Human Genetics

Human Genetics

Multifactorial Developmental Traits

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Cells express phenotypes

inherited traits, acquired traits, illnesses

X-linked Duchenne muscular dystrophy has cellular phenotype before whole-body symptoms appear– lack of dystrophin protein causes muscle cells to collapse when contracting.

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Tissue Types

differentiated cells

290 types of somatic cells

sperm or egg cells

 

stem cells

divide to differentiated cells

replicate through self-renewal

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Generalized Animal Cell

number and type of organelles differ based on cell type/function

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Specialized cells: secretion of milk

secretion of milk is a phenotype of mammary gland lactating cells

 

requires organelles important in secretion

RER

Golgi

vesicular transport

 

 

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Deficiencies of organelles cause disease

lysosomal storage disease: Tay-Sachs

cells rely on number of lysosomes

essential for normal brain function

 

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Inefficiencies of organelles cause disease

mitochondrial myopathies

inefficient cellular respiration leads to ROS

ROS destroys enzymes, DNA

 

 

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Deficiencies of cell-to-cell communication

plasma membrane surface molecules

signal transduction

receptors detect signals from outside the cell and transmit them inward

small molecules, antigens, electrical impulses, mechanic changes, thermal changes, etc.

 

cellular adhesion

molecules help cells attach to other cells

 

 

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epidermolysis bullosa is a defect in skin attachment

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Normal cell division and death

growth, development, repair, healing

balance of mitosis/cytokinesis and apoptosis

precise, genetically programmed sequence of events

required for shaping limbs

 

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The cell cycle is controlled molecularly

molecular checkpoints in cell cycle

internal and external factors affect mitotic clock

 

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Mitosis regulated by hormones, growth factors

hormones are produced by glands

transported in bloodstream to body

binds specific receptor

growth factors are produced by cells

act locally, near site of production

binds receptor type

e.g., Epidermal Growth Factor (EGF) released by damaged cell, stimulates cell division in skin beneath scab

 

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Linear chromosomes protected by telomeres

hundreds to thousands of 6-base repeats

50-200 bases lost after each cell division

after 50 divisions, shortened telomeres signal cell to stop dividing:

most cells go through apoptosis

 

 

 

 

some cells produce telomerase to correct ends, avoid apoptosis

sperm, eggs, bone marrow, and cancer cells

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Stem cells are immortal

divides by mitosis

stem cell

progenitor cell

does not renew

differentiates

 

active telomerase

maintains chromosome ends

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Pathways to Cell Specialization

totipotent

can give rise to every cell type

pluripotent

fewer possible fates

multipotent

few developmental choices

unipotent

one developmental choice

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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Stem cells replace unhealthy cells

human stem donor cells

embryonic stem cells (pluripotent)

using the inner cell mass (ICM) of an embryo

differentiate into any cells of embryo (not trophoblast)

 

induced pluripotent stem (iPS) cells (multipotent)

reprogrammed somatic cells

differentiate into any of several cell types

 

adult stem cells (multi- or unipotent)

tissue-specific or somatic stem cells

differentiate into one or a few cell types

 

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Stem Cells in Health Care

to replace unhealthy cells

 

self-donor

matched donor

cardiomyocytes grown in a dish from iPS cells

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Human development is controlled

stages of mammalian development

zygote after fertilization

fusion of egg and sperm

 

cleavage

first divisions to multi-cell blastocyst

 

embryo for the first 8 weeks

embryonic plate develops from inner cell mass

 

fetus from the start of the ninth week until birth

growth and maturation

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Fertilization

formation of zygote

sperm are activated and drawn to the oocyte

sperm acrosomal enzymes aid sperm penetration

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

two genetic packages meet and merge

 

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Cleavage

formation of blastocyst

period of frequent mitotic divisions

solid ball of 16+ cells (morula)

hollowing of ball to blastocyst

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blastocyst is trophoblast (outer layer) + inner cell mass

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Imprinting errors cause disease

deletion of chromosome 15 imprinted region

Prader-Willi syndrome if deletion inherited from father (no active copy)

Angelman syndrome if deletion inherited from mother (no active copy)

 

Prader-Willi s. phenotype of obesity, NIDDM, excessive hunger, moodiness and conduct disorder

Angelman s. phenotype of failure to thrive, hyperactivity, muscle hypotonia, happy mood

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Importance of genomic imprinting

regulate abundance of key proteins in embryo

imprinted genes in clusters, controlled by imprinting centers

one gene in cluster could be essential

others imprinted in bystander effect

 

uniparental disomy

results in teratoma

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Changes in gene expression in development

over time, in different cell types

programmed differentiation of stem cells

 

cell, tissue, or organ/gland level

changes in sets of proteins available

everything in a cell is due to a gene product

 

inherited or acquired changes in gene expression: epigenetics

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