Human Genetics and Disorders

1. Human Genetics and Disorders

2. Putting it all together… • We have done a lot of stuff, talked about a lot of things, now to solidify everything with some facts.

3. Chromosomes and Genetics • Genes- Segments of DNA that code for traits. • These traits are passed through heredity • These genes are located on chromosomes. • The specific location of each gene on the chromosome is called a locus. • Plural is loci.

4. Autosomal vs Sex Chromosomes • Sex chromosomes are the chromosomes that are responsible for determining the sex of an organism. • This is done by the SRY gene (in humans). This is the Sex Determining Region of the Y chromosome. • All other chromosomes are referred to as Autosomal.

5. Sex Chromosomes • Sex is determined by males. • Though the SRY is responsible for sex determination it is not the only factor in said determination. • Several other genes and hormones play vital parts in the developmental process.

6. Human Genetics • Humans have 23 paired chromosomes • 22 autosomal pairs • 1 pair of sex chromosomes • 46 total • (enough DNA for ~ 70 round trips to the sun.)

7. Human Genetic Disorders • There are many genetic disorders present within the human genome. • Many are passed from generation to generation. • However, with such a long generation time it may be difficult to find how these disorders are passed down or inherited.

8. Ways to Predict • One way we can predict the possibilities is doing what we have been doing • Punnett squares or frequencies and percent. • Another possibility is the pedigree. • Pedigrees are charts that are similar to family trees. • We can use these to diagram disorders to look at possibilities for the future.

9. Pedigrees

10. Genetic disorders and inheritance • Several human genetic disorders, including many cancers, occur because of mutations in cells. • Because these mutations happen in somatic cells (cells other than germ line) those disorders are not inherited. • Some other disorders, on the other hand, are passed from parent to off spring. • -For this to occur the effected chromosome must be in a gamete. • - This disease carrying chromosome may be due to a mutation or other abnormalities.

11. Chromosomes and disorders • One way we can look for genetic disorders is through a process known as karyotyping. • This is a process in which the chromosomes of an individual are lined up by homologous pairs and numbered (or lettered in the case of the sex chromosomes. • By comparing a patient’s karyotype to that of a normal person differences can be detected, and based on locus, diagnosis made.

12. Chromosomes and disorders • www.ncbi.nlm.nih.gov/books/NBK22266/

13. Dominance and disorders • There are dominant disorders • - Reasons they are still in existence? • There are many recessive disorders • - Reasons they are still in existance?

14. Dominance and disorders • Because the likelihood of a dominant disorder is so much greater than a recessive disorder we can look at two ways the disorder remains in the population. • In most cases, a dominant disorder will reduce the fitness of an individual (reducing the chances of survival and reproduction) • -The first way this disorder is still present may be due to mutations in gamete production (the individual producing the gametes will remain unaffected). • - The second way is a delayed expression of the trait, as is such the case in Huntington Disease.

15. Dominance and disorders • Most disorders will be recessive. • This gives them the ability to “hide” within a population, due to the reduced chance of an affected person. • Benefits? • - HETEROZYGOUS ADVANTAGE

16. Inherited Chromosomal Abnormalities • Cause of few disorders,. • - Mainly because many are lethal at a young age • - ***Or may prevent embryotic formation, altogether ***

17. Ways to change the shape of a Chromosome

18. Problems with chromosome numbers • Changes in the number of Autosomal Chromosomes are often lethal • - ~20% of women spontaneously abort. • -this is largely due to the change in chromosome numbers • There is only one case of altered chromosomal number in which the affected can live to adulthood.

19. Problems with chromosomal numbers • Trisomy 21 (3 copies of the 21st chromosome), commonly known as Down Syndrome • The 21st chromosome is the smallest in humans. • Individuals with Down syndrome may have complications with their heart, kidneys , digestive tract, and mental retardation.

20. Problems with chromosomal numbers • Other cases in which abnormal chromosome number leads to a live birth are trisomy of the 13th ,15th , or 18th chromosome • - Though most of these individuals do not make it past a year of life.

21. Problems with chromosomal numbers • Differing numbers of sex chromosomes MAY lead to relatively mild side effects • Klinefelter’s syndrome (XXY males) • Turner syndrome females (x) • XYY Males or XXX Females • Not good: • - XXXY males or XXXX Females

22. Genetic Linkage • The placement of genes along the DNA helps to determine the genetic variation of an individual. • Genes that are close to each other have a better chance of being inherited by the next generation than those that are further apart • This is because of gene linkage

23. Crossing-Over • As homologous pairs of chromosomes line up in meiosis they exchange sections of their genetic material. • This is crossing-over • Genes that are linked due to proximity have a greater chance of crossing-over together.

24. Other sources for genetic diversity • Crossing-over causes genetic diversity • But there are also other ways to do this • Independent Assortment is the random distribution of maternal and paternal genetic information

25. Independent Assortment • Because of the number of chromosomes (23) we can figure the number of different combinations • There are over 8.3 million different combinations per gamete. • That means 8.3 million x 8.3 million = 64 trillion different combinations