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Presentation on theme: "INHERITANCE PATTERNS AND HUMAN GENETICS Chapter 12."— Presentation transcript:


2 Quick review… Genetics is the field of biology devoted to understanding how characteristics are transmitted form parents to offspring.

3 The DOMINANT factor/gene masks the effect of the other factor in the F1 generation. –Use CAPS ex. T for tall The RECESSIVE factor/genes effect can only be seen in the P generation or F2 generation when the DOMINANT gene is absent. –Use lower case ex. t for short Generations: P Tall x Short F1 Tall (tall is dominant) F2 3 Tall : 1 short

4 MENDELS 2 LAWS: #1 LAW OF SEGREGATION: A pair of factors is segregated, or separated, during the formation of gametes. Factors for different characteristics are distributed to gametes independently. #2 LAW OF INDEPENDENT ASSORTMENT:

5 GENOTYPE is the genetic makeup of the organism. TT = homozygous dominant Tt = heterozygous tt = homozygous recessive PHENOTYPE is the physical appearance of that organism. Ex. Tall or short MENDELIAN INHERITANCE- DOMINANCE…. 2 phenotypes only. If someone has the dominant phenotype but you arent sure of Their genotype… use a pedigree (humans) or do a test cross.

6 Other Patterns of Inheritance: 1.Incomplete Dominance- blending seen in heterozygote (ex. pink flowers, brown hair) 2.Codominance- both dominant and recessive phenotypes seen in heterozygote. (ex. type AB blood, roan horse fur color) 3.Polygenic- more than 1 gene determines the phenotype. (Ex. Eye color, Hair color aabbcc) 4.Multiple alleles- more than just 2 alleles (Ex. Blood type = A allele, B allele, O allele is recessive.)

7 EX. Polygenic Inheritance- when the trait is controlled by multiple genes so many phenotypes are possible. AaBbCc x AaBbCc Huge variety in possible Phenotypes of the offspring - skin, hair, eye color - foot size - nose length - height

8 Multiple alleles- trait controlled by three or more alleles. -Ex. ABO blood groups: - TYPE A - TYPE B - TYPE AB Shows Codominance! - TYPE O

9 The process of using phenotypes to deduce genotypes When someone has the DOMINANT phenotype you are uncertain of their genotype. TT or Tt When someone has the recessive phenotype you can be sure of their genotype. tt

10 DIRECTIONS: For each of the following single gene/ Mendelian traits, write your phenotype on the line. Write as much of your genotype as you can be certain. - both alleles if RECESSIVE (rr) - one allele if DOMINANT (R __) Repeat the process by studying two blood relatives (parents work the best) Use a pedigree.

11 1. HAIR TYPE very curly or straight TT, Tt tt

12 2. Hair Color Dark or Light DD, Dd dd

13 3. Hair Line Continuous or Widows Peak WW, Ww ww

14 4. Iris Color Pigmented or Blue EE, Ee ee

15 5. Lens of Eye Astigmatism or Normal AA, Aa aa

16 6. Nose Shape Roman (convex) or Concave NN, Nnnn

17 7. Ear Lobe Free/Long or Attached LL, Llll

18 8. P.T.C. Taster Tasteror Nontaster RR, Rrrr

19 9. Tongue Curling Can curlor Can not curl CC, Cc cc

20 10. Point of chin Dimpled or NO dimple II, Iiii

21 11. Number of Fingers Polydactylism or Normal # PP, Pp pp


23 12. Little Finger Bent or Straight FF, Ff ff

24 13. Hypermobility of Thumb Loose Jointed or Not so HH, Hhhh

25 14. Thumb Extension Hitchhikers Thumb or Not HH, Hh hh

26 15. Middigital Hair Present or Absent MM, Mm mm

27 16. Palmar Muscle Normal (2) or Long (3) UU, Uu uu

28 17. Allergies Tendency Or No tendency AA, Aa aa

29 18. Veins VaricoseorNormal VV, Vvvv

30 19. White Skin Spotting Freckles or No freckles SS, Ssss

31 20. White Forelock

32 LIST OF STRANGE MENDELIAN TRAITS Ear wiggling Misshapen toes or teeth Inability to smell musk or skunk Lack or teeth, eyebrows, nasal bones or thumbnails Whorl in the eyebrow Tone Deafness Hairs that are triangular in cross-section or that have multiple hues (colors) Hairy knuckles, palms, soles, or elbows Egg-shaped pupils Magenta urine after eating beets Sneezing fits in bright sunlight.

33 DNA in chromosomes contain information to make proteins. Geneticists use their knowledge of DNA and the way chromosomes behave to study how traits are inherited and expressed.

34 The parents genotype can be a gene pair of either: - TT homozygous dominant - tt homozygous recessive - Tt heterozygous The parent can make gametes (sperm or eggs), through the process of MEIOSIS, that have either one or the other of the gene pair in it.

35 SEX DETERMINATION MORGANs Fruit fly (Drosophila) breeding experiments of the 1900s revealed the identity of sex chromosomes. In males they were different XY; in females they were the same XX. The other chromosomes (22 in humans) are AUTOSOMES.

36 The male determines the sex of the offspring… <--The FEMALE XX can only make X gametes. <--The MALE XY can make either X gametes or Y gametes.

