Biology

• Define gamete


  a sex cell
• Define gonad


  the organs which produce gametes
• Define menstruation


  occurs at the beginning of the menstrual cycle, the endometrium (uterine lining) is shed
• Define ovulation


  occurs in the middle of the menstrual cycle, one ovum (egg) is released from an ovary
• Define fertilisation


  The joining of gametes
• Define zygote


  a single fertilised cell
• Define embryo


  The phase between a zygote and fetus. (it becomes an embryo after 2 weeks of cell division).
• Recall the 4 nitrogen bases and their complimentary pairs in DNA


  Adenine - Thymine

  Cytosine - Guanine
• Define dominant allele


  dominant alleles are expressed over recessive alleles
• Define recessive allele


  are only expressed when no dominant allele is present
• Define heterozygous 


  a genotype in which the alleles are different (e.g Bb)
• Define homozygous


  A genotype in which the alleles are the same (e.g BB/bb)
• Define genotype


  the combination of alleles
• Define phenotype


  the physical visible effect of the allele
• Compare asexual and sexual reproduction


  Sexual reproduction involves the union (fertilisation) of sex cells to form a zygote whereas asexual reproduction produces offspring without the union of sex cells

  Offspring from asexual reproduction are genetically identical clones of their parent cells whereas offspring from sexual reproduction are genetically different
• Compare asexual and sexual reproduction

  Due to asexual reproduction producing genetic clones, in a changing environment sections of the population may die out whereas the offspring resulting from sexual reproduction have a greater chance of survival due to their genetic variety.

  However, sexual reproduction wastes energy to find a mate while asexual reproduction can produce large numbers of offspring very quickly
• Identify the functions of the male reproductive systems

  Testis: are male gonads. Produces sperm.

  Epididymis: where sperm cells mature

  Vas deferens: where sperm cells travel along during ejaculation

  Seminal vesicle & Prostate gland: adds an alkaline, sugar-rich fluid to the sperm, it is then called semen

  Urethra: the tube inside the penis. Where semen is transferred along the penis out the man's body

  Penis: used to introduce semen into the vagina (via ejaculation when erect)

  Scrotum: the sac that contains the testes, epididymis and vas deferens
• Identify the functions of the female reproductive systems

  Ovaries: are female gonads. Produces ova (eggs)

  Fallopian tubes/oviducts: where the egg is fertilised after travelling here after ovulation

  Uterus: it's lining is where the zygote implants and where the embryo will develop

  Vagina: receiving site of the penis during intercourse, and birth canal

  Cervix: base of the uterus

  Endometrium: the layer of tissue that lines the uterus.
• Oestrogen


  Repairs and thickens the uterine lining. Its levels peak in the pre-ovulation phase by a growing follicle
• Progesterone


  Maintains the uterine lining. If there is no implantation of an embryo (pregnancy), progesterone levels drop which triggers menstruation
• LH (Luteinising Hormone)


  Triggers ovulation (egg release from a follicle). It's levels peak in the middle of the menstrual cycle
• FSH (Follicle Stimulating Hormone)


  Increases follicle development (ovum maturation) in the ovaries. Its levels are higher at the start of the menstrual cycle
• Menstrual cycle

  1. Menstruation: the start of the menstrual cycle, the lining of the endometrium is shed

  2. Pre-ovulation: an ovum (egg) is maturing within one of the ovaries

  3. Ovulation: occurs in the middle of the cycle. Process where an ovum (egg) is released from an ovary

  4. Post-ovulation: uterine lining continues to thicken (preparing for implantation of an embryo). If the fertilisation of the ovum doesn't occur, progesterone levels will decrease, triggering the start of menstruation
• LH and FSH


  Made by the pituitary gland at the base of the brain
• Oestrogen and progesterone


  Made by the ovaries
• Describe the meaning of karyogram


  A graphical depiction of a karyotype (a picture of a person's chromosomes).

  
• Describe the meaning of maternal and paternal chromosomes

  Chromosomes (maternal): one of the two gene copies (alleles) for each trait, derived from the female

  Chromosomes (paternal): the other allele contained in the diploid somatic body cell (23 pairs of chromosomes), derived from the male
• Describe the meaning of homologous chromosome

  Pairs of chromosomes that contain the same versions of the same genes. ( 1 maternal and paternal homologous). --> matching chromosomes to form each pair
• Describe the meaning of autosomes

  Any chromosome that is not a sex determining chromosome. One of the numbered chromosomes.
• Describe the meaning of sex chromosomes


  The X and Y chromosomes. Present in both sex cells (ova and sperm) and somatic cells (body cells)
• Describe the meaning of haploid

  a sex cell with 23 single unpaired chromosomes, thus contains a single allele for each trait (22 single chromosomes, 1 sex-determining chromosome).
• Describe the meaning of genes


  a stretch of DNA contains genes. Genes carries information that determines traits. Genes are a sequence of nucleotides (section of DNA molecule).
• Describe the meaning of alleles

  variations/copies of a gene. One of two or more versions of a gene. Determines genotype and phenotype
• Describe how the sex of a baby is determine

  XX (girl) or XY (boy) chromosomes seen on the karyogram

  The father's sperm determines the sex. The sperm cell can carry either an X or Y chromosome. The mother's egg is always a X chromosome

  When the sperm and egg combine to fertilise, the zygote will either have XX or XY chromosomes.

  Therefore, every couple has a 50% chance of having a boy or girl
• Describe the structure of and identify the major components of DNA (Deoxyribonucleic acid) in nucleotides


  N (Nitrogenous) bases: Cytosine, Guanine, Adenine, or Thymine

  Deoxyribose sugar: Between N base and phosphate group. Looks like a squashed pentagon

  Phosphate groups: a phosphate molecule. Looks like a small circle

  Nucleotides: the building blocks of DNA is made up of. Two chains or "backbones" of nucleotides bound together by hydrogen bonds forms DNA

  
• Describe the structure of and identify the major components of chromosomes


  Chromatids: One of the two identical halves of a chromosome that has been replicated in preparation for cell division. (Duplicated chromosomes look like a cross and are called "sister chromatids"

  Centromeres: A specialised region on a chromosome where the two sister chromatids are tightly connected during cell division.

  
• Recall the base pair rule

  Equality in quantity in base pairs

  • concentration of adenine = concentration of thymine etc.
  • Matching pairs have a 1:1 ratio of %
  • all 4 bases combined together must equal 100%
• Describe the relationship between DNA, genes and chromosomes


  In each cell in the body (approx. 37 trillion), there is a nucleus

  In the nucleus of each cell, there are 23 pairs of thread-like structures called chromosomes

  Each chromosome is made up of long strands of DNA

  A stretch of the DNA contains genes
• What is the difference between somatic and sex cells

  sex cells contain half the number of chromosomes as somatic cells (body cells).

  somatic cells are diploid while sex cells (gametes) are haploid
• Compare somatic and sex cells

  Somatic body cells:

  • 46 chromosomes (23 pairs); 22 pairs of homologous chromosomes and 2 sex-determining chromosomes
  • 2 alleles for each trait
  • created via mitosis

  Sex cells (gametes):

  • 23 single unpaired chromosomes, 1 of which is a sex-determining chromosome
  • 1 allele for each trait
  • new cells are derived from diploid cells via meiosis