Cell Division Quiz

Chromosomes and Genes

Each human chromosome is made up of only one double helix strand of DNA. Each one has between 50 million and 250 million nucleotides. One human DNA strand stretched out would be between 0.6 inches and 3.0 inches long (15-75 millimeters) All the DNA in one nucleus would stretch 6 feet (1.8 meters)

In order to get all of this genetic information to fit into a microscopic cell nucleus the DNA strand needs to be wound very compactly.

Genes

A gene is a segment of DNA that codes for a specific trait

-A trait is a characteristic that is inheritable (can be passed on to offspring)

-The specific location of a gene on the DNA is called a locus (loci for plural)

-Different chromosomes contain different amounts of genes

-The largest human chromosome is chromosome 1

-It has more than 3,000 genes on it

-The smallest human chromosome is chromosome 22

-It has about 600 genes on it

A Karyotype is a picture of all of an individuals chromosomes

Different species have different amounts of chromosomes

In each human cell...

-A human has 23 pairs of chromosomes

-A Human has 46 chromosomes all together

-Even though a human has 46 they only have 23 different ones since a human has two of each chromosome. One set from mom one set from dad.

Diploid and Haploid

-If an organism or cell has two of every chromosome it is called Diploid (Meaning Double)

-Diploid organisms receive one set from each parent

-Humans are a diploid organism

-An organism or cell that only has one of every chromosome is called Haploid (Meaning Half)

-There are some organisms that are haploid and usually reproduce asexually

-Gametes are haploid cells because they will fuse with another haploid and become a diploid cell

-Humans have two different types of cells

-Gametes- sex cells like sperm and eggs which are haploid and contain half of your DNA

-Somatic cells-body cells which are diploid and contain all of your DNA

Chromosomes

-There are autosomes which are chromosomes that both males and females have in common

-And then there are sex chromosomes that are different depending if you are male or female

-For example a human has 44 autosomes and 2 sex chromosomes or 22 pairs of autosomes and 1 pair of sex chromosomes.

-In mammals the sex chromosomes are X and Y

-The X chromosome is the female chromosome and the Y chromosome is the male chromosome

-If you have a Y chromosome you are male

-XX= Female and XY=Male

Chromosomes that contain the same genes are called homologous chromosomes

-Just because they have the same genes does not mean that they are identical

-They have the same genes but they have different alleles (different versions of those genes)

-For example humans have two of chromosomes 1-22 so that means both of your chromosomes 1 are homologous, both of your chromosomes 2 are homologous and so on up to chromosome 22.

-When it comes to the sex chromosomes, because females have two X chromosomes, we can say that their X chromosomes are homologous.

-Because males have two different sex chromosomes, an X and a Y, they count as a pair but not a homologous pair. The X and the Y do not contain the same genes.

Parts of a chromosome

Gene Locus