B6-Inheritance, Variation and Evolution

• Decribe DNA


  -DNA stands for deoxyribonucleic acid-it is a chemical that all genetic material in a cell is made up from.

  -It contains coded information-all instructions to put an organism together and make it work.
• What in your DNA determines what inherited charcteristics you have?

  DNA is found in really long structures called chromosomes.

  
  

  Chromosomes normally come in pairs and determine what inherited chacteristics you have.
• What type of strcuture is DNA?

  -DNA is a polymer.

  -Made up of two strands coiled together in the shape of a double helix.
• What is a gene?


  -A gene is a small section of DNA found in a chromosome.

  -Each gene codes for a particular sequence of amino acids,which are put together to make a specific protein.
• How many amino acids are used in a gene?

  Only 20 amino acids are used, but they make up thousands of different proteins.
• What do genes tell us?

  Genes tell cells in what order to put the amino acids together.
• What does DNA determine?

  DNA determines what proteins the cell produces, e.g hameoglobin, keratin

  That basically also detremines what cell it is-RBC/skin cell
• What is a genome?

  The entire set of genetic material in an organism
• What does understanding the human genome help us do?

  1) Allows scientists to identify genes in the genome that are linked to different types of disease.

  2) Knowing which genes are linked to inherited diseases could help us to understand them better and help us develop effective treatments for them.

  3)Scientists can look at genomes to trace the migration of certain populations of people around the world.

  All modern humans are descended from a common ancestor who lived in Africa-so it is almost identifiable but but as people migrated away from Africa,they eventually developed tiny differences in thheir genomes.
• What is sexual reproduction?

  Where genetic information from two organisms is combined to produce offspring which are genetically different to either parent
• What is produced in sexual reproduction?

  The mother and father produce gametes by meiosis-egg and sperm cells in animals.
• In humans, how many chromosomes does a gamete contain?

  -23 chromosomes

  -Instead on having two of each chromosome gamete has one of each
• What happens during fertilisation?


  The egg and the sperm cell fuse together to form a cell with the full number of chromosomes.-half from mother and half from father
• What does sexual reprduction involve?

  -Sexual reproduction involves the fusion of male and female gametes.

  -Because there are two parents ,offspring contains a mixture of their parent's genes.
• Why do offspring inherit features from both parents in sexual reproduction?

  It recieves a mixture of chromsomes from its mom and dad, which decide how the person turns out.
• What does mixture of genetic variation produce?

  Produces variation
• What is asexual reproduction?

  In asexual reproduction,there is only one parent so the offsping are genetically identical to that parent.
• How does asexual reproduction occur?

  Happens by mitosis-an ordinary cell makes a new cell by dividing in two.

  This new cell has exactly the same genetic information as the parent cell.
• What does asexual reproduction involve?

  -Asexual reproduction involves only one parent and no fusion of gametes.

  -There is no mixing of genetic information.

  -This leads to genetically identical offspring (clones).
• How do bacteria, some plants and animals reproduce?

  Asexually
• How do you make gametes with only half the number of chromosomes?

  Cells divide by mitosis

  This process involves two cell divisions.

  In humans-onlt happens in reproductive organs.
• Describe the process of meiosis

  1) Before the cell starts to divide,it duplicates its genetic information, forming two armed chromosomes-one arm of each chromosomes is an eaxct copy of the other arm.

  2) After replication, the chromsomes arrange themselves into pairs.

  3) In the first division in meiosis, the chromosome pairs line up tot he centre of the cell.

  4) The pairs are then pulled apart so ech new cell has only one copy of each chromosome.Some of the fathers chromosmes and some of the mothers chromosomes go into each cell.

  5) In the second division, the chromsomes line up agai in the centre of the cell .The arms of the chromosomes are pulled apart

  6) You get four gametes, each with only a single set of chromosomes in it.Each of the gametes is gentically different from the others because the chromosomes all get shuffled up during meisosis and each gamete only gets half of them at random.
• What happens to the cell produced by gamete fusion?

  1) Aftertwo gameteshave fused during fertilisation, the resulting new cell divides by mitosis to make a copy of itself.2) Mitosis repeats many times to produce lots of new cells in an embryo.3) As the embryo develops, these cells then start to diffrentiate into the different types of specialised cell that make up a whole organism.
• How many chromosomes are in a human body cell?

  46 chromosomes, 23 identical pairs
• Which chromosomes control your characteristics?

  22 matched pairs
• What does the 23rd pair of chromosomes determine?

  determines sex.

  
  

  XX - female

  XY - male
• What chromosomes do males have?

  -An X and Y chromosome.

  -The Y chromosome causes male characteristics.
• What chromosomes do females have?

  -An X and X chromosome

  -The XX combination allows female characteristics to develop
• What happens when sperm is made?

  -The X and Y chromosomes are drawn apart in the first division of meiosis.

  -There is a 50% chance it gets a Y chromosome and 50% chance it gets an X chromosome.
• How do you find the probability of getting a boy or a girl?

  -Draw a genetic diagram

  -Put possible gametes from one parent down one side and the possible gametes of the other parent along the top.

  -Each middle square, fill in the letters from the top and side that line up

  -Pair of letters show the possible combinations.
• What are genetic diagrams?


  Models that are used to show all the possible genetic outcomes when you cross together different genes or chromosomes
• What do the genes you inherit control?

  the characteristics you develop
• What characteristics are controlled by a single gene?

  -Mouse fur colour

  -Red-green colour blindness in humans
• What are alleles?


  different versions of the same gene
• What do we have 2 versions of in the body?

  Two versions of every gene-one of each chromosome in a pair.
• What is homozygous?

  organisms that have two identical alleles for a particular trait
• What is heterozygous?


  organisms have two different alleles for a particular trait.
• What is a dominant allele?

  A form of a gene that is fully expressed, even when two different alleles are present

  -Represented by a capital letter
• What is a recessive allele?


  The gene that will not be expressed if in the presence of a dominant gene

  -Represented by a lower case letter
• What conditions need to be met for an organism to display a recessive characteristic?

  Both of its alleles must be recessive