3. Reproduction and Inheritance

Sexual reproduction:

The process involving the fusion of the nuclei of two gametes to form a zygote and the production of offspring that are genetically different from each other.

Gamete:

Reproductive sex cell that fuses with another gamete during fertilisation.

Zygote:

The diploid cell from which an organism develops, and is formed from the fusion of gametes.

What are the gametes in animals?

Sperm and ovum

What are the gametes in plants?

Pollen nucleus and ovum

Why are gametes different from normal cells?

Gametes contain half the number of chromosomes found in other body cells, they contain a haploid nucleus.

Normal body cells contain … chromosomes

46

Gametes contain … chromosomes

23

How many chromosomes does a zygote have?

46 and it has a diploid nucleus

Advantages and disadvantages of sexual reproduction:

+ve:

• increases genetic variation

• the species can adapt to new environments due to variation, giving them a survival advantage

• Disease is likely to affect population

-ve:

• take time and energy to find mates

• Difficult if isolated members of the species to reproduce

Asexual reproduction:

The process resulting in genetically identical offspring being produced from one parent. This does not involve the fertilisation or gametes.

Why are offsprings from asexual reproduction genetically identical to the parent and to each other?

• One one parent is involved to reproduction therefore there is not mixing of genetic information. Due to this, the offspring is genetically identical.

Binary fission:

When Bacteria produce exact genetic copies of themselves in a type of asexual reproduction

What are the advatages and disadvantages of asexual reproduction?

+ves:

• population can be increased rapidly

• can exploit suitable environments quickly

• quick and energy efficient

-ves:

• limited genetic variation in the population- offspring is genetically identical

• population is vulnerable to changes in conditions- suited to only one habitat

• diseases likely to affect whole population

What is the difference between asexual and sexual reproduction?

Feature	Asexual Reproduction	Sexual Reproduction
Number of parent cells	One	Two
Type of cell division	Mitosis	Meiosis
Level of genetic similarity	Genetically identical	Genetically unique
Sources of genetic variation in offspring	Only one source: mutation	Three sources: 50% of their DNA from each of the two parents new combinations of alleles on the chromosomes in gametes random assortment of chromosomes into gametes during meiosis
Number of offspring produced	Usually relatively large numbers	Usually relatively limited numbers
Time taken to produce offspring	Usually relatively fast	Usually relatively slowly

Describe fertilisation Humans:

Fertlisation in Plants

… are the reproductive organs of plants. Plants produce … whoch contains a nucleus inside that is the male gamete. Pollen is … of locomotion.

• Flowers are the reproductive organs of plants. Plants produce pollen, which contains a nucleus inside that is the male gamete. pollen is not capable of locomotion

Pollination:

The transfer of pollen from the anther to the stigma

What are the two main types of pollination?

Wind pollination and Insect pollination

What is the name of the male and female parts of a flower and what do they include?

Carpel/pistol (female) : stigma, style, ovary

Stamen: anther, filament

Sepal:

protects unopened flower

Petals:

brightly coloured in insect- pollination flowers to attract insects

Anther:

produces and releases the male sex cell (pollen grain)

Stigma:

top of the female part of the flower which collects pollen frain

Ovary:

produces the female sex ovum

Ovule:

prodces the femail sex cell (ovum)

Ovule:

contains the female sex cells

Filament:

a structure that hold the anther

Features of an insect pollinated plant:

Petals: large and bright to attract insects

Scent and nectar: present so insect pushes past stamen (in nectry)

Number of pollen grains: moderate cuz high efficiency

Pollen grains: larger, sticky to be carried away

Anthers: inside flower, stiff and firmly attached to brush against insects

Syigma: inside flower, sticky so pollen grains stick to it

Describe how insect pollination takes place?

Insects will visit flowers to collect nectar. As the insect enters flower, it brushes against the anthers which deposit sticky pollen onto the insects body. When insects visit another flower for nectar, it brishes against the stigma of this second lower and the pollen is deposited.

Features of a wind pollinated plant:

Petals: small and dull

scent and nectar: absent

Number of pollen grains: large amounts

Pollen grains: smooth, small, light

Anthers: outsidethe flower

Stigma: outside the flower

Cross pollination:

Pollination on a different plant of the same species. Increases genetic variation therfore survial. But takes time.

Self pollination:

Pollination on the same plant or flower. Very fast but reduced genetic variation.

