Chapter 12

1. Chapter 12 Inheritance Patterns & Human Genetics

2. Chromosomes & Inheritance Thomas Hunt Morgan- early 1900’s -experiments with fruit fly -observed 4 pairs of chromosomes in fruit flies -also noticed that 3 pairs were the same in males & females but that 1 pair was different. - called these “sex chromosomes”.

3. Recall: Autosomes & Sex Chromosomes • Sex chromosomes- contain genes that determine the gender of an individual. • Autosomes- the remaining pairs of chromosomes that do not directly determine sex. • In mammals - 2 X chromosomes= FEMALE (XX) - 1 X + 1 Y is a MALE (XY)

4. 1:1 male to female ratio • -In meiosis, homologous chromosomes pair up & are separated. • As the pair of homologous Sex chromosomes separate, -each sperm has an equal chance of having an X or a Y -however- the only option for eggs is to receive an X chromosome. • This gives about a 1:1 ratio of males to females in mammals.

5. SRY gene • -About 95 percent of the human Y chromosome has been sequenced—a chunk of DNA called the male-specific region. • They pinpointed 78 genes. • A Y chromosomes gene called SRY (Sex-determining Region Y.) codes for proteins that cause gonads to develop into testes. • Females lack this gene & gonads develop ovaries.

6. Sex determination in other types of organisms: • In some insects, including the grasshoppers, crickets & cockroaches - females have two copies of the sex chromosome (XX) but males have only one (X0). • In some birds & other insects-The ZW sex-determination system is used. It is reversed compared to the XY system: females have two different kinds of chromosomes (ZW), and males have two of the same kind of chromosomes (ZZ). • In some species of reptiles, sex is determined by the temperature at which the egg is incubated. In the red-eared slider turtle, for instance, low temperatures in the nest produce males, while warmer temperatures produce females.

7. Sex determination in other types of organisms: • In ants and bees. Haploid individuals are male. Diploid are generally female but may be sterile males. Thus, if a queen bee mates with one drone, her daughters share ¾ of their genes with each other, not ½ as in the XY and ZW systems. Most plants & fish lack sex chromosomes • Other species, such as some snails, practice sex change: adults start out male, then become female.

8. Sex determination in other types of organisms: • In tropical clown fish, the dominant individual in a group becomes female while the other ones are male. • Some species have no sex-determination system. Earthworm and some snails are hermaphrodites; a few species of lizard, fish, and insect are all female and reproduce by parthenogenesis

9. Gene Location Sex- Linked Genes & Traits Linked Genes Chromosome Mapping

10. Sex- Linked Genes & Traits • Thomas Hunt Morgan observed eye color of fruit flies • Noticed that red was dominant to white eyes. • Did experiment- crossed white -eyed male with red eyed female. • All F1 generation was red- eyed. In F2 generation- ¼ were white eyed. • But in F2 generation-Noticed that all of the white eyed offspring were males. • CONCLUDED- gene for eye color must be on the X chromosome.

11. Sex-Linked traits • are traits that are coded for by alleles on a sex chromosome. • -Genes found on the X chromosome are X-linked genes • - Since the X chromosome is larger- there are more X-linked than Y- linked traits. • NOTE: Since males have only 1 X- a male who carries the recessive allele • will show X-linked trait.

12. Linked Genes • are pairs of genes that tend to be inherited together. • Morgan studied 2 more genes- 1 for body color & 1 for wing length. • Hypothesized that they were linkedwhen saw that offspring were: black short winged -OR- gray & long winged • If they were inherited separately would see ratio of 9:3:3:1 not 3:1

13. Linked genes • Genes which are close together on same chromosome. • Linked genes do not exhibit independent assortment

14. Chromosome Mapping • -A diagram that shows the linear order of genes a chromosome: • -The further apart 2 genes are located on a chromosome, the more • likely that crossing-over will occur. • - A map unit is a unit of 1 % in the frequency of crossing over

15. Many types of mutations • General • Chromosome • Nondisjunction • Gene

16. 4 kinds of Mutations Mutation -a change in the nucleotide-base sequence of a gene or DNA 1. Germ cell- occurs in gametes - do not affect the organism itself 2. Somatic Cell-occur in organism’s body cells - may affect the organism (ex-cancer) - NOT inherited 3. Lethal Mutations-cause death, often before birth 4. Beneficial Mutations- result in phenotypes that are beneficial .

