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CH13 - Mendel and the Gene

What are sex-linked genes? Genes that live on only 1 sex chromosome. The X chromosome carries > 1000 genes; the Y chromosome only 78 genes.
in multiple allelism, there are multiple genes for one trait. How many alleles are involved in the genes that determine human blood type (A, B, AB, and O)? Three alleles determine blood type: A, B, O
explain what Polygenic Inheritance is. Some characteristics show a range of continuous phenotypes instead of discrete, defined phenotypes (ex: height, skin color, and body build, and grain color in wheat).
describe what is happening with gene/s involved in Polygenic Inheritance Phenotypes produced by polygenic inheritance are governed by the interaction of more than two genes at multiple loci Human skin color is controlled by at least 3 genes, each with pairs of incompletely dominant alleles
define Pleiotropy. p. 283 some alleles of a characteristic may create multiple phenotypic effects. Ex: Marfan syndrome, (aka FBN1). (compare Mendel’s rules that specify only one phenotype possible for any allele)truth is that
give an example of Pleiotropy in humans. Example: The SRY gene in male humans' SRY gene stimulates development of gonads into testes, which in turn stimulate development of the prostate, seminal vesicles, penis, and scrotum
define Non-Disjunction. Incorrect separation of chromosomes or chromatids in meiosis
in Mendel's cross-breeding experiment between a "true breeding" (aka pure breeding) purple flower and a true breeding white flower, what resulted in the F1 and F2 generations? F1 generation: all purple flowers F2 generation: 3/4 purple, 1/4 white flowers
Mendel's reciprocal cross experiments repeated cross breeding. 1st: the trait came from the mother 2nd: trait came from the father. What was the result and what did this prove? F1 and F2 were identical regardless of whether the traits came from the mother or father, proving that it didn't matter which parent the gene came from.
Mendel's "genetic model" was later proven by Sutton and Bovieri in which theory? the Chromosome Theory of Inheritance (13.3, 13.4)
Demonstrate Independent Assortment by drawing a Punnett square. Both parents have genotype RrYy. Don't fill in squares, just rows and columns to represent the 4 possible gametes genotypes each parent can produce. p. 273 Independent Assortment: male parent: genotype RrYy gametes:(RY,Ry,rY,ry) female parent: genotype RrYy gametes:(RY,Ry,rY,ry) compare Dependent Assortment: male parent: genotype: RrYy gametes:(RY,ry) female parent: genotype: RrYy gametes:(RY,r
The punnett square for Parents RRYY x rryy results in a F2 Phenotype ratio of 9:3:3:1. Write these in fractions. p. 273 9:3:3:1 9/16 (R-Y-) (R is dominant, Y is dominant) 3/16 (R-yy) (R is dominant, y is recessive) 3/16 (rrY-) (r is recessive, y is recessive) 1/16 (rryy) (both are recessive)
In a punnett square for Parents RRYYZZ x rryyzz, how often will the rryyzz genotype show in the F2 generation? This is like the example on p. 273 but with the additional trait Z. Instead of 4 raised to the 2 (for 2 traits), we raise 4 to the 3 (for 3 traits) and get 64. Thus the all-recessive genotype shows up 1/64 times in F2.
define locus and loci. p. 275 A locus (plural: loci) is a gene's physical location on the chromosome.
Law of Segregation, or Principle of Segregation refers to what stage of meiosis and why? p. 275 the law refers to the separation of alleles in meiosis. Homologs separate in anaphase of Meiosis I, therefore their alleles separate. They are rejoined at fertilization.
what is the difference between dominance and incomplete dominance? p. 283 incomplete dominance: neither allele dominates and there is an intermediate phenotype. codominance: heterozygotes have the phenotype associated with both alleles present. ex: human RBCs can have membrane glycoproteins have both M and N phenotype.
what is a qualitative trait? p. 284-5: A qualitative trait is one that differs by degree (height in humans, kernel color in wheat).
how is polygenic inheritance linked to qualitative traits? p286: in polygenic inheritance, each gene adds a small amount to the phenotype. Ex: the number of red pigment alleles A, B, and C in the genotype determine the degree of redness in the wheat kernal.
is "yellow and wrinkled" an example of a phenotype or a genotype? a phenotype. Phenotypes describe observable traits.
Define genetics. the branch of biology that focuses on the inheritance of traits.
define a gene the hereditary determinant for a trait
Who is Mendel? an Austrian monk who is considered the father of genetics & the first person who brought math into biology. Mendel’s secret to success: good notes, characteristics chosen, mathematics
give an example of self-fertilization (aka "selfing"). the pollen from a garden pea plant's flower falls on the female reproductive organs of that same flower.
Cross Fertilization ("cross pollination") this is how Mendel controlled matings to see how traits passed on: he transferred pollen from one flower to the female reproductive organs of another flower.
define allele different versions of the same gene
An individual's collection of alleles is called its ____ genotype
An individual's collection of observable traits is called its ____ phenotype
What makes an allele recessive or dominant? a recessive allele disappears in the F1 generation but shows up in the F2 generation at the rate of 1 in 4.
