1. Beyond Mendel… Mutations, Gene Linkage, Gene-Mapping, Sex Linkage,
Polygenic Traits,
Non-disjunction, disorders,
Prenatal Diagnosis,
Pedigree Analysis

2. Back to “Beyond Mendel”
Mutations
Definition
Mutations in Genes
Point Mutations
Frame-shift Mutations
Mutations in Chromosomes
Deletion
Duplication
Inversion
Translocation
Back to “Beyond Mendel”

3. Mutations
Definition: A change in the genetic material (DNA or RNA) of a cell
Somatic: If it occurs in body cells, it can’t be passed on to next generation
Germ-line: If it occurs in gametes, it can be passed on to next generation
Back to Mutations

4. Mutations in Genes
Point Mutation: Affects one nucleotide (One nucleotide is replaced by another)
- three types of point mutations
let’s look at one example…
Missense mutations: Code for a different A.A. (ex. sickle-cell anemia)
Nonsense mutations: Code for a stop codon
Silent mutations: Codes for same amino acid

5. Mutations in Genes
Frameshift Mutation: An insertion or deletion that shifts the reading frame
Example of Insertion: TA
Example of Deletion:
CGCATGGAATACC
TEF
THE H
FAT
ATC
CAT
ATA
TET
ATE
THE
HER
RAT AT
Back to Mutations T

6. Deletion: A segment of the chromosome is removed (not just
one nuclotide) A B C D E F G H A B C E F G H
2. Duplication: A segment of the chromosome is repeated A B C D E F G H A B C B C D E F G H
3. Inversion: A segment within a chromosome is reversed
4. Translocation: A segment from one chromosome moves to another, non-homologous one A B C D E F G H A D C B E F G H
Back to Mutations
Examples:
Deletion: Duchenne Muscular Dystrophy (on X chromosome)
Duplication: Huntington’s Disease (Chromosome 4)
Inversion & Translocation: Phenotypically normal, but increased risk of having gametes with abnormal numbers of chromosomes A B C D E F G H M N O C D E F G H M N O P Q R A B P Q R

7. Linked Genes
In flies, grey bodies (G) and normal-wing size (W) are dominant to black bodies (g) and small wing size (w).
In this cross will the F1 grey flies always have normal wings and will black flies always have small wings?

8. Actual Results WHY? 8.5% 8.5% 41.5% 41.5% 41.5% 41.5%
No! However, most of the F1 flies will have either a grey body and normal wings OR a black body with small wings, like their parents
Will the F1 grey flies always have normal wings and will black flies always have small wing sizes?

9. Back to “Beyond Mendel”
Linked Genes
The genes for body color and wing size are “linked”,meaning they are found on the same chromosome.
They will most likely be inherited together and will not undergo Mendel’s Law of
cross over segregates the linked genes g g G G
Independent Assortment W w W w
unless
Back to “Beyond Mendel”

10. Back to “Beyond Mendel”
Gene Mapping
Genes that are closer together on the same chromosome are less likely to cross over, therefore segregate.
Genes that are farther apart on the same chromosome are more likely to cross over and segregate
Genes that are on different chromosomes will always segregate independently
Grey Body
Black Body
Normal wings
Small wings
Back to “Beyond Mendel”

11. Sex-Linkage or (X-linked)
In fruit flies, (R) is the dominant gene for red eyes, and (r) is the recessive gene for white eyes. The gene is found on the “X” chromosome. This is considered X-linked.
Does the gene for eye color exist on the “Y” chromosome? Why or why not?
These are the X and Y chromosomes of a male fly. How is the Y chromosome different from the X? R r r XX XY
What would be the phenotype of this female fly?
What would be the phenotype of this male fly?

12. Sex-Linkage or (X-linked)
Watch this video to clarify your knowledge of sex-linked traits
When genes are sex-linked, we include the X and Y as part of their genotype. For example, the allele for red eye is not “R” but is written as XR. How would you write the allele for white eye? Xr

13. White board practice
What is the possible genotype(s) for this red-eye fly if it is a female?
What is the possible genotype for this red-eye fly if it is male?
Answer the above questions again for this fly.

14. White board practice
You work in a fruit fly lab and you cross a heterozygote red-eye female with a red-eye male. Predict the F1 offspring using a punnett square. What is the phenotypic ratio?

