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Genetics Chapter 4
Terms in this set (69)
Some genes are located in the mitochondrial DNA and dont obey
The law of segregation
Inheritance: This term is commonly applied to the inheritance of alleles that obey Mendel's laws and follow a strict dominant/recessive relationship.
Molecular: 50% of the protein, produced by a single copy of the dominant (functional) allele in the heterozygote, is sufficient to produce the dominant trait.
For Mendel's pea plants, the tall phenotype is determined by a dominant allele and the dwarf phenotype is determined by recessive allele. Suppose there is a cross between true-breeding tall and true-breeding dwarf plants. What is the expected outcome in the second or F2 generation when F1 plants are crossed to each other?
-3:1 phenotype of tall and dwarf respectively
Inheritance: This pattern occurs when the heterozygote has a phenotype that is intermediate between either corresponding homozygote.
I.e a cross between homozygous red-flowered and homozygous white-flowered parents will have heterozygous offspring with pink flowers.
Molecular: 50% of the protein, produced by a single copy of the functional allele in the heterozygote, is not sufficient to produce the same trait as the homozygote making 100%.
Inheritance: This pattern occurs when the heterozygote has a trait that is more beneficial then either homozygote.
Molecular: 3 common ways that heterozygotes gain benefits
- their cells may have increased resistance to infection by microorganisms
- they may produce more forms of of protein diners, with enhanced function
-they may produce proteins that function over a wider range of conditions
Situation in which 2 different allele for a genetic trait are both expressed
Phenotypes of both alleles are expressed
I.e in blood typing, an individual carrying the A and B alleles will have an AB blood type
Molecular: the Codominant alleles encode proteins that function slightly differently from each other, and the function of each protein in the heterozygote affects the phenotype uniquely.
The I^A and I^B phenotypes
Chromosomes that differ between males and females
X-linked inheritance (chromosome)
Inheritance: This pattern involves the inheritance of genes that are located on the x-chromosomes, nut not on the Y. Males are hemizygous for x-linked genes, females have 2 copies.
When a daughter can inherit a sex linked gene from either her mother or father, it must be located on the X chromosome.
X-linked recessive alleles
One form of hereditary deafness is inherited with and X-linked recessive allele. A woman with normal hearing has a son with hereditary deafness. The woman's genotype at this gene locus is heterozygous
Colorblindness is due to the X-linked recessive allele. To be colorblind, females must inherit two copies of this allele and males must inherit one copy.
The X and Y chromosomes contain short regions of this that promote pairing during meiosis I in sperm formation.
Recessive mutant alleles
Pe of allele often leads to a decrease in the production of a functional protein.
Inheritance: this pattern refers to the effect of sex on the phenotype of the individual.
Molecular: sex hormones may regulate the molecular expression of genes. This can influence the phenotypic effect of alleles.
Sex- limited inheritance
Inheritance: this refers to traits that occur in only one of 2 sexes.
I.e Brest development in mammals
Inheritance: an allele that has the potential of causing the death of an organism
Usually inherited in a recessive manner
Ina classic experiment, a cross between two yellow mice produced both yellow and white offspring. Yellow was though to be due to an autosomal dominant allele while white was due to autosomal recessive allele. The yellow mice are known to be heterozygous for the yellow allele. for this cross, the ratio of phenotypes was 2 yellow: 1 white. Yellow is most likely due to this.
Prevalent alleles in a natural population
most commonly-occurring in a population
I.e tall plants, purple flowers, axial flowers, yellow seeds, round seeds, green pods, smooth pods.
In large populations, more then one wild-type alleles may occur
Less frequent alleles that have genetic changes making them defective in protein production
Random mutations occur in populations and alter pre-existing alleles. Tend to be rare in natural populations. Defective in the their ability to express a functional protein.
I.e dwarf plants, white flowers, terminal flowers, green seeds, wrinkled seeds, yellow pods, and constricted pods.
- causes human genetic diseases.
Inability to metabolize phenylalanine. Homozygous individuals are unable.
Temperature sensitive allele
This disease can be prevented by following a phenylalanine-free diet. If the diet isn't followed early in life, it can lead to severe mental impairment and physical degeneration.
Lake of pigmentation in the skin, hair and eyes.
Defect in lipid metabolism. Leads to paralisis, blindness, and early death
Results in death during childhood
Example: In the general population, 1/150 people are carriers for the allele for Tay-Sachs disease. A child with the disease is born to healthy parents who are unaware of their carrier status. the allele that prevents the disease in the parents is a wild-type allele and the one that causes the disease is a mutant allele
Inability to regulate ion balance across epithelial cells. leads to production of thick mucus and results in chronic lung infections, infertility, and organ malfunctions.
