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Gametogenesis HBS2B. Female reproductive system ovary fimbriae uterine tube uterus bladder urethra clitoris labia cervix vagina.

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Presentation on theme: "Gametogenesis HBS2B. Female reproductive system ovary fimbriae uterine tube uterus bladder urethra clitoris labia cervix vagina."— Presentation transcript:

1 Gametogenesis HBS2B

2 Female reproductive system

3 ovary fimbriae uterine tube uterus bladder urethra clitoris labia cervix vagina

4 Male reproductive system

5 1 = prostate 2 = urethra3 = bladder 4 = vas deferens5 = penis glans/head6 = epididymis 7 = testes8 = penis/ erectile tissue9 = scrotum 10 = urinary sphincter11 = foreskin/prepuce12 = seminal vesicles

6 Gametogenesis Gametes are made by a process called gametogenesis. Female gametes are made in the ovaries and male gametes are made in the testes. Gametogenesis involves a special type of division called meiosis. In meiosis, the number of chromosomes is halved, so that when gametes unite in fertilisation, they have the correct number of chromosomes. Human gametes have only 23 chromosomes (and are called haploid cells), while normal human cells have 46 chromosomes (and are called diploid) cells). In males, meiosis produces 4 gametes, whereas in females it produces only 1. The gametes then undergo a period of maturation. In males this occurs in the epididymis, while in females this occurs in the follicle in the ovary, and the uterine tube shortly after ovulation.

7 Events of meiosis

8 Meiosis 1 – the first division prophase I the chromosomes become visible - each chromosome contains two chromatids homologous chromosomes move together & a spindle forms metaphase I homologous pairs of chromosomes line up on the equator, attached by their centromeres anaphase I one of each pair of homologous chromosomes is pulled to either end of the cell telophase I the chromosomes condense cytoplasm is split of and cell divides into two daughter cells, each with 23 chromosomes each chromosome consists of two chromatids

9 Meiosis 2 – the second division prophase II the chromosomes become visible - each chromosome contains two chromatids a new spindle forms, at right angles to the old one metaphase II chromosomes line up on the equator, attached by their centromeres anaphase II one of each chromatid in each chromosome is pulled to either end of the cell telophase II the chromosomes condense cytoplasm is split of and each daughter cell divides into two (ie total of 4 daughter cells), each with 23 chromosomes - each chromosome consists of one chromatid Gametes

10 Comparing mitosis and meiosis MitosisMeiosis Where it occurs Body cellsGonads (reproductive organs) Why it occurs Cell repair, growth, asexual division Sexual reproduction Number of cells produced 24 Number of divisions 12 Number of chromosomes in daughter cells Same as parent (diploid) Half that of parent (haploid) Amount of variation in daughter cells NoneLots

11 Comparing mitosis and meiosis 2 MitosisMeiosis Advantages for reproduction Simple Rapid division Allows variation Disadvantages for reproduction No variationMore complex Slower reproduction

12 DNA Nuclear DNA is arranged in structures called chromosomes, which are only visible when the cell is dividing. Humans have 46 chromosomes arranged as 23 pairs. These chromosomes are passed on in meiosis so that each new individual has 1 of each pair from its mother, and 1 of each pair from its father. Mitochondrial DNA is inherited only from the mother as it is the ovum that provides the cell and its organelles (mitochondria) for the new zygote. The sperm provides only nuclear DNA as the mitochondria in the flagella are rapidly destroyed. Mitochondrial DNA can be used to trace ancestry of people. Meiosis is necessary in order to make sure that the gametes have the correct amount of DNA. DNA (deoxyribose nucleic acid) in found in the nucleus of all cells, and controls protein synthesis, and cell activity. DNA is also found in mitochondria

13 The structure of DNA DNA consists of two strands of alternating sugars and phosphates, with pairs of nuclear bases forming cross-links between the chains. This is called a double helix. A nucleotide is a nuclear base attached to a sugar and a phosphate The four bases are cytosine, guanine, adenine and thymine. Each base links up with its base pair - cytosine with guanine, adenine with thymine Each strand is coiled around the histones so they can fit into a small space. When not dividing, the tangled DNA is called chromatin. The base sequences on the DNA acts as a code that controls the action of the cell. Sections of DNA code which control one feature are called genes, so the DNA sequence is called the genetic code. In order to read the code, that section of DNA must untangle and uncoil from its histone. The code sequences are copied as mRNA, which is used to make proteins. Proteins are used as structural components (eg in cell membranes, skin and hair - keratin, messengers (eg hormones) and as enzymes. Protein synthesis occurs in the ribosomes.

