Year 10 Genetics

1. Year 10 Genetics DNA is the molecule which codes for life Like a big recipe book deciding whether we have blue eyes or green, red hair or blond etc. CLICKVIEW and H/O Hand me down genes family patternsDNA is the molecule which codes for life Like a big recipe book deciding whether we have blue eyes or green, red hair or blond etc. CLICKVIEW and H/O Hand me down genes family patterns

2. The Structure of DNA DNA (deoxyribonucleic acid) is found in the nucleus of living cells Its structure is described as a double helix Like a twisted ladder Side bars are made of alternating sugar and phosphate groups Rungs are known as nucleotide bases Like a twisted ladder Side bars are made of alternating sugar and phosphate groups Rungs are known as nucleotide bases

3. Nucleotide Bases There are four bases Adenine (A) always bonds with Thymine (T) Cytosine (C) always bonds with Guanine (G) The bases determine your genetic code. Much of your DNA is the same as other people�s, but a few changes make all the difference. DNA is a long molecule (about 1m) that is found in the nucleus of pretty much all of your cells. It needs to be specially packaged for it to be stored. EXPT extract DNA Much of your DNA is the same as other people�s, but a few changes make all the difference. DNA is a long molecule (about 1m) that is found in the nucleus of pretty much all of your cells. It needs to be specially packaged for it to be stored. EXPT extract DNA

4. Chromosomes DNA is divided into �chunks� called Chromosomes In humans most cells contain 46 chromosomes arranged into 23 homologous pairs. XX pair is a female XY pair is a male Peas 14 chromosomes, dog 78, fly 8, a type of fern with 630 KARYOTYPE DIAGRAM Homologous pairs have the same structure, one from mum one from dad Each cell therefore has 2 copies of all information Is this male or female?Peas 14 chromosomes, dog 78, fly 8, a type of fern with 630 KARYOTYPE DIAGRAM Homologous pairs have the same structure, one from mum one from dad Each cell therefore has 2 copies of all information Is this male or female?

5. Genes Each chromosome is divided up into genes. Genes code for traits (characteristics), such as fixed or free earlobes. There are two forms of each gene called alleles. WHY? Sometimes we can exaggerate the traits Each cell has 2 copies of each chromosome, one from mum one from dad therefore must have 2 forms of every gene ie allelesSometimes we can exaggerate the traits Each cell has 2 copies of each chromosome, one from mum one from dad therefore must have 2 forms of every gene ie alleles

6. Alleles Every somatic (body) cell has 23 homologous pairs of chromosomes. So each cell has a pair of genes, called alleles, coding for every trait. They may be homozygous (the same) e.g AA Or heterozygous (different) e.g. Aa Remember gametes have 23 single chromosomes so they only have one form of the gene. Alleles are alternative forms of the same gene LOOK at alleles again in a few lessons Remember gametes have 23 single chromosomes so they only have one form of the gene. Alleles are alternative forms of the same gene LOOK at alleles again in a few lessons

7. Sex Determination 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. Sex is determined by chromosome 23 carried by men in the sperm Sex is determined by chromosome 23 carried by men in the sperm

8. Colour blindness is a sex linked trait carried on x chromosome, why is it more prevalent in men? Only 1 X so if mum was a carrier they have 50% chance of showing trait. Women only get it if father is colour blind and mum is a carrier or is colourblindColour blindness is a sex linked trait carried on x chromosome, why is it more prevalent in men? Only 1 X so if mum was a carrier they have 50% chance of showing trait. Women only get it if father is colour blind and mum is a carrier or is colourblind

9. Sex Determination The female donates one of her two X chromosomes The male either an X or a Y Offspring are 50% male, 50% female EXPT Each boy has an X and Y counter Each girl has 2 X counters Put one in each hand and hold behind back. (like paper scissors rock) show one hand. Record the sex of your baby on the board.EXPT Each boy has an X and Y counter Each girl has 2 X counters Put one in each hand and hold behind back. (like paper scissors rock) show one hand. Record the sex of your baby on the board.

