B2.5 Simple Inheritance in Animals and Plants

B2.5 Simple Inheritance in Animals and Plants

1. Cell Division and Growth

   • Cells
     • New cells are needed to replace old ones, repair damaged tissue, grow, etc, but they much have the same genetic material
     • They have a nucleus containing genes (some DNA). Different forms of genes are alleles. Genes are grouped in chromosomes.
       • 46 chromosomes in a nucleus. 23 pairs. One from a pair is inherited from father and one from mother. Gametes have only one of each pair
   • Mitosis
     • two identical cells
     • Same chromosomes
     • asexual
     • no genetic variation
     • Produces copies of chromosomes then cell divides
     • eg, skin
   • Differentiation
     • In embryos cells are unspecialised (stem cells)
     • Some genes are switched on to specialise certain cells and differentiate them
     • In adult animal cells differentiation has already occured so mitosis is common yet plants can still differentiate making them easy to clone

2. Cell Division in Sexual Reproduction

   • Meiosis
     • ova made in ovaries. Sperm in testes
     • Chromosomes are copied, cell divides twice leaving 4 sex cells with half the chromosomes
     • Introduces variety
     • random chromosome areas
   • Fertilisation
     • more variety as they each have 23 chromosomes which pair
     • Meiosis then Mitosis
   • Variation
     • Asexual = no variation
     • sexual = variation

3. Stem Cells

   • The Function
     • egg and sperm fuse to form a zygote (a single cell). This divides to form a ball of cells (embryo). The inner cells of this ball are stem cells which will differentiate
     • bone marrow is a stem cell
     • They are needed for diseased or injured tissue
   • Using Stem Cells
     • Spinal injuries cause paralysis
     • Embryonic stem cells can be cultured and differentiated into the right cells
     • We may be able to grow whole organs
   • Problems with Stem Cells
     • Some embryonic stem cells come from abortions, some from fertility treatment which may cause ethical issues
     • Human rights
     • Slow, difficult, expensive and hard to control
     • May cause cancer
   • The Future
     • There are stem cells in the umbilical cord blood solving ethical issues
     • new ways of growing adult stem cells, and have even grown tracheas.
     • Theraputic cloning uses adult cells to clone an embryo of themselves,

4. From Mendel to DNA

   • Mendel's discoveries
     • Born 1822 worked in a monestry
     • cross bred peas
       • Found a pattern in the characteristic of offspring
     • considered dominant genes
   • DNA
     • Chromosomes are made up of long chain of DNA and are found in nuclei
     • Double helix structure
     • Genes are a small section of DNA
     • Carries instructions to make the proteins that form cell structures
       • include enzymes to control cell chemistry
     • The Genetic code
       • DNA is made of 4 different chemicals
         • grouped into 3s. Each 3 is an amino acid
           • A gene is made of hundreds of thousands of these bases
       • The order of bases controls the order of amino acids to make protein.
       • A mutation in a base will change the whole protein structure
   • DNA fingerprinting
     • DNA is unique to you
       • UNLESS YOU HAVE AN IDENTICAL TWIN
         • Both developed from one cell
     • Your DNA can be used to identify you.
     • Your DNA pattern is more similar to relatives. You can get your pattern from bodily fluids
     • Can be used for crimes and DNA tests in parenting

5. Inheritance in action

   • How inheritance works
     • Sex Chromosomes
       • XX is female, XY is male
     • Genes have different alleles which result in a different protein
     • Most characteristics are controlled by a number of genes but some are only 1.
     • You get dominant and recessive alleles
   • Genetic terms
     • Homozygous - two identical alleles (DD,dd)
     • Heterozygous - an individual with different alleles (Dd)
     • Genotype - the genetic makeup of an individual
     • Phenotype - physical appearance (dimples)
   • Family Trees
     • Can be used for tracing genetic changes
     • Can track diseases

6. Inherited conditions in humans

   • Polydactyly
     • When a baby has excess fingers or toes
     • Caused by a dominant allele
     • If 1 parent has it, you have a 50% chance as half the gametes have the fault. If they are homozygous, you have no chance
   • Cyctic Fibrosis
     • Organs get clogged by mucus
     • Treatment = physiotherapy and antibiotics
     • Caused by a recessive allele
       • must be inherited by both parents
     • Carriers have both alleles but no symptoms because the dominant is healthy
   • The Genetic Lottery
     • When an egg and sperm combine it is up to luck which alleles combine
     • Use a punnet square
   • Curing Genetic Disease
     • Scientists hope genetic engineering will be the answer as they can cut out faulty alleles and replace them with healthy ones
     • Genetic tests show people what faulty alleles they have and the probability of children having them
       • They can then decide whether they want a family. It raises ethical issues

7. Stem Cells and Embryos

   • RELIGION AND SHIZZLE