Chapter 6 Chromosomes & Cell Reproduction

General Information  about 2 TRILLION cells are produced by an adult human body EVERY DAY  new cells are formed when old cells divide  cell division = cell reproduction Examples: a cut that is healing, a fawn growing

Prokaryotic Cell Reproduction o asexual reproduction that produces identical offspring o Binary Fission o two stages: 1. DNA is copied (so each copy with have genetic information 2. cell divides

Eukaryotic Cell Reproduction Gene – a segment of DNA that codes for a protein or RNA molecule; determines how a person’s body develops and functions Chromosome – DNA and proteins associated with DNA

As a cell prepares to divide… 1.Chromosomes become visible 2.DNA is copied 3.It coils up

Chromosome Parts: Chromatids – two exact copies of DNA that make up each chromosome Centromere – the region of the chromsome that holds the two sister chromatids together during mitosis

Human Chromosome Labeled: Chromatid Centromere

Chromatids are separated and one goes into each new cell, ensuring that each new cell will have the same genetics information as the original

How many chromosomes do humans have? 23 sets (pairs) of chromosomes -> 46 chromosomes total Homologous chromosomes (homologues) = chromosomes similar in size, shape, & genetic content You have 23 pairs of homologous chromosomes, one of the homologues in each pair is from your mother and one is from your father Think: who do I look like?

Species have different diploid numbers

Important Terms When a cell contains two sets of chromosomes (one set of 23 from the individual’s mother and a second set of 23 from the individual’s father), we call these cells diploid cells “di” means two Cells that only contain one set of chromosomes (23) are called haploid cells “ha” can start off the word half (or half the number of chromosomes) Somatic cells are all the cells in the body other than gametes Gametes are reproductive cells; ex. Sperm cell, egg cell

n = 23 chromosomes (23) 2(23) = 46 haploid + diploid = Fertilization = fusion of 2 haploid gametes; forms a diploid

Fertilization A fertilized egg is called a zygote, it’s the first cell of a new individual

Of the 23 pairs of chromosomes in humans: 22 pairs (or 44 chromosomes) are autosomes, or chromosomes that are not directly involved in determining the gender of an individual 1 pair (or 2 chromosomes) contain genes that will determine the sex of the individual and these are called sex chromosomes (usually referred to as X & Y chromosomes) XX = FemaleXY = Male

Would this be a boy or girl?

The structure and number of sex chromosomes vary in different organisms. Some insects (grasshoppers) no Y so O stands for absence of chromosome female is XX male is XO In birds, moths, & butterflies males have XX and females are X

Karyotype A photo of the chromosomes in a dividing cell that shows the chromosomes arranged by size Can alert that there is an abnormality in an individual…why?

The presence of all 46 chromosomes is essential for normal development and function Trisomy – humans with more than 2 copies of a chromosome will not develop properly Polydactyly Down syndrome = condition with extra copy of chromosome 21 (trisomy 21)

How does this happen? 1.All the egg cells in a female are present at birth, she will never make more. Males, on the other hand, produce new sperm throughout their adult lives. Therefore, as a female gets older her eggs accumulate damage. 2.Mutations can occur. Doctors are able to perform prenatal testing to check for certain genetic disorders.

Mutations = changes in an organisms’ structures Four types of mutations: 1. Deletion – piece of chromosome breaks off completely; new cell will lack a certain set of genes; usually proves fatal to zygote 2. Duplication – a chromosome fragment that attaches to its homologous chromosomes; carries 2 copies of a certain gene 3. Inversion – a chromosome piece reattaches to the original chromosome but in a reverse orientation 4. Translocation – if a chromosome piece reattaches to a non-homologous chromosome

Deletion – piece of chromosome breaks off completely Duplication – chromosome fragment attaches to its homologous chromosome Inversion – chromosome piece reattaches to the original chromosome but in reverse orientation Translocation – piece reattaches to a non- homologous chromosome