Flashcards in Chap. 5 Understanding Inheritance Deck (68):
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Who was Gregor Mendel?
-1812 to 1884
-an Australian Monk
-known as the father of genetics
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What were two important features of Mendel's work?
1. Simplicity
2. Measured quantitatively
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What are (more specifically) the important points of Mendel's work?
-studied specific characteristics one at a time
-had no knowledge of mitosis, chromosomes, etc.
-studied common garden peas
-readily available and easy to grow
-reproduce quickly
-many different characteristics with two traits
-followed a classic approach to problem solving
-most of his work was destroyed after his death
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Characteristic
A feature of an organism which can be expressed in one of two or more ways, which are known as traits
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Trait
A distinct form of a characteristic
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How did Mendel control the pollination of his pea plants?
He removed the young, immature stamens from flowers chosen to be the female parent. They were separated, covered, and then pollinated by Mendel
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What were Mendel's four conclusions after his monohybrid crosses?
1. The original male and female contain different factors (alleles) (one for tall, one for dwarf)
2. There must be a mix of the factors in the F1 generation because both traits reappear in F2
3. There must be a separation of factors prior to self pollination in order to produce a hybrid offspring
4. The tallness factor must be dominant over the dwarfness and the dwarfness is recessive
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What is Mendel's first law, the law of segregation?
1. An individual contains factors (alleles) in pairs
2. These factors segregate from one another and are distributed to different sex cells
3. Each parent can only contribute one member of a pair of factors to their offspring
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What is the relation of probability to genetics?
The probability of two or more independent events occurring together is the product of individual probabilities of each event occurring separately.
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How do you do a test cross?
Cross a dominant phenotype (the one you are testing) with a known pure bred homozygous recessive plant to determine the genotype of the F1 plant. If 50% of each phenotype, heterozygous
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What are the steps of Mendel's method?
Let R represent the dominant allele
Let r represent the recessive allele
1. Describe the genotypes of the parents
2. Determine the possible gametes each parent could produce
3. Organize the possible gametes using a PUNNETT SQUARE
4. Analyze all the possible genotype combinations by summarizing their gene combinations as a word description and summarize how many zygotes of each combination are possible
5. For each genotype describe the corresponding phenotype and how many are possible
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What is the ratio for a standard monohybrid cross?
3:1
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What is the ratio for a standard (heterozygous) dihybrid cross?
9:3:3:1
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What is Mendel's second law, the law of independent assortment?
Members of different pairs of factors behave independently and assort independently during gamete formation.
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What are conventions of a pedigree chart?
-Roman numerals symbolize generation
-Arabic numbers symbolize individuals within a generation
-birth order is indicated by drawing them from the oldest to the youngest
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In pedigree charts an autosomal dominant allele:
-will usually be transmitted from a parent to at least 50% of the offspring
-will appear in every generation (probably)
-will be expressed in the appearance of the organism
-every individual should have at least one affected parent
-males and females should be affected with equal frequency
-two affected individuals may have unaffected children
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In pedigree charts a recessive recessive allele:
-will occur in offspring but may be absent in parents or other relatives
-will be seen in about 25% of the offspring if both parents are heterozygous.
-Two affected individuals usually produce offspring all of whom are affected
-males and females are equally at risk
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True breeding
Organisms that exhibit the same traits generation after generation
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Cross
The fertilization of a female gamete of specific genetic origin with a male gamete of specific genetic origin
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Genotype
The combination of alleles for any given trait or the organism's entire genetic makeup
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Phenotype
The physical and physiological traits of an organism
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Homozygous
An organism that has two identical alleles of a gene
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Heterozygous
An organism that has two different alleles of a gene
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Test cross
A cross between a parent of unknown genotype and a homozygous recessive parent
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Dihybrid cross
A cross of two individuals that differ in two traits due to two different genes
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Chromosome theory of inheritance
Traits determined by genes are inherited through the movement of chromosomes during meiosis
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Pedigree
A flowchart that uses symbols to show the inheritance patterns of traits in a family over many generations
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What are some autosomal dominant diseases?
Chr. 4: Huntington disease. Neurological, loss of muscle control and cognitive decreases over 15 years. Decreased life
Chr. 13: Retinoblastoma. Tumours in retina in young children, fatal if not treated
Chr. 15: Marfan syndrome: Affects connective tissue leading to weakness in heart, blood vessels, and skeleton. Causes long limbs
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What are some autosomal recessive diseases?
Chr. 7: Cystic fibrosis. Thick mucus build up in lungs, making breathing difficult and leading to infection. Blocks pancreas, hinders digestion, decreased life expectancy
Chr. 11: Sickle cell anemia (codominance): irregular red blood cell shape caused by abnormal hemoglobin protein. decreased life expectancy
chr. 12: phenylketonuria. Prevents breakdown of phenylalanine, leading to developmental and cognitive delays. must be treated immediately
Chr. 15: Tay-Sachs disease: progressive destruction of nervous system caused by lack of enzyme hexosaminidase A, leading to accumulation of lipids in cells. fatal in early childhood
Chr. 18: Neimann-Pick disease: -accumulation of lipids in cells. Decreased life expectancy. Fatal in early childhood
Chr. 19: Maple syrup urine disease: Inability to break down 3 amino acids leading to nerve degeneration. Fatal if not treated
Chr. 20: ADA-SCID: Deficiency in the enzyme adenosine deaminase resulting in minimal immune response and susceptibility to all diseases. Fatal if not treated with bone marrow transplant
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What are types of genetic tests?
Karyotype, FISH (fluorescence in situ hybridization), gene testing, biochemical testing
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What are Karyotypes good for?
-finding errors in chromosome structure and number
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What is FISH good for?
