How can you tell who the parents are? What is the importance of meiosis?

Mendel and DNA Learning objectives: describe Mendel’s work and discoveries and recognise it’s importance describe the structure of DNA and understand how DNA fingerprinting is used to identify individuals explain how genes code for specific proteins in the body (Higher Tier)

Gregor Mendel Gregor Mendel (1822-1884) was an Austrian monk who is regarded as the father of genetics. Mendel carried out pioneering work using pea plants to study the inheritance patterns of a number of characteristics. Mendel observed the following: Characteristics present in plants he crossed appeared in the offspring Some characteristics were dominant over others What we now call Mendelian genetics is the study of inherited characteristics.

Mendel’s Pea Experiments Mendel examined a small number of characters or traits in peas. Each character he studied is determined by one gene, for which there are two types, one dominant and one recessive. He found that these traits were inherited in predictable ratios depending on the traits of the parents. Seed colour yellow dominant over green Pod colour green dominant over yellow Images courtesy of Newbyte.com Pod shape inflated dominant over presed Seed shape round dominant over wrinkled

Mendel’s Pea Experiments Stem length tall dominant over dwarf Images courtesy of Newbyte.com

Results of Mendel’s Experiments Seed shape Round Wrinkled 5474 1850 7324 Round Wrinkled TOTAL 2.96 : 1 Seed colour Yellow Green 6022 2001 8023 3.01 : 1 Pod colour 428 152 580 Green Yellow 2.82 : 1 Pod shape Inflated Constricted 882 299 1181 Inflated Constricted 2.95 : 1 Stem length Tall Dwarf 787 277 1064 2.84 : 1

The History of Mendelian Genetics Mendel’s work was published in 1866, just seven years after Darwin’s theory of the Origin of Species by Natural Selection. At first his work was overlooked. Mendel’s work was rediscovered in 1900 (after his death) by three scientists, working independently on similar plant breeding experiments They gave Mendel credit for the work he had done.

Dominance & Recessiveness Parent plants Purple White X Without knowledge of chromosomes or cell division, Mendel made laws to describe the inheritance of traits in pea plants. Each gene is controlled by two ‘factors’ Factors do not blend, but may be either dominant or recessive. Recessive genes are masked by dominant ones. Recessive genes (e.g. white flowers) may ‘disappear’ in one generation, and reappear in the next. Generation 1 The offspring are inbred (self-pollinated) X Generation 2

Selected Human Hereditary Traits Dominant Recessive Right handedness Left handedness Hair on middle Segment of digits no hair Hitch-hiker’s thumb Normal thumb Polydactylism (extra digits) Normal digits Brachydactylism (short digits) Pattern baldness Normal hair Free ear lobes Attached ear lobes Polydactylism is a dominant trait; a normal number of digits is the recessive condition. In this crowd of men, almost all show some degree of pattern baldness, a dominant trait. Hitch-hiker’s thumb Free ear lobe Attached ear lobe Handedness Mid-digit hair

Mendel and DNA Many years later, DNA was discovered as the material from which these inherited factors Mendel described was made. DNA (deoxyribonucleic acid) is the chemical that makes up all chromosomes in the nucleus. When meiosis occurs, the genetic material is divided between the gametes so that each gamete gets one copy of each chromosome. Fertilisation combines maternal and paternal chromosomes. A chromosome consists of several smaller sections, each one is called a gene. A gene is a small section of a chromosome, made of DNA, which is the code for a protein in the organism. Proteins form the physical structures of an organism and are also molecules that control cell chemistry e.g. enzymes

Mendel and DNA Structure of DNA: HT DNA is a very long molecule. Its basic shape is called a double helix. It is composed of four different chemical bases, shown by letters A, T, C and G HT The bases are grouped into threes and each group codes for an amino acid. The order of bases determines the order of amino acids that make up all proteins in the body. Proteins determine how the body looks and how it functions.

DNA fingerprinting All people, unless they are twins, have unique patterns in their DNA that can be used to identify them. The patterns are used to produce a DNA fingerprint. The more closely related you are, the more similarities your DNA will have. Uses of this technique: Paternity tests – can you tell who this person’s father is? Crime solving – who committed this crime? How many patterns should they have in common?

Mendel and DNA Learning objectives - review: describe Mendel’s work and discoveries and recognise it’s importance describe the structure of DNA and understand how DNA fingerprinting is used to identify individuals explain how genes code for specific proteins in the body (Higher Tier)