1. Genetics

2. Gregor Mendel Father of modern genetics Studied pea plants
variety of distinct heritable features, or characters
character variations are called traits
Mating of plants can be controlled
used varieties that were “true-breeding”
plants that produce offspring of the same variety when they self-pollinate
When cross pollination occurs offspring showed a mix of characteristics of both parents

3. LE 14-2 Removed stamens from purple flower Transferred sperm-
bearing pollen from
stamens of white
flower to egg-
bearing carpel of
purple flower
Parental
generation
(P)
Stamens
Carpel
Pollinated carpel
matured into pod
Planted seeds
from pod
Examined
offspring:
all purple
flowers
First
generation
offspring
(F1)

4. Terms Trait Gene Allele Example
specific characteristic that changes from one individual to another
Gene
chemical factors that determine traits
Found in DNA
Genes for various traits are found on chromosomes
Allele
different forms of a gene
Example
Trait = plant height
Alleles (different forms of gene)
Short
Tall

5. Dominance Principle of Dominance
some alleles are dominant and others are recessive
Dominant alleles
are generally expressed using a capital letter
Recessive alleles
are usually expressed using a lower case letter
Ex. Plant height
Dominant = tall (T)
Recessive = short (t)
Each gene is coded for using 2 alleles
One allele from each parent
Dominant alleles control the appearance of the trait
If two recessive alleles are present the recessive condition will be expressed

6. Alleles Homozygous Heterozygous
individual with 2 of the same allele for a given trait
Ex. TT, RR = homozygous dominant
Ex. tt,, rr = homozygous recessive
Can “true breed” = create offspring like self in self polination
Heterozygous
individual with 2 different alleles for a given trait
Ex. Tt, Rr, Ww
Are not “true breeders”

7. Genotype Phenotype The combination of alleles for a given trait
Ex. TT, Tt, tt
Phenotype
The physical appearance caused by the interaction of alleles
In general, if a dominant allele is present then the dominant condition will be shown
Ex. Tall, Short

8. Parent F1 (first filial) F2 (second filial) First generation studied
Offspring of 2 individuals from the parent generation
F2 (second filial)
Offspring of 2 individuals from the first filial generation

9. The Law of Segregation
Each individual contains 2 alleles for each gene (one from each parent)
During meiosis, when the number of chromosomes are reduced (diploid to haploid), gametes are produced that contain one allele for each trait
Segregation = the separation of alleles for a certain trait
Each gamete only carries a single allele for each gene
During fertilization, two gametes fuse forming a diploid cell.
This cell contains 2 alleles for each gene

10. (true-breeding parents) White flowers
LE 14-3
P Generation
(true-breeding
parents)
Purple
flowers
White
flowers
F1 Generation
(hybrids)
All plants had
purple flowers
F2 Generation

12. Allele for purple flowers
Homologous
pair of
chromosomes
Locus for flower-color gene
Allele for white flowers

13. LE 14-5_2 3 : 1 P Generation Appearance: Purple flowers PP White
Genetic makeup:
Gametes P p
F1 Generation
Appearance:
Genetic makeup:
Purple flowers Pp
Gametes: 1 2 P 1 2 p
F1 sperm P p
F2 Generation P PP Pp
F1 eggs p Pp pp 3
: 1

14. Phenotype Genotype PP (homozygous Purple 1 Pp (heterozygous 3 Purple 2
White 1
Ratio 3:1
Ratio 1:2:1

15. Probability The likelihood that a particular event will occur.
Ex. If you flip a coin you have a probability of ½ that you will end up with heads.
What is the probability of flipping 3 heads in a row?
½ x ½ x ½ = 1/8
The principles of probability can be used to predict outcomes of genetic crosses.
Punnet Squares

16. Tt X Tt Cross
Section 11-2
Go to Section:

17. Tt X Tt Cross
Section 11-2
Go to Section:

18. The Testcross
breeding the mystery individual with a homozygous recessive individual

19. LE 14-7 Dominant phenotype, unknown genotype: PP or Pp?
Recessive phenotype,
known genotype: pp
If PP,
then all offspring
purple:
If Pp,
then 1 2 offspring purple
and 1 2 offspring white: p p p p P P Pp Pp Pp Pp P P Pp Pp pp pp

20. The Law of Independent Assortment
Genes for different traits can segregate independently during the formation of gametes.
Genes for different traits are not necessarily linked.

