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GENETICS

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samantha wyatt

on 8 January 2015

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Transcript of GENETICS

GENETICS
Allele (code):
different forms of the same gene
Heterozygous:
having two different alleles on homologous chromosomes
Homozygous
: having two identical alleles on homologous chromosomes




Dominant
: the characteristic that is expressed in the heterozygous condition
Recessive:
the characteristic that remains hidden in the heterozygous condition








Genotype:
genetic information carried by an individual









Remember: as Individuals inherit two alleles the genotype ALWAYS contains 2 letters

Phenotype:
the observable characteristic
Mendel took two pure breeding (same genetic information) plants:

1 x Tall 1 x Short




All plants produced were TALL


Co-dominance
Alternatively heterozygous offspring may display a phenotype that simultaneously expresses the phenotypes of both homozygous parents
This is called
Co-dominance
Phenotype of human red blood cells display incomplete dominance
Learning Objectives
What can we predict from our genes?
NOT ALL ALLELES EXHIBIT DOMINANCE!
Incomplete Dominance
Sometimes the heterozygote has a phenotype
intermediate
between the phenotypes of the two homozygotes.

This is called
incomplete dominance
- Interpret and predict the inheritance of autsomal and sex-linked genes

- Understand and predict the inheritance of genetic disorders

- Interpret and generate pedigree charts

- understand the applications of gene technology and identify the ethical implications
REVISION
Nucleotides
Autosomes
Sex Chromosomes
http://www.abpischools.org.uk/res/coResourceImport/modules/genome/fullscreenflash76f5.cfm?flash=en-flash/mitosistime.swf&title=Mitosis&version=8

Mitosis
Meiosis
Haploid
Diploid
Gametes
Sexual reproduction
http://www.abpischools.org.uk/res/coResourceImport/modules/genome/fullscreenflash7765.cfm?flash=en-flash/meosistime.swf&title=Animation+of+meiosis&version=8
http://www.abpischools.org.uk/res/coResourceImport/modules/genome/fullscreenflashd881.cfm?flash=en-flash/fertilisation.swf&title=Animation+of+fertilisation&version=8
Growth & Repair

what happens when there are
mutations
in the DNA sequence?
Genes found on the X or Y chromosome are called?
Boy
or
Girl?
REVISION
Nucleotides
Autosomes
Sex Chromosomes
http://www.abpischools.org.uk/res/coResourceImport/modules/genome/fullscreenflash76f5.cfm?flash=en-flash/mitosistime.swf&title=Mitosis&version=8

Mitosis
Meiosis
Haploid
Diploid
Gametes
Sexual reproduction
http://www.abpischools.org.uk/res/coResourceImport/modules/genome/fullscreenflash7765.cfm?flash=en-flash/meosistime.swf&title=Animation+of+meiosis&version=8
http://www.abpischools.org.uk/res/coResourceImport/modules/genome/fullscreenflashd881.cfm?flash=en-flash/fertilisation.swf&title=Animation+of+fertilisation&version=8
Growth & Repair

what happens when there are
mutations
in the DNA sequence?
Genes found on the X or Y chromosome are called?
Boy
or
Girl?
Father of modern genetics
Researched with pea plants
Developed ideas of dominance and trait segregation

Gregor Mendel

Mendelian Genetics

Mendelian Genetics

- Height

- Seed Colour

- Seed Shape
Mendel studied pea plant:
He cross pollinated these plants

When these plants were crossed

He found he got a ratio of
3 tall to 1 short

He cross pollinated these plants

He obtained the same results using other characteristics

This led to the following conclusions


1.

