3.2- James Phillips
Understand how the environment, and/or the interaction of alleles, influences the expression of genetic traits.
3.2.1: Explain the role of meiosis in sexual reproduction and genetic variation.
![Picture](/uploads/5/1/6/6/51661907/3042848.jpeg?319)
Gametes, or sex cells, have only half the chromosomes of normal cells. This is because in sexual reproduction each gamete gives exactly half of the offsprings genetic information. Unlike somatic cells they don't go through mitosis. Sex cells divide by meiosis. Unlike mitosis, meiosis results in genetic variation. In meiosis cells go through two cycles of prophase, metaphase, anaphase and telophase, and one interphase prior to the first cycle, known as Meiosis I. DNA synthesis and cell growth both occur in interphase. In meiosis I, the gemete splits into two cells and the chromosomes cross over, increasing variation. In meiosis II, the two cells are divided once again resulting in four cells.
3.2.2: Predict offspring ratios based on a variety of inheritance patterns
Trait inheritance can be affected by many factors, all of which increase genetic variation. Genes can be found on a cells chromosomes, and each gene is composed of many traits. The possible traits that can be passed on are called alleles. Alleles can be either dominant of recessive. A dominant allele will be expressed regardless of the allele it's paired with, while a recessive allele must be paired with another recessive allele to be expressed. Some traits can only be expressed by one order of alleles while others, called polygenic traits can be expressed by multiply orders of alleles. If two different dominant alleles are paired it will result in one of two scenarios, either a blend of both traits will be expressed, which is known as incomplete dominance, or the traits will be co-dominate. Some traits can be carried on the sex chromosomes, most often the X chromosome. Sex linked traits are more likely to be expressed by males, because they only have one X chromosome.
|
A punnet square is the most common way of determining trait expression. To use a punnet square you must first know the number of alleles that contribute to that trait. Next you must determine whether it's homozygous or heterozygous. Homozygous traits have all the same alleles, either they're all dominant or all recessive. Heterozygous traits have different alleles. A dominant allele is represented by the capital letters in the punnet square, while the lower case letters represent recessive traits. The alleles from one parent are placed along the left side of the square and the alleles from the other parent are placed along the top of the square. The letters on the left and on the top are then combined in each square. The resulting combinations are called the genotype, while the trait that is expressed is called the phenotype.
|
3.2.3:Explain how the environment can influence the expression of genetic traits.
![Picture](/uploads/5/1/6/6/51661907/7599384.jpg?250)
If homeostasis can not be maintained mutations are more likely to occur. these mutations can cause bases to be inserted, substituted, or eliminated, resulting in the formation of a different protein causing a different trait to be expressed. Hormones released from environmental stimuli can also have this affect on protein synthesis. Some mutation can be beneficial, these are more likely to be passed on to future generations, and are called adaptations. Take the varying skin colors humans have for example. These different colors are the results of genetic changes caused by environmental factors. The hotter the climate and the more sun exposure the darker the skin of the people that inhabit that area will be, and vice versa.
Activities for 3.2
punnett square practice
http://mhhe.com/biosci/genbio/virtual_labs/BL_05/BL_05.html
genetics game
http://biomanbio.com/GamesandLabs/Genegames/snurfle_meiosis_and_genetics.html
http://mhhe.com/biosci/genbio/virtual_labs/BL_05/BL_05.html
genetics game
http://biomanbio.com/GamesandLabs/Genegames/snurfle_meiosis_and_genetics.html