1. Patterns of Inheritance
Chapter 9
Patterns of Inheritance

2. The historical roots of genetics:
Early 19th century: traits from mom and dad blend like paints to form kid’s traits
______________ (1840’s) : “Father of modern genetics”
Mendel crossed pea plants that differed in certain characteristics (__________ ) and traced from generation to generation; used a mathematical approach
Why did he choose pea plants?
Crossing of traits:
Self fertilize (____________ ) – cross pollen and egg from same parent plant to get identical offspring
Cross Fertilize (__________ ) – cross pollen from one parent plant with the egg of a different parent plant
Gregor mendel

3. And so on… ____ generation is true-breeding – Parent generation
_____ generation = Hybrid offspring of P (parents)
_____ generation = offspring of F1 plants crossed
_____ generation = offspring of F2 plants crossed
And so on…
Parents (P)
White
Purple
Offspring (F1)

4. Mendel hypothesized that there are alternative forms of factors (________ ) = units that determine heritable traits
Flower color
Flower position
Seed color
Seed shape
Pod color
Pod shape
Stem length
Purple
White
Axial
Terminal
Round
Wrinkled
Inflated
Constricted
Tall
Dwarf
Green
Yellow

5. From his experimental data, Mendel deduced that an organism has two genes (___________ ) for each inherited characteristic
For each characteristic (trait), an organism ____________________________, one from each parent.
Think of TRAITS as _________________ and ALLELES as _______________ within each category!
P generation
(true-breeding parents)
F1 generation
F2 generation
Purple flowers
White flowers 
All plants have purple flowers
Fertilization among F1 plants (F1  F1)
of plants have purple flowers 3 4
of plants have white flowers 1
Examples:
Flower Color (trait)
Purple or White (alleles)

6. __________ = physical appearance of the allele for a specific trait (purple/white flower for flower color trait)
_________ = genetic makeup the alleles that represent the phenotype (one dominant, one recessive; or 2 dominant alleles and 2 recessives)
DNA from the Beginning Animations

7. If the 2 alleles of an inherited pair are different, then one determines the organism’s appearance and is called the _____________ allele. (will usually show up more often!)
The other allele has no noticeable effect on the organism’s appearance and is called the _______________ allele. (Is present but does not show up in the appearance)
* If dominant allele is present, it takes over and outweighs the recessive!

8. Dominant and Recessive alleles:
In a genetic cross, CAPITAL letters are used to represent DOMINANT alleles and lower case letters represent the recessive alleles.
MUST USE SAME LETTER FOR EACH TRAIT! (Doesn’t matter the letter you choose!)
Example:
Flower Color (trait) T = purple, t = white
Pea Color R=yellow, r =green

9. HOMOZYGOUS and HETEROZYGOUS
When 2 of the SAME ALLELES are present, it is HOMOZYGOUS for that trait.
HH = homozygous ___________
hh = homozygous ____________
When 2 DIFFERENT alleles are present, it is termed HETEROZYGOUS for the trait.
Hh= __________________
With
homozygous,
you must clarify
which allele-
either
Dominant
or recessive!

10. We can look at the alleles from each parent to determine the probability of those alleles being passed on to offspring.
PUNNETT SQUARE:
Shows a genetic mixing (cross) of alleles from both parents for specific traits.
Punnett Square are use to ______________ __________________ and see inheritance patterns for specific traits!

11. Trait= Flower Color H h Parent #2 H =purple h = white Hh Hh Hh Hh#1 Hh Hh

12. Probability of one offspring from parent cross!
Trait= Flower Color
* If Dominant allele is present, it takes over and outweighs the recessive!
H =purple h = white H h
Genotype =genetic makeup (represented by letters!)
Parent 1 = hh homozygous recessive
Parent 2 = HH homozygous dominant
Offspring= 100% Hh Heterozygous Hh Hh
Probability of one offspring from parent cross!
Phenotype =physical appearance (what the letters represent!) Hh
Parent 1 = white
Parent 2 = purple
Offspring= 100% purple Hh

13. LET’S PRACTICE!!!

14. Homologous chromosomes bear the two alleles for each characteristic
Reside at the same __________ (point) on homologous chromosomes
Genotype: PP aa Bb
Heterozygous P a b B
Gene loci
Recessive allele
Dominant allele
Homozygous for the dominant allele
Homozygous for the recessive allele

15. Mendel’s law of segregation
Predicts that allele pairs from each parent separate (______________) from each other during the production of gametes (sperm/eggs)
P plants
Gametes
Genetic makeup (alleles)
F1 plants
(hybrids)
F2 plants PP pp
All P
All p
All Pp
Sperm 1 2 P p Pp
Eggs
Genotypic ratio
1 PP : 2 Pp: 1 pp
Phenotypic ratio
3 purple : 1 white

16. Actual results support hypothesis
Mendel’s law of independent assortment
States that alleles of a pair __________________ _________________ of other allele pairs during gamete formation
Hypothesis: Dependent assortment
Hypothesis: Independent assortment
RRYY
rryy
Gametes
RrYy RY ry
Sperm Ry
RrYY
RRYy
rrYY
rrYy
RRyy
Rryy
Actual results contradict hypothesis
Actual results support hypothesis
Yellow round
Green round
Yellow wrinkled
Green wrinkled
Eggs
P generation
F1 generation
F2 generation 1 2 4 9 16 3 
Figure 9.5 A

17. 9.8 Genetic traits in humans can be tracked through family ______________________.
Pedigree Key Dd
Joshua
Lambert
Abigail
Linnell
D ?
John
Eddy
Hepzibah
Daggett dd
Jonathan
Elizabeth
Dd Dd dd Dd Dd Dd dd
Female Male
Deaf
Hearing
Female
Male
Mating
Offspring
Figure 9.8 B