14 DNA controls protein synthesis

15 Why are proteins important? Roles of proteins in the body include Structural proteins eg collagen, keratin Enzymes (organic catalysts) eg digestive enzymes Transport proteins eg haemoglobin Regulatory proteins eg hormones Protective proteins eg antibodies, clotting factors Therefore proteins determine what you will look like, and how your body functions

16 DNA replication When cells divide the DNA is copied or replicated. DNA replication occurs during meiosis in interphase, just before prophase starts. During DNA replication the strands s_____________ New bases are added using the b_______ pair rule adenine attaches to __________________ thymine attaches to __________________ cytosine attaches to __________________ guanine attaches to __________________ The separation and attachment of new nucleotides are controlled by enzymes.

17 DNA replication When cells divide the DNA is copied or replicated. DNA replication occurs during meiosis in interphase, just before prophase starts. During DNA replication the strands separate New bases are added using the base pair rule adenine attaches to thymine thymine attaches to adenine cytosine attaches to guanine guanine attaches to cytosine The separation and attachment of new nucleotides are controlled by enzymes.

18 Intercourse During intercourse semen containing male gametes is introduced into the female’s vagina, so as to allow fertilisation. Semen consists of spermatozoa (produced in the testes, and matured in the epididymis) and fluid secretions from the accessory glands. The seminal vesicles secrete sugary fluid, which provides food for the sperm; the prostate secretes alkaline fluid, which neutralises vaginal secretions; and the bulbo-urethral glands secrete mucus, which acts as lubricant. During sexual excitement the erectile tissue of the penis fills with blood, causing the penis to become erect. Contractions of epididymis, vas deferens, and accessory glands cause semen to travel through the vas deferens and then the urethra and finally to be ejaculated from the penis. When the penis is placed in the vagina during intercourse, the semen is deposited at the top of the vagina, just below the cervix. Sexual excitation in the female causes vaginal widening, cervical relaxation, an increase in mucus and alteration in acid secretions, thus allowing sperm to enter the uterus and survive more easily. The sperm move up through the uterus, using their flagella to propel them, heading towards the uterine tubes, where they may find an ovum to fertilise..

19 Fertilisation If they find an ovum, the sperm must burrow through the outer layer of cells, and the cell membrane. The head of the sperm contains enzymes which do this. Once one sperm has entered the ovum, the cell membrane changes so no other can enter and the sperm’s chromosomes combine with the ovum’s chromosome. Because the gametes have only half the chromosomes, they have a much shorter survival time than normal cells - sperm ~72 hours, ova 12 – 24 hours, so in order for fertilisation to occur sperm should be present just before ovulation After fertilisation, the zygote moves down the uterine tube, into the uterus, where it embeds itself in the endometrium, thus initiating pregnancy. Symptoms of pregnancy include: no menstruation, weight gain, enlarged and tender breasts, increased urination, (and sometimes morning sickness) Twins can result in two ways: Identical twins occur when the zygote splits and develops into 2 babies – ie both genetically identical Non-identical twins occur when both ovaries ovulate and both ova are fertilised, so that babies are not genetically identical

20 Multiple choice questions 3 The questions below apply to the following diagram that shows part of an animal cell viewed under a microscope using a 10x ocular lens and a 40x objective lens. The nucleus was measured to be 20  m in diameter. What was the field diameter for the diagram above? a)10  m b)50  m c)100  m d)200  m

21 Multiple choice questions 3 The questions below apply to the following diagram that shows part of an animal cell viewed under a microscope using a 10x ocular lens and a 40x objective lens. The nucleus was measured to be 20  m in diameter. What was the field diameter for the diagram above? a)10  m b)50  m c)100  m d)200  m

22 Multiple choice questions 4 The questions below apply to the following diagram that shows part of an animal cell viewed under a microscope using a 10x ocular lens and a 40x objective lens. Without changing anything else, the observer changed the revolving nosepiece of the microscope to a different magnification. This allowed the image of the entire cell to just fall within the field of view. The cell was then measured to be 200  m long. What was the magnification of the second objective used? a)5 x b)10 x c)20x d)80 x

23 Multiple choice questions 4 The questions below apply to the following diagram that shows part of an animal cell viewed under a microscope using a 10x ocular lens and a 40x objective lens. Without changing anything else, the observer changed the revolving nosepiece of the microscope to a different magnification. This allowed the image of the entire cell to just fall within the field of view. The cell was then measured to be 200  m long. What was the magnification of the second objective used? a)5 x b)10 x c)20x d)80 x


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