Download Grade 9 Science Unit #3: Reproduction and Human Development

Grade 9 Science
Unit #3: Reproduction and Human Development
Topic #1 – Genetic information is passed from parent to offspring
Lesson Topic
1
Variation and
Characteristics
2
Heredity and
Genetics
3
Genetics,
Technology,
Society, and
the
Environment
What you will learn:
- Variation can be discrete or continuous. Variation can be affected by
heredity and the environment
- Heritable characteristics are the traits of an organism that are
inherited from the organism’s parents
- Non-heritable characteristics are traits that are learned or developed
during an organism’s life
- The First Nations and Métis ways of understanding heredity include
the transmission of personality traits as well as physical traits.
- The nucleus of the cell contains DNA which has the genetic
information that is required for cells to divide
- DNA is packaged in the form of chromosomes
- A gene is a segment of DNA that provides information for a
characteristic. An allele is a variation of a gene that provides
information for a trait
- Traits can be dominant or recessive. The combination of alleles from
the parents determines which traits the offspring will have.
- Genetic conditions are passed down from parent to offspring
- Some personal choices and environmental factors can alter a cell’s
DNA
- Developments in the study of genetics have a major impact on
society
- Saskatchewan plays a major role in the study of genetics
1. Variation and Characteristics
When studying genetics, a characteristic is a feature such as eye colour or wing shape. Characteristics
can vary within a species or be the same for the entire species. A trait is a variation of a characteristic.
It describes what the characteristic looks like. With the characteristic of eye colour, people could have
the trait of blue eye colour versus brown eye colour.
Some traits are not visible. Jack pines exhibit variation because some individuals can resist drought
better than others. Magpies show variation because some individuals can fly longer distances. Some
bacteria of the same species can be more resistant to antibiotics.
Heritable and Non-Heritable Characteristics
The transmission of characteristics from one generation to the next is called heredity. Examples of
heritable characteristics are eye colour, hair type, and skin colour. Non-heritable characteristics cannot
be passed on to other generations. An example of non-heritable characteristics include when someone
dyes their hair.
The Dakota people believe that traits are inherited through a spiritual means. When a woman is
pregnant, she looks for a wise relative who leads a healthy lifestyle. This person is present for the
delivery of the baby and cleans the baby’s ears, eyes, and mouth. Prayers are said and ceremonies
performed for the baby. It is believed that the soft spot on a baby’s head is a point of entry for the
baby’s spirit and the baby’s traits and characteristics.
Dene people believe that a baby develops its traits when it is conceived. The pregnant woman is
encouraged to act and speak in a fashion that would promote desirable traits in her child. She would
practise patience, stay calm, and help in her community. The community treats a pregnant woman well
to help her maintain a positive frame of mind and to keep her in happy spirits.
The Nakawe believe that the behaviour and actions of the parents and relatives in the child’s life impact
the baby in the womb.
Discrete and Continuous Variation
Discrete variation refers to traits that have a defined form. It is the “either/or” form of a characteristic.
For example, a particular species of plant may produce only white or purple flower. Continuous
variation refers to traits that have a range of forms. The height of a human can be between 1.2m to
2.1m.
Variation and the Environment
The environment can also affect the traits of an organism. If a plant is placed in a sunny window and the
other in a dim closet, they would soon begin to look very different. Soil acidity will cause flowers to
change colour in some species of plants. Height is a characteristic that is inherited but it can also be
affected by diet. Variations caused by interactions with the environment are usually not passed from
parents to offspring. If a child of tall parents does not receive proper nutrition, he or she probably will
not be as tall as his or her parents.
2. Heredity and Genetics
DNA and the Genetic Code
DNA, or deoxyribonucleic acid, is found in the nucleus of a cell. DNA contains all of the genetic
information required to develop and function any living organism.
