Chapter 14 The Human Genome Pg. 341

Section 14-1 Human Heredity In order to learn more about humans, scientists started looking at our chromosomes. A Chromosome is tightly coiled DNA that becomes visible under a microscope during mitosis (cell division).

Karyotypes Analyzing chromosomes Photograph cells during mitosis (when chromosomes are easy to see). Cut out the picture of the chromosomes Group them together in pairs. This picture of precisely organized chromosomes is called a karyotype.

Karyotypes Allows us to see homologous chromosomes, sex chromosomes, and autosomes.

Humans Humans have 46 chromosomes in a typical body cell. Sperm cells have 23 and egg cells have 23 so when they combine the fertilized egg has a complete set of chromosomes. Sex Chromosomes: determine a persons gender (2). Females = XX Males = XY (the Y chromosome is much smaller than an X) Autosomes: all chromosomes except the sex chromosomes (44) http://en.wikipedia.org/wiki/List_of_organisms_by_chromosome_count

How to write it out! Is this a girl or boy? To write out their karyotype scientists use the following method. Write the total # of chromosomes. 46 Write out the sex chromosome combination XX or XY This example is 46,XY

Try this one!

Did you get… 47, XX +21 There were 47 chromosomes in this karyotype. There were 2 X chromosomes making this person a ……. Now we need to indicate where the extra chromosome was so we do that with a + since it was extra and a 21 to indicate where the extra chromosome was found.

Boy or Girl? Females carry two X chromosomes = XX This means that all human egg cells should carry a single X chromosome (23,X) Males carry one X and one Y = XY Half of all sperm cells should carry an X chromosome (23, X) The other half should carry a Y chromosome (23,Y) These factors ensure that the just about half of all offspring should be 46,XX and half 46,XY. See Punnett Square on pg. 342.

Human Traits Pedigree charts show relationships within a family and are used to determine if a trait is inherited rather than a result of environmental influences.

Circles Represent females Squares Represent Males Genetic counselors use pedigree charts to infer genotypes of family members. Circles Represent females Squares Represent Males See example on pg. 342

The Addiction Gene?? Biological differences that may make someone more or less vulnerable to addiction. It may be harder for people with certain genes to quit once they start or they may experience more severe withdrawal symptoms if they try to quit. Factors that make it harder to become addicted also may be genetic. For example, an individual may feel sick from a drug that makes other people feel good. But someone's genetic makeup will never doom them to inevitably become an addict. Remember, environment makes up a large part of addiction risk. http://learn.genetics.utah.edu/content/addiction/pi/

Genes and the Environment Some human traits are almost impossible to associate with single genes. Some traits are controlled by many genes. Eye shape, ear shape, etc. Many traits are strongly influenced by environmental factors including nutrition and exercise. Good nutrition has lead to an increase in height by 10cm since the 1800’s in Americans and British.

Human Genes Human genome – the complete set of our genetic information. Includes tens of thousands of genes. Difficult to do because of our long generation times, complex life cycle, and produce few offspring. - Completed in early 2000’s

Human Genes Blood Group Genes Human blood comes in a variety of genetically determined blood groups A number of genes are responsible for human blood groups

Human Genes Blood Group Genes Best known blood groups are ABO and the Rh Blood Groups are determined by multiple alleles

Recessive Alleles Genetic disorders have helped scientists learn more about genes. Some disorders are autosomal recessive. The presence of abnormal functioning gene is revealed only when an abnormal or nonfunctioning allele affects the phenotype PKU, Albinism, cystic fibrosis, etc.

