX CHROMOSOME

Y = MALE SEX CHROMOSOME (SMALLER THAN X AND DOES NOT CONTAIN AS MANY GENES)

THOMAS HUNT MORGAN DISCOVERED TRAITS LINKED TO SEX CHROMOSOMES. HE FIRST NOTICED THIS IN FRUIT FLY EYE COLOR.

MORGAN’S 1ST EXPERIMENT:

FEMALE MALE

X

Xr Y

XR

XR

XRXr XRY

XRXr XRY

OFFSPRING: ALL RED EYES