DNA was discovered in 1869. In 1944, Oswald Avery and his colleagues confirmed that it was genetic
material that would determine how traits were passed from one generation to the next. In 1953,
Watson and Crick completed a model of the DNA molecule. The Watson-Crick model of the DNA
molecule can be compared to a ladder that has been twisted into a continuous spiral, this shape is
known as a double helix. Each “rung” pairs up two of the following four chemicals: guanine, cytosine,
adenine, and thymine (or G, C, A, and T for short). Guanine can only pair with cytosine and Adenine can
only pair with Thymine. The arrangement of
these chemicals forms a code called the genetic
code.
The diagram to the left shows how DNA is
organized in the nucleus of a cell. The length
of DNA in one human cell is estimated to be
over 6 ft in length when stretched out.
DNA is organized into larger structures called
chromosomes. In human cells there are 46
chromosomes, or 23 pairs of chromosomes. On
each chromosome there are many genes.
Genes are the sections of DNA that provide the
specific information for development or
functioning. Genes provide the information for
our bodies to create proteins, hormones, and
sugars.
Chromosomes are also organized in two sister
chromatids. You get one copy from your
mother and one copy from your father. These
sister chromatids are exact copies of each
other. Each pair of chromosomes code for the
same genes, but may or may not have the same
alleles of each gene.
Alleles are various forms of the same type of gene that create our different characteristics. Ex/ There is
a specific gene to determine each of the following hair characteristics: colour, straight/curly, thick/thin,
course/fine, etc. The different alleles will determine the different forms of the characteristics.
Dominant and Recessive Traits
Some genes determine the physical traits that differentiate us from one another. Everyone has two
copies of each gene. These copies can be the same allele or different alleles. When the alleles are the
same, the information that they provide is what is expressed. When the alleles are different, the trait
that is expressed is dependent on which of the alleles is dominant. Traits can be described as dominant,
recessive or co-dominant. A dominant trait is one that will be expressed when there are two alleles,
whereas a recessive trait is one that will not be expressed when there are two alleles. Traits that are codominant are traits that can be expressed at the same time. An example of a co-dominant traits are the
gene for blood type, people with type AB blood have both the A gene and B gene.
Examples
Trait
Eye Colour
Vision
Dominant
Brown
Farsightedness
Normal
Hair
Dark
Non-red
Curly
Full head of hair
Widow’s peak
Dimples
Unattached earlobes
Freckles
Broad lips
Extra digits
Fused digits
Short digits
Fingers lack 1 joint
Limb dwarfing
Clubbed thumb
Double – jointedness
Immunity to poison ivy
Normal pigmented skin
Normal blood clotting
Normal hearing
Normal hearing and speaking
Facial Features
Appendages
Other
Recessive
Grey, green, hazel, blue
Normal
Nearsightedness, night
blindness, colour blindness
Blonde, light, red
Red
Straight
Baldness
Normal hairline
No dimples
Attached earlobes
No freckles
Thin lips
Normal number
Normal digits
Normal digits
Normal joints
Normal proportions
Normal thumb
Normal joints
Susceptibility to poison ivy
Albinism
Haemophilia
Congenital deafness
Deaf mutism
How can we explain a two dark haired parents having a blonde haired child?
If parents are hybrids and they each have a dark haired allele and a blonde haired allele, there are four
combinations that can occur in their children.
1. One dark haired allele from the father and a dark haired allele from the mother. The child will
have dark hair
2. One dark hair allele from its mother and a blonde haired allele from the father. The child will
have dark hair
3. One dark hair allele from its father and a blonde haired allele from the mother. The child will
have dark hair
4. One blonde hair allele from the father and a blonde haired allele from the mother. The child will
have blonde hair.
A diagram called a Punnett square can be used to predict the results of a particular cross. The diagram
of the cross of hybrid people shows all possible combinations of genes in the offspring of the parents.
The blond condition is an example of a recessive trait, and the blonde allele is an example of a recessive
allele. A recessive trait appears in the offspring of a recessive allele. A recessive trait appears in the
offspring only if both inherited alleles are recessive alleles. In contrast, even one dominant allele will
cause the dominant trait to appear.
