1. Study of Genes And Inheritance
Austrian Monk studied pea plants to explain
How characteristics are passed from one
generation to another
Genetics
Study of Genes
And Inheritance
Gregor Mendel
(Founder of Genetics)

2. The Work of Gregor Mendel
Section Outline
The Work of Gregor Mendel
Genes (genotype/phenotype)
Gregor Mendel’s “Laws”
Dominance verses Recessive
Monohybrid Cross
Dihybrid Cross
Co dominance (Blood Groups)
Incomplete Dominance (4 O'clock flowers)
Gene Linkage (Autosomal linkage)
Sex Linkage (genes linked to sex chromosome)
Pedigrees (Family Trees)
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3. Analyzing Inheritance
Offspring resemble their parents
Offspring inherit genes for characteristics from their parents.
Recall: Each parent contributes 23 chromosomes (containing many genes) to their offspring.

4. Genes Have “addresses” or Loci
A gene locus – the location of a particular gene on a chromosome
Genes come in alternate forms called alleles.

5. Genotype verses Phenotype
Genotype refers to the total number of genes we inherit (all the genes on our chromosomes)
Phenotype – represents the genes that are actually used and expressed
For example: If you inherit a blue eye allele (b) and a brown eye allele (B)
Genotype Bb
However, your phenotype (actual eye color) would be brown eyes

6. Pure genotype
When we inherit the same allele for a particular trait, we are HOMOZYGOUS
for that trait.
For Example: If you inherit a blue eye allele from both mom and dad your genotype will be bb and your phenotype will be blue eyes.
If you inherit a brown eye allele from both your genotype = BB brown eyes

7. Hybrid Genotype
When we inherit different alleles for a particular genetic trait, we are HETEROZYGOUS for that trait.
For example: If we inherit a blue eye allele from one parent (b) and a brown eye allele from the other parent (B), then your genotype = Bb, and you are heterozygous brown eyed

8. Mendel’s Laws of Inheritance
Gregor
Mendel
experimented with
concluded that
Pea
plants
“Factors”
determine
traits
Some alleles
are dominant,
and some alleles
are recessive
Alleles are
separated during
gamete formation
Mendel referred to
Genes as “factors”
which is called the
which is called the
Law of
Dominance
Segregation
Dominant alleles
Overpower recessive
alleles (always expressed)
Describe how homologous chromosomes separate during meiosis

9. The characteristics that Mendel studied
Were easy-to-observe, contrasting traits
Figure 11-3 Mendel’s Seven F1 Crosses on Pea Plants
Section 11-1
Seed Shape
Seed Color
Seed Coat
Color
Pod
Shape
Pod Color
Flower Position
Plant Height
Round
Yellow
Gray
Smooth
Green
Axial
Tall
Wrinkled
Green
White
Constricted
Yellow
Terminal
Short
Round
Yellow
Gray
Smooth
Green
Axial
Tall
P = Parent (pure)
F1 = First generation offspring
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10. Principles of Dominance
Unlike humans, height in pea plants is determined only by two genes
T= tall and short (t)
Section 11-1
P Generation
F1 Generation
F2 Generation
Tall
Short
Tall
Tall
Tall
Tall
Tall
Short
When Mendel crossed a homozygous Tall plant (TT) with a homozygous Short plant (tt),
all offspring were heterozygous tall (Tt)
When the heterozygous plants
Were crossed , there were 3
Tall and one short plant
What are their Genotypes??
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11. Probability and Punnett Squares
Section Outline
Probability and Punnett Squares
A. Genetics and Probability
B. Punnett Squares
C. Probability and Segregation
D. Probabilities Predict Averages
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12. Punnett Square Monohybrid Cross
The Punnett square show the possible
Alleles that enter gametes
And, how the alleles then recombine
In the offspring
Heterozygous tall parent
Heterozygous
Tall parent

13. Dihybrid Cross: Predicting offspring genotypes
Figure Independent Assortment in Peas
Dihybrid Cross: Predicting offspring genotypes
And phenotypes of two different genetic traits
Section 11-3
R= dominant Smooth seed coat
r= recessive rough seed coat
Y= dominant yellow color
y= recessive green color
Represent possible gene combinations in gametes
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14. Homozygous white parent
Incomplete Dominance in Four O’Clock Flowers
Incomplete dominance does not follow
Mendel’s law of Dominance because
Here when homozygous parent plants
Produce offspring, the color produced
Is different from both parents.
“Blending of colors”
Homozygous Red
parent
Homozygous white parent
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15. Co dominance: both alleles have equal dominance
In some cases both alleles of a genetic trait are of equal strength
Both are expressed
ABO blood groups and fur color in some animals are good examples of
co dominance
Red Blood Cells carry two antigens, A and B antigens are molecules the immune system can recognize

16. A and B Alleles are of Equal Strength (Codominant)
Group O individuals Have NEITHER A or B Alleles; missing a gene
at the Loci where A / B would be (denoted as ii).
Blood Transfusions
Blood Group
Phenotype
Possible
Genotype
Antigen on RBC To
From
Complete ABO punnett square

