1. Biology
Genetics Unit

2. Gregor Mendel Considered the father of modern genetics
He was an Austrian monk in the mid 1800’s
He did many experiments with pea plants

3. Mendel Continued
He discovered the basics for genetics as we know it today
In the following slides, we will cover his major discoveries

4. Dominant Traits In a pair of traits, this one always has an effect
These traits get represented with a capital letter (B)

5. Recessive Traits
A trait that is only seen when two copies of the gene are present
Recessive traits are
represented with a
lowercase letter: b

6. Alleles Different forms of the same trait or gene
Examples would be blue and brown eyes, or hitchhikers and straight thumbs

7. Homozygous
A term describing an organism that has two of the same genes
This could be two dominant traits (BB) or two recessive traits (bb)

8. Heterozygous
A term describing organisms that have two different genes for a trait.
This means they have one dominant and one recessive trait (Bb)

9. Genotype The genes that an organism has for a trait.
For example, attached earlobes are a recessive trait, so a person with them must have two copies of that trait.
Therefore, their genotype is “ee.”

10. Phenotype This is the actual, physical trait that a person has.
For example, if a person has the genes “Ee” for earlobe shape, their phenotype will be the dominant trait, which is free earlobes.

11. Incomplete Dominance
Sometimes, one trait does not dominate the other, and both the dominant and recessive traits are seen.

12. Codominance
With some traits, there can be more than one dominant allele.
A good example is blood type. Type O is recessive, but types A and B are both dominant.

13. Punnett Squares
Punnett Squares are charts that are made in order to predict the results of two organisms reproducing.
Usually only one or two traits are analyzed at a time.

14. Single Trait Punnett Square
The Problem: Brown eyes are dominant and blue eyes are recessive. Cross a heterozygous woman with a homozygous recessive male.
Step 1 – define letters to represent the traits
B – brown b – blue
Step 2 – write down Mom and Dad’s genotypes
Mom Dad
Bb bb

15. Single Trait Punnett Square
Now make the chart and put Mom and Dad’s genes on the chart.

16. Single Trait Punnett Square
Now, bring the genes across and down to determine the genes the possible offspring will have.

17. Two Trait Punnett Square
In this problem we will look at two traits at the same time.
Problem – make a Punnett Square using the following combinations of genes.
Mom Dad
AaBb AABb

18. Two Trait Punnett Square
Now, find the combinations of genes Mom and Dad can pass on.
Mom - AaBb Dad - AABb
AB AB
Ab Ab
aB AB
ab Ab

19. Two Trait Punnett Squares
Now, take those traits and put them on a chart.

20. Two Trait Punnett Squares
Finally, fill in the boxes.

21. Sex-Linked Punnett Squares
These are traits that are only found on the “X” chromosome.
Females have “XX” and males have “XY”
The X chromosome is very large and the Y is very small. Because of this, there is not enough room on the Y for all of the genes on the X.

22. Sex-Linked Punnett Squares
The Problem – Color blindness is a sex-linked recessive trait. Normal vision is dominant. Cross a heterozygous woman with a man who has normal vision.
Step 1 – assign letters to the trait
B – normal b – color blind

23. Sex-Linked Punnett Squares
Step 2 – add genes to Mom and Dad’s X chromosomes
Mom Dad
XBXb XBY

24. Sex-Linked Punnett Squares
Now, add Mom and Dad’s genes to the chart.

25. Sex-Linked Punnett Squares
Finally, fill in the squares on the chart.

26. Pedigree Charts
Pedigrees show the occurrence of specific genetic traits in a family.
Each generation is designated by a Roman numeral
Females are circles and males are squares
When possible, the oldest person in a generation goes on the left. As you go to the right, the people should get younger.

27. Pedigree Charts
In the chart below, the man and woman are connected by a horizontal line. This means they are married.

28. Pedigree Charts
The vertical line dropping from the marriage line indicates children being born.

29. Pedigree Charts
Marriages in generation II are shown below. A first marriage is always shown to the left, the second to the right.

30. Pedigree Charts
Children are then added and generation III is formed. Note how twins are shown.

31. Pedigree Charts
People with the recessive trait are shaded and a key is added to explain the traits.

32. Pedigree Charts
Finally, genotypes are added to the chart.

33. Genetic Mutations
Sometimes errors in mitosis or meiosis cause genetic abnormalities.

34. Non-Disjunction
Daughter cells are made with the wrong number of chromosomes.
Chromosomes don’t separate properly in mitosis or meiosis.
Meiosis daughter cells don’t function and mitosis daughter cells may lead to cancer.

35. Non-Disjunction

36. Duplication A chromosome ends up with an extra copy of a gene.
Several types of replication errors can cause this.

37. Translocation Rearrangement of parts of non-homologous chromosomes.
Depending on the
cells affected, it can
cause cancer or
infertility.

38. Deletion Part of a chromosome is lost during replication.
Can cause diseases, male infertility and death.

39. Frameshift Error
A mutation made by inserting or deleting nucleotides from a DNA strand, not in multiples of 3.
Results in the wrong amino acids being made in a protein.
There are two types, deletions (deleting nucleotides) and insertions (inserting them).

40. Frameshift Errors

41. Inversion A segment of a chromosome is reversed end to end.
There are no known affects, but it is suspected that they may cause a risk for infertility or miscarriage.