Download L8 cells PPt - Moodle

Responding to ill Health
Life Science
Cells
(genetic inheritance & cancer)
US Dept Energy (2005)
https://commons.wikimedia.org/wiki/File:Dna-split.png
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Learning outcomes
 Summarise the role of chromosomes & genes in the
inheritance of characteristics
 Discuss the differences between meiosis and mitosis
in relation to chromosome numbers
 Explain the terms: dominant, recessive, co dominant,
sex linked
 Explain the terms mutation and carcinogenesis and
outline the modes of cancer spread
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Introduction
Genetics - the study of heredity information
transmitted via genetic material (DNA)
DNA in cell nucleus, visible as chromosomes during
cell division
Gene = piece of DNA associated with particular
characteristic, acts as template for protein synthesis
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How a protein is made
DNA in nucleus
proteins
synthesised by
ribosomes in
cytoplasm
information passed
from DNA to
ribosomes via RNA
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DNA and proteins
 A protein = a chain of amino acids in a particular
sequence
 Approx 20 different amino acids
 DNA determines which amino acids are made via a
“genetic”code
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Genes
 All body cells have the same genes
 Different genes are ‘expressed’ in different cells
 e.g
 gene coding for insulin is expressed in certain cells of
pancreas (  cells, islets of Langerhans )
 Genes coding for enzymes which break down glucose
expressed in virtually all body cells
 NB importance of gene expression in right cells, in
right amounts at right times
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Cells and chromosomes
Normal body cells
 diploid (46 chromosomes)
 23 homologous pairs
 i.e. 2 copies of each chromosome
 Half inherited from father and half from mother
 Sum total of chromosomes = karyotype
Cells and chromosomes
 22 autosomes (nos 1 -22)
 Sex chromosomes (no 23)
 Male XY
 Female XX
National Cancer Institute (2007) Karyotype_(normal).
https://commons.wikimedia.org/wiki/File:Karyotype_(normal).jpg
meiosis
 Eggs and sperm must have half the number of
chromosomes of a normal body cell (23 instead of 46
– one member of each homologous pair)
 Why? ………………..
 achieved via a special type of cell division meiosis
 errors in meiosis may  chromosome abnormalities
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Alleles and genes
 One copy of each gene = one maternal & one paternal
 Alleles - different versions of the same gene
 Site of a gene = locus
 At one particular locus on homologous pair , genes
code for the same trait
gene
Allele
A
A
a
B
B
Allele
a
UWS Staff (2015)
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Dominant & recessive traits
alleles may be :
 dominant ( CAPITAL LETTER)
recessive (lower case letter)
e.g.
E = unattached earlobe
e = attached earlobe
EE
http://www.rrnursingschool.biz/unity-companies/genes-and-alleles.html
ee
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Dominant & recessive traits
everyone has 2 of these alleles, therefore 3 possibilities:
 EE
 Ee
 Ee
Homozygotes & heterozygotes
Individuals with:
 EE or ee are homozygotes
(2 copies of the same allele)
 Ee are heterozygotes
(2 different alleles)
genotype
phenotype
EE
unattached
Ee
unattached
ee
attached
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Cell division & reproduction
gametes
Stannered (2007)
https://commons.wikimedia.org/wiki/File:Sexual_cycle.svg
Human Life Cycle
• half paternal genes
• half maternal genes
 Parents  children
only physical link
• sperm/ova produced by
meiosis  half number of
chromosomes
(n = 23: haploid)
• all other cells have 46
(2n = 46: diploid)
• sperm + ovum unite 
diploid zygote  mitosis 
many diploid daughter cells
 embryo:
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Predicting genotypes & phenotypes of children
Each gamete (egg/sperm) receives:
 one copy of each chromosome
 & one allele of each gene
e.g.
 parent with EE genotype all gametes have E allele
 Parent with Ee genotype
 50% of gametes have E allele
 50% of gametes have e allele
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Example
•
•
•
•
father’s genotype Ee – phenotype?
unattached
different types of gamete?