Does a recessive trait make an individual less fit for survival? not necessarily. Dominance and recessiveness in traits do not have anything to do with an individual's fitness. Huntington's disease is fatal & rare, from a dominant gene.
How many alleles do humans have for every gene? two: one from mom, one from dad. One allele comes from each chromosome in the homologous chromosome pair.
describe alleles in the Law of Segregation (p. 275) 2 alleles of a gene separate during meiosis (gametes have 1 allele in 1n or 23 chromosomes), so offspring (sperm + egg = 2n or 46 chromosomes) have 1 allele from mom and 1 allele from dad
Each selection is an individual's genotype. Which are homozygous for the trait represented by H or h? a) HHKk b) HhKK c) hhkk a) HHKk and c) hhkk are homozygous
Each selection is an individual's genotype. Which are homozygous for the trait represented by K or k? a) HHKk b) HhKK c) hhkk b) HhKK and c) hhkk are homozygous
Each selection is an individual's genotype. Which are heterozygous for the trait represented by H or h? a) HHKk b) HhKK c) hhkk b) HhKK is heterozygous
Each selection is an individual's genotype. Which are heterozygous for the trait represented by K or k? a) HHKk b) HhKK c) hhkk a) HHKk is heterozygous
In heterozygous genotype Rr, R represents blue flowers and r represents yellow flowers. What is the dominant phenotype? the dominant phenotype is blue flowers, represented by R.
define genotype. genetic makeup. Mendel worked with phenotype, not genotype, but his work paved the way for its discovery.
define phenotype. physical appearance: identifiable traits.
Mendel's Law of Independent Assortment works in the presence of certain requirements. What are these? 1) you do not genetic recombination 2) the alleles are not on the same chromosome 3) the alles are on the same chromosome but are more than 50 centi Morgan (cM)apart
explain what genetic linked (autosomal linked) is. Different genes locate located on the same chromosome tend to be inherited together: characteristics whose genes tend to assort together are NOT independently assorted, but Linked
What is a sex linked genes? Do they obey Mendelian laws? in a sex-linked gene, the allele for the trait is on sex chromosomes. Sex-linked genes do NOT obey Mendelian laws.
give an example of incomplete dominance. prediction: SS (straight) X ss (curly) = Ss (straight) actual: SS (straight) X ss (curly) = Ss (wavy). If SS is straight hair, ss is curly hair, then Ss heterozygous is wavy hair.
when 2 alleles rather than 1 allele form a new phenotype, what is the word describing their relationship to each other? they are codominant.
In a genetic map, what is the unit of distance between two genes? the unit of distance between two genes is designated by centiMorgans (cM). A cM = the physical distance between 2 alleles that generates 1% recombinant offspring.
AABb (female) X aabb (male) which combo would be the fertilized egg? you need to know the law of segregation and independence a) AAbb b) AaBB c) Aabb d) none c) Aabb. One A must come from female (A) and one A must come from male (a). Thus the offspring must have Aa. One B must come from female (B or b) and one B must come from male (b or b), thus offspring has Bb or bb.
when genes on a chromosome are more distant from each other, are they more or less likely to cross over? they are more likely to cross over, unless the distance is over 50 cM, in which case independent assortment takes over.
In the Incomplete Dominance example with lavendar flowers in the text, what colors in what ratios are in F1 and F2 generations? RR (purple) x rr (white) flower => all F1 have Rr; => F2 is 1:2:1 or RR:Rr:Rr:rr, where Rr is lavendar because neither purple nor white dominate. Note that the 1:2:1 ratio of genotypes matches the 1:2:1 ratio of phenotypes.
segregation of chromosomes means that Each gamete formed in an organism will have one copy of each gene.
two homozygous parents with genotypes RR and rr result in all Rr F1 offspring. Each offspring produces 4 gametes. Where are R and r in the gametes? Each of the 4 gametes contains R or r, due to independent assortment in meiosis. 2 gametes have R, 2 gametes have r.
If an individual is heterozygous for hair color (Hh) and eye color (Ee), what genotypes can its gametes have? Each gamete will contain both genes. Thus the individual can make gametes that contain HE, He, hE, or he.
If an individual with type O blood mates with an individual with type AB blood, what are the possible blood types of their offspring? A and B
define epistasis When different genes interact with each other in a way that influences the phenotype.
In Drosophila, the white-eyed gene (w) is on the X chromosome (w+ = red eyes; w = white eyes). The w+ allele is dominant to w. If a w+ homozygous female is crossed with a wY male, what is the phenotypic ratio of the F2 generation? 2:1:1 (Note that 3:1 is the ratio of red to white).
If an organism is heterozygous for two traits that are linked, how many genotypes are possible in the gametes produced from a single germ-line cell? (assume no crossing over occurs) 2, not 4. Remember that linked genes violate the principle of independent assortment. See Figure 13.13.
If an organism is heterozygous for two traits that are linked, how many genotypes are possible in the gametes produced from a single germ-line cell? (assume 1 crossing over occurs) 4 See Figure 13.14
Created by: biobu on 2009-03-09

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