Father (Db – dark/blonde alleles)
D
Mother (Db –
dark/blonde alleles)
b
D
DD
Db
b
Db
bb
3. Genetics, Technology, Society, and the Environment
Biotechnology
Biotechnology is a scientific term that describes the use or modification of living things to improve our
lives in areas such as medicine, agriculture, and engineering. Although biotechnology has successfully
produced most of our world’s crops and livestock, it takes a very long time - many generations of the
plants and animals – to produce offspring that consistently have the desired combination of traits.
Selective breeding is the process of selecting and breeding individuals with desirable traits to produce
offspring that also have these traits. The grains and fruits you ate for breakfast, in addition to many
other foods, are probably products of selective breeding. Another place that this is used is with horses.
The genes of champion parents are combined with the hope that the offspring will have the prized traits
of both parents. Also, since some cultures have used selective breeding while farming for more than
10 000 years, most of our plants no longer resemble the original species from which they were bred.
Artificial Reproductive Technology refers to any artificial method of joining a male and a female gamete.
Most livestock in Canada are produced by some method of artificial reproduction. With this technology
sperm are collected from a chosen male and inserted into many females. Another reproductive
technology is in vitro fertilization (IVF). The term in vitro means “in glass”. With this technology, sperm
from a male and eggs from a female are collected. In a laboratory, the eggs and sperm are combined in
a Petri dish to fertilize the eggs. This produces many more embryos than could be produced naturally.
Each embryo is implanted into a different female. If implantation is successful, the females will
eventually give birth to the offspring, all of which will be brothers and sisters. Scientists can also
determine the sex of the embryos before they are implanted. By choosing only female embryos, dairy
farmers can guarantee that all the calves produced will be female.
Genetic engineering refers to any technology process that directly alters or changes the DNA of an
organism. Genetic engineering is a rapidly developing science and industry, and every new advance
increases our ability to control the characteristics of organisms. Most genetic engineering involves a
gene from one species being inserted into another species. Bacteria can be genetically engineered to
produce medicine, like insulin. Twenty years ago, insulin had to be extracted from the pancreas of
cattle, and it was expensive to produce. Now, insulin can be produces quickly and cheaply because most
of the world’s supply of insulin comes from genetically engineered bacteria. Another example involves a
micro-organism that produces a toxin that is poisonous to many insects. When the DNA containing the
instructions for producing this toxin is inserted into the DNA of plants, the plant begins to produce the
toxin. When insects eat the plant, they die and growers never need to apply pesticides to the
engineered plants. Since 1990’s cotton, corn, and potatoes have been engineered to produce this toxin.
Biotechnology and Society
Risks in Animals
In agriculture, most individuals in a crop or livestock population are extremely genetically similar as a
result of generations of selective breeding. Now, scientist and breeders can produce an identical copy
of a single animal. The most famous example of this is a sheep named Dolly. Dolly’s cells appeared the
same age as her mother’s, even though Dolly was six years younger. One risk is that herds of genetically
identical individuals may be far more susceptible to disease than more genetically varied herds. Other
problems cattle cloners have reported include numerous examples of unsuccessful pregnancies, birth
defects, and deaths among clones.
Risk in Plants
Most plant crops were produced by selective breeding of wild plants. Weeds are often the wild relatives
of crop plants. Some crops have been genetically engineered to resist herbicides, but there have been
unforeseen problems. Many crop plants can cross-pollinate with their wild weed relatives. Cases have
been reported of genetically engineered canola interbreeding with weeds, and the weeds’ offspring
becoming resistant to herbicides.
Accidental Changes to DNA
Sometimes DNA is accidentally altered or damaged by environmental factors and personal choices.
Usually the damaged DNA is detected by the cell, in which case the DNA is repaired or the cell is
destroyed. However, if the damage is not detected, normal cell function can be disrupted.
Carcinogens
Carcinogens are chemicals or toxins that cause cancer. These chemicals can change a cell’s DNA or
change the way a cell reproduces, resulting in cells dividing uncontrollably and forming tumours.