10. Sometimes It goes Wrong! Xo Turners syndrome XXY Kleinfelters syndrome XXX Metafemale XYY male Turners sterile, small, web neck 1 in 3000 Kleinfelters female characteristics, voice sterile 1 in 1000 XXX tall, limited IQ 1 in 1000 XYY tall, acne, limited IQ 1 in 1000 Explain how separation might not occur Sometimes separation of other chromosomes goes wrong, Trisomy C21 leads to downs syndrome Sometimes very small changes like 1 amino acid in 1 gene on 1 chromosome is copied wrong and this can lead to big physical changes Acondroplasia (dwarfism)Turners sterile, small, web neck 1 in 3000 Kleinfelters female characteristics, voice sterile 1 in 1000 XXX tall, limited IQ 1 in 1000 XYY tall, acne, limited IQ 1 in 1000 Explain how separation might not occur Sometimes separation of other chromosomes goes wrong, Trisomy C21 leads to downs syndrome Sometimes very small changes like 1 amino acid in 1 gene on 1 chromosome is copied wrong and this can lead to big physical changes Acondroplasia (dwarfism)

11. Sexual reproduction Offspring are different from parents (variation) Advantage Survival of the fittest (finches) If change occurs, best adapted will prevail Disadvantage Need a partner!? Gametes are sex cells � sperm and egg They contain half the number of chromosomes (haploid) At fertilisation the gametes fuse to form a zygote with two sets of chromosomes (diploid) Where are sperm and egg formed testes and ovaryWhere are sperm and egg formed testes and ovary

12. Asexual Reproduction All offspring are identical (clones) Advantage Logging trunks straight, bananas no seeds No partner needed Disadvantage Kill one, kill all Strawberry runners Potato tubers Cooch grass rhizome Aphids Human intervention � cuttings, genetic engineering Reproducing without sex = asexual All cells have a full set of genetic information/ instructions to make a new organism Many plants and some animals reproduce asexually, strawberry runner, potato tuber, cooch grass rhizome, aphids man intervenes -plant cuttings Disease or climate change can kill allReproducing without sex = asexual All cells have a full set of genetic information/ instructions to make a new organism Many plants and some animals reproduce asexually, strawberry runner, potato tuber, cooch grass rhizome, aphids man intervenes -plant cuttings Disease or climate change can kill all

13. Cell Division 2 types Mitosis Occurs in body cells Exact copy Growth/repair of organism Meiosis Occurs in GAMETES Results in half the chromosomes Produces variation Cell division must occur to REPAIR, REPLACE or GROW Anyone know the names of 2 types of cell division? Where does it occur Why does it occurCell division must occur to REPAIR, REPLACE or GROW Anyone know the names of 2 types of cell division? Where does it occur Why does it occur

14. Growth, repair, replacementGrowth, repair, replacement

16. Alleles (2 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. What is the definition of an allele � alternative form of a gene Which alleles are passed on is totally random. PICTURE of 2 alleles for flower colour, this is heterozygous allele, purple P is dominant so the flower is purple What is the definition of an allele � alternative form of a gene Which alleles are passed on is totally random. PICTURE of 2 alleles for flower colour, this is heterozygous allele, purple P is dominant so the flower is purple

17. Discrete � you either have it or you don�t EXPT test class for presence of traits and work out genotypeDiscrete � you either have it or you don�t EXPT test class for presence of traits and work out genotype

18. 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 What is the genotype and phenotype of the children ? Genotype Tt, phenotype can roll If the 2 alleles for tongue roll are T and t not all of the genes carried are expressed but they make up the genotype �� Which is dominant what are the possible combinations of the alleles What are the childrens geno and phenoIf the 2 alleles for tongue roll are T and t not all of the genes carried are expressed but they make up the genotype �� Which is dominant what are the possible combinations of the alleles What are the childrens geno and pheno

19. In 1850, Mendel took the examination for certification as a�teacher, but failed. Ironically, some of his lowest marks were in biology. He was then sent by his abbot to the University of Vienna, where he studied physics, chemistry, mathematics, zoology, and botany from 1851 to 1853. Still, he never passed the examination for a teacher's license.In 1850, Mendel took the examination for certification as a�teacher, but failed. Ironically, some of his lowest marks were in biology. He was then sent by his abbot to the University of Vienna, where he studied physics, chemistry, mathematics, zoology, and botany from 1851 to 1853. Still, he never passed the examination for a teacher's license.

