Chapter Four

Modern Genetics

Lesson 4-1

Human Inheritance

Human Inheritance

• You already know, many traits are controlled by a single gene with one dominant allele and one recessive allele.– Example: Hairline- dominant allele is the

widows peak, and the recessive allele is for straight hair.

Human Inheritance

• Some human traits are controlled by a single gene that has more than two alleles – these are called multiple alleles – three or more forms of a gene that code for a single trait.– Example: Blood Type – there are four main

blood types: A, B, AB, and O.

Human Inheritance

• Some human traits show a large number of phenotypes because the traits are controlled by many genes. The genes act together as a group to produce a single trait.– Height and skin color are both examples of

human traits controlled by many genes.

Human Inheritance

• The effects of genes are often altered by the environment – the organisms surroundings.– People’s diet can affect their height.– Climates that are tropical and hot have

organisms with darker skin.

Human Inheritance

• Your sex is controlled by your chromosomes.– If you are female, you have two X

chromosomes.– If you are male, you have one X chromosome,

and one Y chromosome.

*Whether you inherited an X or Y chromosome, is determined by your father.

Human Inheritance

• Genes on the X and Y Chromosomes are often called sex-linked traits.

4-2 – Human Genetic Disorders

• A genetic disorder is an abnormal condition that a person inherits through genes (via chromosomes).– These disorders are caused by mutations – or a

change in a person’s DNA.• Example: Cystic Fibrosis – a thick mucus in the

lungs and intestines . This allele is recessive.

Look-up in your book:

• Look up in your book and tell what the disease is and how it is passed to the next generation – recessive/dominant.– Sickle Cell -– Hemophilia –– Huntington’s Disease -– Down Syndrome -

Sickle Cell

• Is a genetic disorder that affects the blood due to a lack of oxygen. The allele for sickle cell is co-dominant.

Hemophilia

• Hemophilia is the genetic disorder in which a person’s blood clots very slow or not at all. The genetic allele for hemophilia is recessive on the X chromosome-sex linked genetic disorder.

Huntington’s Disease

• Is the example of genetic disorder that is caused by a dominant allele. It is a gradual break down of the cells in your brain and it is fatal.

Down Syndrome

• Due to an extra copy of chromosome 21 down syndrome appears. This is due to a failure of chromosome 21 dividing during meiosis.

Genetic Tools

• Amniocentesis: collection of chromosomes from the placenta fluid. From the fluid, a karyotype (picture) of all the chromosomes is put together. Karyotype is a picture of all the chromosomes in a cell, arranged in pairs.

• Some disorders can be corrected, if found while the baby is in the womb, such as spina-bifida.

4-3 Advances in Genetics

• Three methods that people have used to develop organisms with desirable traits are:

1. Selective breeding: An example would be cows – which cows produce more milk that is most resistant to disease?

• Inbreeding: crossing two organisms that have identical or similar genes. Breeding race horses. Inbreeding leads to a high percentage of genetic disorders.

4-3

• Hybridization: cross 2 genetically different individuals – but in the attempt to produce the best traits from both parents.

–Example: Corn that produces many kernels with resistance to disease.

4-3

2. Cloning: An organism that is genetically identical to the organism from which it was produces.3. Genetic Engineering: genes from one organism are transferred into the DNA of another organism. This is used to cure genetic disorders.

a. Gene Therapy is an experimental method for treating genetic disorders during gene therapy, working copies of a gene are inserted directly into the cells of a person with the genetic disorder.

4-3

• DNA: No two people, except identical twins have the same DNA.– DNA testing is used to identify people: skin,

hair, and blood.

4-3

A genome is all the DNA in one cell of an organism.

DNA Project: THE HUMAN GENOME PROJECT: the goal is to identify the DNA sequence of every gene in the human genome.

We can learn what makes the body work and what causes things to go wrong.