chapter 5 “heredity” p. 126
TRANSCRIPT
CHAPTER 5 “HEREDITY“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 If the trait is hair colorhair color,,
- are possible alleles.
blonde
brunette
red
If the trait is If the trait is eye color,eye color,
- are possible alleles.
blue
brown
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:
Ex. Blue eyesEx. Red hairEx. Attached ear lobes
- called recessive.
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 cross75% chance of tall25% chance of short Coin
FlipProbability = 50% heads / 50% tails Ratio = 1:1
PUNNETT SQUARES
Purebred tall and purebred short cross= All Tall offspring
T T
t tTt TtTt Tt
The crossed offspring produce
3 talls and 1 short
Ratio? Probability? 4:0100% tall 0% short
T T
t tTt TtTt Tt
Tt is a hybrid - or mix.
Notice the 3:1 ratio
Ratio of short to tall?
1:3Probability of
having tall offspring?
75%Probability of
having short offspring?
25%
A punnett square shows the genotype of an organism.
- actual genetic traits (can’t see)
Ex. Bb, TT. -the alleles.
B bBb
BB Bb
Bb bb
phenotype - the visible traits. (can see or touch)
Hazel eyes
Attached ear lobes
If the alleles are the same (BB or tt)- they are called homozygous.
If the alleles are different (Bb or Tt)- they are called 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 = redrr = white
R R
rr
Rr RrRr Rr
Results:
4 Pink! (Rr)Ratio:
Red:white:pink 0:0:4
Ratio: red/pink/white1:2:1
R r
Rr
RR RrRr rr
Results:1 red, (RR)2 pink, (Rr)1 white (rr)
Probability of a red flower?25%
Probability of a pink flower?50%Probability of a white flower?
25%
Ratio: red/pink/white2:2:0
R R
Rr
RR RRRr Rr
Results:2 red, (RR)2 pink, (Rr)0 white (rr)
Probability of a red flower?50%
Probability of a pink flower?50%Probability of a white flower?
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)
Probability of having a girl?
50%Probabilty of having
a boy?50%Ratio of boys to girls?2:2 or 1:1
X X
XY
XX XX
XY XY
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)
Results:XX - 1 normal girlXY - 1 normal
boyXXc - 1 carrier girlXcY - 1 colorblind boy
X Xc
XY
XX XXc
XY XcY
For a girl to be colorblind, the trait must appear on both alleles. (XcXc)
Colorblind TestsColorblind 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 Results:XXh =
two carrier femalesXY =
two normal malesXh
Y
X XXXh
XYXXh
XYProbability of having a hemophilic child?
0%
Probability of having a female carrier?
100%
Hemophilia Ratio of carrier females to normal males?
2:2or 1:1Xh
Y
X XXXh
XYXXh
XYProbability of having a hemophilic female?
0%
Probability of having a normal male?
100%
Hemophilia Results:XXh
= carrier femaleXY
= unaffected maleXhXh
= hemophilic femaleXhY
= hemophilic male
Xh
Y
X XhXXh
XYXhXh
XhY
Probability of having a hemophilic child?
50%
- a record of an organism’s ancestors.- it traces the occurrences of a trait.
(p. 139 in text)
Pedigree
Results:1 normal male1 normal female1 carrier female1 affected male
PedigreeIs the pedigree correct?
Do the punnett!
X XhX
YXXXY
XXh
XhY
The Symbols of a Pedigree:
Read pp. 137 - 138. “Human Genes and Mutations”.
?!!
Female (normal)Male (normal)Female with traitMale with trait
Female carrierMale carrier
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.