Describe the process of fertlisation in plants:

When the pollen grain land of the sticky anther, the sugary syrup causes the grain to grow a pollen tube down the style to the ovary. The pollen nucleus moves down the tube to the ovule and fuses with the ovum. They form a zygote and it starts dividing to develop into an embryo plant.

Describe the formation of a seed and fruit:

After fertlisation. the ovule develops into the seed and the wall of the ovule develops into the seed coat known as testa. The ovary walls develop into a fruit and then the seed is disperesed.

What are theconditions required for germination?

Germination requires the presence of moisture, oxyygen and warm temperature.

Germination:

the start of growth in the seed

When the seed germinates, the embryo begins to grow into a young…

seedling

Name the stuctute that surrounds the plant embryo:

Cotyledons

How are cotyledons adapted to support growth of the seedling?

• they contain food reserves that supply the seedling with energy for growth when it germinates

Describe the process of germination:

1. the seed contains the zygote which divides into cells that then develop into the embryo plant

2. the embryo is supplied wih energy from the cotyledon until it had leaves for photosynthesis

3. After the intake of water, the testa (seed coat) splits.

4. this triggers the production of plumule( first emerging shoot) and radicle( first emerging root)

Describe an example of natural asexual reproduction in plants:

Runners:

• Some plants grow side branches, known as runners, that have small plantlets at their ends

  • Runners are horizontal stems that grow sideways out of the parent plant

• Once they touch the soil, these plantlets will grow roots and the new plantlets will grow and become independent from the parent plant

Describe an example of artificial reproduction in plants:

Cuttings:

A section of the parent plant with a new bud is cut off and replanted. The cutting is often dipped in rooting powder to trigger hormones for new root growth.

Organs in the male reproductive system:

Prostate gland, Sperm duct, Urethera, Testis, Scrotum, Penis

Prostate gland:

produces fluid called smen that provides sperm cells with nutrients

Sperm duct:

sperm passes through the sperm duct to be mixed with fluids produced by the glands before being passed into the urethra for ejaculation

Urethra:

tube running down the centre of the penis that can carry out urine or semen, a ring of muscle in the urethra prevents the urine and semen from mixing

Testis:

contained in a bag o skin(scrotum) and produces sperm (male gamete) and testostrone (hormone)

Scrotum:

sac supporting the testes oustide the body to ensure sperm are kept at a lower temp

Penis:

passes urine out of the body from the bladder and allows semen to pass into the vagina of a woman during sexual intercourse

organs in the female reproductive system:

oviduct, ovary, uterus, cervix, vagina

oviduct:

connects the ovary to the uterus and is lined with cilliated cells to push the released ovum down it. site of fertlisation

Ovary:

contains ova (female gametes) which will mature and develop when hormones are released

uterus:

muscular bag with a soft lining where the fertilised egg(zygote) will be implanted to develop into a foetus

cervix:

ring of muscle at the lower end of the uterus to keep the developng foetus in place during pregnancy

Vagina:

muscular tube that leads to the inside of the woman’s body, where the male’s penis will enter during sex + where sperm is deposited

What are the adaptations of a sperm cell:

• has a flagellum: enables it to swim to the egg

• contains enzymes in the acrosome: to digest through the jelly coat+ cell memb of an egg cell

• contains alot of mitochondria: to provide energy from respiration for locomotion (flagellum)

What are the adaptations of an ovum:

• cytoplasm containing a store of energy: providesenergy for the dividing zygote after fertlisation

• jelly like coating that changes after fertlisaion: forms an impenetratable barrier afetr fertilisation to prevent other sperm nuclei entering the egg cell

How does fertlisation take place in humans?

During sexual intercourse, semen is ejaculated into the vagina of a female. The sperm in the semen follow a chemical trail and swim to the uterus. They travel into the oviducts where they meet the ovum. The head of the sperm releases enzymes that digest the outer layer of the ovum. The fusion takes place and the egg cell releases a thick layer of material that prevents any more sperm cells from entering.

How long does the menstrual cycle last?

