human genetics: concepts and applications 5th edition ricki lewis copyright © the mcgraw-hill...

Human Genetics: concepts and applications5th edition

Ricki Lewis

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Chapter 3

Development


3-2

Developmentthe process of forming an adult from a

single-celled embryo

Cell division

Determination

Differentiation


3-3

Stages of the Human Life Cycle

• Genes orchestrate our physiology after conception through adulthood

• Development is the process of forming an adult from a single-celled embryo

• In humans, new individuals form from the union of sex cells or gametes

• Sperm from the male and oocyte from the female form a zygote


3-4

Male reproductive tract

bladder

urethra

testis

vas deferens

epididymis

bulbourethralgland

seminal vesicle

prostate


3-5

• Sperm cells are made in the seminiferous tubules of the testes (male gonads)

• The prostate gland, seminal vesicles, and bulbourethral glands add secretions to form the seminal fluid

• Sperm mature and are stored in the epididymis (attached to each gonad)

• They leave through the ductus deferens and then the urethra


3-6

Female reproductive tract

vagina

cervix

uterus

ovary

Fallopian tube


3-7

• Oocytes mature in the ovaries (female gonads)

• Each individual oocyte is surrounded by nourishing follicle cells, and each ovary houses oocytes in different stages of development

• Each month, an ovary releases a mature oocyte into the uterine/fallopian tube– If the oocyte is fertilized, it continues to the

uterus where it implants then divides and develops

– If it is not fertilized, the body expels it, along with the uterine-lining via the menstrual flow


3-8

• If the oocyte encounters a sperm cell the two join forming a fertilized OVUM which will then undergo a series of rapid cell division while moving through the tube and within days nestles into the lining of the uterus

• Hormones control the cycle of oocyte development, the menstrual cycle, and the preparation of the uterus to nuture a fertilized ovum


3-9

Replication of chromosomes• Replication is the

process of duplicating a chromosome

• Occurs prior to division

• Replicated copies are called sister chromatids

• Held together at centromere


3-10

Meiosisa cell division forming gametes

Goal: reduce genetic material by half

Why?

from mom from dad child

meiosis reducesgenetic content

toomuch!


3-11

• The cell division that produces gametes with half the number of chromosomes

• Occurs in special cells called germline cells

• Maintains the chromosome number of a species over generations

• Ensures genetic variability via the processes of independent assortment and crossing over of chromosomes


3-12

• Meiosis consists of two divisions –Meiosis I= The reduction division– Reduces the number of chromosomes

from 46 to 23 –Meiosis II= The equational division– Produces four cells from the two

produced in Meiosis I

• Note = Each division contains a prophase, a metaphase, an anaphase and a telophase


3-13

Meiosis: cell division in two parts

Homologsseparate

Sister chromatidsseparate

Result: one copy of each chromosome in a gamete.

Haploid

Diploid

Meiosis I(reductiondivision)

Meiosis II(equationaldivision)

Haploid


3-14

Diploid

Diploid

Haploid


3-15

Diploid


Diploid

Haploid


3-16

Diploid

Haploid


Diploid

Haploid


3-17

Diploid

Haploid



Diploid

Haploid


3-18

Diploid

Haploid



Haploid

Diploid

Haploid


3-19

Meiosis Animation


3-20

A replicated chromosome

Homologs separate in meiosis I and therefore different alleles separate.

homologs

same genesmaybe different alleles

sister chromatids

same genessame alleles

Gene X


3-21

Meiosis I : the reduction division


3-22

Prophase I

Early prophase

Homologs pair. Crossing over occurs.

Late prophase

Chromosomes condense.Spindle forms.

Nuclear envelope fragments.


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Metaphase I

Homolog pairs alignalong the equator of

the cell.

The random alignment pattern determines the combination of maternal and paternal chromosomes in the gametes


3-24

Anaphase I

Homologs separate andmove to opposite poles.

Sister chromatids remain Attached at their centromeres.


3-25

Telophase I

Nuclear envelopes reassemble.

Spindle disappears.

Cytokinesis divides cell into two.


3-26

Interkinesis

• A short interphase between the two meiotic divisions

• Chromosomes unfold into very thin threads

• Proteins are manufactured

• However, DNA is NOT replicated a second time


3-27

Meiosis IIOnly one homolog of each chromosome is present in the cell.

Meiosis II produces gametes with

one copy of each chromosome and thus one copy of each gene.

Sister chromatids carry identical genetic information.

Gene X


3-28

Meiosis II : the equational division

Prophase II(haploid)

Metaphase II(haploid)

Anaphase II(haploid)

Telophase II(haploid)

Four nonidentical

haploid daughter cells


3-29

Prophase II

Nuclear envelope fragments.

