1. Karyotypes

2. Human Chromosomes
Karyotype – a picture of arranged chromosomes. The picture is created by photographing the cell during mitosis and then “cutting and pasting” the chromosomes from the photograph.
Humans have a total of 46 chromosomes. 44 autosomes and 2 sex chromosomes
If you are female, biologists will write it as 46XX, male 46XY.

3. Sex-Linked vs. Autosomal
Autosomal traits are those found on any chromosome other than the sex chromosomes (#’s 1-22 in humans).
Sex-Linked traits are those carried on the sex chromosomes.
Most are carried on the X chromosome
Sex Linked Disorders are less common in women since they have 2 X chromosomes.

4. Karyotype

5. Remember Back…
Disorders can be caused by mutations, which are changes to the normal order of DNA bases (A,T,C,G)
However, not all disorders are caused by point and frameshift mutations.

6. Chromosomal Disorders
Humans should have 23 pairs of homologous chromosomes (one from mom and one from dad)
Some disorders occur based on an improper number of chromosomes. These errors occur during meiosis and are known as nondisjunction.

7. Non Disjunction
candy animation
Nondisjunction is the improper separation of chromosomes during meiosis.

8. EXAMPLES

9. Down Syndrome
Trisomy 21       
Most often, Down syndrome results in three copies of chromosome due to nondisjunction during meiosis.
Chances of a woman having Down syndrome child increase with age.
Down syndrome children have a tendency for leukemia, cataracts, faster aging, and mental retardation.

10. Patau Syndrome Trisomy 13
Eye, brain, circulatory defects and cleft palate
Rarely live past 1 year old (More than 80% die in first year.)
Caused by a nondisjunction

11. Edward’s Syndrome Trisomy 18 80% of affected are female.
Defects in every organ
Rarely live past one year, most die within the first month
Caused by nondisjunction

12. Klinefelter’s Syndrome
Males have one Y chromosome and two or more X chromosomes.
Many do NOT have obvious symptoms. Usually not diagnosed until puberty
Other affected individuals are sterile males; testes and prostate are underdeveloped. Can have language and learning problems.
Individuals have large hands and feet and long arms and legs.

13. Jacob Syndrome
XYY males with Jacob syndrome have two Y chromosomes instead of one.
Results from nondisjunction during meiosis II.
Usually taller than average; suffer from persistent acne; tend to have lower intelligence.         

14. Other Chromosomal Disorders
Another type of chromosomal disorder is chromosome translocation.
This is when the chromosome abnormality is caused by the rearrangement of large sections between nonhomologous chromosomes.
This often results in different cancers.

15. Pedigree Charts
Intro to Pedigree Link

16. Using Pedigrees to study Human Traits
A pedigree is a chart that can be used to study how a trait is passed from one generation to the next.
A pedigree is like a family tree, with genetic information added to it.
A pedigree chart shows the relationship within a family of a single trait.
A pedigree shows you each family member’s PHENOTYPE and then you can infer the genotypes of family members based on when and how a trait is passed from one generation to the next.

17. Pedigree Chart Generation symbols Marriage line
unshaded box = unaffected does not have the condition
Children line
Shaded box = affected (has the condition)
Square = Boy
Circle = Girl

18. Carriers
Child 2 from the 3rd generation has the recessive condition. His parents are not shaded, so where did the condition come from??? aa

19. Carriers
We know that the parents of the child must be carriers (heterozygotes) of the condition.
Since they are un-shaded they do not have the trait.
However, since they produced an offspring with the trait, that tells us they have the recessive allele and passed it on. Aa Aa aa

20. Carriers
Sometimes, but not often you might see carriers as half shaded on a pedigree.

21. Types of Pedigree Charts
Autosomal Dominant
Autosomal Recessive
Sex Linked

22. Autosomal Dominant
A dominant allele carried on any chromosome except for the sex chromosomes.
Only one copy is needed for expression
Not necessarily common
Skipped generations less common
Ex. Huntington’s Disease

23. Autosomal Recessive
A recessive allele carried on any chromosome except for the sex chromosomes.
Two copies are needed for expression
Skipped generations more common
Parents are either affected or carriers
Ex. Cystic Fibrosis

24. Sex Linked
a disorder resulting from a mutation in a gene on a sex chromosome, usually the X chromosome
Males much more affected
Females can be unaffected carriers
Ex. Hemophilia

25. Colorblindness – A Case Study of Mr. Martin

26. Colorblindness Sex-linked recessive (occurs more often in males)
Affected people cannot distinguish between certain colors
Normally, red and green appear as browns
Mr. Martin is colorblind.
(His mother gave him a genetic disease)

27. Colorblind Test Plates

31. A Pedigree of Mr. Martin’s Family Trait: Colorblind

32. Who has the full-blown colorblindness?

34. Who carries the gene for colorblindness, but is not colorblind themselves?

36. seX-linked traits
The colorblind gene is on the X chromosome. Here are to 2 options for males:
XY = not colorblind (X is healthy)
X’Y = colorblind (X is affected)
Since there is no other X chromosome to counteract the defective X, the boy is colorblind.

37. seX-linked traits
The colorblind gene is on the X chromosome. Here are to 3 options for females:
XX = not colorblind (both Xs are healthy)
XX’ = “carrier” but not colorblind (one X is affected, the other is healthy)
X’X’ = colorblind (both Xs are affected)

38. Now lets fill in the genotypes for the family pedigree.

39. XY XX
X’Y
XX?
X’Y
XX’
X?Y XX
X’Y XX
X’Y
X?XI
XX’
XX’
XX’

40. Follow up questions…
3. Why is Lanny’s (III-3) genotype X?Y? (Note: He died when he was 49 years old.)
4. Why is Bambi’s (IV-1) genotype X?XI?
5. Without genetic testing, what is one way that we might know Bambi’s genotype?
6. If a female is colorblind, what 2 things must be true of her parent’s genotypes for this gene?