topic 4: genes and inheritance
Parents pass on traits or distinguishing characteristics such as eye and hair colour to their children through their genes. Many health conditions and diseases are also genetic. Genes may also influence some behavioural characteristics, such as intelligence and natural talents.
Genes are the blueprint for our bodies. Almost every cell in the human body contains a copy of this blueprint, mostly stored inside a special sac within the cell called the nucleus. Genes are part of chromosomes, which are long strands of a chemical substance called deoxyribonucleic acid (DNA). Therefore, genes are made up of DNA.
Genes are the blueprint for our bodies. Almost every cell in the human body contains a copy of this blueprint, mostly stored inside a special sac within the cell called the nucleus. Genes are part of chromosomes, which are long strands of a chemical substance called deoxyribonucleic acid (DNA). Therefore, genes are made up of DNA.
Define the terms:
- Genotype as genetic makeup of an organism in terms of the alleles present (e.g. Tt or GG)
- Phenotype as the physical or other features of an organism due to both its genotype and its environment (e.g. tall plant or green seed)
- Homozygous as having two identical alleles of a particular gene (e.g. TT or gg). Two identical homozygous individuals that breed together will be pure-‐breeding
- Heterozygous as having two different alleles of a particular gene (e.g. Tt or Gg), not pure breeding
- Dominant as an allele that is expressed if it is present (e.g. T or G)
- Recessive as an allele that is only expressed when there is no dominant allele of the gene present (e.g. t or g)
Explain that genes exist in alternative forms called alleles which give rise to differences in inherited characteristics
Sexually reproducing species, including humans and other animals, have two copies of each gene. The two copies, called alleles, can be slightly different from each other. The differences can cause variations in the protein that’s produced, or they can change protein expression: when, where, and how much protein is made. Proteins affect traits, so variations in protein activity or expression can produce different phenotypes.
A dominant allele produces a dominant phenotype in individuals who have one copy of the allele, which can come from just one parent. A recessive allele will produce a recessive phenotype, the individual must have two copies, one from each parent. An individual with one dominant and one recessive allele for a gene will have the dominant phenotype. They are generally considered “carriers” of the recessive allele: the recessive allele is there, but the recessive phenotype is not.
A dominant allele produces a dominant phenotype in individuals who have one copy of the allele, which can come from just one parent. A recessive allele will produce a recessive phenotype, the individual must have two copies, one from each parent. An individual with one dominant and one recessive allele for a gene will have the dominant phenotype. They are generally considered “carriers” of the recessive allele: the recessive allele is there, but the recessive phenotype is not.
Explain that variation within a species can be genetic, environmental, or a combination of both
Some variation within a species is inherited, and some variation is due to the environment.
Inherited variation
Variation in a characteristic is the result of genetic inheritance from the parents. Children usually look a bit like their father, and their mother. They will not be identical to either of their parents. This is because they receive half of their inherited features from each parent.
Each gamete contains half of the genetic information needed for an individual. During fertilisation a new cell is formed with all the genetic information needed for an individual.
Examples of inherited variation in humans:
Environmental causes of variation
Characteristics of species can be affected by factors such as climate, diet, accidents, culture and lifestyle. For example, if you eat too much you will become heavier, and if you eat too little you will become lighter. A plant in the shade of a big tree will will grow taller as it tries to reach more light.
Variation caused by the surroundings is called environmental variation.
Examples of features that show environmental variation:
Mixed variation
Some features vary because of a mixture of inherited and environmental causes. For example, identical twins inherit exactly the same features from their parents. But if you take a pair of twins, and twin 'A' is given more to eat than twin 'B', twin 'A' is likely to end up heavier.
Inherited variation
Variation in a characteristic is the result of genetic inheritance from the parents. Children usually look a bit like their father, and their mother. They will not be identical to either of their parents. This is because they receive half of their inherited features from each parent.
Each gamete contains half of the genetic information needed for an individual. During fertilisation a new cell is formed with all the genetic information needed for an individual.
Examples of inherited variation in humans:
- eye colour
- hair colour
- skin colour
- lobed or lobeless ears.
- Gender is inherited variation too, because whether you are male or female is a result of the genes you inherited from your parents.
Environmental causes of variation
Characteristics of species can be affected by factors such as climate, diet, accidents, culture and lifestyle. For example, if you eat too much you will become heavier, and if you eat too little you will become lighter. A plant in the shade of a big tree will will grow taller as it tries to reach more light.
Variation caused by the surroundings is called environmental variation.
Examples of features that show environmental variation:
- your language and religion
- flower colour in hydrangeas - these plants produce blue flowers in acidic soil and pink flowers in alkaline soil.
Mixed variation
Some features vary because of a mixture of inherited and environmental causes. For example, identical twins inherit exactly the same features from their parents. But if you take a pair of twins, and twin 'A' is given more to eat than twin 'B', twin 'A' is likely to end up heavier.
