Huntington’s Disease!

Hamza KhanJeremy Tague

Period 2January 29, 2010

Summary of Huntington’s Disease

Overview and Symptoms:– Occurs from the genetically programmed

degeneration of nerve cells– Causes uncontrolled movement, lose of

intellectual faculties, and emotional disturbance

Interesting Facts:– No family history found in 1-3% of people

with Huntington’s Disease– HG will definitely affect your life if one is

inherited with the HG gene.

Location

• Located in the Autosomal Chromosome

• Not a Sex Chromosome (Not X-Linked)

• Localized on the 4th Autosomal chromosome pair. Chromosome #4

• Located in every chromosome except for sex chromosomes

Mode of Inheritance

• Inherited disease (Autosomal Dominant)

• From parent to child• Each child has 50% chance of inheriting the disease

• If child does not develop disease they cannot pass it on to later generation.

Alleles• Each person has 2 alleles per gene.• We represent dominant alleles by a

capital letter• We represent recessive alleles by a small

letter• HH means they have 2 bad genes• Hh means they have 1 bad gene, and 1

good gene• hh means they have 2 good genes

Punnett Squares

• Ratio of the chance of offspring inheriting Huntington’s Disease; ratio determined by parents

• Each punnett square represents the chances PER CHILD

Hh hhHh hh

H h

h

h

MotherFather

HH HhHh hh

H h

H

h

heterozygous dominant

homozygous recessive

homozygous dominant

Probability Using Ratios and Percentages

• Ratios:– Must equal 4; 4 possibilities– Ratio is lined up in this format:

Homozygous dominant : heterozygous dominant : homozygous recessiveex: 1 : 2 : 1ex: 1HH : 2Hh : 1hh

• Percentages:– Must equal 100; each possibility equals

25%– Put percentages into the ratioex: 25% : 50% : 25%ex: 25%HH : 50%Hh : 25%hh

HH HhHh hh

H hH

hPercentages Pie Chart

What Do These Letters Mean?!

• H= dominant allele Huntington’s Disease; h=recessive allele no Huntington’s Disease

• Phenotype – what you seeHH= Huntinton’s Disease is present

Hh= Huntington’s Disease is present ( also there is a no Huntington’s Disease carrier)

hh= no Huntington’s Disease

• Genotype – what is in the genesHH= Homozygous dominant(Huntington’s

Disease)Hh= Heterozygous dominant(Huntington’s

Disease)hh= Homozygous recessive(no Huntington’s

Disease)

Genotype and Phenotype Probability

• Phenotype:– Ratios:

• 3 HH: 1 no HH

– Percentages:• 75% HH: 25% no HH

• Genotype:– Ratios:

• 1HH : 2Hh : 1hh

– Percentages:• 25%HH : 50%Hh :

25%hh

HH Hh

Hh hh

H h

H

h

Student Practice

Phenotype:Ratio:

Percentage:

Genotype:Ratio:

Percentage:

H H

H

h

HH HH

Hh Hh

4 HH: 0 no HH 100% HH :0% no HH

2HH : 2Hh

50%HH: 50%Hh

PedigreeCircle: Male

Square: Female

All Blue: Homozygous Recessive. No bad gene. Person has no disease

All Green: Homozygous Dominant. Two bad genes. Person has the disease

Blue/Green: Heterozygous Dominant. 1 bad gene and 1 good gene. Person carries the bad gene and can pass it one, but is not infected.

STUDENT PRACTICE!• Circle: Male• Square: Female:• Red:

• White:

• Red/White:

Homozygous Recessive

Homozygous Dominant

Heterozygous DominantQUESTIONS!

1. What do you call a half white/half red gene?

2. What genes must the parents have in order for a child to be homozygous Recessive?

3. What are all the possibilities of children can two Homozygous Dominant parents have?