BA Genetics - basic assign PDF

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Basic assignment: Genetics

1.

Genetic variation is created through sexual reproduction by 3 processes. What are they and explain what they do.

There are 3 major processes mean variation is the norm for sexual reproduction: 1)Independent assortment in which chromosomes line up by homologous pairs during meiosis I, then maternal and paternal chromosomes are shuffled randomly leads to genetic variation. 2)Random fertilization is another reason that leads to genetic variation. Insofar as a sperm and an egg(both) contain around 8 million possible combination of chromosomes, the possibility that any one specific sperm will fertilize any particular egg is exceptionally small. 3)Crossing over occurs when homologous chromosomes line up during meiosis I, creating new hybrid chromosomes that increases gene variation. 2. What are some of the mistakes that can happen in meiosis that would produce an abnormal number of chromosomes. Explain 2 of these. When chromosomes fail to separate properly, it results in nondisjunction (when chromosomes separation failed, so gametes are too many or too few). One of the example is Down syndrome, when a human being got 3 copies of chromosome 21. The another one is sex chromosome nondisjunction, it also may result in different types syndromes such as Turner syndrome. 3. What is the difference between character and traits Gregor Mendel deduced the basic principles of inheritance for the first time, since then the genetics study improved greatly, so we can understand better heredity or transmission of traits from one generation to the next. One of these inherited feature(character) is human eye, and each possible variation of a character is a trait. 4. Cross a homozygous purple flower with a heterozygous purple flower where purple ( P) is dominant and white (p) is recessive. Show work in a Punnett square then give genotype % and phenotype%. Homozygous purple flower – PP Heterozygous purple flower – Pp PP x Pp P p

P PP Pp

p PP Pp

% Phenotype – 100% purple % Genotype – 50 % homozygous purple, 50 % heterozygous purple

5. Explain the law of segregation and the law of independent assortment and how it applies to inheritance of genes “The law of segregation states that the two alleles for a character separate during gamete formation.” Lecture presentation, chapter 5.12. For example, to find out if a black cat is BB or Bb, we should mate it with brown one. Black cat most likely has BB genotype if all kitties are black, and 2 black and 2 brown if Bb. “The law of independent assortment states that the inheritance of one character has no effect on the inheritance of another.” – lecture presentation, chapter 5.13. As an example, dihybrid cross, when two hearing dogs have few deaf puppies suggests that the genes for certain things are assorted independently. 6. Give examples and explain pleiotropy, polygenic inheritance and sex linked inheritance. Pleiotropy is single gene gives the expression of multiple gene Pleiotropy is a process in which single gene gives the expression of multiple traits. As example, phenylketonuria – genetic disorder which is caused due to the low metabolism of the amino acids. Polygenic inheritance – a single phenotypic itrait which is controlled by 2 or more genes. For example: skin and eyes color. Sen linked inheritance is a trait in which genes are present on the sex chromosomes. In humans X chromosomes is infused e.g.: colorblindness ....