The human body contains 100 trillion cells. There is a nucleus inside each human cell (except red blood cells). Each nucleus contains 46 chromosomes, arranged in 23 pairs. One chromosome of every pair is from each parent. The chromosome s are filled with tightly coiled strands of DNA. Genes are segments of DNA that contain instructions to make proteins— the building blocks of life.
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The human body contains 100 trillion cells. There is a nucleus inside each human cell (except red blood cells). Each nucleus contains 46 chromosomes, arranged.
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The humanbody contains100 trillioncells.
There is anucleus insideeach humancell (except redblood cells).
Each nucleuscontains 46chromosomes,arranged in 23 pairs.
Genes are segmentsof DNA that containinstructions to makeproteins— thebuilding blocksof life.
Gametes and Zygote
Sperm
Ovum
Gametes(reproductive cells)
Fertilization Zygote
Sperm
Cell with 46 chromosomes (only one pair of homologouschromosomes is shown here). Each member of the pair has begun to replicate similar tomitotic cell division.
First meiotic cell divisionbegins, but does not proceedas in mitosis. Instead of thereplicated chromosome splitting apart, one member of eachhomologous pair becomes a part of the first-generation daughter cell.
The second meiotic division proceeds after the first is completed;now the replicated chromosomeacquired in the first-generationdaughter cell splits apart.
Each of the four gametesproduced by the two-step processnow has acquired one memberof the pair of homologouschromosomes.
The Process of Meiosis for Sperm Cells
Cell nucleus with a pair of chromosomes
Chromosomes split and replicate to producetwo identical pairs
The pairs separate, and the cell divides
Each daughter cell now has a pair of chromosomes that is identical to the original pair
The Process of Mitosis
GENOTYPE AND PHENOTYPE
GENOTYPE: Set of genetic traits a person inherits; a person’s inborn capacity or potential
PHENOTYPE: Set of traits a person actually displays, resulting from a combination of the person’s genotype (potential) and life experiences that modify that potential
X
X X
Y
NormalFather
Carrier Mother
XX
Normal
Daughter
(25%)
XX
Carrier
Daughter
(25%)
XY
Normal
Son
(25%)
XY
Hemophilic
Son
(25%)
Inheritance of Hemophilia, a Sex-Linked Disorder
FR
EQ
UE
NC
Y O
F D
OW
N S
YN
DR
OM
E (
PE
R 1
000)
MATERNAL AGE (YEARS)
15 20 25 30 35 40 45 50
100
90
80
70
60
50
40
30
20
10
0
Relationship Between Maternal Age and the Incidence of Down Syndrome
r
D r
rNormalFather
Affected Parent(Has the Disorder)
DrAffected
(25%)
rrnormal(25%)
DrAffected
(25%)
rrnormal(25%)
Inheritance of a Dominant Gene Disorder
(50%) (50%)
Inheritance of a Recessive Gene Disorder
D
r
CarrierFather
Carrier Mother
DrAffected
(25%)
rrnormal(25%)
DrAffected
(25%)
rrnormal(25%)
D r
Risk of Selected Genetic Disorders
ChromosomalDown SyndromeKlinefelter syndrome (XXY)Fragile X syndrome
1/8001/800 men1/1,200 male births1/2,000 female births1/3,00 women
1/300 - 1/1001/2,3001/15,000 - 1/5,000
1/2,500 white persons (risk of being a carrier is 1/25)1/625 African Americans (risk of being a carrier is 1/10)1/3,600 Eastern European Jews(risk of being a carrier is 1/30 -
1/300)
1/2,500 male babies
1/1251 - 2/1,0001/1,000 - 1/5,000
Who Should Seek Prenatal Counseling?
1. Couples who already have a child with some serious defect such as Down
syndrome, spina bifida, congenital heart disease, limb malformation, or
mental retardation
2. Couples with a family history of a genetic disease or mental retardation
3. Couples who are blood relatives (first or second cousins)
4. African Americans, Ashkenzzi Jews, Italians, Greeks, and other high-risk
ethnic groups
5. Women who have had a serious infection early in pregnancy (rubella or
toxoplasmosis) or who have been infected with HIV
6. Women who have taken potentially harmful medications early in
pregnancy or habitually use drugs or alcohol
7. Women who have had X rays taken early in pregnancy
8. Women who have experienced two or more of the following: stillbirth,
death of a newborn baby, miscarriage
9. Any woman thirty-five years or older
Source: Adapted from Fienbloom & Forman (1987) p. 129
The Concept of Range of Reaction for Intellectual PerformanceIn
tell
ectu
al P
erfo
rman
ce (
IQ)
High
Restricted Enriched
Average
Average
child A child B child C
Rea
ctio
n R
ange
Low
Type of Environment
KEY COMPARISONSTYPE OF STUDY OBJECTIVE
Same geneticrelatedness,differentenvironments
Twin
Adoption
Differencesin geneticrelatedness,same environment
Identical twinstogether
Identical twinsapart
Identical twinstogether
Fraternal twinstogether
Measuring the effects of Nature and Nurture: Twin and Adoption Studies
+0.10
+0.20
+0.30
+0.40
+0.50
+0.60
+0.70
+0.80
+0.90
+1.00
Cor
rela
tion
of IQ
sco
res
Identical twins reared together
Identical twins reared apart
Non-identical twins reared together
Siblings reared together
Siblings reared apart
Unrelated children reared together
Unrelated children reared apart
Correlations of IQ Scores
Ris
k
Prevalence ingeneral population
Fraternal twins
20
10
Major depression
Identical twins
Bipolar disorder
Prevalence ingeneral population
Fraternal twins
Identical twins
40
30
60
50
80
70
Blastocyst CleavageMorula Zygote
Fertilization
Ovulation
Maturefollicle
Implantationbeginning
Developingfollicles
Uterinewall
Ovary
Uterus
Cervix
Vagina
Fallopian tube
5 6
4
7
3 2 1
The Germinal Stage of Prenatal Development
Zygote Implantation of the Embryo
Fallopian tube
Ovary
Uterus
Cervix
Vagina
Embryo joinedto uterine wall
Ovary
Blastocyst
Fallopian tube
Conception
ImplantationFirstmissedperiod
Secondmissedperiod
OvumZygoteEmbryo
7 6 5 4 3 2 1 0
Weeks since fertilization
4 weeks 6 ½ weeks
7 weeks 9 weeks
15 weeks
Development During the Embryonic and Fetal Stages
Cell culture
Cells
Chromosome analysisBiochemical tests
Amniotic fluid
CentrifugeUterine wall
Placenta
Chorion
Amnioticfluid
Cell
Full termFetal period (in weeks)Embryonic period (in weeks)