Gene is expressed at different stages of development
Defect in lipid metabolism. Muscle weakness in infancy, early blindness, and progressive mental and motor deterioration.
Lesch- Nyhan syndrome
Inability to metabolize purines, which are bases found in DNA and RNA. Leads to self-mutation behavior, poor motor skills, and usually mental impairment Nd kidney failure.
The type of mutation that leads to increased expression of an altered protein in a cell which doesn't normally express the protein
A mutant allele may be over expressed or expressed in the wrong cell
In which the protein encoded by the mutant gene acts antagonastically to the normal protein.
In a heterozygote, the mutant protein contracts the effects of the normal protein, thereby altering the phenotype.
If I heterozygous individual shows a disease phenotype despite having one functional allele.
The dominant mutant allele loses its function so that heterozygous individual shows an abnormal phenotype or disease phenotype.
Mutant allele may affect phenotype via this, in which the dominant mutant allele is a loss-of-function allele.
Is a situation in which an allele that IS expected to cause a particular phenotype does not.
Suppose a genetic test shows that a woman has inherited the dominant BRCA1 allele that causes breast cancer. If she does not develop breast cancer in her lifetime, the phenomenon is called this.
Term used to describe the outcome of traits is the degree to which the trait is expressed.
In the case of polydactyl, the number of extra digits can vary.
I.e a person with several extra digits (toes) would have high expressivity, whereas a person with a single extra digit would have low expressivity.
Example: Greig cephalopolysyndactyl, A developmental disorder determined by dominant allele, can affect hands, feet, head and/or face. And one family, the mother had used fingers on both hands while the daughter not only had fused fingers but also developed malformations in her toes and school. This outcome is explained by variable expressivity
Temperature sensitive allele
The phenotypic effects are dependent on the temperature
Example: Himalayan coloring in rabbits is due to a dominant allele that codes for a tyrosinase enzyme which participates in the production of the dark pigment melanin in cold temperatures, dark coloring is only found in the ears, nose and feet of the animal. White coloration develops on the body areas were blood flow keeps the animal warm. The tyrosinase enzyme is most likely this
The ability to prevent the symptoms of phenylketonuria by restricting the diets of patients who inherit the disease is in example of this effect on the phenotype.
Norm of reaction
Effects of environmental variation on a phenotype. Specifically its the phenotype range seen in individuals with a particular genotype.
Example: Cutting from a single yarrow plant were grown at different altitudes in the Sierra Nevada mountain range. The plane pieces had 38cm, 40cm and 30cm of growth at a low, medium and high elevations respectively. This range of phenotypes is this.
Heterozygote exhibits it
A condition which a phenotype is intermediate between the corresponding homozygous individuals
Situation in which one allele doesn't completely dominate another allele, and therefore results Ina new phenotype
In 1905, Carl Correns first observed this phenomenon in the color of the 4 o'clock (Mirabilis jalapa)
Overdominance or heterozygote advantage
The phenomenon in which a heterozygote has greater reproductive success compared with either of the corresponding homozygotes
While causing sickle cell anemia and homozygous individuals, the product of the Hb^S allele provides resistance to malaria in individuals with the HB^A HB^S genotype. This advantage to heterozygotes demonstrates this.
Within a population, a single gene is typically found in 3 or more alleles
ABO group of antegens
Determines blood type in humans.
Is an example of multiple alleles and illustrates yet another allelic relationship called codominanace
That groups of interconnected sugars in the plasma membrane of red blood cells, that act as surface antigens
Small difference in the structure:
-GalNAc in antigen A
-galactose in antigen B
Are molecular structures that are recognized by antibodies produced by the immune system
O blood type
Can donate to all.
Can only receive O.
No antigen. Produces anti A&B antibodies
Homozygous ii, produces relatively short Oligosaccharides, which is called H antigen.
Humans of all all blood types don't normally produce antibodies against H antigen
A blood type
A homozygous (I^A I^A) or a heterozygous (I^A i) will have this blood type.
The red blood cells of his individual will contain the surface antigen known as A.
A person with blood type A makes antibodies to blood type B
B blood type
A homozygous (I^B I^B) or a heterozygous (I^B i) will have this blood type.
The red blood cells of his individual will contain the surface antigen known as B.