Chromosomes are again condensed and visible

Spindle forms.


3-30

Metaphase II

Chromosomes align along equator of cell.


3-31

Anaphase II

Sister chromatids separate and move to opposite poles.

Centromeres divide


3-32

Telophase II

Nuclear envelope assembles.

Chromosomes decondense (uncoil).

Spindle disappears.

Cytokinesis divides cell into two.


3-33

Results of meiosis

Gametes

Four haploid cells

One copy of each chromosome

One allele of each gene

Different combinations of alleles for different genes along the chromosome


3-34

Mitosis Meiosis

Number of divisions

12

Number of daughter cells

2 4

Genetically identical?

Yes No

Chromosome # Same as parent Half of parent

Where Somatic cells Germline cells

When Throughout life At sexual maturity

Role Growth and repair Sexual reproduction


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3-36

Recombination (crossing over)

• Occurs in prophase of meiosis I

• Generates diversity

•Creates chromosomes with new combinations of alleles for genes A to F.

a

b

c

d

e

f

A

B

C

D

E

F

A

B

C

D

E

F

a

b

c

d

e

f


3-37




Letters denote genes Case denotes alleles


A

B

C

D

E

F

a

b

c

d

e

f

c

d

e

f

A

B

a

b

C

D

E

F


3-38




Letters denote genes Case denotes alleles


A

B

C

D

E

F

a

b

c

d

e

f

c

d

e

f

A

B

a

b

C

D

E

F


3-39

Chiasmata

Crossing over

or recombination

events create

chiasmata.


3-40

Independent assortment

The homolog of one chromosome can be inheritedwith either homolog of a second chromosome.


3-41

Mitosis vs. Meiosis Animation


3-42

Spermatogeneis

Stem cells in testes divide mitotically to

create a pool of spermatocytes.

Spermatogenesis is the process of

forming the mature sperm.

Meiosis produces four spermatids.


3-43

• A diploid spermatogonium divides by mitosis to produce a stem cell and another cell that specializes into a primary spermatocyte

• In meiosis I, the primary spermatocyte produces two haploid secondary spermatocytes

• In meiosis II, each secondary spermatocyte produces two haploid spermatids

• Spermatids then mature into a tad-pole shaped spermatozoa


3-44

Spermatogenesis: sperm formation


3-45


3-46


3-47

Spermatogenesis Animation


3-48

Oogenesis

• A diploid oogonium divides by mitosis to produce a stem cell and another cell that specializes into a primary oocyte

• In meiosis I, the primary oocyte divides unequally forming a small polar body and a large secondary oocyte

• In meiosis II, the secondary oocyte divides to form another polar body and a mature haploid ovum


3-49

Oogenesis: ovum formation

• One of four meiotic products becomes an ovum.

• The three remaining meiotic products are polar bodies.


3-50


3-51

• Unlike spermatogenesis, oogenesis is a discontinuous process

• A female begins meiosis when she is a fetus– Oocytes arrest at prophase I until puberty– After puberty, meiosis I continues in one or

several oocytes each month but halts again at metaphase II

–Meiosis is only completed if the ovum is fertilized


3-52

Oogenesis

Oogonium(diploid)

Mitosis

Primaryoocyte(diploid)

Meiosis I

Secondaryoocyte(haploid)

Meiosis II

(if fertilizationoccurs)

First polar bodymay divide (haploid)

Polarbodiesdie

Ovum (egg)

Secondpolar body(haploid)

a

A

X

X

a

X

A X

a

X

a

X

Matureegg

A

X

A

X


3-53


3-54

Oogenesis versus Spermatogenisis


3-55

Maturation of the Follicle and Oocyte


3-56

Fertilization

• Fertilization is the joining of sperm and ovum.

• Meiosis II in the ovum is completed at the time of fertilization forming one ovum and one polar body.

• Following fertilization, chemical reactions occur preventing additional sperm from entering the ovum.


3-57

• Union of sperm and ovum

• In the female, sperm are capacitated and drawn to the secondary oocyte

• Acrosomal enzymes aid sperm penetration

• Chemical and electrical changes in the oocyte surface block entry of more sperm

• The two sets of chromosomes fuse into one nucleus, forming the zygote


3-58


3-59

Stages of development


3-60

Cleavage

• Mitotic cell division creates more cells.• Cells are called blastomeres.• A period of frequent mitotic divisions– Resulting cells are called blastomeres

• Developing embryo becomes a solid ball of 16+ cells called a morula

• The ball of cells hollows out to form a blastocyst


3-61

BlastocystThe developing embryo becomes ahollow ball of cells and is called a blastocyst.