State that continuous variation is influenced by genes and environment, resulting in a range of phenotypes between two extremes, e.g. height in humans
The characteristics of an organism, such as its height, shape, blood group or sex, are known as its phenotype. Differences in phenotype between the members of a population are caused by differences in:
Some characteristics are controlled almost completely by the organism’s genotype, with the environment having little or no effect. For example, a person’s blood group (group A, B, AB or O) is controlled by the genes that code for protein
antigens on the surface of their red blood cells. A person’s blood group is not affected by the environment in which they develop. Such characteristics are controlled by genes at a single location and show discontinuous variation.
Characteristics that are affected by both genotype and environment often show continuous variation. Human height is a characteristic showing continuous variation. A person can be any height within the human range. The most common height will be somewhere between the extremes of the range. If a graph is drawn showing the frequency distribution of the different height categories it will be bell-shaped. Characteristics that show continuous variation are controlled by genes at many loci, known as polygenic inheritance, and also by the
environment, either directly or by influencing gene expression.
- genetic make-up or genotype
- the environment in which an individual develops.
Some characteristics are controlled almost completely by the organism’s genotype, with the environment having little or no effect. For example, a person’s blood group (group A, B, AB or O) is controlled by the genes that code for protein
antigens on the surface of their red blood cells. A person’s blood group is not affected by the environment in which they develop. Such characteristics are controlled by genes at a single location and show discontinuous variation.
Characteristics that are affected by both genotype and environment often show continuous variation. Human height is a characteristic showing continuous variation. A person can be any height within the human range. The most common height will be somewhere between the extremes of the range. If a graph is drawn showing the frequency distribution of the different height categories it will be bell-shaped. Characteristics that show continuous variation are controlled by genes at many loci, known as polygenic inheritance, and also by the
environment, either directly or by influencing gene expression.
Describe patterns of monohybrid inheritance using a genetic diagram
Punnett square diagrams are used to predict all the possible gene combinations that could result from the mating of parents. A monohybrid cross represents the inheritance pattern of a single trait, whereas a dihybrid cross represents the inheritance patterns of two traits that are linked
Intepret pedigree charts
A pedigree chart is a tool for genetic or genealogical research. It is similar in structure to a family tree, but is more of a working document. It may include specific information about an area of study, such as hereditary diseases, for example. A pedigree chart may be used for humans, but can also be useful for studying the lineage of show dogs and race horses.
Pedigrees use a standardized set of symbols, squares represent males and circles represent females. Pedigree construction is a family history, and details about an earlier generation may be uncertain as memories fade. If the sex of the person is unknown a diamond is used. Someone with the phenotype in question is represented by a filled-in (darker) symbol. Heterozygotes, when identifiable, are indicated by a shade dot inside a symbol or a half-filled symbol.
Pedigrees are commonly used in families to find out the probability of a child having a disorder in a particular family. its two most prominent goals are to discover where the genes in question are located (x, y, or autosome chromosome), and to determine whether a trait is dominant or recessive. Pedigrees show an autosomal disease when it is a 50/50 ratio between men and women the disorder is autosomal. it is considered an x-linked disease when most of the males in the pedigree are affected the disorder is x-linked. Another use of the pedigrees is to determine whether the disorder is dominant or recessive. if the disorder is dominant, one of the parent must have said disorder. however, if it is recessive, then neither parent has to have it
Pedigrees use a standardized set of symbols, squares represent males and circles represent females. Pedigree construction is a family history, and details about an earlier generation may be uncertain as memories fade. If the sex of the person is unknown a diamond is used. Someone with the phenotype in question is represented by a filled-in (darker) symbol. Heterozygotes, when identifiable, are indicated by a shade dot inside a symbol or a half-filled symbol.
Pedigrees are commonly used in families to find out the probability of a child having a disorder in a particular family. its two most prominent goals are to discover where the genes in question are located (x, y, or autosome chromosome), and to determine whether a trait is dominant or recessive. Pedigrees show an autosomal disease when it is a 50/50 ratio between men and women the disorder is autosomal. it is considered an x-linked disease when most of the males in the pedigree are affected the disorder is x-linked. Another use of the pedigrees is to determine whether the disorder is dominant or recessive. if the disorder is dominant, one of the parent must have said disorder. however, if it is recessive, then neither parent has to have it
Recall how the sex of a person is determined
Sex-linked traits
image from starksbiology.wikispaces.com
A particularly important category of genetic linkage has to do with the X and Y sex chromosomes. These not only carry the genes that determine male and female traits but also those for some other characteristics as well. Genes that are carried by either sex chromosome are said to be sex linked.
Men normally have an X and a Y combination of sex chromosomes, while women have two X's. Since only men inherit Y chromosomes, they are the only ones to inherit Y-linked traits. Men and women can get the X-linked ones since both inherit X chromosomes.
