Multifactorial Inheritance and Genetic Disease. Non-nuclear Genes and Their Inheritance. Polygenic Inheritance and Gene Mapping. Sex Chromosomes and Sex Determination. Sex Determination in Honeybees. Test Crosses.
Biological Complexity and Integrative Levels of Organization. Genetics of Dog Breeding. Human Evolutionary Tree. Mendelian Ratios and Lethal Genes. Environmental Influences on Gene Expression. Epistasis: Gene Interaction and Phenotype Effects. Genetic Dominance: Genotype-Phenotype Relationships. Phenotype Variability: Penetrance and Expressivity. Citation: Lobo, I. Nature Education 1 1 How does this term prove an experiment's results are worth special attention?
Aa Aa Aa. Forming and Testing a Hypothesis. How Math Merged with Biology. The chi-square value is calculated using the following formula:. Level of Significance. References and Recommended Reading Harris, J.
American Naturalist 46 , — Jones, J. Philosophical Magazine 50 , — Pierce, B. Article History Close. Share Cancel. Revoke Cancel. Keywords Keywords for this Article. Save Cancel. Flag Inappropriate The Content is: Objectionable. Flag Content Cancel. Email your Friend. Submit Cancel. This content is currently under construction. Explore This Subject. Gene Linkage. The Foundation of Inheritance Studies.
Methods for Studying Inheritance Patterns. Variation in Gene Expression. Topic rooms within Gene Inheritance and Transmission Close. No topic rooms are there. Or Browse Visually. Other Topic Rooms Genetics. Student Voices.
Creature Cast. Simply Science. Green Screen. Green Science. Bio 2. The Success Code. Why Science Matters. The Beyond. Plant ChemCast. Postcards from the Universe. Sex cells normally only have one copy of the gene for each trait e. Each of the two Punnett square boxes in which the parent genes for a trait are placed across the top or on the left side actually represents one of the two possible genotypes for a parent sex cell.
Which of the two parental copies of a gene is inherited depends on which sex cell is inherited--it is a matter of chance. If you are not yet clear about how to make a Punnett Square and interpret its result, take the time to try to figure it out before going on. Why is it important for you to know about Punnett squares? The answer is that they can be used as predictive tools when considering having children.
Let us assume, for instance, that both you and your mate are carriers for a particularly unpleasant genetically inherited disease such as cystic fibrosis.
Of course, you are worried about whether your children will be healthy and normal. For this example, let us define "A" as being the dominant normal allele and "a" as the recessive abnormal one that is responsible for cystic fibrosis. As carriers, you and your mate are both heterozygous Aa. This disease only afflicts those who are homozygous recessive aa.
If a carrier Aa for such a recessive disease mates with someone who has it aa , the likelihood of their children also inheriting the condition is far greater as shown below. On average, half of the children will be heterozygous Aa and, therefore, carriers.
The remaining half will inherit 2 recessive alleles aa and develop the disease. It is likely that every one of us is a carrier for a large number of recessive alleles. Some of these alleles can cause life-threatening defects if they are inherited from both parents.
In addition to cystic fibrosis, albinism, and beta-thalassemia are recessive disorders. Your goal is to produce a variety of plant that is both insect resistant and fast growing. What percentage of the offspring would you expect to have both characteristics? Probability is the likelihood, or chance, that a certain event will occur. The easiest way to understand probability is with coin tosses see Figure below. When you toss a coin, the chance of a head turning up is 50 percent. This is because a coin has only two sides, so there is an equal chance of a head or tail turning up on any given toss.
Tossing a Coin. Competitions often begin with the toss of a coin. Why is this a fair way to decide who goes first? If you choose heads, what is the chance that the toss will go your way? If you toss a coin twice, you might expect to get one head and one tail. But each time you toss the coin, the chance of a head is still 50 percent. What if you tossed a coin ten times?
You would probably get more or less than the expected five heads. For example, you might get seven heads 70 percent and three tails 30 percent. The more times you toss the coin, however, the closer you will get to 50 percent heads. For example, if you tossed a coin times, you might get heads and tails. The same rules of probability in coin tossing apply to the main events that determine the genotypes of offspring.
These events are the formation of gametes during meiosis and the union of gametes during fertilization.
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