21. LE 14-8 P Generation YYRR yyrr Gametes YR yr YyRr F1 Generation
Hypothesis of
dependent
assortment
Hypothesis of
independent
assortment
Sperm 1 YR 1 Yr yR yr
Sperm 4 4 1 4 1 4
Eggs 1 YR yr 2 1 2 1 YR
Eggs 4
YYRR
YYRr
YyRR
YyRr 1 YR
F2 Generation
(predicted
offspring) 2
YYRR
YyRr 1 Yr 4
YYRr
YYrr
YyRr
Yyrr 1 yr 2
YyRr
yyrr 1 yR 4
YyRR
YyRr
yyRR
yyRr 3 4 1 4 1 yr 4
Phenotypic ratio 3:1
YyRr
Yyrr
yyRr
yyrr 9 16 3 16 3 16 3 16
Phenotypic ratio 9:3:3:1

22. The Spectrum of Dominance
Complete dominance
phenotypes of the heterozygote and dominant homozygote are identical
Codominance
two dominant alleles affect the phenotype in separate, distinguishable ways
Incomplete Dominance
phenotype of F1 hybrids is somewhere between the phenotypes of the two parental varieties

23. LE 14-10 P Generation Red CRCR White CWCW Gametes CR CW Pink CRCW
F1 Generation
Gametes 1 1 2 CR 2 CW
Sperm 1 2 CR 1 2 CW
Eggs
F2 Generation 1 CR 2
CRCR
CRCW 1 2 CW
CRCW
CWCW

24. Frequency of Dominant Alleles
Dominant alleles are not necessarily more common in populations than recessive alleles
Polydactyl individuals
1/400 in the U.S.

25. Multiple Alleles more than two allelic forms Example – blood type
four phenotypes: A, B, AB, O
Three alleles: IA, IB, and i.

27. Pleiotropy multiple phenotypic effects
Ex. multiple symptoms of certain hereditary diseases, such as cystic fibrosis and sickle-cell disease

28. Polygenic Traits Traits controlled by 2 or more genes
Ex. Eye color, hair color, skin color

29. Skin color 20/64 15/64 6/64 1/64 AaBbCc AaBbCc aabbcc Aabbcc AaBbcc
Fraction of progeny
6/64
1/64

30. Epistasis
a gene at one locus alters the phenotypic expression of a gene at a second locus
Ex. Coat color of mice
One gene determines the pigment color (with alleles B for black and b for brown)
The other gene (with alleles C for pigment color and c for no pigment color ) determines whether the pigment will be deposited in the hair

31. LE 14-11 BbCc BbCc Sperm BC bC Bc bc BC BBCC BbCC BBCc BbCc bC BbCC9 3 4 16 16 16

32. Nature and Nurture: The Environmental Impact on Phenotype
phenotype for a character depends on environment as well as genotype
Ex. hydrangea flowers
same genotype range from blue-violet to pink
depends on soil acidity

33. Human Inheritance Humans are not good subjects for genetic research
generation time is too long
parents produce relatively few offspring
breeding experiments are unacceptable
Personal Pedigree

34. Pedigree Analysis Pedigree
family tree that describes the interrelationships of parents and children across generations
Can be used to make predictions about future offspring

35. Dominant trait (widow’s peak)
LE 14-14a
First generation
(grandparents) Ww ww ww Ww
Second generation
(parents plus aunts
and uncles) Ww ww ww Ww Ww ww
Third
generation
(two sisters) WW ww or Ww
Widow’s peak
No widow’s peak
Dominant trait (widow’s peak)

36. Recessive trait (attached earlobe)
LE 14-14b
First generation
(grandparents) Ff Ff ff Ff
Second generation
(parents plus aunts
and uncles)
FF or Ff ff ff Ff Ff ff
Third
generation
(two sisters) ff FF or Ff
Attached earlobe
Free earlobe
Recessive trait (attached earlobe)

37. Down’s Syndrome Occurs in 1/800-1,000 births Caused by nondisjunction
Trisomy 21 = three copies of chromosome 21

38. Frequency of Down Syndrome Per Maternal Age
Age (years)
Frequency of Fetuses with Down Syndrome to Normal Fetuses at 16 weeks of pregnancy
Frequency of Live Births of Babies with Down Syndrome to Normal Births
----
1 / 1250
1 / 1400
1 / 1100
1 / 900 32
1 / 750 33
1 / 420
1 / 625 34
1 / 325
1 / 500 35
1 / 250
1 / 350 36
1 / 200
1 / 275 37
1 / 150
1 / 225 38
1 / 120
1 / 175 39
1 / 100
1 / 140 40
1 / 75 41
1 / 60
1 / 85 42
1 / 45
1 / 65 43
1 / 35
1 / 50 44
1 / 30
1 / 40
45 and older
1 / 20
1 / 25
Return to Prenatal Testing for Down Syndrome Return to Down Syndrome: Health Issues Homepage

39. Down’s Syndrome
The image shows a karyotype of a person with Down’s Syndrome, Trisomy 21

40. Sex Chromosome Disorders
Turner’s Syndrome (XO)
underdeveloped ovaries, short stature, webbed neck, and broad chest. Individuals are sterile, and lack expected secondary sexual characteristics. Mental retardation typically not evident.