17. Alleles for Normal and Sickle Hemoglobin also Co dominant
N = Allele for normal hemoglobin
S = Allele for Sickle hemoglobin
NN = Homozygous for Normal hemoglobin
NS = Heterozygous; both Normal and Sickle hemoglobin – Resistance to Malaria
SS = Homozygous for Sickle (Disease/ Fatal)

18. Sickled cells
Sickled cells do not move through the capillaries and block blood flow, depriving cells of oxygen and nutrients.
Painful

19. Human Karyotype 23 Pairs of Chromosomes
A Karyotype is a picture of a cell’s
Chromosomes grouped in homologous pairs

20. A Family Tree
Section 14-1
To understand how traits are passed on from generation to generation, a pedigree, or a diagram that shows the relationships within a family, is used.
a circle represents a female
a square represents a male.
The horizontal line that connects a circle and a square represents a marriage.
Vertical lines show
Children of that couple
A filled-in circle or square shows that the individual has the trait being studied.
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21. Human Pedigree
Other pedigree typical symbols to know

22. Human Chromosomes 22 pairs of Autosomes; 1 pair of Sex chromosomes
Humans have 23 pairs of chromosomes
22 exist as homologous pairs called AUTOSOMES
Genes located on autosomes called Autosomal
1 pair exist as Sex chromosomes
Genes located on sex chromosomes are called sex-linked

23. Hypercholesterolemia
Disorders located on Autosomal Genes:
Concept Map
Section 14-1
Autosomal
Disorders
caused by
Dominant
Alleles
Recessive alleles
Co dominant alleles
include
include
include
Albinism
Galactosemia
Tay-Sachs disease
Huntington’s disease
Sickle cell disease
Cystic fibrosis
Phenylketonuria
Achondroplasia
Hypercholesterolemia
Go to Section:

24. Cystic fibrosis – autosomal recessive disorder- “affected”
Individual receives defective allele from both carrier parents
Section 14-1
Chromosome # 7
CFTR gene
The most common allele that causes cystic fibrosis is missing 3 DNA bases. As a result, the amino acid phenylalanine is missing from the CFTR protein.
Normal CFTR is a chloride ion channel in cell membranes. Abnormal CFTR cannot be transported to the cell membrane.
The cells in the person’s airways are unable to transport chloride ions. As a result, the airways become clogged with a thick mucus.

25. Autosomal Dominant Genetic Disorders
Only one dominant gene is needed to express the trait (disorder)
Achondroplasia -dwarfism
Huntington’s Disease- Mental deterioration and uncontrollable movements; middle age
Hypercholesterolemia – excess cholesterol and heart disease

26. Sex-linked = Genes found on the X and Y chromosomes
If a gene is found on the X or the Y chromosome, it is said to be a sex-linked trait.
Because the X chromosome is much larger than the y
Sex-linked genes are generally found on the X chromosome
More than 100 sex-linked genetic disorders have
Been linked to the X chromosome
If the

27. Sex Linked Genes Males have just one X chromosome, thus all
X-linked alleles are expressed in males, even if
They are recessive

28. Examples of Sex-linked Traits Stats in US:
Red-green colorblindness (1out 10 males)
Male Pattern Baldness – Premature hair loss
Hemophilia- missing blood clotting factor(s)
(1 out of 10,0000 males)
Duchenne Muscular Dystrophy – progressive weakening and loss of skeletal muscle (1 out of 3000 males)

29. Colorblind – sex-linked traits always expressed
Figure Colorblindness
Colorblind – sex-linked traits always expressed
In males (they have no other gene to mask it)
Section 14-2
Father
(normal vision)
Normal vision
Colorblind
Male
Female
Daughter
(normal vision)
Son
(normal vision)
Mother (carrier)
Daughter
(carrier)
Son
(colorblind)
Females need to have two copies of the defective allele to be
Colorblind; so colorblind females are more rare
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30. Red-Green Colorblindness
What do you see?

31. Hemophilia sex-linked recessive

32. Homologous chromosomes fail to separate
Other Genetic Disorders: Nondisjunction
Section 14-2
Homologous chromosomes fail to separate
Meiosis I:
Nondisjunction
Meiosis II
Nondisjunction of Homologous chromosomes during meiosis of gametogenesis
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33. Nondisjunction
RECALL: If nondisjunction occurs, abnormal numbers of chromosomes may enter gametes
Downs Syndrome – autosomal nondisjunction of chromosome #21 - individuals having 47 chromosomes instead of 46
Turner’s and Kleinefelter’s Syndrome – nondisjunction of sex chromosomes

34. Phenotype determined by more than one pair of alleles
Height in pea plants is controlled by one pair of alleles.
The allele for a tall plant is the dominant allele (T)
The allele for a short plant is the recessive one (t).
What about people?
Are the factors that determine height more complicated in humans?

35. Many Human phenotypes are Polygenic
Often genetic traits in humans are determined by more than one pair of alleles
Called Polygenic traits
Height, pigmentation, intelligence are three examples of such traits
Phenotypes are expressed in “ranges”, rather than “either/ Or”

36. Generic Bell Curve for Polygenic Trait
Section 16-1
AKA: “Normal” Curve
Frequency of Phenotype
Phenotype (height)