Learning Intentions Understanding the structure of the: Chromosomes DNA Karyotype activity

Chromosomes

Types of chromosomes

Autosomes Autosomes are numbered from 1 to 22 on the basis of their size. Chromosome number1- largest Chromosome number 22-smallest Matching pair is known as homologous Non-matching pair is known as non-homologous

Human chromosomes in order of size

Sex Chromosomes 23rd pair is known as sex chromosomes (X and Y) Female possesses (XX) Male possesses (XY) In terms of size: X-greater Y-smaller

e.g. Turner’s syndrome, which results in only one sex chromosome (XO) Trisomy: three copies of a chromosome instead of the normal pair of two e.g. the addition of a number 21 chromosome that results in Down syndrome within each cell Monosomy: a condition in which there is only one copy of a particular chromosome (rather than two) in a cell e.g. Turner’s syndrome, which results in only one sex chromosome (XO)

Karyotype The number and general appearance (size, shape and banding) of a set of chromosomes in a somatic cell

Telomere a cap of DNA on the tip of a chromosome that enables DNA to be replicated safely without losing valuable information Protect our genetic data Each time the cell divides, these telomeres shorten When the telomeres drop below a certain length, the cell stops dividing and dies

Dr Elizabeth Blackburn -1970s

Genotype: Genetic instructions (contained in DNA) inherited from parents at a particular gene locus Phenotype: Characteristics that result from the expression of an organism’s genotype. Phenotype depends on both the genotype and the environment.

Karyotype Activity

DNA

Learning intentions Understanding the structure of DNA Understanding mitosis cell divisions

DNA-Deoxyribonucleic acid It is a type of nucleic acid It was discovered by Friedrich Miescher in 1869 DNA was isolated from the nuclei of white blood cells from pus on bandages.

Structure of DNA  DNA was made up of repeating units called nucleotides. Each of these nucleotides consisted of a sugar a phosphate group a nitrogenous base.

DNA is made up of nucleotides

The nitrogenous bases are of four different types: adenine (A)  thymine (T) guanine (G) cytosine(C)

A nucleotide is made up of a phosphate group, a sugar and a nitrogenous base.

Base Pairing rule: A with T and G with C In 1950, Erwin Chargaff came up with the concept of base pairing. This concept states that in DNA every adenine (A) binds to a thymine (T) and every cytosine (C) binds to a guanine (G). This is now known as Chargaff’s rule.

Base pairing rule

Triplet A sequence of three nucleotides in DNA that can code for an amino acid. For example, the triplet base sequence CAA codes for the amino acid, valine.

Summary of DNA structure

Protein Synthesis:

RNA Type of nucleic acid RNA contain the sugar ribose It has Uracil instead of thymine It is shorter and single-stranded The triplet code is RNA is called codon

Transcription The process by which the genetic message in DNA is copied into a mRNA molecule