Organisms have two codes for each characteristic

2. Codes can be different

3. Offspring inherit one code from their father and one code from their mother

4. One type of code can mask another type of code

Important Terminology
Punnet Squares
P generation
F1 generation
F2 generation
Both traits had
re-appeared!
For the P generation what is the genotype and the phenotype of the plants?
Pure breeding tall plant
Pure breeding short plant
Genotype from one parent goes here
(one letter per square)
Genotype from one parent goes here
(one letter per square)
T
T
t
t

REPRESENTED BY LETTERS!
usually the first letter of the dominant trait
CAPITAL "BIG" LETTER = Dominant Allele
lowercase "little" letter = Recessive allele
QUESTION
If
B
represented an allele for

Brown eyes
and
b
represented an allele for
blue eyes

1. would the genotype BB have a brown eye phenotype or blue eye phenotype?

2. What phenotype would the genotype Bb have?


3. A homozygous brown eye mother and a blue eye father are expecting their first child, will the child have blue eyes or brown eyes?
Why did mendal see a
see only tall plants in the FI generation but a
3:1 ratio in the F2 generation?
Inheritance
Tracey and Anthony are expecting their first child.

Tracey has a Widow Peak, like her mother. However, Tracey's dad has a straight hairline like her husband Anthony.

What are the chances of their child also having a widow peak? (
Widow's peak is dominant over straight hairline)
Egg Plant colour is an example of incomplete dominance
A cross between a homozygous black chicken and a homozygous white chicken produces a heterozygous gray chicken!
Individuals can either be homozygous or heterozygous with blood type O

A woman heterozygous for type A blood and a man heterozygous with type B blood could have offspring with which blood types?


Antigens
are found on the surface of red cells that detect the presence of foreign blood cells
Antigens stimulate the production of
Antibodies
that are capable of destroying foreign red blood cells
INHERITANCE OF SEX LINKED GENES

Genes located on the Y Chromosome determine
Y-linked characteritics
Genes located on the X chromosome determine
X-Linked characteristics
Notation for Writing Sex Linked Genotypes
1. You must show which chromosome the sex-linked allele is attached to (X or Y)

2. Display the nature of interaction between the alleles by representing dominance as a superscript capital letter and recessive as a superscript lower case letter.

Colour Blindness: X- linked Disease
Cell in the human eye contain pigments capable of absorbing red, green and blue light.
The red and green pigments are encoded by genes on the x chromosome
Red-Green colour blindness is a defects of the red and green pigments

Red-Green colour blindness is inherited as a recessive X-linked gene
A
carrier
does not display the phenotype of the disease, however can pass the diseased allele on to offspring

WHY CAN’T MALES BE CARRIERS?

Genetic Disorders
- Disease alleles may be located on autosomes or sex chromosomes

- Disease alleles may can be dominant or recessive to the normal allele
Genetic Disorders are not always inherited - they can arise due to spontaneous chromosome abnormalities
Chromosome abnormalities are a result of errors in meiosis.

If the chromosomes fail to desperate correctly the offspring can have additional or less chromosomes
Down Syndrome
Turner Syndrome
Genetic Testing
- Used to recognize the potential for a genetic condition at an early stage

- For parents who are at risk of passing on a genetic condition it can help alleviate anxiety associated with the uncertainty

- Allows early intervention that may lessen or prevent the development of the condition

- Genetic Testing can be
prenatal
or
postnatal
Pregnancy
- The fetus gets oxygen and nutrients from its mothers blood through the placenta (a special organ attached to the uterus)

- The fetus blood travels to the placenta through the umbilical cord

- the fetus floats in liquid called the amniotic fluid

- Waste products and cells the fetus shed are found in the amniotic fluid



Prenatal Genetic Tests
Amniocentesis:
- Used to check for Chromosomal Abnormalities and inheritable genetic diseases

- Performed at approx 15weeks of pregnancy

- A needle is inserted through the abdomen and into the uterus, approx 2 tablespoons of amniotic fluid is withdrawn into the syringe attached to the needle





The cells are then taken to the lab for scientists to grow and perform genetic tests that analyze the chromosomes and certain genes
Prenatal Genetic Tests
- chorionic villi cells are taken from the placenta for genetic testing

