Meiosis and Sexual reproduction

Mendel and Heredity

Modern Genetics

Recombination and linkage practice problems

1. Meiosis

   1. Explain how meiosis results in the transmission of chromosomes from one generation to the next.

      1. Meiosis is a process that ensures the formation of haploid gamete cells in sexually reproducing diploid organisms

         1. Meiosis results in daughter cells with half the number of chromosomes of the parent cell

         2. Meiosis involves two rounds of a sequential series of steps (meiosis I and meiosis II).

   2. Describe the similarities and/or differences between the phases and outcomes of mitosis and meiosis.

      1. Mitosis and meiosis are similar in the way chromosomes segregate but differ in the number of cells produced and the genetic content of daughter cells.

2. Meiosis and genetic diversity

   1. Explain how the process of meiosis generates genetic diversity.

      1. Separation of the homologous chromosomes in meiosis I ensures that each gamete receives a haploid (1n) set of chromosomes that comprises both maternal and paternal chromosomes.

      2. During meiosis I, homologous chromatids exchange genetic material via a process called “crossing over” (recombination), which increases genetic diversity among the resultant gametes.

      3. Sexual reproduction in eukaryotes involving gamete formation-including crossing over, the random assortment of chromosomes during meiosis, and subsequent fertilization of gametes, serves to increase variation.

         1. Do not need to know details of various reproduction cycles of plants and animals.

3. Mendelian genetics

   1. Explain how shared, conserved, fundamental processes and features support the concept of common ancestry for all organisms.

      1. DNA and RNA are carriers of genetic information

      2. Ribosomes are found in all forms of life

      3. Major living feature of the genetic code are shared by all modern living systems

      4. Core metabolic pathways are conserved across all currently recognized domains.

   2. Explain the inheritance of genes and traits as described by Mendel’s laws

      1. Mendel’s laws of segregation and independent assortment can be applied to genes that are on different chromosomes.

      2. Fertilization involves the fusion of two haploid gametes, restoring the diploid number of chromosomes and increasing the genetic variation in populations by creating new combinations of alleles in the zygote

         1. Rules of probability can be applied to analyze passage of single-gene traits from parent to offspring.

         2. The pattern of inheritance (monohybrid, dihybrid, sex-linked, and genetically linked genes) can often by predicted from data, including pedigree, that five the parent genotype/phenotype and the offspring genotypes/phenotypes

            1. Laws of probability:

               1. If A and B are mutually exclusive, then:

                  1. P(A or B) = P(A) + P(B)

               2. If A and B are independent, then:

                  1. P(A and B) = (PA) x P(B)

4. Non-Mendelian genetics

   1. Explain deviations from Mendel's model of the inheritance of traits

      1. Patterns of inheritance of many traits do not follow ratios predicted by Mendel’s laws and can be identified by quantitative analysis, where observed phenotypic ratios statistically differ from the predicted ratios:

         1. Genes that are adjacent and close to one another on the same chromosome may appear to be genetically linked; the probability that genetically linked genes will segregate as a unit can be used to calculate the map distance between them.

      2. Some traits are determined by genes on sex chromosomes and are known as sex-lined traits. The pattern of inheritance from data, including pedigree, indicating the parent genotype/phenotype and the offspring genotypes/phenotypes.

      3. Many traits are the product of multiple genes and/or physiological processes acting in combination; these traits therefore do not segregate in Mendelian patterns.

      4. Some traits result from non-nuclear inheritance:

         1. Chloroplasts and mitochondria are randomly assorted to gametes and daughter cells; thus, traits determined by chloroplast and mitochondrial DNA do not follow simple Mendelian rules

         2. In animals, mitochondria are transmitted by the egg and not the sperm; as such, traits determined by the mitochondrial DNA are maternally inherited.

         3. In plants, mitochondria and chloroplasts are transmitted in the ovule and not in the pollen; as such, mitochondria-determined and chloroplast-determined traits are maternally inherited.

5. Environmental effects on phenotype

   1. Explain how the same genotype can result in multiple phenotypes under different environmental conditions.

      1. Environmental factors influence gene expression and can lead to phenotypic plasticity. Phenotypic plasticity occurs when individuals with the same genotype exhibit different phenotypes in different environments.

6. Chromosomal inheritance

   1. Explain how chromosomal inheritance generates genetic variation in sexual reproduction.

      1. Segregation, independent assortment of chromosomes, and fertilization result in genetic variation in populations.

      2. The chromosomal basis of inheritance provides an understanding of other patterns of transmission of genes from parent to offspring.

      3. Certain human genetic disorders can be attributed to the inheritance of a single affected or mutated allele or specific chromosomal changes, such as non-disjunction.