The cells around the ICM become the extraembryonic membranes role in implantation supports embryo’s growth

Group of cells within the hollow space forms the inner cell mass (ICM).

develops into the embryo.


3-62

• Consists of two main parts– Inner cell mass (ICM), which develops

into the embryo– Trophoblast, which develops into the

placenta

• Implantation in the uterus occurs around day 7

• Certain blastocyst cells secrete human chorionic gonadotropin (hCG)– A sign of pregnancy


3-63

Early development: ovulation to implantation

Figure 3.14


3-64

Germ layers: endoderm, mesoderm and ectoderm


3-65

Gastrulation

• The primary germ layers form in the second week after fertilization– Ectoderm (outermost layer)–Mesoderm (middle layer)– Endoderm (innermost layer)

• This three-layered structure is the gastrula

• Cells in each germ layer begin to form specific organs


3-66

Germ layers

Endoderm the innermost germ layer developslining of GI tract

liver

pancreas

thymus

Ectoderm the outermost germ layer developsskin

nervous system

eye lens

Mesoderm the middle germ layer develops muscle

connective tissue

blood vessels

kidneys


3-67

Supportive Structures

• Structures that support and protect the embryo include:– Chorionic villi – Yolk sac– Allantois– Umbilical cord– Amniotic sac

• By 10 weeks the placenta is fully formed


3-68

Twins

Dizygotic twins

two ova + two sperm

Developing embryo splits during early development

Monozygotic twinsone ovum + one sperm

Same genetic relation as any siblings

Genetically identical

- Arise from two fertilized ova- Same genetic relationship as any two siblings

-Arise from a single fertilized ovum-Embryo splits early during development-Twins may share supportive structures


3-69


3-70


3-71

The Embryo Develops

• Organogenesis is the transformation of the simple three germ layers into distinct organs

• During week 3, a band called the primitive streak appears along the back of the embryo

• This is followed rapidly by the notochord, neural tube, heart, central nervous system, limbs, digits, and other organ rudiments

• By week 8, all the organs that will be present in the newborn have begun to develop– The prenatal human is now called a fetus


3-72


3-73

The Fetus Grows

• During the fetal period, structures grow, specialize and begin to interact

• Bone replaces cartilage in the skeleton

• Body growth catches up with the head

• Sex organs become more distinct

• In the final trimester, the fetus moves and grows rapidly, and fat fills out the skin

• The digestive and respiratory systems mature last


3-74

Critical periods of development

• Organs develop at different times in development: a critical period.

• During its critical period, an organ is vulnerable to toxin, viruses, and genetic abnormalities.

• Altering the normal development may cause birth defects.


3-75

• The time when a particular structure is sensitive to damage is called its critical period

• Birth defects can result from a faulty gene or environmental insult

• Most birth defects develop during the embryonic period

• -These are more severe than those that arise during the fetal period


3-76

Fig. 3.19


3-77

Teratogens are agents causing birth defects

Drugs Thalidomide limb defects Cocaine stroke, nervous system Cigarettes poor growth, low birth weight Alcohol fetal alcohol syndrome (FAS)Nutrients folic acid deficiency neural tube defects vitamin C excess scurvy, immune effects

Viral infection rubella deafness, cataracts, heart herpes death, CNS damage, skin lesions HIV HIV infection, prematurity


3-78

Fetal Alcohol Syndrome


3-79

Onset of genetic disorders • Is the time when a disorder is first observed. • Many disorders have a characteristic time of onset.

Time of onset Disorder

Prenatal Polydactyly

Birth Phenylketonuria

10 years Wilson disease

20 years Marfan syndrome

30 years Breast cancer

40 years Pattern baldness

50 years Alzheimer disease


3-80

Clones

• A clone is a collection organisms derived from the same original cell.

• Genetically identical

• Phenotype may differ because of different life history.

Calves cloned share genes.variation in coat patterns reflect migration of cells during development


3-81

Aging

• Genes may impact health throughout life

• Single-gene disorders that strike in childhood tend to be recessive

• Adult-onset single-gene traits are often dominant

• Interaction between genes and environmental factors – Example: Malnutrition before birth


3-82

• Genes control aging both passively and actively

• A few single-gene disorders can speed the signs of aging

• Segmented progeroid syndromes– Hutchinson-Guilford

syndrome


3-83


3-84

Is Longevity Inherited?

• Aging reflects genetic activity plus a lifetime of environmental influences

• Human chromosome 4 houses longevity genes– Genome-wide screens of 100-year olds are

identifying others

• Adoption studies compare the effects of genes vs. the environment on aging


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human genetics: concepts and applications 5th edition ricki lewis copyright © the mcgraw-hill...

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