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76 Cards in this Set
- Front
- Back
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What is genetics the study of?
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How traits are inherited from one generation to the next.
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What is the basic unit of heredity?
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The gene
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What is genetics?
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It is the study of how traits are passed on from one generation to the next
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What are genes?
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They are composed of DNA and are located on chromosomes
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What are the alternative forms of genes called when they exist in more than one form?
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Alleles
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What is a genotype?
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It is the genetic makeup of an individual
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What is the physical manifestation of the genetic makeup called?
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It is the phenotype
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What did Gregor Mendel do in the 1860s?
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He developed the basic principles of genetics through his experiments with the garden pea
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What did Gregor Mendel study?
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He studied the inheritance of individual pea traits by performing genetic crosses
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What are true breeding individuals?
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They are individuals that if self-crossed produce progeny only with the parental phenotype
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He (Gregor Mendel) crossed true breeding individuals how?
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He crossed true breeding individuals with different traits, mated them, and statistically analyzed the inheritance of the traits in the progeny
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What are the four principles of inheritance Mendel postulated?
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He said genes exist in alternative forms.
An organism has two alleles for each inherited trait, one inherited from each parent. The two alleles segregate during meiosis, resulting in gametes that carry only one allele for any given inherited trait. If two alleles in an individual organism are different, only one will be fully expressed and the other will be silent |
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What is the expressed allele called?
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It is the dominant allele
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What is the silent allele?
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It is recessive
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What is a monohybrid cross?
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It is how Mendelian inheritance can be illustrated. It is a cross between two true-breeding pea plants, one with purple flowers and the other with white flowers
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What is it called when only one trait is being studied in a particular mating?
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A monohybrid cross
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What are the individuals called that are being crossed?
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They are the parental or P generation
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What are the progeny generations called?
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They are the filial or F generations
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What does the purple flower plant have a genotype of?
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PP
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What does the white flower parent have?
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It has a genotype pp
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What is a testcross?
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It is used to determine the unknown genotype of an organism
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How come a testcross is used to determine the genotype of an individule?
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Only recessive phenotypes can be predicted with 100 percent accuracy
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If a phenotype is expressed what are our options for genotype?
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The genotype can be either homozygous dominant or heterozygous
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What is a testcross or backcross?
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It is when an organism with a dominant phenotype of unknown genotype is cross with a phenotypically recessive organism
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What is Mendel’s law of independent assortment?
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The alleles of unlinked genes assort independently during meiosis
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What are diploid species?
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They have chromosomes pairs called homologues
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What can recombination frequencies be used to construct?
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A genetic map
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What is one map unit?
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It is defined as a 1 percent recombinant frequency
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How does a map unit work?
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Recombination frequencies are roughly additive
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What does 'Recombination frequencies are roughly additive' mean?
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If genes are found on a map in the order XYZ, then the recombination frequency between X and Y plus the recombination frequency between Y and Z will be roughly equal to the recombination frequency between X and Z
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What if you are given the recombinant frequencies for X and Y, X and Z, and Y and Z?
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You can determine the relative positions of these genes on the chromosome
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What if you are given the recombinant frequencies for X and Y, X and Z, and Y and Z: If X and Y have a recombination frequency of 8 percent, they are 8 map units apart. If X and Z recombine 12 percent of the time, then they are 12 map units apart. Depending on where you draw Z in relation to X on your map, Y and Z are either 20 map units apart or 4 map units apart. Since we are also given that Y and Z recombine with a frequency of 4 percent, the genes are in the order of XYZ (or ZYX) on the chromosome... HOW?
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If X and Y have a recombination frequency of 8 percent, they are 8 map units apart. If X and Z recombine 12 percent of the time, then they are 12 map units apart. Depending on where you draw Z in relation to X on your map, Y and Z are either 20 map units apart or 4 map units apart. Since we are also given that Y and Z recombine with a frequency of 4 percent, the genes are in the order of XYZ (or ZYX) on the chromosome.
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What is incomplete dominance?
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It is when some progeny phenotypes are a blend of the parental phenotypes
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What is an example of incomplete dominance?
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An example is in snapdragons. If a homozygous dominant red snapdragon is crossed with homozygous recessive white snapdragons, they produce 100 percent pink progeny
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What happens when the pink flowers are self crossed?
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They produce red, pink, and white progeny in the ratio of 1:2:1
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What is codominance?
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It occurs when multiple alleles exist for a given gene and more than one of them is dominant
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What is an example of codominance?
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It deals with multiple alleles in the inheritance of ABO blood groups in humans
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What is blood type determined by?
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It is determined by three different alleles, IA, IB, and i
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With is penetrance?