37 SEX LINKAGE traits caused by genes found on a sex chromosome X-LINKED GENES: Genes located on the X chromosome. Women can be carriers. Ex. gene for ALD (Lorenzos Oil) Y-LINKED GENES: Genes located on the Y chromosome. Only males show these traits. Ex. SRY- triggers male development of testis.

38 Males exhibit X-linked traits more often than women because they only have ONE X chromosome. Females have two X B X b or sex linked genes. Females can be carriers of the bad gene yet not show the disease.. Males only have one X or sex linked gene since they are X b Y. Males have a higher chance of having the condition than if it were on an autosome. THERE IS NO HETEROZYGOUS for men.

39 X-linked Examples: Eye color in Drosophila Red-green colorblindness Male Pattern Baldness Hemophilia Duchenne Muscular Dystrophy ALD (adreno leuko dystrophy)

40 What do you see in the circle? Do your bruises look like this?

41 If a carrier (woman) for hemophilia marries a normal man, what are the chances of having kids who are hemophiliacs? Who are not? What if the man is a hemophiliac???????

42 LINKAGE GROUPS Genes located on the same chromosome are said to be linked. Linked genes tend to be inherited together. Examples: Hair color and intelligence are linked in humans. fur color and deafness in cats are linked.

43 Im kidding about intelligence and hair color being linked. But if they were linked… What would the phenotype(s) be of children of a dumb,blonde & smart,brunette

44 smart,brunette If that smart,brunette had kids w/ a dumb,blonde What kinds of kids could they have? What is the probability of each?

45 Parental Phenotypes: Smart, brunette Dumb, blonde Recombinant Phenotypes: Smart, blonde Dumb, brunette

46 Linked genes result in traits that tend to be inherited together… If the intelligence and hair color genes were linked, wed only see smart-brunettes and dumb-blondes. (HA HA) So, since there are smart blondes- are these genes on separate chromosomes or on the same chromosome yet separated by crossing over????? If you do a test cross of your Heterozygote you can see if the genes Are linked (5:5:1:1) or not (1:1:1:1).

47 Chromosome maps can be created by conducting breeding experiments. Linked genes that separate by crossing over X% of the time are X map units apart. Compare 4 phenotype inheritance to 2 phenotype inheritance. Genes can now be placed on a chromosome in some order.

48 Genes W and Z separate by crossing over 20% of the time. Genes W and X separate by crossing over 5% of the time, and genes Z and X are separated by crossing over 25% of the time. CONSTRUCT A CHROMOSOME MAP. Z W X I I--5--I

49 Mutations, Disease, & Human Mendelian Traits 1.Where they occur/ significance. 2.Types: Chromosome or Gene 3.Diseases & Inheritance Patterns. 4.Using Phenotypes to deduce Genotypes

50 1.Germ cell mutation occurs in the gametes does not effect the organism may be passed on to offspring if fertilized 2.Somatic mutation occurs in the organisms body cells & can affect the organism ex. Skin cancer & leukemia are not passed on to offspring 3.Lethal mutation causes death (often before birth) is not passed on if death occurs before reproduction 4.Beneficial mutation result in phenotypes that are beneficial. beneficial phenotypes lead to increased reproduction.

51 Mutation: a change in the DNA sequence. A) chromosome mutations (affects many genes) B) gene mutations (one gene) A) Chromosome mutations: Cross over errors: 1.Deletion- loss of a piece due to breakage. 2.Inversion- a piece is attached upside down. 3.Translocation- a piece reattaches to a non- homologous chromosome. Segregation Error: 1.Nondisjunction- failure of homologous chromosomes to separate during meiosis. ex. Down Syndrome = Trisomy 21 (egg usually has 2 of #21)

52 Chromosome Mutations nondisjunction

53 B) Gene mutations/ point mutations- are nucleotide differences. 1.Substitution- one nucleotide is switched for another. - ex. sickle cell anemia 2.Frame shift mutations- occur when nucleotides are added or removed either more or fewer than 3 nucleotides at a time. - addition - deletion

54 GENE MUTATION: SUBSTITUTION ex. Sickle Cell Gene- Hemoglobin

55 INHERITANCE OF GENETIC DISEASES follow different Patterns of Inheritance 1.Single allele Dominant 2.Single allele recessive 3.X-linked 4.Sex influenced

56 PEDIGREE ANALYSIS Humans have about 100,000 genes. Most studies are of disease-causing genes. - easy to track through generations.. A pedigree is a family record that shows how a trait is inherited over several generations.

57 1.Single allele DOMINANT- need only one gene to have the disease. - huntingtons disease (1/10,000) Hh - dwarfism Dd - cataracts Cc - polydactyly Pp PATTERN: effected individuals in every generation of both male and female sex.

58 2.Single allele recessive- The individual needs two genes to have the disease. -Albinism aa -Cystic fibrosis (1/200 whites) cc -Phenylketonuria (1/1800) pp -Hereditary deafness dd -Sickle cell anemia (1/500 African-Americans) sc sc -Tay-Sachs disease (1/1600 European Jews) tt Pattern: 2 healthy parents have effected child of either sex.

59 3.X-Linked- women need two genes, men need only one gene. - colorblindness X c X c X c Y -hemophilia (1/7000) X h X h X h Y -muscular dystrophy (1/10,000) X d X d X d Y -Icthyosis simplex -ALD Pattern: more common in males, Can kip generations.


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