Biology Ch. 9
Explain how recessive and dominant disorders are inherited. Provide examples of each.
"Wild type" traits are the most common in nature, and are not always dominant. Albinism, a recessive disorder, is very rare because regular pigmentation is the wild type trait. Yet, it can be carried and not shown, and ¼ of heterozygous parents' offspring are homozygous recessive and are albinos. Dominant disorders are usually less serious, some are very serious, such as dwarfism. Yet, the homozygous dominant genotype embryos usually die, and having this dominant allele is very rare. They are less likely to cause lethal disorders. Huntington's Disease is also an example of a dominant disorder.
Explain how Mendel's law of independent assortment applies to a dihybrid cross.
A dihybrid cross is the cross of two organisms while tracking 2 characteristics instead of only one (monohybrid cross). Mendel's law of independent assortment was that the segregation of the allele pairs of the two tracked characteristics during meiosis were independent of each other, demonstrating that the inheritance of one characteristic had nothing to do with the other. Mendel refuted this hypothesis by crossing F1 generation RrYy (yellow round) peas and seeing that the phenotypes were not RY and ry, but could also be rY and Ry and seeing that some peas were green and round / yellow and wrinkled. The lab cross was the crossing of two black, seeing labs, and saw that the 9:3:3:1 ratio held up, proving independent assortment.
Explain how a testcross is performed to determine the genotype of an organism.
A testcross can determine an unknown genotype by crossing a homozygous recessive individual and an unknown genotype and then using the phenotype of the offspring to determine.
Describe the genetic relationships between homologous chromosomes.
Alleles of homologous chromosomes lie at the same locus, but do NOT have to be the same (homozygous). Each homologous chromosome is passed from one parent. They determine the same characteristics.
Explain why human skin coloration is not sufficiently explained by polygenic inheritance.
Because nature affects skin color, as well as many other things, and cannot be solely determined by genes.
Describe patterns of sex-linked inheritance, noting examples in fruit flies and humans.
Genes on the X and Y chromosomes that pertain to other characteristics are sex linked genes, and the majority are X linked. Eye color in fruit flies is X linked (recessive). Hemophilia is an X linked recessive trait in males, and affect the ability for blood to clot.
Define and distinguish between the following pairs of terms: homozygous and heterozygous; dominant allele and recessive allele; genotype and phenotype. Also, define a monohybrid cross and a Punnett square.
Homozygous means that the alleles of an organism are the same (ex. RR). Heterozygous means that the alleles of an organism are not matching (Rr). Genotype is what the alleles for a certain characteristic are. Phenotype is what characteristics the organism displays. Dominant allele is which allele determines the phenotype, and recessive only determines the phenotype when homozygous recessive. A monohybrid cross is when only one character is tracked. A punnett square is a diagram that determines the probability of the outcomes of crosses.
Explain how sex is genetically determined in humans and the significance of the SRY gene.
Humans have X and Y chromosomes to determine sex, and sperm determines the genotype (eggs can only carry an x). the SRY gene is on the Y chromosome and triggers testes development.
Describe the inheritance patterns of incomplete dominance, multiple alleles, codominance, pleiotropy, and polygenic inheritance. Provide an example of each.
Incomplete dominance is when alls in between the dominant and the recessive allele's phenotypes, ex: red flower w white flower becomes a pink flower hybrid. A human example is hypercholesterolemia. Multiple alleles is when a gene can be found in more than 2 versions, blood types for example have 3 alleles that form 4 different genotype combinations. Codominance is when 2 alleles show their phenotypes equally. Pleiotropy is when one gene influences several characters, sickle cell disease is an example. Polygenetic inheritance is when are the additive effects of 2 or more genes on one single phenotypic character (opposite of pleiotropy), skin color is an example.
Explain why Mendel's decision to work with peas was a good choice. Define and distinguish between true-breeding organisms, hybrids, the P generation, the F1 generation, and the F2 generation.
It was a good choice because he could control the reproduction, he could track the characteristics (round vs wrinkled, green vs yellow) easily. They also had short generation times and produced large amounts of offspring. True breeding organisms are organisms that can self fertilize and produce offspring identical to the parent. Hybrids are offspring of two different varieties/genotypes. The P generation are the true breeding parents, the F1 generation are their hybrid offspring, and the F2 generation are the offspring of the F1 generation.
Explain how linked genes are inherited differently from non-linked genes.
Linked genes are closer on the same chromosome, and generally don't follow the law of independent assortment. They do not follow the 9:3:3:1 Mendel rule.
Explain how Mendel's law of segregation describes the inheritance of a single characteristic.
Mendel's hypothesized that 1) Alleles are alternative versions of genes that account for variations in inherited characters; 2) For each character, an organism inherits two alleles, one from each parent, and they can be the same (homozygous) or different (heterozygous); 3) If alleles differ, one determines the physical appearance is dominant allele, the other has no noticeable affect on appearance, called recessive trait, and 4), his law of segregation, says that gametes only carry one allele for each character because allele pairs separate during meiosis (production of gametes). Thus, the inheritance of a single characteristic is dependent on which allele is put into each gamete (respectively) during meiosis.
Describe T. H. Morgan's studies of crossing over in fruit flies. Explain how crossing over produces new combinations of alleles.
Morgan crossed a wild type fruit fly (gray body, long wings) with a black body/long wings fly, and saw that the recombinants were less likely because they're linked and closer on the same chromosome. Crossing over occurs during Anaphase I of meiosis, when the tetrads transfer alleles, creating recombinant allele pairs and increasing genetic diversity.
Explain how family pedigrees can help determine the inheritance of many human traits.
Pedigrees track the inheritance of traits throughout generations with a family tree by indicating phenotypes and known genotypes.
Explain how Sturtevant created linkage maps.
Sturtevant created Linkage maps, diagrams of relative gene locations according to crossing over frequency. He demonstrated that the closer the alleles/ loci on the chromosome, the lower the recombination frequency.
Define the chromosome theory of inheritance. Explain the chromosomal basis of the laws of segregation and independent assortment.
The chromosome theory of inheritance states tha genes occupy specific loci on chromosomes, and their behavior during meiosis and fertilization causes inheritance pattern. Independent assortment is a result of the random assortment of chromosomes during Anaphase I.
Explain how the sickle-cell allele can be adaptive.
The sickle cell allele affects the type of hemoglobin produced and the shape of red blood cells, causes anemia and organ damage, sickle-cell and nonsickle alleles are codominant, carries of sickle-cell disease are resistant to malaria.
Explain why sex-linked disorders are expressed more frequently in men than in women.
They are expressed more frequently in men because they do not have another allele to combat their recessive allele, and thus cannot be carriers.
Explain how and when the rule of multiplication and the rule of addition can be used to determine the probability of an event. Explain why Mendel was wise to use large sample sizes in his studies.
Use multiplication in order to find out the probability of independent events, and the rule of addition is used to find out "or". Mendel was wise to use large sample sizes in order to prove the mathematical significance of genetics.