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The penetrance of a genotype is the percentage of individuals within the population carrying the allele who actually express the phenotype associated with it
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What is expressivity?
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It is the degree of a genotype to which the phenotype associated with the genotype is expressed in individuals who carry the allele
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Can expressivity be influenced by environment?
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Yes
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What is an example of expressivity being influenced by the enviroment?
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In the fruitfly Drosophila melanogaster, the dominant gene curly (Cy) gives rise to adult flies with abnormal wings that curl up if the pupae are kept at 25C, but remain uncurled if the pupae are kept at 19C.
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So what is the expressivity of the Drosophila melanogaser?
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It is the degree of curliness of the wings
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Most lethal genes are what?
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They are early acting, ire they program an early death for homozygotes, typically during embryonic development
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Can lethal genes ever be good?
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Yes, for example in heterozygous individuals as in the case of sickle-cell anemia. Heterozygous individuals are resistant to malaria, while homozygous individuals have abnormal hemoglobin
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Can lethal alleles be dominant?
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Yes, these are late-acting genes
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What is an example of a dominant lethal gene?
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The gene for Huntington’s disease in humans. It is 100% percent penetrant and fully dominant
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What is the sad part of the dominance feature of Huntingtons disease?
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Since the Huntington’s disease gene isn’t expressed until middle age, most of its victims have already had children by the time of diagnosis
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Will the recessive phenotype for Huntingtons be more or less frequently found in males?
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It will be more frequent
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What are examples of sex-linked recessives?
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The genes for hemophilia and for color-blindness
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Since the gene is carried on the X chromosome, and males pass the X chromosome only to their daughters, what does this imply?
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Affected males cannot pass the trait to their male offspring
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What do x linked genes mean to a male's daughters?
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Males will pass the gene to all of their daughters
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What do x linked genes mean for the daughter concerning the mother?
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The mothers genes determine if she will have it or not (actually not sure what this question is asking)
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So, what does this amount to ultimately?
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Since all of the daughter’s male children will receive their only X chromosomes from her, half of her sons will receive the recessive sex-linked allele
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What does the existance of x linked gene disorders generally mean about affecting populations of men vs. women?
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Sex-linked recessives generally affect only male
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What is a pedigree?
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It is a family tree depicting the inheritance of a particular genetic trait over several generations
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In analyzing pedigrees, what should you look for?
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Individuals with the recessive phenotype
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When analyzing pedigrees why do pay special attention to the recessive genes?
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Matings between them and the dominant phenotype behave as test crosses
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What will the ratio of the phenotypes be among their offspring show in a pedigree?
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It allows the deduction of the dominant phenotype
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What is nondisjunction?
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It is either the failure of homologous chromosomes to separate properly during meiosis I, or the failure of sister chromatids to separate properly during meiosis II
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What happens if during meiosis, the failure occurs in the secondary spermatocytes?
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It results in one gamete with two copies of the chromosome (polyploidy), two normal haploid gametes, and one gamete with no copies of the chromosome, some (aneuploid)
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What can the resulting zygote have in failure with secondary spermatocytes?
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It might have either three copies of that chromosome, which is called trisomy, or might have a single copy of that chromosome, called monosomy
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What is a clinical example of a feature caused by secondary spermatocytes?
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The birth defect Down syndrome, which is caused by trisomy of chromosome 21.
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What is phenotypically wrong with victims of down syndrome?
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They are of short stature, have characteristic facial features, and are mentally retarded
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What more can nondisjunction do to sex chromosomes?
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It can result in individuals with extra or missing copies of the X and or Y chromosomes
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XXY chromosomes are afflicted with what?
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They have Klinefelter’s syndrome
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XXY, What is klinefelters syndrome?
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They are sterile males with abnormally small testes
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Tell me about XO females?
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They have only one sex chromosome and suffer from Turner’s syndrome. It means they fail to develop secondary sexual characteristics, and are sterile and of short stature
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Tell me about XXX females?
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They are referred to as metafemales
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What’s wrong with XXX females?
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They are usually normal and sometimes infertile
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What about XYY males?
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They are normal, though they tend to be taller than average, and according to some studied, may be more violent
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What is a chromosome that loses a fragment said to be called?
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They are said to have a deficiency
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What occurs when the fragment may join with its homologous chromosome?
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It results in duplication
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What happens if a fragment joins with its nonhomologous chromosome?
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It is an event termed translocation
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What else can a fragment do apart from joining with its nonhomologous chromosome?
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It may rejoin its original chromosome, but in the reverse position
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What is it called when a nonhomologous chromosome rejoins in reverse position with it's original chromosome?
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It is called an inversion
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