ch 3 meiosis and development(1)

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Human GeneticsCh 3: Meiosis and Development

Powerpoint Lecture Outline




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Mitosis Review

Mitosis occurs in Somatic Cells (Non-sex Cells)

o Embryogenesiso Growth

o Development

o Repair Injury

One round of cell division occurs

One cell divides to produce two daughter cells

Daughter cells have the same number of chromosomes

as the parental cell

Daughter cells are genetically identical to theparental cell




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Meiosis Overview

Meiosis occurs to produce Gametes (Sex Cells)

o Eggso Sperm

Two rounds of cell division occur

One cell divides to produce four daughter cells

Daughter cells have half the number of chromosomes as the

parental cell. (46 23)

Daughter cells are genetically different from the

parental cells.




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VERY IMPORTANT SLIDE!!!!!




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Gametes

Meiosis is cell division to produce gametes

Individuals form from the union of two gametes

(sperm and oocyte) Meiosis has two divisions of the nucleus

(Meiosis I and Meiosis II) and produces cells

with half the number of chromosomes




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Humans are diploid organisms

Gametes are haploid cells




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Humans are Diploid

We have 23 pairs of Homologous

Chromosomes:

± Same Size

± Centromere in the same place

± Same banding pattern

± Same type of genes (not the exact same

nucleotide sequence) ± One of each pair comes from each parent!




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Human Karyotype




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Meiosis

Reduces the genetic material by half

Why is this necessary?

from mother from father child

meiosis reduces genetic content

Too

Much!

46 46

92

23 23 46

Just

Right!




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Meiosis Occurs with Two Rounds of Cell

Division

Meiosis I ± Reduction Division

± Number of Chromosomes is reduced to half

± Homologous pairs separate

Meiosis II

± Like mitosis but cells have ½ the number of

chromosomes ± Replicated chromosomes are split

± Sister Chromatids separate at the centromere




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Meiosis: Cell Division in Two Parts

Result: one unduplicaetd copy of each chromosome

goes to each gamete.

Haploid

Diploid

Meiosis I

(reductiondivision)

Meiosis II

(equationaldivision)

Haploid

Figure 3.3




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Meiosis

Interphase precedes meiosis I

(Chromosomes are Replicated)

Meiosis IProphase I

Metaphase I

Anaphase I

Telophase I

Meiosis IIProphase II

Metaphase II

Anaphase II

Telophase II

Figure 2.13




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Meiosis I : the reduction division

Prophase I(early)

(diploid)

Prophase I(late)

(diploid)

Metaphase I(diploid)

Anaphase I(diploid)

Telophase I(diploid)

NucleusSpindle

fibersNuclear

envelope

Figure 3.4




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Prophase I




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Metaphase I

Figure 3.4




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Anaphase I

Figure 3.4




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Telophase I/Cytokinesis

Figure 3.4




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Meiosis II : Sister Chromatids Separate

(Like Mitosis)

Prophase II

(haploid)

Metaphase II

(haploid)

Anaphase II

(haploid)

Telophase II

(haploid)

Four

nonidentical

haploid

daughter cells

Figure 3.4




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Prophase II

Figure 3.4




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Metaphase II

Figure 3.4




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Anaphase II

Figure 3.4




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Telophase II/Cytokinesis

F

igure 3.4




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Results of Meiosis

Gametes

Four haploid cells

Contain one copy of each

chromosome and one allele of each gene

Each cell is unique

F

igure 3.4




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Meiosis and Sexual Reproduction Produces Genetic

Diversity in Three Ways

1. Crossing over during Prophase I

(Recombination)

2. Inpendent Assortment during Metaphase I and II

3. Random Fertilization




3-25Fig 3.5

1. Recombination:Homologous

Chromosomes

Exchange Pieces

Of DNA

During Prophase I




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2. Independent AssortmentChromosome pairs can line up in different

orientations at the equator during Metaphase I or II

Figure 3.6

There are 223

possible ways

chromosome pairs

can line up.

