Unit 4 - Genetics Flashcards
What is the law of segregation?
during the production of gametes the two copies of each hereditary factor segregate so that offspring acquire one factor from each parent
What is the law of independent assortment?
when two or more characteristics are inherited, individual hereditary factors assort independently during gamete production, giving different traits an equal opportunity of occurring together.
What is complete dominance?
when the dominant allele completely covers up the recessive allele.
What is incomplete dominance?
When one allele for a specific trait is not completely expressed over its paired allele. This results in a third phenotype in which the expressed physical trait is a combination of the phenotypes of both alleles.
What is codominance?
When two alleles of a gene pair in a heterozygote that are both fully expressed. When alleles for both white and red are present in a carnation, for example, the result is a red and white mixed carnation since both alleles are codominant.
What is Jacob Syndrome?
A rare chromosomal disorder in which males have an extra Y chromosome. Symptoms include tallness, severe acne, learning disabilities, and behavioral problems, like impulsivity. Most cases result from a cell division error in sperm prior to conception.
What is Klinefelter Syndrome?
This disorder results from 1 or more extra X chromosomes in males. Males affected by this disorder tend to have low levels of testosterone, resulting in delayed or incomplete puberty, breast enlargement, reduced facial hair, infertility, and/or genital differences.
What is Triple X Syndrome?
This disorder is characterized by the presence of an additional X chromosome in each of a female’s cells. Other than usually being taller than average, females with this disorder often do not have any symptoms. However, some are affected by learning disabilities, delayed development of speech and motor skills, weak muscle tone, and emotional or behavioral difficulties.
What is a sex-linked trait?
If a gene is found only on the X chromosome and not the Y chromosome, it is said to be a sex-linked trait. Because the gene controlling the trait is located on the sex chromosome, sex linkage is linked to the gender of the individual. Usually such genes are found on the X chromosome. The Y chromosome is thus missing such genes. The result is that females will have two copies of the sex-linked gene while males will only have one copy of this gene. If the gene is recessive, then males only need one such recessive gene to have a sex-linked trait rather than the customary two recessive genes for traits that are not sex-linked. This is why males exhibit some traits more frequently than females. Some common sex-linked traits are hemophilia and red-green color blindness. I
What is sexual reproduction?
A mode of reproduction involving the fusion of female gamete (ovum) and male gamete (spermatozoon), which forms a zygote that potentially develops into genetically distinct offspring.
What are somatic cells?
Somatic cells are all cells in the body except germ cells, which are egg and sperm.
What is synapsis?
In prophase I of meiosis, the replicated homologous pair of chromosomes comes together in the process called synapsis, and sections of the chromosomes are exchanged. You can see that after crossing over, the resultant chromosomes are neither entirely maternal nor entirely paternal, but contain genes from both parents. Synapsis and crossing over occur only in meiosis.
What is a trait?
A phenotypic trait, or simply trait, is a distinct variant of a phenotypic characteristic of an organism; it may be either inherited (inherited trait) or determined environmentally (acquirred trait), but typically occurs as a combination of the two. For example, eye color is a character of an organism, while blue, brown and hazel are traits.
What are the 3 sources of genetic variation and what is it?
Sources:
- Mutation is a change in DNA, the hereditary material of life. An organism’s DNA affects how it looks, how it behaves, and its physiology — all aspects of its life. So a change in an organism’s DNA can cause changes in all aspects of its life.
- Recombinationn of genes through sexual reproduction-Sex can introduce new gene combinations into a population and is an important source of genetic variation. Crossing over, independent assortment, and sex are the principle mechanisms that maintain genetic diversity within populations.
- Genetic flow is any movement of individuals, and/or the genetic material they carry, from one population to another. If gene versions are carried to a population where those gene versions previously did not exist, gene flow can be a very important source of genetic variation. “
What is turner syndrome?