- used to diagnosis chromosomal abnormalities and inheritable genetic diseases
- completed at 10 -12 weeks
of pregnancy

Eg.
Huntingtons Disease
(dominant defective gene on chromosome 4 or
Cystic Fibrosis
(recessive defective gene on chromosome 7)
Chorionic Villus Sampling (CVS):
Postnatal Genetic Tests
- All babies in Australia get screen for the inheritance of life threatening diseased alleles such as Cystic Fibrosis
Screening involves taking blood from the babies heel at 48-72hours old
The sample is sent to the lab for testing
Pre-Implantation Genetic Diagnosis (PGD)
PGD involves the removal of cells from a 3 day old embryo created by IVF (eggs are removed from the female and fertilized by sperm in the laboratory)

The cells can then be tested for chromosomal abnormalities or genetic diseases such as cystic fibrosis

If the cells are diagnosed as being clear of genetic disorders the embryo will be transferred into the uterus for development
Prenatal Genetic Testing
Maternal Blood Tests:
- non invasive method for identifying chromosome abnormalities
- can be done in the first trimester (9 - 13 weeks) or the second trimester (14 - 18 weeks)

The blood tests measure two substances found in the blood of all pregnant women:
Pregnancy-associated plasma protein screening (PAPP-A)-
a protein produced by the placenta in early pregnancy.
Human chorionic gonadotropin (hCG)
--a hormone produced by the placenta in early pregnancy.

Abnormal levels are associated with an increased risk for chromosome abnormality.


Phenylketonuria (PKU)
– a disorder where the liver does not produce enough of a particular enzyme and cannot metabolise (break down) phenylalanine, which is one of the 20 amino acid building blocks of protein. If untreated, PKU can lead to intellectual disability

Hypothyroidism
– a condition where the thyroid gland is underactive and fails to make enough hormones. The thyroid gland helps regulate metabolism. A lack of thyroid hormone can cause severe intellectual disability and growth problems. Early detection and treatment enables children to be healthy

Cystic fibrosis
– a condition where organs such as the lungs and pancreas secrete abnormal mucus that clogs the affected organs and stops them working properly

Other rare metabolic disorders
– there are many other rare metabolic disorders caused by faults in the breakdown of proteins and fat. Early detection and treatment, before babies become sick, results in a better outcome.

The screening looks for the following inherited diseases:
Pedigrees
Observing pedigrees can help identify the nature of inheritance, as well as predict genotypes

A Couple
Their children
How do we determine the inheritance pattern of an allele?
Autosomal Dominant
- Visible in every generation

- NEVER have two unaffected parents giving rise to affected children
Autosomal Recessive:
- Not visible in every generation
- There are male and female carriers
- Carriers/unaffected parents can have affected children
Dominant X-Linked
- Only female carriers

- Mostly males affected
Colourblindness is a
recessive X-linked gene


What is the genotype of the mother in the first generation?


Why are all the sons in generation 2 colourblind?


What is the genotype of the mother (labeled number 2) in generation 2?
Determining Genotypes from Pedigrees
GENETIC MODIFICATION
(genetic engineering)
- Genetic Engineering is when an organisms genes are artificially modified in ways not possible through traditional breeding techniques
Diabetes- type 1
- Individuals can not control the amount of glucose in the blood because their body does not produce the hormone:
insulin
- Insulin regulates glucose blood level because it transports glucose into muscle cells to be used as energy.
Golden Rice
To help prevent Vitamin A deficiency in poor countries scientist have genetically modified rice to contain a gene from a daffodil that catalyzes the production of vitamin A in the edible part of the rice
http://splash.abc.net.au/res/teacher_res/1-GMfoods.html
There is lots of controversy surrounding Genetic Modification!
The above pedigree shows the inheritance pattern of the autosomal unattached earlobe allele. The Unattached earlobe allele (E) is dominant over attached earlobes allele(e).

Are there any individuals that are homozygous for the dominate allele in the above pedigree?



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