Transcript `Duplo Figure Articulated Child Old with Yellow Legs, Red

MODERN GENETICS
Sex Determination
Being male or female is due to the
presence of certain chromosomes
Sex Determination
Autosomes :
chromosomes that do
not determine sex
In humans there are
22 pair
(44)autosomes
Sex Determination
Sex chromosomes: 1
pair (2) chromosomes
that determine the
sex of the offspring
One is called “X” and
the other “Y”
Sex determination
Females are
Males are
XY
XX
Sex Determination
Sex Determination
The sex of an individual is determined at
fertilization
The male determines the sex of the child
Sperm can be X or Y
Eggs can only be X
Female (XX) gets 1 X from mother and 1 X
from father
Male (XY) gets X from mother and Y from
father
Whose
chromosomes
determine the
gender of the baby?
X
Y
X
XX
XY
X
XX
XY
50% girls
50% boys
SEX-LINKED TRAITS
A trait that is controlled by a gene found on the
sex chromosomes (usually X chromosome)
The chance of showing the trait is affected by
the sex of the individual (usually male)
Genes for certain traits are carried on the X
chromosome and there are no alleles for these
genes on the Y chromosome (the Y
chromosome is smaller, less room for alleles)
SEX- LINKED TRAITS
Females do not show trait because they
have a good dominant allele on other X
chromosome. Only show trait is are
homozygous recessive
Males only have one X so recessive trait
shows
XX
XY
Sex-Linked Genes
Men are more susceptible. They
only need one bad chromosome to
get the disease. Women would
have to have two.
XX
XY
SEX-LINKED TRAITS
EX.- COLOR BLINDNESS (Red/Green)
Females are carriers but males show trait
XX
C
XX
Normal female
Normal female (carrier!)
C C
XX Colorblind female
XY Normal male
C
XY Colorblind male
Sex-Linked Punnett
Squares!
Cross a
carrier female
with a
normal male.
Sex-Linked Punnett
Squares!
X
C
Y
C
C
X XX XY
X
X
X
XY
What percent of males are
colorblind?
X
C
Y
C
C
X XX XY
X
X
X
XY
What percent of males are
colorblind?
X
C
Y
C
C
X XX XY
X
X
X
XY
What percent of females are
colorblind?
X
C
Y
C
C
X XX XY
X
X
X
XY
SEX-LINKED TRAITS
Ex.- Hemophilia- disease in which blood
has poor clotting ability, more frequent in
males than females
Ex.- Duchenne Muscular Dystrophymuscle tissue of affected individual breaks
down
PEDIGREE CHART
A diagram that shows the presence or
absence of a particular trait in each
member of each generation
Gene Linkage
Genes for 2 different traits (non-allelic) are
located on the same homologous
chromosome and are inherited together
“ Linked Together”
Ex- Pea Plants- height and seed color
genes are linked
(Tall & Yellow or Short & Green)
Gene Linkage
Blond Hair & Blue
Eyes
Red Hair & Freckles
Crossing Over
The process in which pieces of
homologous chromosomes are exchanged
during synapsis during first meiotic division
Produces new alleles on chromosomes
Explains why linkage doesn’t always occur
Increases variability in offspring
Multiple-Gene Inheritance
Two or more pairs of
genes affect the same
characteristic
Polygenic inheritance
Ex- height in humans