Meiosis and Sexual Reproduction

DNA● In our body cells we have a full set of DNA

● We get half of our DNA from our mother, and the other half from our father.

● In order to get a full set of chromosomes, an egg cell with half of your mother’s DNA, and a sperm cell with half of your father’s DNA had to combine

Genes versus Chromosomes● Genes are the

individual codes

● Genes are pieces of chromosomes

http://sciencelearn.org.nz/Contexts/Uniquely-Me/Sci-Media/Images/Cell-chromosomes-and-DNA

Diploid and Haploid● Diploid means there is a full set of chromosomes. All human body cells

are diploid.● Haploid means there is only half a full set of chromosomes. All human

sex cells are haploid.● All sex cells must be haploid in order to keep the correct number of

chromosomes during fertilization.● If sex cells were diploid you would have twice as many chromosomes as

you should!

Gametes● Sexual reproduction involves special cells called

gametes or sex cells (eggs and sperm)● Gametes combine during fertilization to form a new

cell called the zygote.● The process of meiosis ensures that gametes only have

23 chromosomes (not 46).

Zygotes● When the sex cells unite: sperm + egg = zygote● Zygotes divide by mitosis to eventually form all the

cells and tissues in a new individual.● The new individual will have a unique set of traits

because s/he is a combination of genes from both parents

Fertilization● The fusion of

gametes to combine DNA

http://www.ivfcenterhawaii.com/content/ivf_treatments/in_vitro_fertilization.html

Chromosome pairs● The union of gametes gives a zygote with 46

chromosomes in a human.● Using a microscope, these chromosomes can be

arranged in pairs, based on their size and shape● The matching pairs are called homologous pairs● You received one of each pair from your mother and

one from your father

Sexual Reproduction● A process that creates a new organism by combining

the genetic material of two parents

http://www.bbc.co.uk/schools/gcsebitesize/science/edexcel_pre_2011/genes/reproductionandcloningrev1.shtml

Meiosis● Cell division which eggs and sperm (sex cells) are

produced.● The production of sex cells, which are not genetically

identical, through two rounds of cell division.● Remember: mitosis is 1 round of cell division, meiosis is

2 rounds

Meiosis● Meiosis is like mitosis twice in a row, but the second

time the genetic material is not duplicated so each gamete ends up with 23, rather than 46, chromosomes

● Instead of having 2 cells with a full (diploid) set of chromosomes at the end, there will be four cells with a haploid set of chromosomes at the end!

Meiosis I and Meiosis II● There are 2 parts to meiosis: meiosis I and meiosis II● The end result is 4 haploid sex cells, each with half the

number of chromosomes.

Meiosis I

Meiosis II

Recombination or Crossing Over

● This occurs during Prophase I

● It allows for some exchange of genetic traits which leads to genetic variation

https://uoitbio2013.wordpress.com/mitosis-vs-meiosis/meiosis/

Genetic Variation or Genetic Diversity● Differences in characteristics between members of the

same species○ humans, apple trees, dogs, flies, etc.

● We are unique yet similar to family members and to some classmates. Why?○ Sexual reproduction passes on genes○ Species share genes

Variation in Traits● At the beginning of this unit you looked at some

genetic traits and saw differences within the class for eye color, tongue rolling, etc.

● You should now realize that these differences are the result of the process of recombination and sexual reproduction

Review and Wrap-up● Watch the Amoeba Sisters video on Meiosis:

○ https://www.youtube.com/watch?v=toWK0fIyFlY

● Complete the video recap worksheet for the video: ○ http://www.amoebasisters.

com/uploads/2/1/9/0/21902384/video_recap_of_meiosis_by_amoeba_sisters_final.pdf

● Complete the Meiosis Internet Lesson:○ https://lpscience.fatcow.com/jwanamaker/animations/meiosis.html○ http://www.pbs.org/wgbh/nova/body/how-cells-divide.html