Why do you share some but not all characters of each parent? Meiosis Why do you share some but not all characters of each parent?

Heredity Heredity Passing of genetic traits from parent to offspring Chromosome theory of heredity Chromosomes carry genes Gene = unit of heredity

What Meiosis is all About Meiosis allows the creation of unique individuals through sexual reproduction.

Two different types of cells Somatic Cells are “body” cells and contain the normal number of chromosomes . Examples would be … skin cells, brain cells, etc. Diploid Gametes are the “sex” cells and contain only ½ the normal number of chromosomes. Haploid Sperm cells and ova are gametes.

Genes A gene is an address – a location on the chromosome and in the DNA sequence where info for a specific trait is located.

Homologous Chromosomes Pair of chromosomes (maternal and paternal) similar in shape and size. Each locus (position of a gene) is in the same position on homologues. Humans have 23 pairs of homologous chromosomes. 22 pairs of autosomes 1 pair of sex chromosomes Homologous pairs (tetrads are duplicated) carry genes controlling the same inherited traits.

Homologous Chromosomes (because a homologous pair consists of 4 chromatids it is called a “Tetrad”) eye color locus hair color Paternal Maternal

Autosomes In Humans the “Autosomes” are sets 1 – 22 (The Autosomes code for most of the offspring’s traits)

In Humans the “Sex Chromosomes” are the 23rd set XX chromosome - female XY chromosome - male

Sex Chromosomes the 23rd set

Boy or Girl? The Y Chromosome Decides X chromosome Y chromosome

In The Beginning Two Reproduction where the genetic material combined is called sexual reproduction Two cells, a sperm and an egg, unite to form a zygote, the single cell from which the organism develops Meiosis is the process of producing sperm and eggs (gametes) – the number of chromosomes are halved

Meiosis Parent cell – chromosome pair Chromosomes copied 1st division - pairs split 2nd division –4 gamete cells with ½ the original number of chromosomes

Gametes Are Haploid Gametes have exactly one set of chromosomes, this state is called haploid (1n) Regular cells have two sets of chromosomes, this state is called diploid (2n) Why?

Two Important Accomplishments 1) Meiosis takes a cell with two copies of every chromosome (diploid) and makes cells with a single copy of every chromosome (haploid). In meiosis, one diploid cells produces four haploid cells.

Two Important Accomplishments 2) Meiosis scrambles the genes that each sex cell (egg or sperm) receives. This makes for a lot of genetic diversity. This happens through independent assortment and crossing over. Genetic diversity is important for the evolution of populations and species.