BSC 114 Lecture Notes - Lecture 20: Punnett Square, Mendelian Inheritance, Genetic Variation

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graysardine594

24 Mar 2016

School

University of Alabama

Department

Biological Sciences

Course

BSC 114

Professor

Steven Marcus

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Document Summary

Genetic variation produced in sexual life cycles contributes to evolution. Mutations (changes in the nucleotide sequence of an organism"s dna) are the original source of genetic diversity. Reshuffling of different versions of genes during sexual reproduction produces genetic variation. The behavior of chromosomes during meiosis and fertilization is responsible for most of the genetic variation that arises in each generation. Homologous pairs of chromosomes orient randomly at metaphase i of meiosis. In independent assortment, each pair of chromosomes sorts maternal and paternal homologs into daughter cells independently of the other pairs. The number of combinations possible when chromosomes assort independently into gametes is 2n, where n is the haploid number. For humans (n = 23), there are about 8. 4 million (223) possible combinations of chromosomes. Crossing over produces recombinant chromosomes, which combine genes inherited from each parent. Crossing over begins very early in prophase i, as homologous chromosomes pair up gene by gene.

Related Questions

Which of the following is NOT one of the three wayssexual reproduction shuffles alleles to produce newcombinations?

A) Homologous chromosomes sort independently as theyseparate during anaphase I of meiosis.

B) Homologous chromosomes sort independently as theyseparate during metaphase II of meiosis.

C) During prophase I of meiosis, pairs of homologouschromosomes cross over and exchange genes.

D) Further variation arises when sperm randomly unitewith eggs in fertilization.

bluehound895

Which statements pertaining to genetic variability are correct? Check all that apply (note that wrong answers will be deducted from right answers)!

Crossing over is defined by the exchange of chromosome pieces during metaphase one of meiosis.

If a germ cell (i.e. parent cell before meiosis) had only two pairs of homologous chromosomes (i.e. 4 chromosomes total) there are 2 possible combinations of maternal and paternal chromosomes in gametes.

Siblings produced by sexual reproduction are different because sperms are different from one another and eggs are different from one another, and the combination of an egg and sperm is basically unique.

Random fertilization means that all possible combinations of eggs and sperm are equally likely, i.e. it is pure chance which sperm fuses with which egg.

Individual chromosomes contain thousands of genes. This means that during each crossing over event, more than one gene is exchanged between paternal and maternal chromosomes.

limedonkey586

Question 1 (2 points)

In which phase of cell division is marked by the dissolution of the nuclear membrane, the condensation of chromosomes, and the formation of the mitotic spindle?

Question 1 options:

	prophase
	metaphase
	telophase
	anaphase

Question 2 (2 points)

The physical separation of cells during cell division is called:

Question 2 options:

	Cytokinesis
	Telophase
	Interphase
	Chromosome
	Cell plate

Question 3 (2 points)

Meiosis is necessary for sexual reproduction; the gametes formed during this process before fertilization are _______________.

Question 3 options:

	Haploid
	Diploid
	Zygote
	Homologous
	Tetrads

Question 4 (2 points)

Mitosis is the process by which a ___________ cell separates the chromosomes in its nucleus into two identical sets of nuclei.

Question 4 options:

	eukaryotic
	prokaryotic
	bacterial
	all of these are correct

Question 5 (2 points)

Which of the following statements about crossing over is INCORRECT?

Question 5 options:

	It occurs between homologous chromosomes
	It allows for two parents to produce many different types of offspring
	It contributes to genetic diversity in a population
	It occurs during prophase I of mitosis

BSC 114 Lecture Notes - Lecture 20: Punnett Square, Mendelian Inheritance, Genetic Variation

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