2. The Genetics Slide Show Gregor Mendel GHB 2004

3. The unit of inheritance Gene:

4. Chromosome Genes Chromosome: A bundle of DNA containing many genes B A C

5. Different versions of the same gene Alleles: Bb

6. Bb DNA gene chromosome Different versions of the same song are like… alleles Tape: -it is used to record information - it is like… One song or track on the tape is like a… A cassette is a large bundle of tape containing many tracks. It is like a…

7. Physical appearance Phenotype: Brown eyes Blue eyes Red flowers White flowers

8. The combination of alleles which you carry for a particular gene Genotype: BBbBbb Genotype: BBGenotype: BbGenotype: bb

9. An allele which is always expressed when it is present… Dominant allele: … it cannot be masked by another allele. Bb

10. An allele which can be masked by another allele… Recessive allele: … it is only expressed when two copies are present. bb

11. …homozygous …heterozygous If an individual has two copies of same allele of a gene on a pair of chromosomes the individual is… If an individual has two different alleles of a gene on a pair of chromosomes the individual is… bBBBbb The prefix homo- means… ‘same’ The prefix hetero- means… ‘other’

12. A cell which contains two copies of each chromosome is… diploid Normal body cells are diploid

13. A cell which contains one copy of each chromosome is… haploid Gametes (sex cells) are haploid Sperm Ovum Pollen Plant egg cell

14. Sperm cells are produced by … meiosis The chromosomes in the nucleus are copied Four haploid daughter cells are produced Each haploid daughter cell contains only one of the two alleles from the diploid parent cell Diploid parent cell

15. Ova are also produced by meiosis Haploid Diploid parent cell

16. Fertilization: An ova and a sperm fuse to form a diploid zygote Ova Sperm Zygote The zygote contains one allele from each parent This process is random

17. Inheritance of eye color b b Genotype is: bb Phenotype is: Blue

18. B B Genotype is: BB Phenotype is: Brown

19. B b Genotype is: Bb Phenotype is: Brown

20. B b Genotype is: Bb Phenotype is: Brown

21. The same rules apply to inheritance in plants as apply to inheritance in animals. The male gamete or sex cell is … … pollen The female gamete is… … the egg cell

22. Plant genes can have dominant and recessive alleles … a red flower r The recessive allele r produces … … a white flower R The dominant allele R produces … Example:

23. A genetic cross in plants: Rr x Rr There is only one way to make a homozygous plant with two dominant genes… RR RR … and only one way to make a homozygous plant with two recessive genes rr rr

24. In the genetic cross Rr x Rr there are two ways of making a heterozygous plant… Rr R r Rr OR … so, heterozygous offspring are twice as likely as either homozygous dominant or homozygous recessive offspring

25. We can show the likeliness or probability of different genotypes in different ways: 1. As a percentage -Probability of RR is… ¼ ½ 25% Probability of Rr is…50% Probability of rr is…25% 2. As a fraction -Probability of RR is… Probability of Rr is… Probability of rr is… ¼ 3. As a ratio -RR : Rr : rr = 1 : 2 : 1

26. There are three ways to make a plant with red flowers… RR RR Rr rR Rr … one produces a homozygous plant… … and two produce heterozygous plants…

27. …but, there is only one way to produce a plant with white flowers… rrrr So, in the genetic cross, Rr x Rr… …red flowers are three times more likely than white flowers!!!

28. We can show the likeliness or probability of different phenotypes in different ways: 1. As a percentage -Probability of red is… ¾ ¼ 75% Probability of white is…25% 2. As a fraction -Probability of red is… Probability of white is… 3. As a ratio -red : white = 3 : 1

29. The Punnett Square We can use the Punnett Square to work out the probability of the different genotypes and phenotypes in a genetic cross Step 1: Write down the genotypes of the parents. = Rr x Rr x Step 2: Write down the genotypes of the gametes that each parent produces. pollen Egg cells = R + r

30. Step 3: Draw your Punnett Square Step 4: Write the genotype of the different gametes into your Punnett Square Step 5: Write in the different ways in which the gametes can be combined… Egg cells Pollen Rr R r RRRr rRrr …this shows you the possible genotypes of the offspring Genotypes of offspring

31. Egg cells Pollen Rr R r RRRr rRrr Probability of Genotypes There are four possible ways to combine egg cells and pollen Count up how many times each genotype appears in the Punnet Square – this gives you its probability: ¼ Probability of RR is… Probability of Rr is… Probability of rr is… ¼ = 25 % = ½ 2 4 = 25 % = 50 % The ratio of RR : Rr : rr is… 1 : 2 : 1

32. Egg cells Pollen Rr R r RRRr rRrr Probability of Phenotypes Look at the genotypes of the offspring in your Punett Square… …decide which phenotype each one should produce. Count up how many times each phenotype appears in the Punnet Square – this gives you its probability: Probability of red is… ¾ = 75 % Probability of white is… ¼ = 25 % The ratio of red : white is… 3 : 1