Download XY - Horizon

CHAPTER 5
“HEREDITY”
P. 126
Chapter Five “I Cans”
Heredity
1. I can draw a Punnett Square and determine the possible
outcomes of the crosses.
2. By using a pedigree, I can track a trait over several generations.
3. I can distinguish between genotypes / phenotypes and
heterozygous / homozygous traits.
4. I can identify dominant and recessive traits and use a Punnett
Square to identify the possible traits of the offspring.
Heredity
- is the passing of traits from
parent to offspring.
Genetics
- the study of how
traits are inherited
through the action
of alleles.
- are different
forms of the same
trait
If the trait is hair color,
blonde
brunette
- are possible alleles.
red
If the trait is eye color,
blue
brown
- are possible alleles.
hazel
Genetics was ‘started’ by
Gregor Mendel.
- he experimented with
pea plant traits in the
1800’s.
- is considered the
‘father’ of genetics.
(p. 127 -128)
Purebred
- an organism that
always produces the
same traits in its
offspring.
Ex. St. Bernards
produce St. Bernards
Ex. Siamese cats
produce Siamese
kittens
Mendel “crossed”
traits and discovered
that some traits
appear more often.
- called dominant
Ex. Brown eyes
over blue eyes.
Ex. Tall pea plants
over short plants.
The dominant trait
“masks” the hidden
trait:
- called recessive.
Ex. Blue eyes
Ex. Red hair
Ex. Attached ear
lobes
Mendel then allowed the “crossed” tall
and short plants to reproduce.
- surprising results.
- out of 4 plants =
3 tall / 1 short
(because the tall were
dominant)
- always got a 3:1 ratio.
What is the ratio of girls to boys
in your row?
What is the ratio of plants to
people in this room?
Because of ratios, Mendel could create
probabilities of what the offspring would
be.
- he could predict which
traits would appear.
Ex. The offspring of the tall
and short plant cross
75% chance of tall
25% chance of short
Coin Flip
Probability = 50% heads / 50% tails
Ratio = 1:1
PUNNETT SQUARES
T
t
Tt
t
Tt
T
Tt
Tt
Purebred tall and
purebred short cross
= All Tall offspring
The crossed
offspring produce
3 talls and 1 short
T
t
Tt
t
Tt
T
Tt
Tt
Ratio? Probability?
4:0
100% tall 0% short
Tt is a hybrid - or
mix.
Notice the 3:1 ratio
Ratio of short to
tall?
1:3
Probability of
having tall
offspring?
75%
Probability of
having short
offspring?
25%
A punnett square shows the
genotype of an organism.
B
B
b
b
BB
Bb
Bb
bb
- actual genetic traits
(can’t see)
Ex. Bb, TT.
-the alleles.
phenotype - the visible traits.
(can see or touch)
Hazel eyes
Attached ear lobes
If the alleles are the If the alleles are
same (BB or tt)
different (Bb or Tt)
- they are called
- they are called
homozygous.
heterozygous.
(or purebred)
(or hybrid)
(for animals only!)
ASSIGNMENT:
WORKSHEET
“WHAT IS GENETICS?
P. 132 SELF CHECK
1 - 4 (ON BACK)
Incomplete dominance - when one trait
is not dominant over another.
Ex. four o’clock
flowers
RR = red
rr = white
R
R
r
Rr
Rr
r
Rr
Rr
Results: 4 Pink! (Rr)
Ratio: Red:white:pink
0:0:4
Results:
R
R RR
r
Rr
r
1 red, (RR)
Rr
2 pink, (Rr)
1 white (rr)
rr
Ratio: red/pink/white
1:2:1
Probability of a pink
flower?
50%
Probability of a red
flower?
Probability of a
white flower?
25%
25%
Results:
R
R RR
r
Rr
R
2 red, (RR)
RR
2 pink, (Rr)
0 white (rr)
Rr
Ratio: red/pink/white
2:2:0
Probability of a pink
flower?
50%
Probability of a red
flower?
Probability of a
white flower?
50%
0%
Polygenic inheritance - when a group of
genes not just two combine to form
a trait.
Ex. blood type, eye
color, skin color,
height, etc.
Codominance
- a phenotype that is blended or
“mixed”
Sex Determination
- the male determines the sex of the
offspring.
XX = female (two X chromosomes)
XY = male (one X, one Y chromosome)
X
X
X XX
XX
Y XY
XY
Probability of having
a girl?
50%
Probabilty of having a
boy?
50%
Ratio of boys to girls?
2:2 or 1:1
WORKSHEET
“PUNNETT SQUARES”
Sex-linked Disorders
- inherited “conditions” linked
to the X chromosome.
Ex. color blindness,
hemophilia.
- these disorders are carried
on the females’ X
chromosome.
(the female is a carrier)
X
Xc
X XX
c
XX
Y XY
c
XY
Results:
XX - 1 normal girl
XY - 1 normal boy
XXc - 1 carrier girl
XcY - 1 colorblind
boy
For a girl to be colorblind, the trait
must appear on both alleles. (XcXc)
Colorblind Tests
How a colorblind person would see a
strawberry plant:
Hemophilia - a disease where the
blood will not clot. It was common in
the royal families of Europe.
Hemophilia
X
X
Xh XXh XXh
Results:
XXh =
two carrier females
XY =
two normal males
Y XY XY
Probability of having a hemophilic child?
0%
Probability of having a female carrier?
100%
Hemophilia
X
X
Xh XXh XXh
Ratio of carrier females
to normal males?
2:2
or 1:1
Y XY XY
Probability of having a hemophilic female?
0%
Probability of having a normal male?
100%
Hemophilia
X
Xh
Xh XXh XhXh
Y XY XhY
Results:
XXh
= carrier female
XY
= unaffected male
XhXh
= hemophilic female
XhY
= hemophilic male
Probability of having a hemophilic child?
50%
Pedigree
- a record of an organism’s ancestors.
- it traces the occurrences of a trait.
(p. 139 in text)
Pedigree
Is the pedigree
correct?
Do the punnett!
X
Xh
X XX XXh
Y XY XhY
Results:
1 normal male
1 normal female
1 carrier female
1 affected male
The Symbols of a Pedigree:
Female (normal)
Male (normal)
Female with trait
Male with trait
Female carrier
Male carrier ?!!
Read pp. 137 - 138.
“Human Genes and Mutations”.
ASSIGNMENT:
WORKSHEET
“GENETICS”
Chapter Five “I Cans”
Heredity
1. I can draw a Punnett Square and determine the possible
outcomes of the crosses.
2. By using a pedigree, I can track a trait over several generations.
3. I can distinguish between genotypes / phenotypes and
heterozygous / homozygous traits.
4. I can identify dominant and recessive traits and use a Punnett
Square to identify the possible traits of the offspring.