Unit 6, Section 2: Patterns of Inheritance Flashcards
What is continuous variation, and what are some examples?
Continuous variation occurs when a trait shows a wide range of values without distinct categories, meaning individuals vary gradually from one extreme to another.
• Examples include human traits like height, weight, and skin color, which can take any value within a range.
• This variation is often influenced by multiple genes and environmental factors.
How is continuous variation represented on a graph, and what does it indicate?
Continuous variation is shown as a normal distribution (bell curve) on a graph, with most individuals around the average and fewer at the extremes.
• This distribution suggests that the trait is polygenic (controlled by many genes) and influenced by environmental factors.
What is discontinuous variation, and how does it differ from continuous variation?
Discontinuous variation refers to traits that have distinct, separate categories, with no intermediate values.
• Examples include blood groups in humans (A, B, AB, O) and some flower colors.
• This variation is often controlled by a single gene or a few genes, leading to clear-cut phenotypes.
How is discontinuous variation represented on a graph?
Discontinuous variation is depicted with a bar graph showing distinct categories, with each bar representing a separate phenotype.
• There are no intermediate states, only specific categories (e.g., blood type A, B, AB, and O).
How can genes influence variation within a species?
Genetic factors contribute to variation, as individuals inherit different alleles.
• Traits influenced by many genes (polygenic traits) often display continuous variation.
• Single-gene (monogenic) traits usually lead to discontinuous variation, where only a few phenotypes are possible.
How does the environment contribute to variation?
The environment can affect the expression of certain traits, causing phenotypic differences among individuals with similar genotypes.
• Examples include plant growth, which can be influenced by sunlight and water, and animal fur thickness, which may change with the season.
• Environmental factors can modify traits, contributing to continuous variation.
What are examples of traits influenced by both genes and environmental factors?
Traits like height, intelligence, and flower color can be influenced by both genetic predisposition and environmental conditions.
• For example, plants may have the genetic potential to grow tall, but factors like water, nutrients, and light availability can impact their actual height.
What is a monogenic characteristic, and how does it differ from polygenic traits?
Monogenic traits are controlled by a single gene, typically resulting in discontinuous variation (distinct categories).
• Polygenic traits involve multiple genes and usually exhibit continuous variation, where the phenotype shows a range rather than discrete categories.
• An example of a monogenic trait is violet flower color, while human skin color is polygenic.
What is an allele and how do dominant and recessive alleles differ in terms of inheritance?
An allele is a variant form of a gene. Dominant alleles (e.g., “N”) are expressed in the phenotype even if only one copy is present. Recessive alleles (e.g., “n”) only show their effect if both alleles are recessive, as in a homozygous genotype (nn).
What is the significance of genotype in inheritance, and how is it represented?
Genotype refers to the genetic makeup of an organism, specifically the alleles it possesses for a particular trait. It is represented by letters (e.g., NN, Nn, or nn), where uppercase indicates a dominant allele and lowercase a recessive allele.
Describe what phenotype means and how it is determined.
Phenotype is the observable physical or biochemical characteristics of an organism, determined by its genotype (the combination of alleles) and environmental factors. For example, having one or two “N” alleles might result in normal wings, while “nn” might result in vestigial wings in an organism.
Explain the terms “homozygous dominant,” “homozygous recessive,” and “heterozygous.”
Homozygous dominant (e.g., NN) means both alleles are dominant, leading to the dominant phenotype. Homozygous recessive (e.g., nn) means both alleles are recessive, resulting in the recessive phenotype. Heterozygous (e.g., Nn) means one dominant and one recessive allele are present, typically displaying the dominant trait.
What is the purpose of a Punnett square, and how is it used in genetics?
A Punnett square is a tool used to predict the genotypes and phenotypes of offspring based on the alleles of the parents. By filling in the grid with parental alleles, one can visualize the possible genetic combinations and their likelihood
How do you use a Punnett square to determine the probability of specific genotypes?
To use a Punnett square, list the alleles of one parent across the top and the other parent down the side. Fill in each box by combining these alleles, which shows the possible genotypes of the offspring. The ratio of genotypes in the boxes gives the probability of each outcome.
What is codominance and give an example involving human blood types.
Codominance occurs when both alleles in a heterozygous genotype are fully expressed. For example, in human blood types, the IA and IB alleles are codominant, so individuals with the genotype IAIB have an AB blood type, expressing both A and B antigens.
