Why do all of us look different? Big Question

What makes you who you are? If you were looking at a couple who are expecting a child, what traits could you predict for the child just by observing the parents? Possible student responses: hair color, eyes, skin, height, body type, facial features, etc. Next, ask students which traits could be a possible combination of their parents? Skin color, facial features, etc.

Key Points Meiosis is a process of cell division used to create sex cells. Meiosis makes four daughter cells from one parent cell. The cells at the end of meiosis have half the number of chromosomes as the original. In meiosis, the chromosomes in the new cells are genetically different.

Why meiosis? We can’t put 46 and 46 together…it just wouldn’t work! All human somatic cells have 46 chromosomes We can’t put 46 and 46 together…it just wouldn’t work! Because of this meiosis is used to halve the number of chromosomes in the sex cells and allows for genetic variation!

Haploid vs. Diploid? We call somatic cells diploid because they have double the number of chromosomes (2 copies of each) Hint: diploid = double We call gametes haploid because they have half the number of chromosomes (1 of each) Hint: haploid = half Human somatic cells contain 46 chromosomes. Human gametes have 23 chromosomes.

What does meiosis make? Gametes: Sex Cells (sperm and egg in humans) Gametes are haploid cells. You breathe in sex cells all the time. Every time you have ketchup on your burger…

Homologous Pairs Each pair of homologous chromosomes has genes for the same traits (ex: hair color). These genes are arranged in the same order but the two chromosomes are not necessarily identical to each other.

What is Crossing-over? Crossing over is where homologous pairs trade genetic information. This allows for genetic variation!!!!

DNA has been replicated. Homologous Pairs NOT Sister Chromatids Crossing Over 2 Different Cells Meiosis Video

With half the number of chromosomes! DNA is NOT replicated between meiosis I and meiosis II. 4 Different Cells With half the number of chromosomes!

When we put together 2 haploid cells what type of cell will we have?

What’s a zygote? Zygote- Cell that forms what a male gamete and a female gamete join their DNA and make a new organism. Zygotes are diploid.

What is Genetic Variation? Genetic variation is when different members of the same species have different traits. Hint: Crossing over = Genetic Variation!

What is the Law of Independent Assortment? The chromosomes separate independently from each other. Example: Hair color and eye color move independently. You can have your mother’s hair color and your father’s eye color.