Genes located on the X chromosomes (some cause diseases)
The Y is much smaller, contains few genes
Sex Linked Disorders
Color Blindness (red-green)
Hemophilia ("bleeders disease)
Duchenne Muscular Dystrophy (weakening/loss of skeletal muscles)
Men normally have an X and a Y combination of sex chromosomes, while women have two X's. Since only men inherit Y chromosomes, they are the only ones to inherit Y-linked traits. Men and women can get the X-linked ones since both inherit X chromosomes.
Genes located on the X chromosomes (some cause diseases)
The Y is much smaller, contains few genes
Sex Linked Disorders
Color Blindness (red-green)
Hemophilia ("bleeders disease)
Duchenne Muscular Dystrophy (weakening/loss of skeletal muscles)
Explain the importance of DNA fingerprinting
DNA fingerprinting is a test to identify and evaluate the genetic information-called DNA (deoxyribonucleic acid)-in a person's cells. It is called a "fingerprint" because it is very unlikely that any two people would have exactly the same DNA information, in the same way that it is very unlikely that any two people would have exactly the same physical fingerprint. The test is used to determine whether a family relationship exists between two people, to identify organisms causing a disease, and to solve crimes.
DNA fingerprinting is done to:
Find out who a person's parents or siblings are. This test also may be used to identify the parents of babies who were switched at birth.
Solve crimes (forensic science). Blood, semen, skin, or other tissue left at the scene of a crime can be analyzed to help prove whether the suspect was or was not present at the crime scene.
Human DNA profiles can be used to identify the origin of a DNA sample at a crime scene, or test for parentage.
DNA fingerprinting is done to:
Find out who a person's parents or siblings are. This test also may be used to identify the parents of babies who were switched at birth.
Solve crimes (forensic science). Blood, semen, skin, or other tissue left at the scene of a crime can be analyzed to help prove whether the suspect was or was not present at the crime scene.
Human DNA profiles can be used to identify the origin of a DNA sample at a crime scene, or test for parentage.
image from dnafingerprintingx.yolasite.com
Key Terms
|
gene
allele Mendel DNA codominance |
F1 generation
F2 generation homozygous pedigree |
recessive
genotype phenotype sex determination X |
ratio
Punnett Square test cross Y |
heterozygous
dominant chromosome complete |
Class Material:
Part 1 Variation
Part 2 Working Out Genotypes
Part 3 Pedigree Charts
Part 4 Sex - Linked Traits
Genetics (study guide)
Mendal's Work webquest
Phenotype PTC practical
"Genetics activity"
Punnet Square worksheet
Royal Family Pedigree
Pedigree Chart activity
Blood Type Punnet Square
The Genetics of Parenthood
Genetics Protocol activity
Sex Linked Traits review worksheet.
Sex Linked Traits worksheet
Useful Links:
Mendell's Peas inactive web lab
Article on Inherited Traits
Click here for additional information from Biology On Line
Check out the NOVA video clip on Finding Genetic Diseases
BBC Bitesize Inheritance Activities
You and Your Genes
BBC News: Light shed on how genes shape face
Video Clips
Mendal's Work webquest
Phenotype PTC practical
"Genetics activity"
Punnet Square worksheet
Royal Family Pedigree
Pedigree Chart activity
Blood Type Punnet Square
The Genetics of Parenthood
Genetics Protocol activity
Sex Linked Traits review worksheet.
Sex Linked Traits worksheet
Useful Links:
Mendell's Peas inactive web lab
Article on Inherited Traits
Click here for additional information from Biology On Line
Check out the NOVA video clip on Finding Genetic Diseases
BBC Bitesize Inheritance Activities
You and Your Genes
BBC News: Light shed on how genes shape face
Video Clips
Paul Andersen explains simple Mendelian genetics. He begins with a brief introduction of Gregor Mendel and his laws of segregation and independent assortment. He then presents a number of simple genetics problems along with their answers. He also explains how advances in genetic knowledge may lead to ethical and privacy concerns.
Paul Andersen introduces the Punnett Square as a a powerful tool in genetic analysis. He tries to address major misconceptions that students have when use a Punnett Square. He gives a number of examples of monohybrid crosses and one example of a dihybrid cross. The square is a simple tool that uses the outcome of meiosis to determine possible offspring in a cross.
Hank and his brother John discuss heredity via the gross example of relative ear wax moistness.
Paul Andersen describes the major mutations found in the living world. He starts with an analogy comparing the information in DNA with the information in a recipe. Changes in the DNA can result in changes to the protein, like changes in the recipe can result in changes in the food. He describes the three major point mutations; substitutions, deletions and insertions. He also describes several chromosomal mutations.
Explore inheritance when carried on the X chromosome with the Amoeba Sisters!
Richard Resnick shows how cheap and fast genome sequencing is about to turn health care (and insurance, and politics) upside down.