Turner syndrome is when a chromosomal disorder in which a female is born with only one X chromosome. In Nondisjunction, the sex chromosomes fail to separate during the formation of a sperm (or egg). When sperm with no X chromosome unites with a normal egg to form an embryo, that embryo will have just one X chromosome (X rather than XX). As the embryo grows and the cells divide, the X chromosome will be missing from every cell of the baby’s body.Turner syndrome can cause a variety of medical and developmental problems, including short height, failure to start puberty, infertility, heart defects, certain learning disabilities and social adjustment problems.
What does Autosomal Dominant mean?
A pattern of inheritance in which an affected individual has one copy of a mutant gene and one normal gene on a pair of autosomal chromosomes. Examples of diseases inheroted this way include Huntington disease and neurofibromatosis.
What is Neurofibromatosis?
This disorder is autosomal dominant. It refers to 3 types of inherited conditions that are clinically and genetically distinct and carry a high risk of tumor formation, particularly in the brain. Possible symptoms include learning disabilities, enlargement and deformation of bones, and hearing loss.
What is Huntington’s Disease?
This disease is autosomal dominant and causes the progressive degeneration of nerve cells in the brain. It usually insets in the 30s or 40s and leads to cognitive and psychiatric disorders.
What does Autosomal Recessive mean?
A genetic condition that appears only in individuals who have received two copies of an autosomal gene, one copy from each parent. The gene is on an autosome, a nonsex chromosome. An example of this pattern of inheritance is cystic fibrosis.
What is Sickle Cell Anemia?
This disease is autosomal recessive in which there aren’t enough healthy red blood cells to carry adequate oxygen throughout your body, because blood cells are rigid and sticky and are shaped like sickles.
What is Cystic Fibrosis?
This disease is autosomal recessive and causes severe damage to the lungs and digestive system by affecting the cells that produce mucus, sweat and digestive juices.
What is nondisjunction?
Nondisjunction during meiosis produces eggs or sperm cells that don’t have the normal number of chromosomes. If nondisjunction occurs during anaphase I of meiosis I, this means that at least one pair of homologous chromosomes did not separate. The end result is two cells that have an extra copy of one chromosome and two cells that are missing that chromosome. If nondisjunction occurs during anaphase II of meiosis II, it means that at least one pair of sister chromatids did not separate. In this scenario, two cells will have the normal haploid number of chromosomes. Additionally, one cell will have an extra chromosome (n + 1) and one will be missing a chromosome (n - 1).
What is down Syndrome?
Down syndrome is usually caused by an error in cell division called “nondisjunction.” Nondisjunction results in an embryo with three copies of chromosome 21 instead of the usual two. Prior to or at conception, a pair of 21st chromosomes in either the sperm or the egg fails to separate. As the embryo develops, the extra chromosome is replicated in every cell of the body. This type of Down syndrome, which accounts for 95% of cases, is called trisomy 21. It is a congenital disorder causing intellectual impairment and physical abnormalities including short stature and a broad facial profile.
What is a zygote?
A zygote is a fertilized egg cell that results froma female gamete(egg, or ovum) with a male gamete (sperm). In the embryonic development of humans and other animals, the zygote stage is brief and is followed by cleavage, when the single cell becomes subdivided into smaller cells. The zygote contains all the essential factors for development, but they exist solely as an encoded set of instructions localized in the genes of chromosomes.
What is Tay-Sachs?
This disoder is autosomal recessive and progressively destroys neurons in the brain and spinal cord. It is usually apparent in infancy and is quickly fatal. Characteristic features include muscle weakness, loss of motor skills, hearing loss, seizures, and other problems with movement, speech, and mental illness.
What is PKU?
This disorder is autosomal recessive. It is caused by a defect in the gene that helps create the enzyme needed to break down phenylalanine, an amino acid, which eventually builds up, especially if one eats a lot of protein.
What is it called when there is improper separation of chromosomes during meiosis that leads to an abnormal number of chromosomes in offspring. (Ex: Down syndrome, Turner’s syndrome, Klinefelter’s syndrome.)
Nondisjunction
The first two individuals that mate in a genetic cross are considered to be in what generation?
P Generation
