Entrance Activity – DNA, Genes, Chromosome How much do you remember from last class? With a partner, write each of the following terms separately on a sticky and order them from largest to smallest: DNA, Genes, Chromosomes, Nucleotide, Nucleus, Cell Check with the other pair at your table to compare How many chromosomes do humans have? Draw a simple diagram of a chromosome and label a gene on it. 

So, Where Do Babies Come From? Meiosis & Sexual Reproduction

Learning Goals B1ii: learn about the outcomes of meiosis B1i: describe factors that lead to changes in a cell's genetic information (chromosome mutations, crossing over & independent assortment) B2i: distinguish between male and female gametes B2ii: describe how a zygote forms (fertilization) B3ii: relate sexual reproduction to the adaptability of organisms

Group Discussion Questions Take 5 minutes with your group to discuss and record questions #1-8

Meiosis – Think About It Meiosis is a special version of cell division that occurs only in the testes and ovaries; the organs that produce the sperm and eggs. Why is this different? Normal body cells have a complete set of chromosomes. If normal body cells from mom and dad fused to form a baby, the fertilized egg would have twice as many chromosomes as it should.

Purpose of Meiosis Meiosis is sometimes called "reduction division" because it reduces the number of chromosomes to half the normal number so that when fusion of sperm and egg occurs, baby will have the correct number. Therefore the purpose of meiosis is to produce gametes; the sperm and eggs.

Before Cells Divide Cells make copies of their chromosomes before they divide. So for a brief moment, human cells have 92 chromosomes! Normal 46 chromosomes Right before cell division Each X shape is actually two identical chromosomes!

2 Phases of Meiosis Meiosis I The homologous (matching) chromosomes separate. Two haploid (half the amount of chromosomes) daughter cells are the result after the cell splits Meiosis II The sister chromatids (each half of the X) in each cell produced in Meiosis I separate. The result is 4 haploid cells, each having half the number of chromosomes

Phases of Meiosis

Gamete formation How is gamete formation different in males than in females? Equal division of cytoplasm and organelles = 4 surviving haploid sperm cells Unequal division of cytoplasm and organelles = 1 surviving haploid egg cell (other 3 get reabsorbed)

Fertilization Once a haploid sperm cell and a haploid egg cell have formed, they need to come together to produce a diploid zygote. The zygote (a single cell made from a sperm penetrating an egg) can then undergo mitosis to produce more cells and form a embryo. Vocab: ~ haploid (n) = half the number of chromosomes ~ diploid (2n) = the full number of chromosomes (the number found in a somatic cell)

After this, the zygote undergoes mitosis to develop into an embryo

Check for Understanding Have we met our learning goals? B1ii: learn about the outcomes of meiosis B2i: distinguish between male and female gametes B2ii: describe how a zygote forms (fertilization)

Sexual Reproduction Sexual reproduction requires two parents and produces offspring that are different to their parents Remember, asexual reproduction requires one parent and produces offspring that are genetically identical to each other and to the parent.

Genetic Diversity Species that reproduce sexually have genetic diversity (variation in a species) ie – everyone looks different (except identical twins) Genetic diversity comes about because sexual reproduction shuffles the DNA from the parents through independent assortment and crossing over. This causes the offspring to be better or possibly worse suited to survive in an environmental change

Crossing Over Crossing over – parts of non-sister chromatids “cross-over” each other and switch pieces of DNA. This creates an infinite number of genetic possibilities for just one gamete

Independent Assortment In Meiosis I, the matching chromosomes line up with varying possibilities, then split and are sorted randomly (independently) which causes up to 70 trillion different combinations! https://www.youtube.com/watch?v=vA8aMpHwYh0 https://www.youtube.com/watch?v=toWK0fIyFlY (amoeba sisters https://www.youtube.com/watch?v=qCLmR9-YY7o good vidoe

Some Cool information for discussion!

Chromosome mutations The possible changes are chromosomes being lost, duplicated, inverted, or moved in one chromosome or moved to a whole other chromosome

Example: fruit flies with these types of mutations are know to grow legs in place of their antennae or eyes on their wings!

Learning Goals – Check for understanding B1i: describe factors that lead to changes in a cell's genetic information (chromosome mutations, crossing over & independent assortment) B3ii: relate sexual reproduction to the adaptability of organisms

Diagnosing Genetic Disorders Karyotype – a picture containing all of the organisms chromosomes organized by size, centromere, and banding pattern Scientists use karyotypes to help diagnose genetic disorders or syndromes Syndromes are diseases with symptoms that appear together Ex. – Down Syndrome is caused by an extra 21st syndrome