17.1 - Studying Inheritance Flashcards
Who established the basic laws of inheritance and when was his work rediscovered?
- Gregor Mendel, a scientist and monk.
- Although Mendel’s work was initially overlooked, it was rediscovered at the beginning of the 20th century.
- His experiments on pea plants led to the understanding of how characteristics are passed from one generation to the next, laying the foundation for modern genetics
What does genotype refer to?
- Genotype refers to the genetic composition (or make-up) of an organism.
- It includes all the alleles an organism possesses.
- The genotype sets the potential limits for an organism’s characteristics.
- e.g. might determine height as 1.8 meters tall, but factors such as diet and environment influence whether the individual reaches that potential.
- In this way, the genotype interacts with environmental factors to shape the ultimate traits of the organism.
How does genotype influence an individual’s characteristics?
- The genotype determines the range within which an individual’s characteristics can vary.
- However, environmental factors play a significant role in the expression of these characteristics.
- For instance, while a person’s genotype may allow them to grow to a certain height, factors like nutrition and the availability of essential elements such as calcium during critical developmental stages can prevent them from reaching their full genetic potential.
- Thus, genotype establishes potential, while the environment influences actual outcomes (which is the phenotype)
What is phenotype?
- Phenotype is the observable or biochemical characteristics of an organism.
- It is the result of the interaction between the organism’s genotype and the environment.
- While the genotype provides the genetic potential, environmental factors can modify the phenotype.
-For instance, a person’s height may be influenced by their genetic makeup, but poor nutrition or lack of essential nutrients could alter the height that is expressed. In this way, the phenotype represents the combined effects of genetic and environmental influences.
What is a gene?
- A gene is a length of DNA that consists of a sequence of nucleotide bases.
- This sequence typically codes for a specific polypeptide, which in turn may influence a particular characteristic.
- Genes are the fundamental units of heredity, and the information they carry is crucial for the development and function of an organism.
What is an allele?
- An allele is one of the different forms of a gene.
- In any given organism, only one allele of a gene can occur at the locus (position) of a particular chromosome.
- However, since organisms with diploid cells have pairs of chromosomes (called homologous chromosomes), two loci exist, each of which can carry one allele of the gene.
What is the locus of a gene?
- The locus is the specific position or location of a gene on a particular DNA molecule.
- Each gene occupies a fixed position, or locus, on its respective chromosome.
- In diploid organisms, chromosomes occur in homologous pairs, and each pair carries two loci for the same gene, one on each chromosome.
- The arrangement of alleles at these loci influences whether an organism will express a specific characteristic.
What does homozygous mean?
- Homozygous refers to an organism that has two identical alleles for a given gene at the loci on a pair of homologous chromosomes. (E.g. AA or aa)
- An organism can be homozygous for either dominant or recessive alleles.
What does heterozygous mean?
- Heterozygous refers to an organism that has two different alleles for a given gene at the loci on a pair of homologous chromosomes. (Aa)
- In most cases, when two different alleles are present, only one of them (the dominant allele) is expressed in the organism’s phenotype, while the other (the recessive allele) is not.
What is the difference between a dominant and recessive allele?
- A dominant allele is one that expresses itself in the phenotype, even when only one copy is present in a heterozygous individual.
- In contrast, a recessive allele is only expressed in the phenotype when an organism has two identical copies of the recessive allele, that is, when the organism is homozygous recessive. When a recessive allele is paired with a dominant allele, its effect is masked in the phenotype.
What does homozygous dominant and homozygous recessive mean?
- An organism is considered homozygous dominant when it has two identical dominant alleles for a particular gene.
- On the other hand, an organism is homozygous recessive when it has two identical recessive alleles.
What does codominance mean?
- Codominance occurs when two alleles both contribute to the phenotype of an organism, rather than one being dominant over the other.
- In cases of codominance, both alleles are expressed equally in the phenotype.
- For example, in shorthorn cattle, an allele for red hairs and an allele for white hairs are both expressed, resulting in a roan coat color, which is a blend of red and white hairs.
- Another example is human blood type, where both A and B alleles are codominant, leading to the AB blood group, which has both A and B antigens present on red blood cells.
What are multiple alleles?
- Multiple alleles refer to a situation where a gene has more than two allelic forms.
- However, because diploid organisms have only two chromosomes in each homologous pair, only two alleles can be present in any given individual.
- An example of a system with multiple alleles is the ABO blood grouping system in humans, where three different alleles (A, B, and O) determine blood type.
- Even though there are three possible alleles, any single individual can only inherit two of these alleles, one from each parent.
Fill the gaps:
The genetic composition of an organism is called the (1) and any change to it is called a (2) and may be inherited by future generations. The actual appearance of an organism is called the (3). A gene is a sequence of (4) along a section of DNA that determines a single characteristic of an organism. It does this by coding for particular (5) that make up the enzymes needed in a biochemical pathway.
- Genotype
- Mutation
- Phenotype
- Nucleotides/bases
- Polypeptides
Fill the gap:
The position of a gene on the DNA of a chromosome is called the (6). Each gene has two or more different forms called alleles. If the two alleles on a homologous pair of chromosomes are the same they are said to be (7), but if they are different, they are said to be (8). An allele that is not apparent in the phenotype when paired with a dominant allele is said to be (9). Two alleles are called (10) where they contribute equally to the appearance of a characteristic.
- Locus
- Homozygous
- Heterozygous
- Recessive
- Codominant
