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Reproduction Year 10 What is the purpose of reproduction? To pass on genetic material which will ensure the survival of the species Reproduction • 2 types: • Asexual Reproduction – Budding – Binary Fission (‘split in two’ as in bacteria) – Use of a ‘host’ cell (as in viruses) – Spores – Vegetative (cutting, rhizomes) • Sexual Reproduction – Seed Formation by way of Pollen and Egg fusion Puffball Asexual Reproduction • All offspring are identical (clones) Advantage – Quick population growth – No partner needed – Logging trunks straight, bananas no seeds Disadvantage – Kill one, kill all •Strawberry runners •Potato tubers •Cooch grass rhizome •Aphids • Human intervention – cuttings, genetic engineering Sexual Reproduction • Offspring are different from parents (variation) Advantage – Survival of the fittest (finches) – If environmental change occurs, increased chance of species survival. Disadvantage – Need a partner!? – Energy wastage The Structure of DNA • DNA (deoxyribonucleic acid) is the genetic material found in the nucleus of living cells • Its structure is described as a double helix Animation of DNA in the body Chromosomes • DNA is divided into “chunks” called Chromosomes • Humans have 23 pairs of chromosomes • Why? • 1 from Mum, 1 from Dad • XX pair is a female • XY pair is a male • Karyotype diagram Genes • Each chromosome is divided up into genes. • Genes are a sequence of DNA that codes for a trait, such as fixed or free earlobes. • Alleles are alternative forms of the same gene Sometimes the appearance can be enhanced by other means… Gametes • Gametes (sex cells) only have 23 single chromosomes. Why? • During fertilisation the egg and sperm come together to give a new cell with 23 pairs of chromosomes. Gametes • A gamete is a single cell, one from each parent, that creates a new individual • Female gamete is known as an ovum or egg • Male gamete is known as a sperm • Each human gamete has 23 chromosomes • All other cells in your body have 46 chromosomes. • When the egg and sperm fuse, a new life is produced, having all 46 chromosomes Fertilisation • This is the process when the chromosomes of the egg and sperm combine, creating a new individual • Fertilisation may occur inside the animal or in the environment (water) • The single cell organism (zygote) starts to divide into an embryo then a foetus • Nine months is required for the foetus to develop into a fully developed newborn baby Male reproductive Organs • Penis – Insertion of semen • Urethra – Tube expelling sperm and urine • Scrotum – Temp. regulation • Testes – Make sperm and testosterone • Vas deferens – Transports sperm • Seminal vesicle – Produce fluid to help motility of sperm Female reproductive organs • Vagina – Birth canal • Cervix – Allows passage of sperm and menstrual blood • Uterus – Egg implantation site – Expands to hold baby • Ovary – Produces eggs and hormones • Fallopian tube – Allows passage of egg – Site of conception Menstrual Cycle • Once a month an egg leaves the ovaries (ovulation) • travels down the fallopian tubes towards the uterus • Before ovulation Oestrogen stimulates the uterus lining to build up in preparation for pregnancy • If the egg is fertilized by a sperm it attaches to the wall of the uterus and develops into a baby. • If the egg isn't fertilized it doesn't attach to the wall so the uterus sheds the extra lining. • The blood and unfertilized egg leave the uterus through the vagina. This is a menstrual period. Menstrual Cycle • Hormones are the chemical messengers which co-ordinate the 28 day cycle Changes during puberty • Hormonal changes cause: – – – – – – – Growth spurt Hair growth Body shape changes Voice changes Menstruation begins Body odour Emotions fluctuate Amphibian life cycle • Create a poster which explains the life cycle of a frog. • Groups of 4 (think about the make up of your team not just friends!) • Marked on teamwork • Informative resources • Presentation • Timescale? amphibian Alleles • Every body cell has 23 pairs of chromosomes. WHY? • During fertilisation one came from Mums