Tuesday, 27 September 2011

3.22, 3.23 Sex determination

Recall that the sex of a person is controlled by one pair of chromosomes XX in a female and XY in a male.
Describe the determination of sex offspring at fertilisation using a genetic diagram.

In  females they carry a pair of chromosomes X,X (at the same length) and in males they carry XY (X is longer than Y). So when they mate - X x Xy they produce two possibilities XX (female) or XY (male) which is at the ratio of 1:1. So it's the male who determines the sex of their offspring.

3.18 Codominance

Recall the meaning of the terms: dominant, recessive, homozygous, phenotype, genotype and codominance.
Lets breed a red flower with a white flower.
RR (red flower) x WW (white flower) => Pink (RW)
If you breed Pink (RW) with another Pink (RW) => you will get the following genotypes: RR, RW, RW, WW
This means that there is a 25% chance that the offspring will be red, 25 % chance that the offspring will be white and 50% it will stay pink.

Wednesday, 21 September 2011

3.19 b F1 x F1 Cross

Describe the patterns of monohybrid inheritance using a genetic diagram
If you want to test for the genotype you always breed with the homozygous recessive. For example, if found a wild black mouse and want to determine the genotype, test it with a white mouse. (in mice white fur is recessive)

3.19 a P1 x P1 Cross

describe patterns of monohybrid inheritance using a genetic diagram
monohybrid: having one gene

from the cross we can see all the combination leads to 'Rr' which means that they will all be red because 'R' is the dominant gene and will be all heterozygous 'Rr'.

3.18 Phenotype

Recall the meaning of the terms: dominant, recessive, homozygous, heterozygous, phenotype, genotype and condominance.

<=homozygous: having the same alleles for a single trait 

<=heterozygous: having two different alleles for a single trait 

(definition sources: http://biology.about.com/od/geneticsglossary/g/heterozygous.htm http://biology.about.com/od/geneticsglossary/g/homozygous.htm)

Saturday, 17 September 2011

3.2 Fertilization

Understand that fertilization involves the fusion of a male and female gamete to produce a zygote that undergoes cell division and develops into an embryo

The process of fertilization happens between adult male and female.
  • The cells in testis and in ovaries have a complete cell of chromosomes and this is called diploid (2n) which is a complete set of chromosomes and for human it is 46
  • The cells divide to form cells with half sets of chromosomes, this type of cell division is called meiosis this makes the cell go from a diploid number to a haploid number(n) which is a 1/2 set so in humans it is 23 (there are 23 chromosomes in the sperm cell and 23 chromosomes in the egg cell)
  • During sexual reproduction the two cells are brought together and joint/fused together, so forms 1 cell. This process is know as fertilization. Which involves the combining of half set of chromosomes and another half set of chromosomes to make a full set of chromosomes (n+n=2n/in humans 23+23=46)
  • This cell is known as a zygote.
  • We have a combination with a male and female chromosomes. This cell then goes through the process of cell division called mitosis, in which the cells will divide to get 2 cells, they will both contain 46 chromosomes. They will then divide. All cells contain 2n diploid number.
  • When we have sufficient cells, this will then be called an embryo.
  • This principle holds truth for all sexually reproducing organisms but the numbers are for human only
Process of fertilization:

3.9 a Male Reproductive System

Recall the structure and function of the male and female reproductive systems

  • Stores urine
  • To carry out the process of meiosis which produces a gamete called the sperm cells
  • Where sperm cells are stored
  • To carry sperm cells to penis during sexual stimulation
  • Contains 20%-30% volume of semen and is known to carry sugars and is alkali
  • The alkali is to neutralize the acidic secretion of the vagina
Seminal Vesicles
  • They also produce sugar based alkaline substances
  • Contains 70% of volume of semen
  • The common tube which joins the left right testis and the left and right vasderens
  • Carries semen/urine down penis
  • Carry sperm cells into the vagina during sexual intercourse
Diagram of a male reproductive system:

3.9 b Female Reproductive System

Recall the structure and function of the male and female reproductive systems

Before the pregnancy occurs, the size of the uterus is no larger than an orange. Don't confuse this with the large size of the pregnant women's uterus.

  • Where meiosis occurs
  • Production of Eggs
Oviducts (fallopian tubes)
  • Carry eggs to uterus
  • where fertilization might take place
  • wall of uterus made from muscle
  • this is the part that will stretch during pregnancy and contract during giving birth
Lining of the Uterus
  • Accepts and develops the fertilizing eggs which will develop into the embryo then into the child
  • develop of the placenta also happens here
  • Entrance to the uterus
Uterus space
  • Where sperm cells move and where the egg cells move
  • where embryo is developed into a unborn child
  • Where penis is introduced at the end and where sperm cells enter the uterus
  • collects the sperm cells and allow them to pass through the cervix then into the uterus

Diagram of a female reproductive system:

Wednesday, 7 September 2011

3.12 Amniotic fluid

Understand how the developing embryo is protected by amniotic fluid.

In the space between the uterus and the embryo there is amniotic fluid which protects the developing embryo - if the fluid which is largely water cannot be compressed it absorbs the pressure. If any blows force is applied to the outside uterus wall, the pressure will be absorbed to protect the embryo.

3.11 Placenta

Describe the role of the placenta in the nutrition of the developing embryo

In the picture we can see a developing embyro:

When the child is in the uterus it is surrounded by amniotic fluid at this time the child cannot digest and can't breath but is also not adequate able to excrete. The child obtains nutrition by the umbilical cord of the placental structure growing out of the embryo. The placental structure connects the maternal blood vessel to the child's blood vessel, placenta biologically grows out of a developing embryo but also does not grow out of the mother. The blood vessels inside the placenta are the child's placenta including artery and the vein. The placenta grows into the wall of the Uterus of the mother. During pregnancy, the mother continues to eat which means that there will be amino acids, glucose and fats in the blood which will travel through her blood stream, to the placenta and then through to the embryo. The placenta has a large surface area and the barrier is really thin to allow an adequate area for exchange between the mother's blood and the baby's blood. The baby, produces molecules back to the mother, which is things like carbon dioxide and urea.