Todays Plan

1
Todays Plan

• Genetic Linkage
• Polygenic traits
• Probability
• Human Genetics
• Genetic testing
• Gene therapy

2
Linkage

• Two genes on the same chromosome are said to be
  linked.
  
• Linked genes also show distinctive patterns of
  inheritance

3
(No Transcript)
4
(No Transcript)
5
Polygenic traits

• Inherited traits that show a continuous
  distribution of phenotypes (e.g., height in
  humans, skin color in humans), are usually traits
  affected by alleles at many genes.
• Polygenic traits are common - simple one-locus
  traits (like Mendel studied) are relatively
  rare.
  
• Polygenic traits show continuous variation (bell
  curve) and unpredictable inheritance

6
A model for understanding inheritance of
polygenic traits
7
Probability Basics

• All probabilities can be expressed as a number
  between 0 (never happens) and 1 (happens always).
  P (heads) 0.5
  
• To find the probability of two independent events
  happening together, multiply the individual
  probabilities. P (three heads in a row) 0.5 x
  0.5 x 0.5 0.125 or 1/8
• If there are two or more ways to get to the same
  result, add the probability of each way. Example
  (dice)

8
Did Mendel cook his data?

• In peas the number of chromosomes is 2n 14
• Mendel studied exactly 7 traits
• Each of those traits is on a different
  chromosome
  
• Therefore, Mendel never had to explain the
  patterns you get with linked genes.
  
• What are the chances of picking seven traits, one
  each from seven chromosomes?
  

9
(No Transcript)
10
Human Genetic Diseases I

• Most genetic diseases are caused by recessive
  alleles on autosomes
  
• Harmful recessive alleles can persist if they are
  not too common, despite natural selection,
  because homozygous recessive individuals will be
  rare
• Examples
• Phenylketonuria or PKU
• Cystic fibrosis - 4 of whites are carriers
• Sickle-cell anemia - 10 of African-Americans are
  carriers
  

11
Probability and Human Genetics

• If one in 25 whites carries the defective allele
  that causes CF, then what is the chance that a
  given white child will have CF?
  
• If the defective allele that causes red-green
  colorblindness is on one out of every 100 human X
  chromosomes, what proportion of men will be
  colorblind? What proportion of women will be
  colorblind?

12
Human Genetic Diseases II

• Some rare genetic diseases are caused by dominant
  alleles - e.g., Huntingtons Disease
  
• Others (e.g., hemophilia) caused by sex-linked
  genes

13
Human Genetic Diseases III

• Chromosomal disorders cause some genetic
  diseases
  
• Aneuploidy - having the wrong number of
  chromosmes
  

14
(No Transcript)
15
(No Transcript)
16
(No Transcript)
17
(No Transcript)
18
Human Genetic Diseases II

• Chromosomal disorders cause some genetic
  diseases
  
• Aneuploidy - having the wrong number of
  chromosmes
  
• Effects of aneuploidies - table

19
(No Transcript)
20
Human Genetic Diseases II

• Chromosomal disorders cause some genetic
  diseases
  
• Aneuploidy - having the wrong number of
  chromosmes
  
• Effects of aneuploidies - table
• Causes of aneuploidies - homologous chromosomes
  fail to separate during the first meiotic division

21
(No Transcript)
22
1/12
1/32
1/110
1/365
1/1925
1/1205
1/885
23
Genetic testing

• During pregnancy
• Amnioscentesis
• Chorionic villus sampling
• Of adults
• For recessive traits (e.g., sickle cell)
• For dominant traits or other genes (e.g.,
  Huntingtons disease, BRCA1)

24
Genetic testing

• During pregnancy
• Amnioscentesis
• Chorionic villus sampling
• Of adults
• For recessive traits (e.g., sickle cell)
• For dominant traits or other genes (e.g.,
  Huntingtons disease, BRCA1)