17. Examples of beneficial mutations- (fromhttp://www.talkorigins.org/faqs/mutations.html) Sickle cell resistance to malaria • The sickle cell allele causes the normally round blood cell to have a sickle shape. • The effect of this allele depends on whether a person has one or two copies of the allele. • It is generally fatal if a person has two copies. • If they have one they have some sickle shaped blood cells. In general this is an undesirable mutation because the sickle cells are less efficient than normal cells. • In areas where malaria is prevalent it turns out to be favorable because people with sickle shaped blood cells are less likely to get malaria from mosquitoes.

18. Examples of beneficial mutations- (fromhttp://www.talkorigins.org/faqs/mutations.html) Lactose tolerance Lactose intolerance in adult mammals has a clear evolutionary explanation; the onset of lactose intolerance makes it easy to wean the young. Human beings, however, have taken up the habit of eating milk products. This is not universal; it is something that originated in cultures that kept cattle and goats. In these cultures lactose tolerance had a strong selective value. In the modern world there is a strong correlation between lactose tolerance and having ancestors who lived in cultures that exploited milk as a food.

19. 4 Types of Chromosome Mutations 1. Deletion- loss of a piece of chromosome due to breakage. 2. Inversion – a chromosome piece breaks off, flips around backwards & reattaches 3. Translocation – a piece of chromosome breaks off & attaches to a non-homologous chromosome 4. Non-Disjunction – a chromosomes fails to separate from its homologue during meiosis.

20. Examples of Chromosomal Mutations: Deletion & Inversions http://staff.jccc.net/PDECELL/evolution/mutations/mutation.html

21. Translocation mutation http://staff.jccc.net/PDECELL/evolution/mutations/mutation.html

22. An example of a human disorder with a deletion error: • Cri du chat syndrome- • missing part of chromosome 5- • cry of infants is similar to that of a meowing kitten, due to problems with the larynx and nervous system. • About 1/3 of children lose the cry by age 2.

23. Types of non disjunction: 1. Trisomy- an extra chromosome from a non-disjunction error during meiosis I or II leads to an individual with an extra chromosome in every cell of his/her body.  2. Monosomy- is a deficiency in number of chromosomesand is defined as only one copy of a chromosome that is normally present in two copies.  These eggs and sperm, which contain one less chromosome, have 22 chromosomes.  When fertilized, the outcome is 45 chromosomes in total.  Monosomies are less likely to survive when compared to trisomies.

24. What causes non-disjunction? • The cause of non-disjunction is unknown.  Non-disjunction seems to be a chance event.  Nothing that an individual does or doesn't do during their reproductive years can cause these chromosomal changes.  We do know that non-disjunction occurs more frequently in the eggs of women as they get older.

25. Non- Disjunction Disorders with an extra chromosome( these folks have 47 instead of the normal 46 chromosomes in people): • Down syndrome- extra 21 • Edward’s Syndrome- extra 18 • Patau syndrome – extra 13

26. Examples Non disjunction: • Extra #21= Down’s Syndrome • Extra #18= (most don’t live beyond 1st 7 months)This girl is now 6.) http://starbulletin.com/96/03/25/news/story2.html

27. Sex-chromosome abnormalities may also be caused by nondisjunction. • Klinefelters Syndrome- XXY ( extra X) • Turners Syndrome – only 1 X- missing a second X (XO) • Super males XYY • Any combination (up to XXXXY) produces maleness. Males with more than one X are usually underdeveloped and sterile. • XXX and XO women are usually sterile

28. 4 Types of Gene Mutation 1. Point Mutation- the substitution, addition or removal of a single nucleotide, occurs within a single gene or segment of DNA 2. Substitiution- one nucleotide replaces another 3. Frameshift Mutation- if some nucleotides are deleted- whole segment moves 4. Insertion Mutation – one or more nucleotides added- also causes a frameshift

29. Which type of gene mutation do you think would cause the most serious errors? • Point mutation • Substitution • Frameshift

30. Example: substitution error • Just 1 Amino Acid is a Substitution ERROR in Sickle Cell Hemoglobin • Causes Hb to be sickle shaped instead of round- can’t fit into red blood cells & changes their shape too.

