Reproduction

• What is sexual reproduction?

  Type of reproduction

  Involves the production of gametes by meiosis

  A gamete from each parent fuses to form a zygote

  Genetic information from each gamete is mixed so the resulting zygote is unique.
• What are gametes?

  Sex Cells

  Haploid (half the number of chromosomes)
• What is meiosis?

  Form of cell divison that forms gametes in reproductive organs

  Chromosome number is halved

  Involves two divisons

  
• What must occur prior to meiosis?

  Interphase - copy of genetic information are made during this process
• What happens during the first stage of meiosis?

  Chromosomes line up along the cell equator.

  The pair of chromosomes are seperated and move to opposite poles of the cell (the side to which chromosome is pulled is random forming variation)

  Chromosome number is halved
• What happens during the second stage of meiosis?

  Chromosomes line up along the cell equator

  The chromatids are seperated and move to opposite poles

  Four unique haploid cells are produced
• Why is meiosis important for sexual reproduction? (2)

  -It increases genetic variation

  -It ensures future zygote formed is diploid
• Describe fertilisation and it's resulting outcome.

  Gametes join together to restore the normal number of chromosomes and then the new cell divides by mitosis (which creates the number of cells)

  As the embryo develop the cells differentiate
• Describe the circumstances in which malarial parasites reproduce sexually and asexually

  Sexual reproduction in mosquitoes (see infection and response unit)

  Asexual reproduction in human host
• Describe the circumstances in which fungi reproduce sexually and asexually

  Sexual reproduction to give variation

  Asexual reproduction to produce spores.
• Describe the circumstances in which plants reproduce asexually and sexually

  Sexual reproduction to produce seeds

  Asexual reproduction by runners or bulb divison
• What is DNA and what shape does it have?

  A double stranded polymer of nucleotides and form double helix

  Found in nucleus (see cell biology)
• Define Genome.

  The entire genetic material of an organism
• Why is understanding the human genome important?

  Searching for genes linked to certain types of diseases

  Understanding and treating inherited disorders

  Tracing human migration patterns from the past
• What is a chromosome?

  A long coiled molecule of DNA that carries genetic information in the form of genes.
• How many chromosomes do the human body have?

  46
• How many chromosomes do gametes have?

  23
• Define Gene

  A small section of DNA that codes for a specific protein
• What are alleles

  Different versions of the same gene.
• What is a dominant allele?

  A version of a gene where only one copy is needed for it to be expressed

  
• What is a recessive allele?

  An allele that is only expressed when paired with another recessive allele.
• What is meant when an organism is homozygous?

  When an organism has two copies of the same allele.
• What is meant when an organism is heterozygous?

  When an organism has two different versions of the same gene
• What is a genotype?

  The genes present for a trait
• What is a phenotype?

  Visible Characteristic
• How are dominant alleles represented in a punnett square?

  Capital letters.

  
• How are recessive alleles represented in a punnett square?

  Lower case
• What is the problem with single cell crosses?

  Most characteristics are controlled by multiple alleles not just one.
• What is an inherited disorder?

  A disorder caused by the inheritence of genetic alleles
• Give 2 examples of inherited disorders.

  Polydactyly - caused by dominant allele

  Cystic Fibrosis - caused by recessive allele
• How are embryos screened for inherited disorders?

  During IVF, one cell is removed (from 8 cell embryo) and tested for disorder-causing alleles. If the cell does not have any indicator alleles, the orginitating allele is placed implanted into the uterus.
• What is gene therapy?

  The insertion of a normal allele into the cells of a person with an inherited disorder to functionally replace the faulty allele.
• Ethical concerns with Genetic therapy:

  -Some people believe it is going against God

  -genes could go into gametes and be passed into future generations
• What are sex chromsomes?

  Chromosomes that determine an individual's sex.

  XX - Women

  XY - Men
• What does the inheritence of a Y chromosome mean that an embryo turns into a male?

  Testes develop in an embryo that is stimulated by a gene present in the Y chromosome
• What is a sex-linked characteristic?

  A trait that is determined by genes located on the sex chromosomes.
• Why are the majority of alleles found on the X chromsome rather than the Y chromosome?

  The X chromosome is larger than the Y chromosome so more genes are carried on it
• Why are men more likely to express a phenotype for a recessive sex-linked trait then woman?

  Many genes are on the X chromosome and have no counterpart on the Y chromosome

  Women (XX) have two alleles for each sex-linked gene whereas men (XY) only have the X chromosome once so one recessive allele in the X chromosome produces a recessive phenotype