This equals 8,388,608

different possible

combinations!




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3. Random Fertilization

Each ovum is genetically unique

Each sperm is genetically unique

About 250 million sperm are produced by

males each day

Fertilization by the sperm is random

**Each human is genetically unique. There is

less than a 1/70 trillion chance that your genetics would occur randomly**




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Two Process Produce the Gametes in

Humans

Spermatogenesis occurs in males and

produces sperm.

Oogenesis occurs in females and produces

ovum (eggs).

Each gamete only has 23 chromosomes!




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Male Reproductive Tract

bladder

urethra

testis

vas deferens

epididymis

bulbourethral

gland

seminal

vesicle

prostate

Figure 3.1




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Female Reproductive Tract

vagina

cervix

uterus

ovary

uterine tube

Figure 3.2




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Spermatogenesis

Stem cells in testes dividemitotically to producespermatocytes

Spermatocytes divide by meiosisto produce four equal sizedhaploid spermatids that matureinto four sperm

.

Figure 3.9




3-32Fig 3.8

Spermatogenesis Occurs in the

Seminiferous Tubules in the Testes




3-33Fig 3.7

Sperm Formation: Spermatogenesis

46 xsms

46 xsms

23 xsms

23 xsms




3-34Fig 3.9

Sperm

Structure




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Oogenesis: Ovum (Egg) Formation

Cells of the ovary divide to form primary oocytes Primary Oocytes divide by meiosis

Unequal cytoplasmic division occurs

Does not occur daily as in males

± At birth, primary oocytes are arrested in prophase I

± At ovulation, a primary oocyte progresses through metaphase

II

± Meiosis II does not complete unless the oocyte is fertilized.

The four meiotic products produce one functional ovum and threepolar bodies.




3-36Fig 3.12

Oogenesis Occurs in the Ovaries




3-37Fig 3.11

46 xsms

46 xsms

23 xsms

23 xsms

Females areborn with

eggs in

this stage

Oocytes are

released in

this stage

during ovulation

Egg Formation: Oogenesis




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Fertilization

Fertilization is the union of sperm and ovum

After fertilization, chemical reactions occur preventing additional sperm from entering the ovum

The ovum

completes

meiosis II after

fertilization




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Spermatogenesis Oogenesis




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Statistics of Fertilization and Live BirthOf every 100 secondary oocytes exposed to sperm:

84 are fertilized

69 implant

42 survive one week or longer

37 survive six weeks or longer

Only 31 are born alive

½ of all Fertilized eggs that do not

survive have chromosomal defects




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Stages of Development

Table 3.2




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Early Development:

Ovulation to Implantation

Figure 3.14




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Germ Layers:

Endoderm, Mesoderm, and Ectoderm

Figure 3.15




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Embryo Develops

Figure 3.18




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Multiple Births

Dizygotic twins

Form from two different zygotes

Two ova are fertilized

Same genetic relationship as any siblings

Monozygotic twins

One ova is fertilized

Developing embryo splits during early

development

Genetically identical




3-46Figure 3.16




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Critical Periods of Development

Organs develop at different times: a critical period

During its critical period, an organ is vulnerable to

toxins, viruses, and genetic abnormalities

Altering the normal development may cause birth

defects




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Critical Period: Time when genetic

Abnormalities, Toxic Substances or Viruses can Alter a Specific Structure

Causes:1. Abnormal gene(s)

2. Toxic substances

3. Viruses

C © G C f




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Toxic Substances: Teratogens are

chemicals or other agents that cause

Birth Defects.

ThalidomideCocaine

Smoking

AlcoholNutrients: too many

or too few

C i ht © Th M G Hill C i I P i i i d f d ti di l




3-51Fig 3.21

Fetal Alcohol Syndrome can

Cause Distinct Physical Characteristics

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Maturation and Aging

Genes may impact health throughout life Single gene disorders are expressed early in life and tend

to be recessive

Adult onset single gene traits are often dominant

Interaction between genes and environmental factors

Example: malnutrition before birth

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