Smoking cigarettes is extremely dangerous because cigarettes contain thousands of chemicals, many of
which are toxic carcinogens.
Asbestos is another carcinogen. It was commonly used in building as insulation throughout Canada and
the United States starting in 1870s. It is able to resist fire, electrical and chemical damage, so it seemed
and excellent building material. Almost one hundred years later it was realized that inhaling the tiny
fibres can cause irreparable damage to cells by physically breaking strands of DNA. This can lead to
cancer in people who are exposed to asbestos on a regular basis.
Pesticides are chemicals that are sprayed onto crops to try to eliminate pests that cause damage to
crops. Some pesticides are also carcinogens and many people and animals consume them without
realizing. This is done when you drink water that contains small amounts of pesticides, eating food that
has not been thoroughly cleaned to remove the chemicals, or by inhaling chemical particles from the air.
Sun Exposure
Over exposure to the ultraviolet rays from sunlight and from tanning beds is a major cause of skin
cancer. Moderate exposure to sunlight is important, since it allows our bodies to produce vitamin D.
Over exposure damages DNA, which could result in cancer. Research shows that even a single use of a
tanning bed can be extremely damaging and may greatly increase the chance of getting skin cancer.
Genetic Conditions
Genetic conditions may be passed from parents to their child as a recessive trait. To inherit the
condition, offspring would have to inherit a recessive allele from each parent. Genetic conditions can
also occur as a result of an error in the copying of DNA during cell reproduction. Changes to a cell’s DNA
that cause genetic conditions are usually random, and result from small changes in the order of the
chemicals in the DNA
Male infertility – when males are unable to produce sperm that are viable or able to fertilize and egg.
Approximately 10% of all male infertility cases are recognized as a genetic condition. This type of
infertility is a result of a mutation in the DNA.
Breast Cancer – mutations in the certain genes can make cells reproduce at an abnormal rate, which can
causes tumour to form. Some forms of breast cancer (about 10% of cases) are genetic others are a
mutation that forms in the genetic code.
Sex-linked Genetic Conditions – Sex chromosomes are the x and y chromosomes. Females have two x
chromosomes, while males have one x and one y chromosome. Some genes are located only on the Y
chromosome, but many more genes are located exclusively on the x chromosome. Males are more
likely to inherit sex-linked genetic disorders because they receive only one x chromosome. If a male
inherits an affected x chromosome with a recessive allele, he will automatically display the recessive
trait because the Y chromosome does not have the matching gene that could mask the effect of the
recessive allele. Where as females have a chance of having the dominant gene on the second x
chromosome. Examples of sex-linked genetic conditions include: colour blindness and haemophilia (a
disorder in which the blood is unable to clot)
Trisomy 21 (Down Syndrome) – occurs in people when there is a third chromosome 21. People with this
disorder often have smaller body frames and limbs, large tongues, and large, round eyes. They typically
develop more slowly, both physically and mentally. Despite developmental delays, people with trisomy
21 can lead active productive lives.
Canadian and Saskatchewan Contributions to the Study of Genetics
Scientists in Saskatchewan try to discover the causes for genetic conditions in order to try to prevent
them. Once this is done they can test parents to determine if they are at risk of having a baby with
certain conditions. Two Saskatchewan scientists contributed to the study of a gene responsible for
babies being born without any arms or legs. Now, support and testing is being offered to family
members at risk of carrying the gene for this condition. In 1962, a Saskatchewan medical student
discovered a gene responsible for causing significant learning disabilities in males.
Two Canadian scientists have become internationally recognized for their findings about the effects of
radiation on human chromosomes.
Another scientist discovered an important cell structure that is only found in female cells, now known as
the Barr body. This information in used at the Olympics to determine the gender of athletes if there
were concerns that an athlete was attempting to compete in the opposite gender.
The gene responsible for causing cystic fibrosis was discovered by a Toronto geneticist and his associates
in 1989.