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Genetics. Introduction. Each newborn begins its existence at the point of conception when a sperm cell from a male unites with an ovum from a female to form a single cell called a zygote.
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Introduction • Each newborn begins its existence at the point of conception when a sperm cell from a male unites with an ovum from a female to form a single cell called a zygote. • At the moment of conception an individuals characteristics are determined, these characteristics are laid down in structures known as chromosomes. • Chromosomes are thread like structures called genes.
Each chromosome carries hundreds of genes and these determine individual characteristics such as hair, eye colour, sex, height, body shape, size, blood group and all aspects of development e.g. Puberty
At conception human beings receive 46 chromosome – 23 from the sperm and 23 from the ovum. At the moment of conception the chromosomes from the male sperm pair off with the chromosomes from the female ovum. • One way in which the genes on the chromosome interact and create characteristics is determined by dominant and recessive genes. • A dominant gene will always express itself – this mean that it will be seen. A recessive gene will over powered by a dominate gene, this means that you will not be able to see the characteristic
Gender • 22 pairs of chromosomes control the development of most of the body. The twenty third pair of chromosomes – the X and Y chromosomes determine the individuals sex. • A female only produces ova which contain X chromosomes but males produce sperm which carry X or Y chromosomes. • Half of the sperm produced carry X chromosomes and half of the sperm produced carry a Y chromosome. • If a sperm carrying an X chromosome fertilises the ovum first, then an XX combination will result producing a female child. Therefore it is the male partner who determines the sex of the child • (see attached diagram)
Sometimes at conception the resulting zygote is genetically abnormal. In many cases, these will be aborted spontaneously and the woman may never know she was pregnant and many others die later in pregnancy. (approx 1 % of children born in Aus has a chromosomal abnormality, genetically inherited disorder or genetically influenced defect).
There are conditions where abnormalities in chromosomes are known to cause specific syndromes or diseases
Turners Syndrome • Turner’s syndrome is a random genetic disorder that affects females. The main characteristics include short stature and infertility. Usually, a female has two X chromosomes. However, in females with Turner’s syndrome, one of these chromosomes is missing or abnormal. The missing genes cause the abnormalities and features found in women with Turner’s syndrome.
Diagnosis The condition may be diagnosed at various life stages: • Before birth (prenatally) - usually if an amniocentesis has been performed or abnormalities are seen during an ultrasound • At birth - due to certain physical features • In childhood - when the young girl doesn’t grow at a similar rate to her peers • During the teenage years - when puberty fails to arrive • In adulthood - during investigations for infertility.
Features of Turners Syndrome • Significant featuresThe most significant features of Turner’s syndrome include: Short stature - average adult height is 143cm (4’8”) • Infertility - due to underdeveloped ovaries • Congenital heart defects • Spatial awareness issues - problems with tasks such as maths • Absence of menstruation (amenorrhoea) • Hearing problems. • Less significant features may include: Sunken, wide chest with broadly spaced nipples • Extra skin on the neck • Puffy hands and feet
Treatment Turner’s syndrome is a lifelong condition. However, many treatment options are available to help affected girls and women reach their potential in all aspects of life. Treatment aims to correct any physical defects and help bring about puberty. Options include: Surgery to correct any heart defects • Growth hormone therapy to increase height • Hormone replacement therapy to trigger menstruation and the development of secondary sexual characteristics such as breasts • Regular monitoring to check hormone levels • Regular follow-up and management of medical conditions • Treatment for the management of complications such as high blood pressure • Assisted reproduction.
Down Syndrome • People with Down syndrome have an extra chromosome 21 in their genetic make-up. • Down syndrome is the most common genetic condition and occurs in all races and cultures at around the same rate. In Victoria, between 45 and 60 babies will be born with Down syndrome each year. Some level of intellectual disability is the only feature common to all people who have Down syndrome, although a range of other features are also associated with the condition. These include characteristic physical features and a number of health and developmental indications.
Down Syndrome Down syndrome is usually recognisable at birth and confirmed by a blood test. A doctor can usually tell if a baby has Down syndrome from their physical appearance. • Prenatal tests that can help to detect Down syndrome in a foetus include: • Ultrasound scans • Amniocentesis • Chorionic villi sampling.
Down Syndrome - Physical Characteristics • There are a number of physical characteristics associated with Down syndrome, although each person with Down syndrome may display only a few of these. The most common physical characteristics include: Eyes – nearly all people with Down syndrome have a slight upward slant of the eyes. There can also be a small fold of skin on the inside of the eye. • Face – this is often rounded and tends to have a flat profile. • Stature – Babies are usually smaller and weigh less at birth than others. Children tend to grow more slowly and are commonly smaller than other children their age. Adults with Down syndrome are commonly smaller than in the general population. • Despite some common physical characteristics, people with Down syndrome resemble other members of their family more than they resemble each other. • Babies with Down syndrome reach the same developmental milestones (such as smiling, sitting up, crawling, walking, talking and toileting) as all babies, but with some degree of delay. Speech and language development is often the area of greatest delay.
Cystic Fibrosis • Occurs in approx 1 in every 2500 births • Children with the disease have excessive amounts of salt in their sweat and procude thick mucus which block the pancreas and lungs causing many long term problems • Their lifespan are considerably reduced
Haemophillia • Is a blood clotting disorder where one of the essential clotting factors is deficient. Haemophiliacs have differing degrees of severity. • It almost exclusively affects males and is passed on through unaffected females who carry the defective gene. • There is no cure and it is a lifelong condition.