15. White board practice
Balding is a trait that can occur in females although it is rare. What genotype must a female be in order to be bald?
Why, then, is balding a trait more common in men then women?
Adult on-set male-pattern baldness is thought to be a sex-linked recessive trait.
Your dad is going bald and your mother complains that if you or your go bald the gene for baldness is your dad’s fault.
Use a Punnett square to prove to your mother that the gene would actually come from her side.

16. Sex-linked or X-linked
Time to reinforce your knowledge with a lab!
Back to “Beyond Mendel”

17. Polygenic Traits Definition: Traits controlled by two or more genes
Examples: Skin color, height

18. Back to “Beyond Mendel”
Polygenic Traits
Skin Color
Height
What about our height? Does it form the same pattern?
Activity: Let’s create a histograph of the height of all students in class!
Back to “Beyond Mendel”

19. Non-disjunction Disorders
Definition: When members of homologous chromosomes fail to separate during Meiosis I – or – when sister chromatids fail to separate during Meiosis II.
Examples: Down Syndrome, Turner’s syndrome, Klinefelter’s syndrome
Meiosis I
Meiosis II
Abnormal Gametes
Back to “Beyond Mendel”
Normal Gametes

20. Prenatal Diagnosis: Amniocentesis
1. Amniotic fluid withdrawn
Fetus (14 – 16 weeks)
2. Centrifuge
Fluid
Several weeks later
Fetal Cells
Placenta
3. Karyotype
Uterus
Cervix
Cell culture

21. Prenatal Diagnosis: Chorionic villus sampling (CVS)
1. Suction tube inserted through cervix
Fetus (8 – 10 weeks)
Fetal cells
Placenta
Chorionic villi
2. Karyotype
Several hours

22. Interpret these karyotypes
Sex:
Male

23. Interpret these karyotypes
Klinefelter’s syndrome

24. Interpret these karyotypes
Down Syndrome

25. Genetic Disorder Brochure Assignment
You will be assigned one of the following genetic disorders:
1) Color Blindness 2) Klinefelter’s syndrome
3) Cystic Fibrosis 4) Marfan’s Syndrome
5) Down’s Syndrome 6) Patou’s Syndrome
7) Duchenne Muscular Dystrophy 8) Phenylketonuria
9) Edward’s Syndrome 10) Sickle Cell Anemia
11)Fragile X Syndrome 12) Tay-Sachs Disease
13)Hemophilia 14) Turner’s Syndrome
15)Huntington’s Disease 16) Werner’s Syndrome
You will work alone on this project. If you have a disease that a classmate has, you may collaborate during research, but you must each create your own brochure and present it in a different way.
Be careful of plagiarism! Plagiarised projects will automatically a zero, possibly even a double zero score!

26. Generally: A genetic family tree
A Pedigree is…
Generally: A genetic family tree
Specifically: It is a chart of the genetic history of family over several generations.

27. Pedigree A = tongue roller a = can not roll tongue Aa ? aa ? ? ? ? aa
Can you figure out the rest of the genotypes on your own?
male
Mating couple
female
Shaded = trait being followed
Children/Siblings

28. Other Pedigree Symbols
Examples of connected symbols:
Fraternal twins
Identical twins

29. Other Pedigree Symbols
Affected
X-linked
Autosomal carrier
Deceased
Back to Overview

30. Interpreting a Pedigree Chart
Determine if the pedigree chart shows an autosomal or X-linked disease.
If most of the males in the pedigree are affected the disorder is .
If it is a 50/50 ratio between men and women the disorder is
X-linked
autosomal

31. Example of Pedigree Charts
Is it Autosomal or X-linked?

32. Answer
Autosomal

33. Interpreting a Pedigree Chart
Determine whether the disorder is dominant or recessive.
If the disorder is dominant, one of the parents must have the disorder.
If the disorder is recessive, neither parent has to have the disorder because they can be heterozygous.

34. Example of Pedigree Charts
Dominant or Recessive?

35. Answer
Dominant

36. Example of Pedigree Charts
Dominant or Recessive?

37. Answer
Recessive

38. Summary Pedigrees are family trees that explain your genetic history.
Pedigrees are used to find out the probability of a child having a disorder in a particular family.
To begin to interpret a pedigree, determine if the disease or condition is autosomal or X-linked and dominant or recessive.