Chapter 8 Notes Day 6

1
Chapter 8 Notes (Day 6)
Objectives 1) Define through example sex-linked
traits and polygenic inheritance. 2) Identify
other factors that might control gene expression.
http//www.glennalicious.org/archives/blood-cells-
2.jpg
2
SEX-LINKED INHERITANCE
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)
3
THOMAS HUNT MORGAN DISCOVERED TRAITS LINKED TO
SEX CHROMOSOMES. HE FIRST NOTICED THIS IN FRUIT
FLY EYE COLOR. MORGANS 1ST EXPERIMENT
X
FEMALE
MALE
Xr Y
XRXr
XRY
OFFSPRING ALL RED EYES
XR
XRY
XRXr
XR
4
THOMAS MORGAN
5
POLYGENIC INHERITANCE
POLYGENIC INHERITANCE TRAIT CONTROLLED BY MORE
THAN ONE GENE. EXAMPLE HUMAN HEIGHT WHICH IS
CONTROLLED BY 5 GENES. EACH GENE HAS 2 ALLELES.
THE MORE CAPITAL (DOMINANT) ALLELES A PERSON HAS,
THE TALLER THEY WILL BE.
6
ENVIRONMENTAL INFLUENCES
EXTERNAL ENVIRONMENTAL FACTORS, SUCH AS LIGHT,
CAN DETERMINE HOW SOME GENES ARE EXPRESSED, IF AT
ALL. INTERNAL ENVIRONMENTAL FACTORS (HORMONES)
CAN CONTROL HOW CERTAIN GENES ARE EXPRESSED.
EXAMPLES OF SUCH GENES ARE HOSE THAT DETERMINE
HORN SIZE IN MOUNTAIN SHEEP, MALE PATTERN
BALDNESS, AND FEATHER COLOR IN PEACOCKS