Pedigree Analysis

7.4 Human Genetics and Pedigrees

KEY CONCEPT

A combination of methods is used to study human
genetics.

7.4 Human Genetics and Pedigrees

• Human genetics follows the patterns seen in other

organisms.

• The basic principles of genetics are the same in all sexually

reproducing organisms.
– Inheritance of many human

traits is complex.

– Single-gene traits are

important in understanding
human genetics.

7.4 Human Genetics and Pedigrees

• Females can carry sex-linked genetic disorders.

• Males (XY) express all of their sex linked genes.
• Expression of the disorder depends on which parent carries

the allele and the sex of the child.

X

Y

What is a Pedigree?

• A chart that shows how a trait is inherited

within a family over several
generations.

• Each generation is represented by Roman

numerals and each individual in each
generation is numbered left to right.

• We can use a pedigree chart and key to

determine the genotype and phenotype
of the family members and the genetic
inheritance patterns of traits can be
tracked.

• ​Pedigree charts are a way of showing inheritance patterns over a number of generations.

• They are often used to study the inheritance of genetic disorders.

• Individuals are identified by their generation number and their order number in that generation.

• For example, II-6 is the sixth person in the second row.

• If the chart on the right were illustrating a human family tree, it would represent three generations:

  • grandparents (1-1 and I-2) with three sons and one daughter.

  • Two of the sons (I1-3 and II-4) are identical twins, but did not marry or have any children.

  • The other son (I1-1) married and had a daughter and another child (sex unknown).

  • The daughter (Il-5) married and had two sons and two daughters (plus a child that died in infancy).

• For the particular trait being studied, the grandfather was expressing the phenotype (showing the trait) and the grandmother was a carrier.

• One of their sons and one of their daughters also show the trait, together with one of their granddaughters.

Multiple Choice

What is this?

• Pedigree

• Karyotype

• Venn diagram

• Punnett Square

Symbols Used in Pedigrees

•Circles represent females
•Squares represent male
•Horizontal lines represents mating/marriage
•Vertical lines represents children

• Unshaded represents unaffected individuals

• Fully Shaded represents affected individuals

• Half-shaded represents carriers

Parts of a
Pedigree

Unaffected

Female

Unaffected

Male

Mating

Offspring

Affected
female
offspring

Unaffected

male offspring

Multiple Choice

What does a filled in square represent?

• Not affected Female

• Not affected Male

• Affected Male

• Affected Female

Multiple Choice

How many generations are shown in this pedigree?

• 1

• 2

• 3

• 4

Multiple Choice

What does an open circle represent?

• Not Affected Male

• Not Affected Female

• Affected Male

• Affected Female

Multiple Choice

How many kids did the mother and father from the first generation have?

• 2

• 4

• 5

• 6

7.4 Human Genetics and Pedigrees

• A pedigree is a chart for tracing genes in a family.

• Phenotypes are used to infer genotypes on a pedigree.
• Autosomal genes show different patterns on a pedigree

than sex-linked genes.

7.4 Human Genetics and Pedigrees

• If the phenotype is more common in males, the gene is

likely sex-linked.

Multiple Choice

What is the pattern of inheritance shown in this pedigree?

• autosomal dominant

• autosomal recessive

• sex-linked dominant

• sex-linked recessive

Multiple Choice

Analyze the following pedigree. What type of inheritance pattern is shown?

• autosomal dominant

• autosomal recessive

• sex-linked dominant

• sex-linked recessive

Multiple Choice

For the pedigree below, shaded symbols represent afflicted people. Males are squares; females are circles. If the trait is a sex-linked trait carried on the X chromosome, what is true about the mother represented by circle 1?

• She has the genotype XXY.

• She has two alleles for the disorder.

• She is a carrier for the disorder.

• She has no alleles for the disorder.

Multiple Choice

The trait in pedigree in Figure 14–5 has two alleles: P (dominant) and p (recessive). The black symbols show the dominant phenotype, and the white symbols show the recessive phenotype. What is the genotype of individual number 1?

• Pp

• P

• p

• PP

Multiple Choice

How many generations are shown in the pedigree below?

• 2

• 4

• 6

• 8

7.4 Human Genetics and Pedigrees

• Several methods help map human chromosomes.

• A karyotype is a picture of all chromosomes in a cell.

X Y

7.4 Human Genetics and Pedigrees

• Karyotypes can show changes in chromosomes.

– deletion of part of a chromosome or loss of a

chromosome

– large changes in chromosomes
– extra chromosomes or duplication of part of a

chromosome

Multiple Choice

Examine the pedigree below. Identify the type of inheritance pattern shown in the pedigree.

• Autosomal dominant

• Autosomal recessive

• X-linked recessive

• X-linked dominant

Multiple Choice

In the diagram, individual III-3 indicates

• a female with no freckles

• a male with no freckles

• a male with freckles

• a female with freckles

Multiple Choice

In the diagram, individual II-1 indicates

• a female with no freckles

• a male with no freckles

• a male with freckles

• a female with freckles

Multiple Choice

What is the Genotype of individual I-1?

• FF

• Ff

• ff

• Can't know for sure

Multiple Choice

What is the Genotype of individual II-6?

• FF

• Ff

• ff

• Can't know for sure

Multiple Choice

What is the Genotype of individual III-2?

• FF

• Ff

• ff

• Can't know for sure