1. Standard Biology Chapter 27 Human Genetics
27.1 The Role of Chromosomes
Very complicated compared to peas!

2. Chromosome Number
Each human sperm and egg has 23 different chromosomes
Each human body cell has 46 chromosomes (23 pair)
Different organisms have different number of chromosomes- most are paired (Homologous)
Table 27-1 Chromosome Number p. 566 (next slide)

3. Chromosome Number 12 6 Pea 14 7 Onion 16 8 Corn 20 10 White Pine 24
Animal or Plant
#Chromosomes Body Cell
#Chromosomes Sex Cell
Red Clover 12 6
Pea 14 7
Onion 16 8
Corn 20 10
White Pine 24
Cat 38 19
Rabbit 44 22
Chicken 78 39

4. A Way to Tell Chromosome Number
Amniocentesis: a look at chromosomes in fetus
Performed weeks gestation
Needle inserted into mother’s abdomen into amniotic fluid surrounding the fetus. Some fluid removed which also contains cells from the fetus.
Cells grown for 10 days, watch for dividing cells.

5. A Way to Tell Chromosome Number
Amniocentesis, cont.
Study the dividing cells (easy to see chromosomes as sister chromatids)
Arrange chromosomes in a karyotype

6. Karyotype
Chromosome smear
Karyotype

7. Karyotype Ordered arrangement of chromosome pairs by number
Largest is #1, smallest is #22
Match up banding pattern on chromosomes
Can determine sex of fetus by sex chromosomes
XY is male
XX is female
Y chromosome is much smaller
than X

8. A Way to Tell Chromosome Number
Chorionic villi sampling (same idea as amniocentesis)
Use a piece of the placenta
Can do earlier in pregnancy and get results sooner
May not be as accurate

9. Sex- A Genetic Trait Chromosomes # 1-22 are autosomes
Don’t determine sex
Are the same in males and females
Called non sex or body chromosomes
Males are XY so make X sperm and make Y sperm
Females are XX so only make X eggs

10. Sex- A Genetic Trait

11. Sex- A Genetic Trait
Males determine the sex of the child

12. Standard Biology Chapter 27 Human Genetics
27.2 Human Traits

13. Humans have many traits: those you can see and those you can’t.

14. Survey of Human Traits
Dominant traits
Freckles
Dimples

15. Survey of Human Traits Recessive traits Attached ear lobes
Straight hair
Nonroller tongue
Short eyelashes

16. Survey of Human Traits L=long eyelash trait l=short eyelash trait
Both parents are heterozygous and have long eyelashes
Expect 3:1 long to short eyelashes in offspring or expressed as a %, expect 75% long eyelashes children and 25% short eyelashes children

17. Survey of Human Traits L=long eyelash trait l=short eyelash trait
Both parents are heterozygous and have long eyelashes L LL Ll l ll Ll

18. Incomplete Dominance One trait not completely dominant over the other
Heterozygotes show in between trait
Example: Snapdragon flower color R=red, r=white; Parents are pink (heterozygous)

19. Incomplete Dominance

20. Incomplete Dominance Example: Sickle cell Anemia p. 574
RR=round red blood cells
R’R’= sickle red blood cells

21. Incomplete Dominance Sickle cell Anemia
Serious health problems because sickle cells cannot carry enough oxygen
Causes pain and fatigue (tiredness) because sickle cell block capillaries
Sickle cell Anemia most in African Americans

22. Incomplete Dominance Sickle cell Anemia
RR’= both round and sickle red blood cells
Usually no health problems because enough health red blood cells to carry oxygen

23. Blood Types in Humans Blood Type Genes Dominant Recessive A AA or AO O
BB or BO AB
A and B
none OO

24. Blood Types in Humans Three genes: A, B, and O
A and B are dominant to O
A and B are codominant

25. Genes on the X Chromosome
Sex chromosomes carry genes
X chromosome has many genes because it is a large chromosome
Y chromosome has few genes because it is a small chromosome
X chromosome and Y chromosome do have the same genes

26. Genes on the X Chromosome
Females are XX have 2 copies of each gene
Males are XY have 1 copy of X genes and 1 copy of Y genes

27. Color Blindness

28. Color Blindness Color blindness gene on X chromosome p. 576
Red and green shades look alike
Females 2 copies of color blindness gene; color blind if both copies are recessive (cc)/ not color blind if heterozygous (Cc) or if homozygous dominant (CC)

