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.

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)

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.

Now you try it on the computer. Type in Karyotyping Activity on Google. Be sure to read through the information and fill out your worksheet.

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. Genetic counselors use pedigree charts to infer genotypes of family members. http://www.accessexcellence.org/RC/VL/GG/nhgri_PDFs/pedigree.pdf See example on pg. 342

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

Genetic Disorders Genetic disorders have helped scientists learn more about genes. Some disorders are autosomal recessive. Albinism, cystic fibrosis, etc. Others are autosomal dominant. Dwarfism, Huntington’s disease, etc. Some are even codominant Sickle cell disease.

Cracking the Code of Life Watch the following video clips and take notes on the things you learn from each section. http://www.pbs.org/wgbh/nova/genome/program.html

Section 14-2 Human Chromosomes Almost every human cell contains more than 3 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 repetative 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 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. 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…

Hemophilia and Colorblindness are sex linked traits, the punnett square below shows how a woman who is a carrier passes the trait to her son, but not her daughters.

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.

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 homologous pairs of chrmomosomes fail to separate. If nondisjunction occurs an abnormal number of chromosomes will end up 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 susceptability to diseases. Higher incedince 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.