Download HMH 7.4 notes - Deer Creek Schools

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.
Apply: Why can the genetics of
pea plants and fruit flies be applied
to humans?
Fig. 4.1 - The widow's peak, or pointed hairline, is a
phenotype produced by a dominant autosomal gene.
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.
• The X chromosome has about 1100 known genes, including many that
cause genetic disorders. The Y chromosome is about 1/3 the size of the
X and has only about 250 know genes.
Y
X
These X and Y chromosomes
are duplicated and
condensed. (color SEM;
magnification about 15,000X
Contrast: How can carriers differ between autosomal and sex-linked disorders?
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.
Tracing Autosomal Genes Figuring
out genotypes from phenotypes
requires you to use a process of
elimination. You can often
determine which genotypes are
possible, and which ones are not.
7.4 Human Genetics and Pedigrees
• If the phenotype is more common in males, the gene is likely
sex-linked.
Tracing Sex-Linked
Genes Figuring out genotypes from
phenotypes requires you to use a
process of elimination. You can
often determine which genotypes are
possible, and which ones are not.
7.4 Human Genetics and Pedigrees
Fig. 4.4 – Red-Green Colorblindness
• A person with normal color vision can easily distinguish between
different colors. A person who is red-green colorblind cannot.
Phenotype
Genotype
Phenotype
Genotype
Normal
Vision
XMXm or
XMXM or XMY
Red-green
colorblind
XmXm or XmY
7.4 Human Genetics and Pedigrees
Several methods help map human chromosomes.
• A karyotype is a picture of all chromosomes in a cell.
Fig. 4.5 - A
karyotype can
help show
chromosomal
disorders. This
is a normal
karyotype.
Interpret: Is this
karyotype of a male
or female? How do
you know?
XY
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
A karyotype can help show chromosomal disorders, such as the deletion
in chromosome 1. (LM; magnification 8000 X)
7.4 Human Genetics and Pedigrees
A karyotype can help show chromosomal disorders, such as
the extra chromosome 21 in Down syndrome. (colored LM;
magnification 11,000 X)