B12: Reproduction


B12.1: Types of Reproduction

  • in asexual reproduction, there is no fusion of gametes and only one parent. there is no mixing of genetic information, leading to genetically identical offspring
  • only mitosis is involved in asexual reproduction
  • sexual reproduction involves the fusion of gametes formed by meiosis. meiosis leads to the formation of non-identical cells, sperm and egg cells in animals and pollen and egg cells in flowering plants. 
  • in sexual reproduction there is a mixing of genetic information that leads to variation in the offspring.
1 of 7

B12.2: Cell Division in Sexual Reproduction

  • cells in the reproductive organs divide by meiosis to form the gametes
  • body cells have two sets of chromosomes, gametes only have one set.
  • in meiosis, the genetic material is copied and then divided twice to form four gametes. each gamete has a single set of chromosomes. 
  • all gametes are genetically different from each other. 
  • gametes join at fertilisation to restore the normal number of chromosomes. the new cell divides by mitosis. the number of cells increase and as the embryo develops, the cells differentiate
2 of 7

B12.3: DNA and the Genome

  • the genome of an organism is the entire genetic material of that organism.
  • the whole human genome has now been studied and this will have great importance for medicine in the future.
  • the genetic material in the nucleus of a cell is composed of DNA. DNA is a polymer made up of two strands forming a double helix. 
  • a gene is a small section of DNA on a chromosome. each gene codes for a particular sequence of amino acids to make a specific protein. 
3 of 7

B12.4: Inheritance in Action

  • some characteristics are controlled by a single gene. each gene may have different forms called alleles. 
  • the alleles present, or genotype, operate at a molecular level to develop characteristics that can be expressed as the phenotype.
  • if two alleles are the same, the individual is homozygous for that trait. if the alleles are different they are heterozygous.
  • a dominant allele is always expressed in the phenotype, even if only one copy is present. a recessive allele is only expressed if two copies are present. 
  • most characteristics are the result of multiple genes interacting rather than a single gene. 
4 of 7

B12.5: More About Genetics

  • direct proportion and ratio are used to express the outcome of a genetic cross. 
  • punnett squares and family trees are used to understand genetic inheritance. 
  • punnett squares predict the outcome of a monohybrid cross. 
  • ordinary body cells contain 23 pairs of chromosomes: 22 control body characteristics and the sex chromosome pair controls the gender.
  • in humans, the female sex chromosome is **, in males it is XY. 
5 of 7

B12.6: Inherited Disorders

  • some disorders are inherited. 
  • polydactyly is a dominant phenotype which can be inherited from either or both parents. 
  • cystic fibrosis is a recessive phenotype and is caused by recessive alleles which must be inherited from both parents. 
6 of 7

B12.7: Screening for Genetic Disorders

  • cells from embryos and fetuses can be screened for alleles that may cause many genetic disorders. 
  • embryo and fetal cells are used to identify genetic disorders but screening raises economic, social and ethical issues. 
7 of 7


No comments have yet been made

Similar Biology resources:

See all Biology resources »See all Reproduction resources »