31. Sickle Cell - Disease or Trait: • Normally, a person inherits two genes (one from each parent) that produce normal hemoglobin (hemoglobin A). • A person with sickle cell trait inherits one normal beta-globin gene (hemoglobin A) and one defective gene (hemoglobin S) (this can actually be a good thing – it provides some protection from malaria, which infects RBCs!) • A person with sickle cell disease inherits 2 bad copies- only makes HgS

32. Human Genetics Inheritance of Traits 1. Pedigrees - be able to draw & read these! 2. Patterns-learn about genetic disease by looking at patterns of inheritance over several generations. Genetic Traits & Disorders 1. Polygenic Inheritance 2. Complex Characters 3. Multiple Alleles 4. Incomplete Dominance 5. X-linked Traits 6. Sex- Influenced Traits 7. Single Allele Traits

33. Inheritance of Traits • Pedigree - a diagram that shows how a trait is inherited over several generations

34. Reading a pedigree HE SHE • males are represented by squares • females by circles. • An individual who exhibits the trait , • (for example, someone who suffers from Marfan syndrome), is represented by a filled symbol. • A horizontal line between two symbols is a mating DAD MOM

35. Reading a Pedigree • The offspring: • are connected to each other by a horizontal lineabove the symbols • and to the parents by vertical lines.

36. Example pedigree: • Is the mom or dad in generation I affected by a trait? • How many offspring are shown in generation II? • How many daughters & sons in generation II? • How many have the trait? • How many offspring does daughter #1 have? How many have the trait?

37. Dominant traits • are passed on to a son or daughter EVEN if only one parent has it. • Every affected individual has at least one affected parent • Affected individuals who mate with unaffected individuals have a 50% chance of transmitting trait to each child • Two affected parents may have unaffected children.

38. Recessive pedigrees: • Where did the trait seen in generation III come from? • Traits can be passed on to children if both parents, even if they may seem "normal”, are carriers of the recessive trait.

39. Recessive traits: summary • are passed on to children from both parents, although the parents may seem perfectly "normal." • Characteristics of recessive pedigrees are: • An individual who is affected may have parents who are not affected; • All the children of two affected individuals are affected; • In pedigrees involving rare traits, the unaffected parents of an affected individual may be related to each other.

40. Recessive pedigree: If individuals 2 + 3 in generation 3 have more children- will they be affected? Can Individual #8 in gen. 3 have any unaffected children? Can individual #9 in gen 3 have affected children?

41. Example pedigree of cystic fibrosis www.cfscreening.com.au/.../CF/CFInherited.shtml

42. Genetic Traits & Disorders Polygenic Inheritance - traits influenced by several genes (most human characteristics) example- skin color is additive effect of 6 genes

43. Genetic Traits & Disorders 2. Complex Characters • traits influenced by both genes & environment • Example- height

44. Genetic Traits & Disorders 3. Multiple Alleles- • genes with 3 or more alleles. • Example- human blood type. IA, IB, i • 3 alleles- both IA & IB are dominate over i, Codes for sugars that are on blood cell surface. • four different blood types- A, B, AB, O

45. http://www4.alief.isd.tenet.edu/cahowe/Anatomy/powerpoints/ THE%20CARDIOVASCULAR%20SYSTEM_files/slide0005_image007.gif • What are the 2 genotypes for “type B? • Which blood type can donate to all the others? (universal donor?) • Which blood type makes antibodies (will clot against) both A & B blood types?

47. Blood typing card- what is the blood type and how do you know?

48. Off topic but interesting: What is Hemolytic disease of the fetus (unborn baby)? • occurs when the maternal immune system is sensitized to the baby's red blood cells. • The surfaces of the red blood cells are covered with antigens, categorized as Rh, Kell, ABO, Duffy, Kidd, platelet, and MN antigens. • When the fetus's antigens are different from those of the mother, the mother's immune system recognizes the baby's red blood cells as foreign and becomes sensitized to them. • In a subsequent pregnancy, there is risk for hemolytic disease. • If the fetus carries antigens different from the mother's, the mother's immune system responds by destroying the baby's red blood cells, a process known as hemolysis. • This results in anemia, and if left untreated, death.

49. Genetic Traits & Disorders 4. Incomplete Dominance • there is an intermediate phenotype • Human example- wavy hair is the intermediate between straight & curly hair (remember chapter 9 plant example: - pink 4 o’clock flowers, In between red & white flowers)

50. Genetic Traits & Disorders 5. X-linked Traits • Traits that are on the X chromosome. • Since males only have one X chromosome- they are affected more than females • Females have 2 chances to get a good copy of the gene but males only get 1 chance.