Regents Biology

11.3 – Beyond Mendelian Genetics

Originally prepared by Kim B. Foglia Revised and adapted by Nhan A. Pham

Regents Biology

Beyond Mendelian Genetics §  Peas are genetically simple - most traits are controlled by single gene - each gene has only 2 version: 1 completely

dominant (A), 1 recessive (a) §  But it’s usually not that simple!

Regents Biology

Incomplete dominance §  Hybrids have “in-between” appearance - RR = red flowers (RR) - rr = white flowers (WW) - Rr = pink flowers (RW)

rr

Regents Biology

Incomplete dominance true-breeding red flowers

true-breeding white flowers

X P

100%

100% pink flowers 1st

generation (hybrids)

self-pollinate

������25% white

2nd

generation

25% red 1:2:1

50% pink

Regents Biology

Incomplete dominance

R W male / sperm

R

W

fem

ale

/ eg

gs RR

RW WW

RW

25%

1:2:1

25%

50%

25%

1:2:1

% genotype

% phenotype

RR

RW

RW

WW

25%

50%

RW x RW

Regents Biology

Codominance §  equal dominance §  Alleles for black feathers

(B) and white feathers (b) are codominant à both will express

§  How is that different from the snapdragons before?

Regents Biology

Multiple Alleles §  Most genes exist in more than 2 allelic forms

Ex: human ABO blood groups have 3 versions: A, B, i -  A and B alleles are codominant -  both A and B alleles are dominant over i allele à both

phenotypes will be expressed -  code for different sugars on the surface (serve as

“name tags”) of red blood cells

Regents Biology

Genetics of Blood type

pheno-type genotype antigen

on RBC antibodies in blood

donation status

A A A or A i type A antigens

on surface of RBC

anti-B antibodies __

B BB or B i type B antigens

on surface of RBC

anti-A antibodies __

AB AB both type A &

type B antigens on surface

of RBC

no antibodies universal recipient

O i i no antigens on surface

of RBC

anti-A & anti-B antibodies

universal donor

Regents Biology

Blood donation

clotting clotting

clotting clotting

clotting clotting clotting

Regents Biology

Epistasis §  One gene alters the phenotype

of another gene Ex: coat color in mice is

controlled by 2 separate genes - C,c: pigment (C) or no

pigment (c) - B,b: more pigment

(black=B) or less (brown=b) - cc = albino,

no matter B allele - 9:3:3:1 becomes 9:3:4

Regents Biology

Epistasis in Labrador Retrievers

§  2 genes: E, e and B, b

§  color (E) or no color (e)

§  how dark color will be: black (B) or brown (b)

E–B– E–bb eeB– eebb

Regents Biology

Polygenic §  Many genes, one trait §  Some phenotypes are

determined by additive effects of 2 or more genes

§  humans -  skin color -  height - weight -  eye color -  intelligence -  behaviors

Regents Biology

Human skin color §  determined by many genes §  AaBbCc x AaBbCc - can produce a wide range

of shades - most children have

intermediate skin color - some can be very light

and very dark §  How does this work?

Regents Biology

Albinism Johnny and Edgar Winter

albino Africans

melanin = universal brown

color

Regents Biology

OCA1 albino Bianca Knowlton

Regents Biology

Human Height §  How does this work?

Regents Biology

Beyond Mendelian Genetics

http://www.youtube.com/watch?v=rIe7mPXkYhs

Regents Biology

§  Phenotype is controlled by both������ environment and genes

Color of Hydrangea flowers is influenced by soil pH

Human skin color is influenced by both genetics and environmental conditions

Environment effect on genes

Coat color in arctic fox influenced by heat sensitive alleles