Recessive Alleles Phenylketonuria (PKU) – lack the enzyme to break down phenylalanine Must have inherited the allele for the trait from both parents

Dominant Alleles Expressed even when the recessive allele is present Achondroplasia (Dwarfism) Huntington's Disease (nervous system disorder)

Codominant Alleles Sickle cell disease – small change in DNA of a single gene Common in African Americans Red Blood cells are bent and twisted

Sickle Cell Hemoglobin – protein in red blood cells that carries oxygen In sickle cell patients one DNA base change makes an amino acid for valine not glutamic acid (different sequence of amino acids)

Section 14-2 Human Chromosomes Almost every human cell contains more than 6 billion base pairs of DNA. All of our DNA is packaged into 46 chromosomes. Genes make up a small part of your chromosomes. Only 2% of the DNA in your chromosomes functions as genes, which make proteins, that give us our traits. Genes located close on the same chromosome are usually passed on together.

Chromosomes 21 and 22 Smallest human autosomes. These were the first two chromosomes to be sequenced. Chromosome 22 Contains around 545 genes Very important to human health. Contains long stretches of repetitive DNA that do not code for proteins. Unstable sites that can easily rearrange Chromosome 21 is similar, also having many regions with no genes.

Chromosome 21 Sequence

Chromosome 22

Sex Linked Genes Genes located on both the sex chromosomes (X and Y). These are called sex-linked genes. More than 100 genetic disorders have been mapped to the X chromosome. Males have just one X chromosome. Thus ALL X-linked alleles are expressed in males, even if they are recessive. Color blindness, hemophilia, muscular dystrophy, etc. Three genes associated with color vision are located on the X chromosome The Y chromosome is much smaller and carries only a few genes.

X Chromosome Contains around 1,000 genes! Learning disabilities Colorblindness pg.350 Hemophilia Muscular Dystrophy Etc…

X-Chromosome Inactivation Females = XX Males = XY If one X is enough in males why do females need 2? In female cells, one X chromosome is randomly switched off. This turned off chromosome turns into a dark spot in the nucleus called a Barr body. A condensed x chromosome that is inactive

Cat Coat Color In cats, a gene that controls coat color is on the X chromosome. One X may have an allele for orange spots, the other X may have an allele for black spots. XoXb Females can be calico because in some parts of their body the Xo is activated and in other areas the Xb is activated. Males can only have spots of one color.

Chromosomal Disorders During meiosis, errors can happen. The most common error is called non-disjunction. Nondisjunction is when pairs of chromosomes fail to separate during meiosis (sex cell formation) which causes an abnormal number of chromosomes in a sex cell. If fertilized, a child may be born with a chromosomal disorder. http://www.biostudio.com/d_%20Meiotic%20Nondisjunction%20Meiosis%20I.htm

Down’s Syndrome Trisomy means three bodies. “Trisomy 21” means that a person has 3 number 21 chromosomes. This gives a person Down Syndrome. In the US 1 out of 800 babies has Downs. Symptoms Mental retardation Increased susceptibility to diseases. Higher incidence of birth defects.

Sex Chromosome Disorders Turner’s Syndrome: only 1 X Sterile females (don’t go through puberty) Affects 1 in 2,500 girls Short stature 4’7 Webbed neck Abnormal bone development

Klinefelter’s Syndrome In Males they have XXY (or XXXY) Sterile Affects physical, language and social development. Taller, less muscle, less facial hair, breasts all due to low testosterone.

No X There have been no reported instances of babies born without an X Chromosome X chromosome contains genes vital for the survival and development of an embryo

Videos Williams Syndrome Turners Achondroplasia PKU Amish Children of Glass

Project time Look at a chromosome map and select a genetic disorder we can find in its genes. http://www.ornl.gov/sci/techresources/Human_Genome/posters/chromosome/chooser.shtml You will be making an informational presentation or brochure about this disorder or a chromosomal disorder of your choice.

Genetics Unit Review What are genes? What are SNP’s? http://www.watchknow.org/Video.aspx?VideoID=3775&CategoryID=1138 What are SNP’s? http://www.watchknow.org/Video.aspx?VideoID=7256&CategoryID=1138 Where do your genes come from? http://www.watchknow.org/Video.aspx?VideoID=7255&CategoryID=1138