29. Color Blindness
Males 1 copy of color blindness gene; color blind if the one is recessive (c)/ not color blind if the one gene is dominant (C)
Males are more likely to be color blind
Females are carriers when they are heterozygous (Cc)
Example: Normal male (XCY), female carrier (XCXc)

30. Color Blindness Example: Normal male (XCY) female carrier (XCXc) XC XC

31. Color Blindness Example: Color blind male (XcY), female carrier (XCXc)
50% color blind females
50% color blind males Xc
XCXc
XcXc Y
XCY
XcY

32. Color Blindness
This is called a sex-linked genes because it is located on the X chromosome
Another sex linked gene is hemophilia (blood clotting disorder)

33. Standard Biology Chapter 27 Human Genetics
27.3 Genetic Disorders
About 600 babies born each day in the U.S. with a disorder,
some are genetic disorders.

34. Errors in Chromosome Number
Can happen if baby has more than 46 chromosomes
Can happen if baby has less than 46 chromosomes
Can happen if sperm or
egg have more or less
than 23 chromosomes

35. Errors in Chromosome Number
Error happens during meiosis when sister chromatids don’t separate correctly; get one sex cell with 22 the other with 24 chromosomes
Can happen to any of your chromosomes

36. Down Syndrome (Trisomy 21)
3 copies of chromosome #21

37. Down Syndrome (Trisomy 21)
mental retardation, heart problems, facial abnormalities

38. Down Syndrome (Trisomy 21)
1 in 700 births
Increasing incidence with increasing age of mother

39. Turner’s Syndrome Female with only 1 X chromosome (X0)
No neck, short, mental retardation, do not develop secondary sex characteristics
1 in 5000 births

40. Genetic Disorders and Sex Chromosomes
Hemophilia
Failure of blood to clot
Bruising
Significant in royal families of Europe (Russia)

41. Genetic Disorders and Sex Chromosomes
Color blindness
Cannot distinguish red/green shades

42. Genetic Disorders and Autosomes
Dyslexia (dominant gene)
“Word blindness”
See and/or write letters and words backwards, difficult to learn to read

43. Genetic Disorders and Autosomes
PKU- phenylketonuria
Amino acid phenylalanine can’t breakdown in body, builds up causing mental retardation
Now tested at birth and babies are given special diet with low levels of this amino acid

44. Genetic Counseling
Looks at family history to determine genetic disorder
Use of genetics to predict and explain traits in children
Genetic counselor- person trained to interpret medical information and counsel patients

45. Genetic Counseling Answer questions:
How did the baby get this disorder?
If the baby is healthy, does it have a problem gene?
Is the trait dominant or recessive?
What will happen to baby’s health as it gets older?
What are the chances that future children will have the trait?
What medical treatment is available?

46. Genetic Counseling
Genetic counselors use a pedigree (diagram of family history) that can show how a certain trait is passed along in a family

47. Cystic Fibrosis Recessive genetic disorder
Symptoms of disease: excess and thick mucus, respiratory problems and digestive problems
Child with the disease
1 in 4 chance if parents are heterozygous F f F FF Ff f Ff ff

48. Cystic Fibrosis Pedigree1 2 I II 1 2 3 4 5 1 2 3 4
III 1 2 3 4 IV 5

49. Pedigree Analysis Are females Are males
Shaded in circles and squares are affected individuals
Roman Numerals (I – IV) are generations
Lines across represent mating
Lines down represent offspring

50. Understanding the Pedigree
Count the number of affected males and affected females. If most males and few or no females most likely sex linked trait.
Look at the affected individuals. If every individual with the trait has a parent with the trait then this trait is dominant. If non-affected parents produce an offspring with the trait then it is recessive.
Determine the phenotype and genotype of every individual

51. Understanding the Pedigree
Affected males: 1
Affected females: 2
No affected individual has parent with the trait, means recessive
All affected individuals would be homozygous recessive, aa
All parents of affected individuals would be heterozygous, Aa
Siblings of affected individuals would be heterozygous (Aa) or homozygous dominant (AA)
Means not sex linked

52. Cystic Fibrosis Pedigree1 2 I Aa Aa II 1 2 3 4 5 aa ? Aa ? ? 1 2 3 4
III ? ? Aa Aa 1 2 3 4 IV 5 ? aa ? aa ?
? Would be AA or Aa