50% E ,50% e
•
•
•
•
mother’s genotype ee – phenotype?
attached
different types of gamete?
all e
Example – Punnett’s Square to predict progeny
continued
• Ear lobe attachment of children?
father
E
e
e
Ee
ee
Ee
ee
mother
e
• Probability of having a child with attached
earlobes
• 50%
1. Autosomal dominant disorders
Only one copy of allele needed for individual to be
affected
Example 1 - Neurofibromatosis
 Tumour-like
growths on skin
 gene on chromosome 17
 variable expressivity
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1. Autosomal dominant - neurofibromatosis
Nicke.me (2011)
https://commons.wikimedia.org/wiki/File:Dermal_Neurofibroma.jpg
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Autosomal Dominant Disorders
Prediction example – neurofibromatosis
•
•
•
•
father’s genotype Nn – phenotype?
neurofibromatosis
different types of gamete?
50% N ,50% n
•
•
•
•
•
•
mother’s genotype ?
nn
phenotype?
normal
different types of gamete?
all n
Example - continued
• Possible genotypes of children?
mother
n
n
N
Nn
Nn
n
nn
nn
father
Probability of having child with
neurofibromatosis?
50%
Autosomal dominant disorders
Example 2 - Huntingdon disease
 degenerative brain disorder
 gene on chromosome 4
 faulty production of neurotransmitter (GABA)
 uncontrolled movement
 impaired speech, dementia
 late onset
Why is late onset a problem?
Sufferer may already have reproduced before disease
becomes apparent
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Autosomal recessive disorders
 2 alleles of abnormal gene  disease
 1 allele of abnormal gene = ‘carrier’
Examples:
Cystic fibrosis
 1 in 2000 births, (1 person in 22 = carrier)
 Thick viscous mucus (chloride ion channels faulty)
PKU




1 in 5000 births
enzyme lacking for breakdown of phenylalanine
Accumulation  mental retardation
Babies put on diet low in phenylalanine until brain fully developed (7yrs)
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Sex linked inheritance
 XY = male
 XX = female
 Male determines sex of child (always an X
chromosome from mother)
 X chromosome larger than Y
 Alleles on X chromosome may not have equivalent on
Y
Sex linked inheritance
 Male has only one X chromosome (this is referred to
as being hemizygous) and must therefore express the
alleles on that chromosome, whether they are
dominant or recessive.
 Female has two X chromosomes:
A female needs two copies of
an X-linked recessive allele
to express it, a male needs only one
Sex linked inheritance
X –linked recessive disorders
Men cannot be carriers, women can.
Many more men than women likely to be affected by
the disorder
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Example – red-green colour blindness
X C = normal vision, X c = colour blind
• man’s genotype?
• X CY
• phenotype?
• normal
• different types of gamete?
• 50% X C 50% Y
•
•
•
•
•
•
mother’s genotype ?
X CX c
phenotype?
carrier
different types of gamete?
50% X C 50% X c
Example - continued
Chances of colour-blind boy?
• possible genotypes of children ?
Chances of colour-blind girl?
mother
XC
XC
XC XC
Xc
X CX c
father
Y
Y XC
YXc
Mutations & disorders
Mutations (changes in sequence of DNA bases)
may result in changed properties of proteins for
which they code
caused by e.g.
 errors of ‘copying’
 environmental factors
 heritable if in germ cells
not heritable if in body cells (somatic mutations)
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Regulation of genes
 A complex subject!
 Genes are switched on or switched off as appropriate
e.g.
 Certain genes are switched on to stimulate cell
division
 When adequate growth has been achieved other
genes are switched on to inhibit cell division
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Mutations & cancer
 Cancer occurs when gene mutations 
uncontrolled growth & division of cells
 Several mutations needed over many years
 Process of cancer development = carcinogenesis
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Carcinogens
Carcinogens –
 agents which predispose to tumour development
 Cause mutations in the genes that control normal cell
growth & development
 Can be:
 Chemical
 Physical
 viral
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Cancer
 Tumour (neoplasm) may be benign or malignant
 Malignant tumour = cancer
 Normal cells are differentiated (resemble parent
cell)
 Cancer cells usually undifferentiated (do not
resemble cell from which they were derived)
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Cancer
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Some tissues more affected by metastatic spread:
 LUNGS pulmonary circulation
 LIVER hepatic portal circulation
 BRAIN, KIDNEY, BONE – large blood supplies
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