42. Sex Chromosome Disorders
Klinefelter’s Syndrome (XXY)
Nondisjunction in males
Some development of breast tissue, little body hair is present; typically tall, with or without evidence of mental retardation. Males with XXXY, XXXXY, and XXXXXY karyotypes have a more severe presentation, and mental retardation is expected.

44. Recessively Inherited Disorders
Only expressed in individuals that are homozygous recessive
Carriers
heterozygous individuals
carry the recessive allele
phenotypically normal

45. Albinism

46. Cystic Fibrosis most common lethal genetic disease in the
1/2,500 people of European descent
results in defective or absent chloride transport channels in plasma membranes
Symptoms:
mucus buildup in some internal organs
abnormal absorption of nutrients in the small intestine

47. Sickle-Cell Disease 1/400 African-Americans Incompletely recessive
caused by the substitution of a single amino acid in the hemoglobin protein in red blood cells
Symptoms:
physical weakness
Pain
organ damage
even paralysis

48. Sickle Cell Anemia

49. Dominantly Inherited Disorders
Achondroplasia
form of dwarfism
lethal when homozygous for the dominant allele

50.                           
Achondroplasia

51. no obvious phenotypic effects until about 35 to 40 years of age
Huntington’s disease
degenerative disease of the nervous system
no obvious phenotypic effects until about 35 to 40 years of age

52. Some Autosomal Disorders in Humans
Type of Disorder
Disorder
Major Symptoms
Disorders caused by recessive alleles
Albinism
Lack of pigment in hair, skin, and eyes
Cystic Fibrosis
Excess mucus in lungs, digestive tract, liver; increased susceptibility to infections; death in childhood unless treated
Phenylketonuria
Accumulation in brain cells; lack of normal pigment; mental retardation
Tay-Sachs Disease
Lipid accumulation in brain cells; mental deficiency; blindness; death in early childhood
Disorders Caused by dominant alleles
Achondroplasia
Dwarfism (one form)
Huntington’s Disease
Mental deterioration and uncontrolled movements; appears in middle age
Disorders caused by codominant alleles
Sickle Cell Anemia
Sickled red blood cells; damage to many tissues

53. Multifactorial Disorders
Genetic factors
Environmental factors
Ex. Cancer, heart disease

54. Genetic Testing and Counseling
Genetic counselors can provide information to prospective parents concerned about a family history for a specific disease

55. Counseling Based on Mendelian Genetics and Probability Rules
Using family histories, genetic counselors help couples determine the odds that their children will have genetic disorders

56. Tests for Identifying Carriers
For a growing number of diseases, tests are available that identify carriers and help define the odds more accurately

57. Fetal Testing Amniocentesis chorionic villus sampling (CVS)
liquid that bathes the fetus is removed and tested
chorionic villus sampling (CVS)
sample of the placenta is removed and tested
ultrasound and fetoscopy
allow fetal health to be assessed visually in utero

58. LE 14-17a Amniocentesis Amniotic fluid withdrawn A sample of
amniotic fluid can
be taken starting at
the 14th to 16th
week of pregnancy.
Fetus
Centrifugation
Placenta
Uterus
Cervix
Fluid
Fetal
cells
Biochemical tests can be
performed immediately on
the amniotic fluid or later
on the cultured cells.
Biochemical
tests
Several
weeks
Fetal cells must be cultured
for several weeks to obtain
sufficient numbers for
karyotyping.
Karyotyping

59. LE 14-17b Chorionic villus sampling (CVS) A sample of chorionic villus
tissue can be taken as early
as the 8th to 10th week of
pregnancy.
Fetus
Suction tube
inserted through
cervix
Placenta
Chorionic villi
Fetal
cells
Biochemical
tests
Karyotyping and biochemical
tests can be performed on
the fetal cells immediately,
providing results within a day
or so.
Several
hours
Karyotyping

60. Newborn Screening
Tested at birth
Ex. Phenylketonuria (PKU)