Chapter 9: Patterns of inheritance

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Chapter 9 Patterns of inheritance
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• Discuss pictures of family members

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OBJECTIVES

• Be able to define various terms relating to
  Mendelian genetics
• Know the basic principles of Mendelian genetics
• Understand exceptions to Mendels theories
• Know how to do Punnett square problems

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Mendelian Genetics

• Gregor Mendel
• Studied genetic patterns in peas and flowers
• Principle of segregation
• Alleles separate during gamete formation
• Independent assortment
• Each pair of alleles segregate during gamete
  formation
• Genes are not linked

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Exceptions to Mendels theories

• There may be more than two alleles for a gene
• A single gene can affect many phenotypic
  characteristics
• A single characteristic may be influenced by many
  genes
• Some genes are linked
• Crossing over produces new combination of alleles

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Different terms

• P generation Parental generation
• F1 generation
• offspring of the first cross
• Result of crossing the parents
• F2 generation
• Offspring produced from crossing the F1
  generation
• Punnett Square
• Used to determine the different genotypes of the
  crosses

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More terms

• Alleles alternative forms of a gene
• Homozygous when the two genes have the same
  allele
• Heterozygous when the two genes have different
  alleles

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More terms

• Dominant the trait is expressed with only one
  allele
• Recessive need two alleles for a gene for the
  trait to be expressed
• Phenotype an organisms expressed or physical
  traits
• Genotype genetic makeup, what genes it has

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Example of Punnett Squares
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Some traits are genetically inherited

• What are some examples?

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Some diseases are caused by a mutation in a
single gene

• Recessive diseases
• You need two copies of the gene to get the
  disease
• Cystic Fibrosis
• Sickle Cell Anemia
• Tay-sachs disease
• Dominant disease
• You only need one mutated copy to get the disease
• Huntingtons disease

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Fetal testing can detect many inherited disorders
early in pregnancy

• Amniocentesis
• Take amniotic fluid surrounding the fetus
• Chronic Villus Sampling
• Take tissue from the fetus
• Ultrasound
• produce a picture of the fetus
• Alpha fetal protein in the blood
• results from Downs Syndrome or neural tube
  defects

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Many genes have more than two alleles in the
population

• Codominance more than one allele can be dominant

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Blood types
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A single gene may affect many phenotypes
pleiotropy
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A single characteristic can be influenced by many
genes polygenic inheritance

• Examples skin color, height

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Genetic testing can detect disease-causing alleles

• Prenatal testing for genetic disorders
• Tay-Sachs disease
• Carrier testing
• determine if you carry the recessive allele that
  could be passed on to your offspring
• You need to produce children with someone who
  also carries the allele
• New borne screening
• Can detect disease after baby is born and start
  treatment
• PKU

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Questions about the use of genetics?

• If you know that you or the fetus has a disease,
  what will you do then?
• What are the capabilities of science? Would you
  want to use these capabilities?
• In vitro fertilization and preimplantation
  genetic diagnosis
• Should technology be used to help infertile
  couples, to prevent diseases or should it also be
  used to pass on desired traits?

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Predictive testing

• Determine if you are at risk for developing a
  disease
• Examples
• Breast cancer BRCA1, BRCA2
• Huntingtons disease
• Why would you want or not want to be tested?

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Genes on the same chromosome tend to be inherited
together

• linkage
• if genes are on the same chromosome, they tend to
  be inherited together

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Crossing over produces new combinations of alleles
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Chromosomes determine your sex

• Males - XY
• Females XX
• Sex chromosomes also contain genes for other
  characteristics besides what sex you will be

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Sex linked disorders affect mostly males

• Hemophilia
• Color blindness
• Duchenne Muscular Dystrophy
• X- linked recessive diseases
• If males get one abnormal X with the gene, they
  will get the disease
• Females need two abnormal Xs to get the disease
• Punnett square for X-linked or sex linke ddiseases

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Punnett square for two genes

• Discuss what to do for 2 genes