Antibodies directed against blood type B would recognize which carbohydrate on the Oligosaccharides attached to red blood cells? - galactose
Sex-influenced inheritance (alleles)
Refers to the phenomenon in which an allele is dominant in one sex but recessive in the opposite sex
Phenomenon of heterozygotes
The genes that govern sex-influenced traits are autosomal, not on the X or Y chromosome
Sex-limited inheritance (traits)
In which a trait occurs in only one of the two sexes
Such genes are controlled by sex hormones or by the pathway that leads to male and female development
Sex-limited traits are responsible
In which members of the opposite sex have different morphological features
A phenomenon involving animals of the same species but of opposite sexes that have different physical features.
This phenomenon is common among many animal species is often striking among various species of birds in which the male has more ornate plumage than the female
When the absence of a specific protein results in a lethal phenotype that encodes, the protein is considered an essential gene for survival
1/3 of all genes are essential genes
Not all lethal mutations occur in essential genes, although the great majority do
Non essential genes
Are not absolutely required for survival, although they are likely to be beneficial to the organism
Conditional lethal alleles
When lethal alleles may kill an organism only when certain environmental conditions prevail
Temperature-sensitive (ts) lethal alleles
Cause an organism to die only in particular temperature rages.
Have been observed in many organisms, including Drosophila
Act only in some individuals
Of course, any particular individual cannot be semidead
Within a population, a semi lethal allele will cause some individuals to die but not all of them.
Age of onset
Age when disease symptoms appear
The multiple effects of a single gene on the phenotype (many traits)
Occurs for several reasons:
1. The expression of a single gene can affect cell function in more than one way. For example, a defect in a micro tubule protein may affect cell division and cell movement.
2. A gene may be expressed in a different cell type in a multicellular organism
3. A gene may be expressed at different stages of development
It is revealed when research study the affects of gene mutations
A second cross in which the sexes and phenotype are reversed
For example, An affected female animal is crossed to an unaffected male. This cross produces female offspring that are carriers and male offspring that are all unaffected with muscular dystrophy.
Is used to describe the single copy of an x-lined gene in the male.
A male mammal is said to be hemizygous for x-linked genes.
Because males of a certain species, such as humans, have a single copy of the X chromosome another distinctive feature of x-linked inheritance is that males are more likely to be affected by rare recessive x-linked disorders
Sex-linked gene (chromosome)
Refers to a gene that is found on one of the two types of sex chromosomes but not on both
Genes found in homologous regions of the X and Y chromosome demonstrate this.
The inheritance pattern for gene that is located on the sex chromosome but appears to be inherited like an autosomal gene is this.
Psedoautosomal refers to the idea that the inheritance pattern of the Mic2 gene is the same as the inheritance pattern of a gene located on an autosome even though the Mic2 gene is actually located on the sex chromosome.
As in autosomal inheritance, males have 2 copies of pseudoautosomally inherited genes, and they can transmit the genes to both daughters and sons.
Genes located on the Y chromosome.
The gene on the mammalian Y chromosome that is essential for the development of make characteristics is called Sry.
Never transmitted from father to son.
Sickle cell disease
The ratio of phenotypes is 1:2:1 for offspring from a cross between two individuals who are heterozygous for this
Sickle cell anemia
Individuals with an Hb^S HB^S genotype suffer from this because they produce hemoglobin S, a variant that's causes their red blood cells to form a crescent shape when oxygen is low.
Muscle cells in pro with Duchenne muscular dystrophy show weakening of the cytoskeleton due to deficiency of this protein
Which of the following statements is TRUE of a pink-flowered four o'clock plant?
It is heterozygous at the locus that controls flower color
A son has the blood type A (I^A i). The father of the boy is known to be AB. Which is not a possible genotype for the mom.
A son has the blood type B (I^B i). The father of the boy is known to be AB. In order for the son to donate blood to his mother, what must be the moths genotype?
If a person with O blood type needs a transfusion, which of the following blood types could act as a donor
Why is an individual with blood type O considered a universal donor?
Neither the A or B antigens are present on type O red blood cells.
An inheritance pattern in which the alleles of one gene mask the phenotypic effects of the alleles of a different gene
Occurs because two or more different proteins participate in a common function
A phenomenon in which 2 parents that express the same or similar recessive phenotypes produce offspring wi a wild-type phenotype
Gene modifier effects
A phenomenon in which an allele of one gene modifies the phenotypic outcome of the alleles of a different gene
A pattern in which the loss-of-function in a single gene has no phenotypic effect, but the loss of function of 2 genes has an effect
How the allele if variants of two different genes affect a single trait
Was discovered by William Bateson and Reginald Punnett in 1906
Y-linked inheritance pattern (gene)
Very distinctive. The gene is transmitted only from fathers to sons
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