Download Single Genes With Multiple Alleles The Sex Chromosomes Traits

Human Inheritance
Chapter 6, Section 1
Pages 192-198
Patterns of Human Inheritance
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Some traits are controlled by single genes with two alleles
Others by single genes with multiple alleles
Others controlled by many genes that act together
Single Genes With Two Alleles
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Several traits are controlled by a single gene with one dominant allele and one recessive allele
These trails have distinctively different phenotypes, or physical appearances
Traits Controlled by Many Genes
Single Genes With Multiple
Alleles
Multiple alleles are genes with three or more forms of a gene that code for a single trait
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Even though a gene may have multiple alleles, a person can carry only two of those alleles
Because chromosomes exist in pairs carrying only one allele for each gene
The Sex Chromosomes
Sex chromosomes are one of the 23 pairs of chromosomes in each body cell
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Carry genes that determine whether a person is male or female.
Carry genes that determine other traits.
Traits Controlled by Many Genes
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Some human traits show a large number of phenotypes because the traits are controlled by genes
Genes act together as a group to produce a single trait
Four genes control height in humans
Eyes, skin, hair color controlled by multiple genes
Girl or Boy?
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Sex chromosomes that do not always match
Girt =xx (matches)
Boy = XY (doesn't match)
Sex Chromosomes and Fertilization
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All female eggs carry X chromosomes
Half of the male's sperm carry Y chromosomes and the other carry X chromosomes
Female (X) + Male M = XY (male)
Female (X) + Male (X) = XX (female)
Inheritance of Colorblindness
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Controlled by recessive allele on X chromosome
More males than females have colorblindness but females carry recessive gene.
Carrier is a person who has one recessive allele for a trait and one dominant allele.
Only females can be carriers
Sex-Linked Genes
Sex-linked genes are on X and Y chromosomes because alleles are passed from parent to child on sex chromosomes
Traits controlled by sex-linked genes are called sex-linked traits
Most of the genes on the X chromosomes are not on the Y chromosome; therefore not all genders have the same traits
The Effect of Environment
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Many of an organism's characteristics are determined by an interaction between genes and the environment
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Diets can affect predetermined height
Skills can improve hand-eye coordination
Human Genetic Disorders
Chapter 6, Section 2
Page 199-203
Genetic Disorder
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An abnormal condition that a person inherits through genes or chromosomes
Causes of Genetic Disorders
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Some genetic disorders are caused by changes in DNA of genes
Other disorders are caused by changes in the overall structure or number of chromosomes
Cystic Fibrosis
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Body produces abnormally thick mucus in lungs and intestines affecting breathing
Caused by recessive allele on one chromosome
Result of a mutation in which three bases are removed from DNA molecule
Sickle-Cell Disease
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Affects hemoglobin, a protein in red blood cells that carries oxygen.
Cells change shape and clog vessels preventing oxygen exchange
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Allele is codominant with normal allele
A person with two sickle-cell alleles will have disease
A person with one normal and one sickle-cell allele will produce both types of cells but no symptoms
Down Syndrome
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Cells have an extra copy of the chromosome 21, a total of three
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Occurs when chromosomes fail to separate during meiosis
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Causes mental retardation
Hemophilia
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Sex-linked disorder in which a person's blood clots very slowly or not at all
Caused by a recessive allele on the X chromosome
Pedigrees
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One important tool that geneticists use to trace the inheritance of traits in humans is a pedigree.
A pedigree is a chart or "family tree" that tracks which members of a family have a particular trait.
Managing Genetic Disorders
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Today, doctors use tools such as karyotypes to help diagnose genetic disorders
People with genetic disorders are helped through medical care, education, job training, and other methods
Genetic Counseling
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Help couples understand their chances of having a child with a particular genetic disorder
Counselors use tools such as karyotypes, pedigree charts, Punnett squares
Karyotypes
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Doctors uses a karyotype to examine the chromosomes
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Karyotype is a picture of all the chromosomes in a cell
Arranged in pairs
Dealing With Genetic Disorders
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Education and job training assist individuals with disorders to live a productive life