UNIT 7 DAY 6

Pedigrees

TODAY’S PROBLEM What information does a family tree show?

Answer what do you think in 1 – 2 sentences

REVIEW: WHAT ARE THE TYPES OF CHROMOSOMES?

Karyotype pictureAutosomal: Chromosomes 1-22

Sex: X and Y chromosomes, determine whether a person is a male or female

KP1: WHAT ARE GENETIC DISORDERS?

Genetic disorders are diseases caused by mutations in DNA in gametes

These disorders are passed down from parent to child

Different disorders have different modes of inheritance

KP2: WHAT ARE MODES OF INHERITANCE?

The way something is passed down from parent to offspring

There are three main modes of inheritance

1. Autosomal dominant—only need one copy of a gene to be affected

2. Autosomal recessive—need two copies of the gene to be affected

3. Sex-linked recessive—gene is on the X chromosome, need 2 copies to be affected (UNLESS MALE—only need 1, b/c only have 1 X chromosome)

CHECK

What mode of inheritance is this showing???

KP3: WHAT IS A PEDIGREE AND HOW DO I INTERPRET IT?

A Pedigree is a chart or family tree that traces the inheritance of a trait.

Females are always circles, males are always squares Half-shaded = carrier of gene

(but not affected) Solid shaded = affected

Each horizontal line represents a generation.

Children will always appear on a line directly below their parents.

CHECK

Circle a carrier Square a male Star an affected person

KP4: HOW CAN I USE A PEDIGREE TO DETERMINE MODES OF INHERITANCE?

You can use clues in the pedigree to determine mode of inheritance

1. If… Autosomal dominant All generations affected, no carriers! Equal number of males and females affected

2. If… Autosomal recessive Generations are skipped Equal number of males and females affected

3. If… Sex-linked recessive Generations are skipped Female carriers only More males are affected

KP5: WHAT ARE THE STEPS TO SOLVE A PEDIGREE PROBLEM?

Step 1: Are generations skipped? Yes=recessive, No=dominant

Step 2: Are there carriers? Yes=recessive, No=dominant

Step 3: If “Yes=recessive”

Are more men affected? Yes=sex-linked, No=autosomal

Are there only female carriers? Yes=sex-linked, no=autosomal

KP6: HOW DO I PREDICT THE GENOTYPE OF INDIVIDUALS IN A PEDIGREE? Determine mode of inheritance shown in

pedigree Determine genotype options (BB, bb, or

Bbcarrier) Use children as clues

EXAMPLE

What is the mode of inheritance ? What are my options? Are generations skipped? Are there carriers? Are more men affected? Are there only female carriers?

?

SEX-LINKED RECESSIVE!