-details of chromosomal abnormalities. Is based on visualizing, through fluorescence, a targeted region on a chromosome. Can be used for Chronic myelogenous leukemia where part of chrom. 9 has broken off and attached to chrom 22
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What is gene testing used for?
Mutations in the DNA sequence of a gene. Breast cancer susceptibility genes BRCA1 and BRACA2.
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What is biochemical testing good for?
Abnormal enzymes and other proteins due to the mutation of a gene that codes for that protein. Good for Tay-Sachs disease due to lack of hexosaminidase A protein
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What is gene therapy?
A technique aimed at treating genetic disorders by introducing the correct form of the defective gene into a patient's genome. A copy of a normal gene is inserted into a vector, normally a virus. Once inserted the person can use that gene to make correct proteins.
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What are the current problems with gene therapy?
-viruses present a potential immune response
-benefits are shortlived. The genes do not get integrated and are not passed on when the cell divides.
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What is codominance?
Both alleles are expressed. Written as Capital for characteristics and superscript capital for allele. Both homozygous described as homozygous dominant. Heterozygous is heterozygous codominant.
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What is incomplete dominance?
Both partially expressed, in between. Written the same as codominant except heterozygous is heterozygous incomplete dominance
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How do we track multiple alleles?
Any letter, capital with superscripted numbers in order of dominance. Recessive to all is lowercase.
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What blood types are there?
A (IA allele) B (IB allele) AB (IAIB) O (i)
Rh+ (R), Rh- (r)
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What is the pattern of inheritance for blood types?
Muliple alleles where i is recessive and A and B are codominant.
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What is an example of incomplete dominance in human disease?
Familia hyper-cholesterolemia. Malfunction of LDLR gene causing high cholesterol. People with one allele will be affected but not as severely.
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What is an example of codominance in human disease?
Sickle cell anemia. Causes hemoglobin to be C shaped which can cause blockages. Heterozygotes produce sickle cells but rarely experience the symptoms. In fact they have a higher resistance to malaria.
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What is heterozygous advantage?
A survival benefit for individuals who are heterozygous
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How does environment affect genes?
May be influenced by surroundings. Gene for Himalayan rabbits (black on feet, ears) caused by cold temp.
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What is continuous variation?
A gradual range of variation in one trait resulting from the activity of many genes
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What is a polygenic trait?
A trait that is controlled by more than one gene. All the genes together are called a polygene.
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How much larger is the X chromosome?
2000 genes vs. 100
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What are linked genes?
Genes that are on the same chromosome and tend to be inherited together. They do not follow the mendelian phenotypic ratio. They do not always stay linked due to crossing over. All genes on a chromosome are called a linkage group.
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How is gene linkage used for chromosome mapping?
Alleles separate with a predictable frequency. The closer together the less frequently they separate. This can help determine the relative locations of genes. It is only useful for plants and organisms that reproduce rapidly.
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Why are drosophila melanogaster a good choice for the study of sex linked inheritance?
-produce many offspring and reproduce rapidly
-have X and Y chromosomes
-have easily identifiable traits
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What was the first research into sex linked traits?
Thomas Hunt Morgan used fruit flies and discovered that males had white eyes more than expected (F1 generation all females were red eyed but half of males were white eyed). 1910
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What is the pattern for X-linked dominant?
Affected males pass the allele only to daughters who have 100% chance of getting the disease. Affected females will have 100% affected offspring
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What is the pattern for X-linked recessive?
-affect more males than females
-unaffected parents could only pass to sons
-affected male will have no affected children but daughters will 100% be carriers
-affected female will have 100% affected sons and 100% carrier daughters
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What are X-linked recessive traits in humans?
Red-green colour vision deficiency (CVD)
Duchenne muscular dystrophy
Hemophilia (prevents blood clotting. Common in royal families)
Adrenoleukodystrophy (build up of fatty acids causes progressive brain damage)
Severe combined immunodeficiency (SCID) (Low white blood cell counts)
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What is an X-liked dominant disease?
Hypophosphatemia (softening of bone leading to deformity)
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What is a Y-linked trait?
Hairy ears
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What are Barr bodies?
Inactive X chromosomes. Every cell has only one functioning X chromosome. One is deactivated early in fetal development.
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What is Duchenne muscular dystrophy?
X-linked recessive. 1987 Canadian researchers identified the gene. Symptoms begin around age 2-6. Most boys are in a wheelchair by age 12.
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How do we write sex linked alleles?
X^D, X^d, Y
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How do we identify the genotypes XDY or XdY?
Monozygous dominant/recessive
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What did scientists disover thanks to the human genome project?
1. Only about 2 percent of the nucleotides in the human genome make up our genes and code for all the proteins in our body
2. The estimated 25 000 total number of genes is much less than scientists predicted.
3. Over 50% of our DNA consists of stretches of repeating sequences
4. There is very little genetic variation within our species. About 99.9% of DNA is almost exactly the same in all people.
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What is bioinformatics?
A field of study that deals with using computer technology to create and analyze large databases of information. It exists thanks to advances in
1. Techniques to sequence biological molecules
2. Computer database software
3. Communication technology to share information
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What is genomics?
The study of genomes and the complex interactions of genes that result in phenotypes.
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What is a SNP?
A single nucleotide polymorphism. They are one letter of a genetic code compared to others. Variations can help determine the cause of diseases. They can serve as markers for genes or linked genes. There are currently arround 10 million SNPS
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What are haplotypes?
Regions of genetically linked variations. Basically a group of SNPs. The HapMap project is attempting to develop a map of all the genetic variations in the human genome.
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What are epigenetics?
The study of how changes in the inheritance of certain traits or phenotypes are based on changes to gene function and not to changes in DNA sequence. The changes are not necessarily permanent. They could be a response to environmental change. Can determine whether genes are turned on or off.
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