1. PEDIGREES
AP Biology
Ms. Gaynor

2. The Study of Human Genetics Continues to Advance…
Can’t use humans
We use pedigrees
A family tree
describes the interrelationships of parents and children across generations
used to make genetic predictions about future offspring

3. Inheritance patterns of particular traits can be traced and described using pedigreesWw ww WW or
First generation
(grandparents)
Second generation
(parents plus aunts
and uncles)
Third
generation
(two sisters) Ff ff
FF or Ff FF
Widow’s peak
No Widow’s peak
Attached earlobe
Free earlobe
(a) Dominant trait (widow’s peak)
(b) Recessive trait (attached earlobe)
Figure A, B

5. GENERATIONS

6. Example of Pedigree Charts
Is it Autosomal or X-linked?
Take a minute and try to decide if this slide is autosomal or X-linked.

7. Is it Autosomal or X-linked?

8. Recessively Inherited Disorders
Many genetic disorders are inherited in a recessive manner
Need 2 recessive alleles (ex: ff)
Some people are carriers
heterozygotes, who carry recessive allele but are show “normal” phenotype
Can pass down recessive allele to offspring

9. HUMAN DISORDERS

10. recessive autosomal disorder
Cystic Fibrosis (ff)
recessive autosomal disorder
Affect mostly Caucasians
Symptoms
Mucus buildup organs
Abnormal absorption of nutrients in small intestine

11. Sickle-Cell Disease (dd)
recessive autosomal disorder
Affects mostly African-Americans
Caused by point mutation in hemoglobin protein in red blood cells
Symptoms
Physical weakness
pain
organ damage/paralysis

12. Achondroplasia (Aa only)
Autosomal dominant
only need 1 dominant allele
In Achondroplasia…homozygous dominant embryos DIE in utero
AA’s CAN’T be born

13. Achondroplasia Genetic Problems
What chance does 2 parents w/ achondroplasia have of:
having a normal heighted child?
AA = ¼ Aa = ½ aa = ¼
AA die in utero so never born
So…1/3 chance of having “normal” height
Aa x Aa AA Aa aa
1/3
2/3

14. Achondroplasia Genetic Problems
What chance does 2 parents w/ achondroplasia have of:
having a child who
looks like them?
AA = ¼ Aa = ½ aa = ¼
AA die in utero so never born
So…2/3 chance
Aa x Aa AA Aa aa
1/3
2/3

15. Huntington’s Disease (HH or Hh)
Autosomal dominant
Huntington’s disease (HD)
degenerative disease of nervous system
No obvious phenotypic effects until about ~35 yo HD
Normal

16. Nondisjunction of sister chromatids in meiosis II
Figure 15.12a, b
Meiosis I
Nondisjunction
Meiosis II
Gametes
n + 1
n  1
n – 1
n –1 n
Number of chromosomes
Nondisjunction of homologous
chromosomes in meiosis I
Nondisjunction of sister
chromatids in meiosis II
(a)
(b)

17. Human Disorders Due to Chromosomal Alterations
Down syndrome
Is usually the result of an extra chromosome 21
trisomy 21

18. Klinefelter syndrome
a result of an extra chromosome in a male, producing XXY individuals
1/2000 live births

19. Turner syndrome
Is the result of monosomy X, producing an X0 karyotype
1/5000 live births
Only known monosomy in humans
Normal intelligence
Sterile