Genetics and Inheritance

1. Part 2: Modes of inheritance Genetics and Inheritance Year 10 Biology

2. 2. Genes are passed on from one generation to the next! From one generation to the next! You are a product of maternal and paternal chromosomes passed on from your parents!

3. 3. Genes are passed on from one generation to the next! Inheritance The passing of characteristics from one generation to the next This double set of genetic instructions (one set from each parent) makes up your genotype (your set of genes). The visible expression of the genotype as a particular trait or feature is called the phenotype. The phenotype may also be influenced by your environment

4. 4. Genes are passed on from one generation to the next! Your Phenotype is influenced by environmental factors!

5. 5. Genes are passed on from one generation to the next! Your phenotype is determined by your genotype During fertilisation, the zygote receives a pair of each set of chromosomes, the paternal and maternal chromosomes. Two forms of the same gene (one from mum one from dad) These alternate forms of a gene are called alleles Alleles can code for a dominant traitor a recessive trait

6. 6. Genes are passed on from one generation to the next! • Alleles can code for a dominant traitor a recessivetrait • Dominant alleles are shown in capitals • Recessive alleles are shown in lower case letters. • The recessive trait is hidden in the presence of the dominant trait

7. 7. Genes are passed on from one generation to the next! Your alleles can be Homozygous or Heterozygous • Homozygous = two of the same alleles • Heterozygous = two different alleles A genotype for a particular gene can be described as: -Homozygous dominant -Homozygous recessive -Heterozygous

8. 8. Genes are passed on from one generation to the next! Your Genotype

9. 9. Genes are passed on from one generation to the next! Explain some unexpected phenotypes! A heterozygous genotype means you carry a recessive allele that may be passed on to the next generation. The allele is recessive so doesn’t show up as a phenotype in the parents But can show up as a phenotype in the offspring

10. 10. Genes are passed on from one generation to the next! Degrees of Dominance Complete Dominance The expression of one trait is dominant over the other Partial Dominance Co-dominance Heterozygote has the characterisitcs of both parents (e.g. human blood groups) Incomplete Dominance Heterozygotes show a phenotype that is intermediate between the phenotypes of the homozygotes (e.g. flower colour of snap dragons)

11. 11. Genes are passed on from one generation to the next! Co-dominance Heterozygote has the characteristics of both parents (e.g. human blood groups)

12. 12. Genes are passed on from one generation to the next! (e.g. flower colour of snap dragons) Incomplete dominance Heterozygotes show a phenotype that is intermediate between the phenotypes of the homozygotes.

13. 13. Genes are passed on from one generation to the next! Suggest how red, white and pink flowered offspring can result from pink flowered parents

14. 14. Genes are passed on from one generation to the next! Degrees of Dominance Complete Dominance The expression of one trait is dominant over the other Partial Dominance Co-dominance Heterozygote has the characterisitcs of both parents (e.g. human blood groups) Incomplete Dominance Heterozygotes show a phenotype that is intermediate between the phenotypes of the homozygotes (e.g. flower colour of snap dragons)