28 days

Ovulation:

the release of an egg occurs about halfway through the cycle

Menstruation:

The shedding of the uterus lining when the egg is not fertlised ( lasts 5-7 days)

Describe the change in hormones during the menstrual cycle:

• The pituitary gland produces FSH which stimulates the development of a follicle in the ovary. An egg develops inside the follicle and the follicle produces the hormone oestrogen

• Oestrogen causes growth and repair of the lining of the uterus wall and inhibits production of FSH. When oestrogen rises to a high enough level it stimulates the release of LH from the pituitary gland which causes ovulation (usually around day 14 of the cycle)

• The follicle becomes the corpus luteum and starts producing progesterone. Progesterone maintains the uterus lining (the thickness of the uterus wall). If the ovum is not fertilised, the corpus luteum breaks down and progesterone levels drop. This causes menstruation, where the uterus lining breaks down and is removed through the vagina - commonly known as having a period

• If pregnancy does occur the corpus luteum continues to produce progesterone, preventing the uterus lining from breaking down and aborting the pregnancy

• It does this until the placenta has developed, at which point it starts secreting progesterone and continues to do so throughout the pregnancy

What is the function of the placenta?

The placenta is an organ, where the mother’s and baby’s blood are in proximity for the exchange of glucose, amino acids, fatty acids, water, oxygen, mineral ions vitamins, antibodies and waste products (co2 + Urea). The foetus’s blood connect to the placenta by the umbilical cord.

How is the placenta adapted for its function?

• The placenta is adapted for this diffusion by having a large surface area(fetal villi) and a thin wall for efficient diffusion

• The placenta acts as a barrier to prevent toxins and pathogens getting into the foetus’s blood

Describe the pocess of implantation:

• After fertlisation, the zygote travels towards the uterus while dividing and forming an embryo (takes 3 days).

• the embryo embeds itself in the thick lining of the uterus (implantation) and grows

• a placenta is formed where the embryo is attached

• the embryo is surrounded by amnotic fluid

What is Amniotic fluid:

a fluid made from the mother’s plasma, held in the amniotic membrane/ sac which protects the embryo by cushioning it from bumps to the mother’s abdomen.

Gestation period:

the growth of the embryo in the uterus ( 9 months)

What hormones are responsible for secondary sexual characteristics?

Females: Oestrogen

Males: Testosterone

Female secondary sexual characteristics:

• breasts develop

• body hair grows

• menstrual cycle begins

• hips get wider

Male secondary sexual characteristics:

• growth of penis and testes

• growth of facial and body hair

• muscles develop

• voice breaks

• testes start to produce sperm

Genome:

the entire set of genetic material for an organism

Genomes are made up of…

Genes

Genes:

a small section of DNA that codes for a particular sequence of amino acids

Alleles:

Different versions of a gene. Having 2 alleles of the same type is called homozygous. Having 2 alleles that are different to one another is called heterozygous.

Examples of proteins:

• structural proteins ( collagen)

• Enzymes (Amylase)

• Hormones (LH)

Functions of genes:

• Genes control our characteristics as they code for proteins that play important roles in what our cells do

the DNA double helix super coils to form…

Chromosomes

Chromosomes are found in the…

nucleus

Sex chromosome in females:

xx

Sex chromosome in males:

xy

What is DNA?

(Deoxyribonucklec acid) is th genetic material found in the nucleus of a cell. It is a polymer made up of two strands coiled around to make a double helix. The strands are formed from a sugar phosphate backbone with bases joined together by complementary base pairings.

What are the 4 bases in DNA?

• Adenine

• Thymine

• Guanine

• Cytosine

Adenine pairs with …

thymine

Guanine pairs with…

cytosine

How many copies of each chromosome do we have?

2

How many copied of each gene do we have?

2

How many alleles do we have for 1 gene?

2

Phenotype:

observale characteristics of an organism

Genotype:

The combination of alleles that control each characteristic (BB, Bb, bb)

Dominant alleles:

• A dominant allele only needs to be inherited from one parent in order for the characteristic to show up in the phenotype

Recessive alleles:

• A recessive allele needs to be inherited from both parents in order for the characteristic to show up in the phenotype.

Polygenic inheritance:

when characteristics are controlled by more than one gene ( such as eye colour)

True or false: Only a father can pass on a y chromosome:

True

How is the sex of an off spring determined? (Human)

• All egg cells and sperm will have an x chromosome

• only half of the sperm will have a y chromosome

Mitosis:

nuclear division giving rise to genetically identical cells (daploid cells)

What is mitosis used for?

• growth, repair of damaged tissue, replacement of cells and asexual reproduction

Describe the process of mitosis:

1. Each chromosome in the nucleus is duplicated.

2. The nuclear memebrane breaks down

3. chromosomes line up along the centre of the cell

4. once the chromatids have been sperated, the cell begins to divide(cytokinesis)

5. two genetically identical daughter cells are produced

All cells in the body ( except gametes) are produced by … of a zygote.

Mitosis