egg and one from Dads sperm • So each cell must have a pair of genes, called alleles, coding for every trait. • They may be the same e.g AA • Or different e.g. Aa Alleles – alternative forms of the same gene • Alleles are assigned letters to distinguish one from another e.g. Tongue roll alleles T or t. • Alleles may be dominant or recessive depending on whether the trait is seen. • Recessive – blue eyes – Small letter • Dominant – hitchhikers thumb, tongue roll – Capital letter • The characteristics displayed are known as phenotype. Alleles • Genotytpe is the genetic make up of an individual • E.g. Tongue roll alleles are represented by T or t • What are the 3 possible genotypes? – TT, Tt, tt Genotype Father Mother TT tt Phenotype Can roll Can’t roll • What is the genotype and phenotype of the children ? – Genotype Tt, phenotype can roll Punnet Square • All possible combinations of gametes can be shown (father can roll TT, mother can’t tt) • The genotype of all offspring can be worked out • Can work out the chances or ratio of any combination occurring in this case: • Genotype 100% Tt • Phenotype 100% Can roll Fathers sperm M o t h e r s e g g T T t Tt Tt t Tt Tt Punnet Square • What are the Genotypes of children? • What are the phenotypes? • Roller, non roller • What is the ratio of phenotypes? • 3:1 • How can we tell if the genotype of a tongue roller is TT or Tt? Fathers sperm M o t h e r s e g g T t T TT Tt t Tt tt GENETICS PROBLEMS In humans, blue eyes are recessive to brown: Dad (Blue eyes) Mum (Brown eyes) Is Mum homozygous for brown eyes? Baby (Blue eyes) ________ How do you know? (complete the Punnett square) MICE In mice, albino is a recessive trait Big Momma mouse Poppa mouse Stuart Little Complete the Punnett square to show how Stuart ended up an albino If there were 8 babies in the litter, how many would we expect to have normal colouring? _________ LABRADORS In Labs, black is the dominant trait The pups are all black These 2 are mated What is the genotype of the pups? _____________ The pups grow up and 2 are mated Here are their kids… Show how this came about (draw the Punnett square) What percentage would we expect to have golden colouring? ____________ Eye colour In eye colour the brown eye allele is dominant, so we call it B, and the blue eye is recessive, so we call it b: BB Bb bb Homozygous brown-eyed parent Heterozygous brown-eyed parent Blue-eyed parent What would the offspring have? – This is an example of monohybrid inheritance Eye colour Example 1: A homozygous brown-eyed parent and a blue-eyed parent: X BB Parents: Example 2: 2 heterozygous brown-eyed parents bb Bb X Bb Gametes: B B b b B b B b Offspring: Bb Bb Bb Bb BB Bb bB bb All offspring have brown eyes 25% chance of blue eyes Eye colour Example 3: A heterozygous brown-eyed father and a blue-eyed mother: Bb bb B b b b Bb Bb bb bb Equal (50%) chance of being either brown eyed or blue eyed. Example questions 1) In mice, white fur is dominant. What type of offspring would you expect from a cross between a heterozygous individual and one with grey fur? Explain your answer with a genetic diagram. 2) A homozygous long-tailed cat is crossed with a homozygous short-tailed cat and produces a litter of 9 long-tailed kittens. Show the probable offspring which would be produced if two of these kittens were mated and describe the characteristics of the offspring (hint: work out the kitten’s genotype first). DISCRETE HUMAN CHARACTERISTICS Discrete is “not continuous” – it must be one of a few possibilities. Possible Dominant Dominant Phenotype Genotypes Trait Gene Location Recessive Phenotype Recessive Genotype color of iris 2 not blue EE or Ee blue ee widow's peak 4 peak PP or Pp no peak pp cheek dimples 5 dimples DD or Dd not dimples dd face freckles 9 freckles FF or Ff no freckles ff mid-digital hair 10 hair HH or Hh no hair hh Hitchhiker's thumb 17 straight TT or Tt curved tt Hallux length (toes) 20 long 2nd toe BB or Bb long big toe or bb = to 2nd toe ear lobes 21 free LL or Ll attached ll tongue rolling 22 ability RR or Rr no ability rr cleft chin 16 cleft YY or Yy no cleft yy