20. Anther is male part To stop self pollination Next slide for answerAnther is male part To stop self pollination Next slide for answer

21. Crossing 2 heterozygous parents gives offspring 3:1 ratioCrossing 2 heterozygous parents gives offspring 3:1 ratio

22. Punnet Square This is a monohybrid cross 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 Only 1 gene responsible for the trait, hair / eye colour many genes involved Dihybrid (don�t worry) Each small square represents 25%, � Therefore all children will be genotype Tt and pheno rollers why?Only 1 gene responsible for the trait, hair / eye colour many genes involved Dihybrid (don�t worry) Each small square represents 25%, � Therefore all children will be genotype Tt and pheno rollers why?

23. 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? Father and mother are both heterozygous What percentage of children are able to roll their tongue? 75% What proportion/fraction of children cannot roll their tongue? � If the couple have 8 children how many are tongue rollers? 6 Explain why only 6 are able to roll their tongues when both parents can? 2 get homozygous recessive alleles How can we tell if the genotype of a tongue roller is TT or Tt � TEST crossFather and mother are both heterozygous What percentage of children are able to roll their tongue? 75% What proportion/fraction of children cannot roll their tongue? � If the couple have 8 children how many are tongue rollers? 6 Explain why only 6 are able to roll their tongues when both parents can? 2 get homozygous recessive alleles How can we tell if the genotype of a tongue roller is TT or Tt � TEST cross

24. No baby has to get a blue recessive from each parentNo baby has to get a blue recessive from each parent

25. 6 normal 3 in 4 chance x26 normal 3 in 4 chance x2

26. Bb, 25%Bb, 25%

27. Test / Back Cross Shows the genotype of an unknown Eg. Dominant phenotype - Purple flower Genotype could be Pp or PP Cross with homozygous recessive (Pure Breeding) e.g. pp phenotype white 2 results All purple so genotype is PP Half purple so genotype is Pp The phenotype is purple flower but we don�t know what the geno is Draw punnet square work out what the offspring will be Might be important in dog breeding to know if you are mating pure breeding animals, any recessive traits which show up will cost you lots of money!The phenotype is purple flower but we don�t know what the geno is Draw punnet square work out what the offspring will be Might be important in dog breeding to know if you are mating pure breeding animals, any recessive traits which show up will cost you lots of money!

28. Pedigree Diagrams Method for studying the inheritance of genes Male Female Affected male Mating One way of showing how a trait is passed on through generations is a pedigree chart. It is like a family tree and shows those who are have a trait, and what sex each is. One way of showing how a trait is passed on through generations is a pedigree chart. It is like a family tree and shows those who are have a trait, and what sex each is.

29. Pedigree Diagrams Genotype inside, Phenotype under two generation pedigree Which is the father (square), how many children, M or F Who has the trait? father expresses the trait, as does his daughter, but no other family members What are the missing genotypes? Which are homozygous rr Which are heterozygous Rrtwo generation pedigree Which is the father (square), how many children, M or F Who has the trait? father expresses the trait, as does his daughter, but no other family members What are the missing genotypes? Which are homozygous rr Which are heterozygous Rr

30. Pedigree Chart Recessive or the parents in generation 1 would show the trait Chance � trait is shown if offspring are homozygous recessive, the chance of this from heterozygous parents is � (25%) Recessive or the parents in generation 1 would show the trait Chance � trait is shown if offspring are homozygous recessive, the chance of this from heterozygous parents is � (25%)

34. http://www.bbc.co.uk/schools/gcsebitesize/biology/variationandinheritance/index.shtml