18. Recessive Disorders- Most human genetic disorders are recessive
Parents
Offspring
Sperm
Normal Dd 
D d
Eggs D d DD
(carrier) dd
Deaf
Figure 9.9 A

19. Dominant Disorders- Some human genetic disorders are dominant
Parents
Offspring
Sperm
Dwarf Dd
Normal dd 
D d
Eggs d
Achondroplasia – cause of dwarfism
Figure 9.9 B

20. 9.10 New technologies can provide insight into genetic legacy
Identifying Carriers
For an increasing number of genetic disorders, tests are available that can distinguish carriers of genetic disorders and can provide insight for reproductive decisions
Fetal Testing: ____________________ and ______________________________________________ (CVS) allow doctors to remove fetal cells that can be tested for genetic abnormalities
Fetal Imaging- _________________________ uses sound waves to produce a picture of the fetus

21. NON-MENDELIAN GENETICS
ALL OF THE FOLLOWING ARE EXCEPTIONS TO MENDEL’S RULES!!!
Mendel’s principles are valid for all sexually reproducing species, HOWEVER, genotype often does NOT dictate phenotype in the simple way his laws described.

22. When an offspring’s phenotype is in between the phenotypes of its parent, it exhibits _________________________.
P generation
F1 generation
F2 generation
Red RR
Gametes 
White rr
Sperm
Eggs
Pink Rr R r rR 1 2
Figure 9.12 A

23. Involves 3 alleles of a single gene
In a population, _________ _________(2 or more options) often exist for a single trait.
Example: The ABO blood type in humans
Involves 3 alleles of a single gene
The alleles for A and B blood types are ____________________ and both are
expressed the phenotype

24. __________________ - a single gene can affect a phenotype in many ways
Individual homozygous
for sickle-cell allele
Abnormal hemoglobin crystallizes,
causing red blood cells to become sickle-shaped
Sickle-cell (abnormal) hemoglobin
Sickle cells
Breakdown of
red blood cells
Clumping of cells
and clogging of
small blood vessels
Accumulation of
sickled cells in spleen
Physical
weakness
Anemia
Heart
failure
Pain and
fever
Brain
damage
Damage to
other organs
Spleen
Impaired
mental
function
Paralysis
Pneumonia
and other
infections
Rheumatism
Kidney
5,555
Figure 9.14

25. _________________ inheritance- creates a multiple variations of phenotypes
P generation
F1 generation
F2 generation
Sperm
Eggs
aabbcc
(very light)
AABBCC
(very dark)
AaBbCc  1 8 64 6 15 20
Skin color
Fraction of population
Figure 9.15

26. THE CHROMOSOMAL BASIS OF MENDEL’S LAWS OF INHERITANCE
All round yellow seeds (RrYy)
Metaphase I of meiosis (alternative arrangements)
Anaphase I of meiosis
Metaphase II of meiosis
Gametes
F1 generation
F2 generation
Fertilization among the F1 plants
(See Figure 9.5A)
1 4 RY ry R y Y r rY Ry 9
: 3
: 1
Figure 9.18

27. Not accounted for: purple round and red long
Experiment
Explanation: linked genes
PpLI  PpLI
Long pollen
Observed Prediction
Phenotypes offspring (9:3:3:1)
Purple long
Purple round
Red long
Red round
Parental
diploid cell
PpLI
Most
gametes
offspring
Eggs
3 purple long : 1 red round
Not accounted for: purple round and red long
Meiosis
Fertilization
Sperm
284 21 55
215 71 24
P I
P L
Purple flower
Certain genes are called _____________ GENES- tend to be inherited together because they reside close together on the same chromosome.
Figure 9.19

28. 9.20 Crossing over produces new combinations of alleles
Crossing over can separate linked alleleS producing gametes with recombinant chromosomes A B a b
Tetrad
Crossing over
Gametes
Figure 9.20 A

29. _____________________:
Experiment
Gray body,
long wings
(wild type)
GgLI
Female 
Black body,
vestigial
wings
ggll
Male
Offspring
Gray long
965
944
206
185
Black vestigial
Gray vestigial
Black long
Parental
phenotypes
Recombinant
Recombination frequency =
= 0.17 or 17%
391 recombinants
2,300 total offspring
Explanation
(female)
(male) G L g l
Eggs
Sperm
_____________________:
Performed some of the early studies of crossing over using the fruit fly Drosophila melanogaster.
Figure 9.20 C

30. SEX CHROMOSOMES AND SEX-LINKED GENES
In mammals, a male has one X chromosome and one Y chromosome and a female has two X chromosomes.
The Y chromosome has genes for the development of testes.
The _________________________ chromosome allows ovaries to develop.
(male)
(female)
Parents’
diploid
cells
Sperm
Egg
Offspring
(diploid) 44 + XY XX 22 X Y
Figure 9.22 A

31. A _________ has to receive the allele from both parents to be affected
The inheritance pattern of sex-linked genes is reflected in females and males.
A _________ receiving a single X-linked allele from his mother will have the disorder
A _________ has to receive the allele from both parents to be affected
Female
Male
Sperm Xr Y XR
Xr Y 
XR XR
XR Xr
XR Y
Eggs
R = red-eye allele
r = white-eye allele
Xr XR
Xr Xr
Figure 9.23 B
Figure 9.23 C
Figure 9.23 D

32. Examples: _____________________________
Sex-Linked
Most sex-linked human disorders are due to __________ allele and are mostly seen in _______________.
Examples: _____________________________
Queen
victoria
Albert
Alice
Louis
Alexandra
Czar
Nicholas II
of Russia
Alexis
Figure 9.24 A
Figure 9.24 B