Genetics Chapter 4

Genetic polymorphism

In large populations, more then one wild-type alleles may occur

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

Albinism

Lake of pigmentation in the skin, hair and eyes.

Some genes are located in the mitochondrial DNA and dont obey

The law of segregation

Gain-of-function mutations

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

Y-linked inheritance pattern (gene)

Very distinctive. The gene is transmitted only from fathers to sons

Conditional lethal alleles

When lethal alleles may kill an organism only when certain environmental conditions prevail

Essential gene

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

Multiple alleles

Within a population, a single gene is typically found in 3 or more alleles

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

Gene redundancy

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

Complementation

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

Reciprocal cross

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.

Semilethal alleles

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

Epistasis

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

Antigens

Are molecular structures that are recognized by antibodies produced by the immune system

Non essential genes

Are not absolutely required for survival, although they are likely to be beneficial to the organism

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

Temperature-sensitive (ts) lethal alleles

Cause an organism to die only in particular temperature rages. Have been observed in many organisms, including Drosophila

Sex chromosome

Chromosomes that differ between males and females

Tay-Sachs disease

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

Sandhoff disease

Defect in lipid metabolism. Muscle weakness in infancy, early blindness, and progressive mental and motor deterioration.

ABO group of antegens

Determines blood type in humans. Is an example of multiple alleles and illustrates yet another allelic relationship called codominanace

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.

Pseudoautosomal inheritance

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.

Holandric

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.

Incomplete dominance

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)

Gene interaction

How the allele if variants of two different genes affect a single trait Was discovered by William Bateson and Reginald Punnett in 1906

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.

I^A I^B

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?

I^B i

Haploinsufficiency

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.

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

Dominant-negative mutations

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.

Phenylketonuria

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.

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.

Cystic fibrosis

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

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.

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.

Incomplete penetrance

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%.

Overdominance

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

Simple mendelian

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

Lethal allels

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.

Sex-influenced inheritance

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

Incomplete penetrance

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.

Hemizygous

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

Mutant alleles

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.

Dystrophin

Muscle cells in pro with Duchenne muscular dystrophy show weakening of the cytoskeleton due to deficiency of this protein

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.

X-linked alleles

Never transmitted from father to son.

If a person with O blood type needs a transfusion, which of the following blood types could act as a donor

O

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.

Recessive mutant alleles

Pe of allele often leads to a decrease in the production of a functional protein.

Wild-type alleles

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.

Sex-linked gene (chromosome)

Refers to a gene that is found on one of the two types of sex chromosomes but not on both

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

Sexual dimorphism

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

Codominance

Situation in which 2 different allele for a genetic trait are both expressed Phenotypes of both alleles are expressed Inheritance: 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

Expressivity

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

Oligosaccharides

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

Homology

The X and Y chromosomes contain short regions of this that promote pairing during meiosis I in sperm formation.

Environmental effects

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.

Pleiotropy

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

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.

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

Sickle cell disease

The ratio of phenotypes is 1:2:1 for offspring from a cross between two individuals who are heterozygous for this