1. PEDIGREES

2. What is a Pedigree?
A visual representation of how a trait is inherited through generations.
Earliest generations are at the top.
Each row is one generation.
Circle = female, Square = male
Dark shading = affected
SOMETIMES the genotypes are shown below each individual.
SOMETIMES heterozygous individuals are “half shaded.”

3. Indicates the first, second, and third generations.
How to read a Pedigree
Mating I
I-1 and I-2’s offspring 1 2
II-4 mates with II-3
Indicates the first, second, and third generations. II 1 2 3 4
II-3 and II-4’s offspring
III 1 2 3
Is individual II-2 male or female? _______________
Is individual III-1 male or female? _______________
Is individual II-4 affected? __________. How do you know? _________________.

4. Analyzing Pedigrees BOTH A & B are heterozygous - Ff
In humans, the attached earlobe allele is recessive. The free earlobe allele is dominant. F f
What are the genotypes of A and B?
Clues:
Neither A or B have attached earlobes.
(How do you know?)
Neither A or B have the homozygous recessive genotype. Could they be heterozygous?
3) A and B have children with the ff genotype.
BOTH A & B are heterozygous - Ff
Try figuring it out using Punnett Squares!

5. Autosomal Recessive Traits
Trait is rare in pedigrees
Trait often skips generations (hidden in heterozygous carriers).
Trait affects males and females equally.
Example: Cystic Fibrosis

6. Autosomal Dominant Traits
Trait is common in pedigrees
Trait is found in every generation
There are few autosomal dominant human diseases. Why? (Hint: if the disease is fatal, how likely will the allele be passed on?)
Example: Achondroplasia (causes dwarfism)

7. X-linked Recessive Traits
Trait is rare in pedigrees.
Trait skips generations.
Affected fathers DO NOT pass the trait to their sons.
Males are more often affected than females.
Example: Duchenne Muscular Dystrophy

8. CHANGES IN DNA

9. How do Traits Come About?
There were not always blue-eyed people.
Came about 6,000 years ago.
In fact, EVERY inherited trait had to “arrive” at some point throughout history.
There were not always genetic disorders like cystic fibrosis or sickle cell anemia.
New traits and disorders appear due to
CHANGES IN DNA.

10. Mutation A change in the normal sequence of DNA
This can be caused by external factors
Chemicals, radiation, etc.
This can be caused by internal factors
problems with DNA replication
Mutations are RANDOM.
If in a SOMATIC CELL – change will not be passed on to offspring.
If in a SEX CELL –change WILL be passed on to offspring.
There are about 4000 known diseases or disorders caused by changes in genetic material.

11. MUTATIONS ARE NOT ALWAYS HARMFUL!
In fact, they are the basis for EVOLUTION – the reason why organisms are they way they are!
Watch the following video and remember, it is the MUTATIONS that cause new or modified traits which help an individual survive. (ie. Longer necks)

12. GENETIC DISORDERS 3 WAYS A GENETIC DISORDER CAN ARISE:
Change to a single gene
Entire Chromosomes duplicated or missing.
Multiple changes to one or more genes combined with environmental factors (Causing Cancer)

13. 1. Single Gene Mutations Recall that ONE GENE codes for ONE PROTEIN
If a gene is changed, the protein will be changed.
Each protein in our bodies carry out specific tasks.
Structural or Functional
Example: Cystic Fibrosis
Cause: The mutation affects the production of a protein that helps salt (NaCl) move into and out of cells.
Physical Effects:
Excessive mucus production on the outside of cells.
Mucus clogs the lungs, affecting respiratory function.

14. During Meiosis, chromosomes are equally divided between gametes.
Recall:
During Meiosis, chromosomes are equally divided between gametes.

15. 2. Nondisjunction – Causes one less or one more chromosome in each gamete
What would happen if any of these gametes were fertilized with a normal gamete?

16. Some Autosomal Nondisjunction Disorders
Down Syndrome – Trisomy 21
An extra chromosome 21.
Chances of having a baby with down syndrome increases with mother’s age. If over 40yo, 1/40 chance.
Edwards Syndrome – Trisomy 18
An extra chromosome 18
Usually fatal – brain, heart, facial, kidney, and stomach malformations.

17. Sex Chromosome Nondisjunction Disorders
Turner Syndrome
Female missing an X chromosome
Short in height, abnormal bone development, low hairline at back of neck
Triple X Syndrome
Female with an extra X chromosome
Very mild effects – may be taller, smaller head, speech and learning difficulties
Klinefelter’s Syndrome
Male with extra X chromosome
Usually no obvious symptoms
Some have little body hair, enlarged breasts, wide hips, and testicles remain small.
XYY Syndrome
Male with extra Y chromosome.
Usually very tall, suffer severe acne during adolescence.
Increased risk for learning/behavioural problems
What if a male zygote was missing the X chromosome?
Will not develop properly, resulting in death
There are too many important genes on the X chromosome. It cannot be missing.