Pedigrees

Visual Maps for Chromosome Inheritance

Please Do Now:

1.What are the three types of Mutations?

1.In your own words, describe a Karyotype. (Hint: Think back to Thursday/Friday’s Chromosome Lab). What are two uses for a Karyotype?

2.Explain why creating a visual “map” of genetic inheritance for a disease, that includes multiple generations would be useful.

There are 4 ways chromosomes can mutate and all of them are associated with human disorders.

A Closer Look at Chromosomal Mutations:

Chromosomes and InheritanceGenes (traits) are carried on chromosomes.

Knowledge of chromosome number and structure will affect future advances in basic genetics, human health, and evolution.

A normal human male karyotype.

Many Genetic Diseases are Autosomal Recessive Traits

An autosome is any chromosome other than an X or Y. sickled red

blood cell

normal red blood cell

Sickle cell anemia is a recessive autosomal disease common in areas where malaria is endemic.

Endemic means common to a certain area.

What Works in Peas (genetically speaking) Works in People

¼ of offspring of two carriers of a recessive allele are expected to show the recessive trait; ½ of offspring are expected to be carriers.

Many Human Traits are Autosomal Dominant Traits

For disease traits, autosomal dominant inheritance is far less common than autosomal recessive inheritance.

Pedigree Analysis is a Key Tool in Human Genetics

Analyzing a pedigree is like puzzle-building – you try things (assigning potential genotypes) until the pieces fit and you’re as certain as you can be about genotypes and how disorders are transmitted (autosomal vs. X-linked; dominant vs. recessive).

Pedigree ChartsMales =

Females =

Unaffected individuals= Empty

Carrier (not ill) = Half filled

Affected Individuals= Filled inDead individuals =

Pedigrees; Basic rules• Each generation is assigned a Roman numeral (I,

II, II, IV.), beginning with the earliest generation

• Individuals within generations are assigned Arabic numerals (1,2,3…) beginning with the left and moving to the right.

I

II

1 2

1 2 3 4 5

People who have children together are connectedby a horizontal line:

Their children are connected to them with a vertical line. Siblings are connected as shown.

Aa Aa

A aA

a

Patterns of dominant traits

• trait tends to appear each generation

• normal and affected individual expected to produce normal and affected children (approximate 1:1 ratio)– Affected individuals generally heterozygous if

it is a rare trait• Aa x aa ---> 1/2 Aa; 1/2 aa

Patterns of dominant traits

• at least one parent must be affected in order for children to be affected– Aa x aa

• normal parents will always produce normal offspring– aa x aa ---> aa

Autosomal dominant traitsAutosomal dominant traits There are few

autosomal dominant human diseases (why?), but some rare traits have this inheritance pattern

Only need to get the trait from one parent to be affected.

ex. ex. achondroplasia (a achondroplasia (a sketelal disorder sketelal disorder causing causing dwarfism)dwarfism)

A Pedigree of a Dominant Human Trait

Note that the trait appears in every generation and ½ the offspring of an affected heterozygote are expected to show the trait.

Patterns of recessive traits

• may appear to “skip” generations

• most children of normal and affected parents are normal– AA x aa ---> Aa

• all children of two affected parents will be affected– aa x aa ---> aa

Patterns of recessive traits

• normal parents may produce affected offspring– Aa x Aa ---> 3/4 normal; 1/4 affected

• affected children often result when parents are blood relatives

A Pedigree of a Recessive Human Trait

Note that the trait can appear in offspring of parents without the trait.

Heterozygotes who do not show the trait are termed carriers.

Amyotrophic lateral sclerosis (ALS)Lou Gehrig’s disease; Dominant – one gene is enough to give the disease.1/50,000 (?)

? It is a disease of the nerve cellsin the brain and spinal cord thataffects voluntary muscle movement.

Xeroderma pigmentosum (XP)inability to repair UV damage to DNA; skin tumors, death

Autosomal Dominant or recessive?

People with XPcan NOT be exposed to to any sunlight.

X-linked Inheritance – When Men and Woman Play by Different Rules

Behind the 8-ball? Colorblindness is an X-linked recessive trait.

X-linked Inheritance

There are many X-linked recessive traits.

Bellringer 3/11/14

1. In the pedigree above, how many generations are there?

2. What is the genotype of the two shaded shapes.3. Explain how the affected children were able to

inherit the disease, yet their parents did not.

The disease represented is an autosomal recessive disease called Tay-Sachs Disease.

T- normal t- Tay-Sachs Disease