6 1 reproduction

Sexual reproduction is the reproductive process during which the nuclei of two gametes fuse to form a zygote and genetically different offspring are produced.

Fertilisation is the fusion of gamete nuclei.

Gametes are sex cells, such as sperm and ovum (eggs) in animals, and pollen nucleus and ovum in plants. They contain half the number of chromosomes found in other body cells and are haploid.

Asexual reproduction is the reproductive process that results in genetically identical offspring from one parent.

Offspring produced by asexual reproduction are genetically identical to the parent and to each other, as there is no fusion of gametes and no mixing of genetic information, resulting in clones.

Sexual reproduction involves two parents while asexual reproduction involves one parent.

Meiosis is required for sexual reproduction.

Meiosis is a type of nuclear division that produces genetically different cells. The cells produced by meiosis are gametes (sex cells).

Meiosis is essential for sexual reproduction as it produces gametes (sperm cells and egg cells) with half the normal chromosome number.

False. Meiosis results in genetically different cells.

During meiosis the chromosome number is halved from diploid (46) to haploid (23). For this reason meiosis is known as reduction division.

The process of meiosis involves the following events:

Meiosis increases genetic variation by creating new combinations of maternal and paternal chromosomes in each gamete, leading to unique offspring.

The daughter cells produced by meiosis can be described as follows:

Meiosis is crucial because it ensures that gametes (sperm and egg cells) have half the chromosome number, allowing for the correct chromosome number after fertilisation.

Meiosis produces four daughter cells.

Some key differences between meiosis and mitosis might include:

Advantages of sexual reproduction are:

Sexual reproduction requires the production of specialised gametes and the search for a mate, which can be energetically costly and time-consuming.

Advantages of asexual reproduction:

Asexual reproduction lacks genetic variation, making offspring vulnerable to changes in the environment. It may also lead to the accumulation of harmful mutations and limit adaptability to new conditions.

Malarial parasites reproduce asexually in the human host, but sexually in the mosquito.

Many fungi reproduce asexually by spores but also reproduce sexually to give variation.

False. Many plants produce seeds sexually, but also reproduce asexually by runners such as strawberry plants, or bulb division such as daffodils.

The genome is the entire set of genetic material of an organism.

DNA (deoxyribonucleic acid) is the molecule that contains the instructions for growth and development of all organisms.

False. DNA is a polymer made up of two strands forming a double helix.

Chromosomes are located in the nucleus of cells.

A gene is a short length of DNA found on a chromosome that codes for a particular sequence of amino acids, to make a specific protein.

Genes code for different types of proteins.

The Human Genome Project was an international, collaborative research effort to determine the DNA sequence of the entire human genome and record every gene in human beings.

The human genome can help study human migration patterns because different populations of humans living in different parts of the world have developed very small differences in their genomes.

It is important to understand the human genome because it allows us to:

The four nucleotide bases in DNA are:

Complementary base pairing refers to the specific pairings of nucleotide bases in DNA.

False. A pairs with T

DNA is a polymer made up of two strands coiled around each other to form a double helix. The strands consist of a sugar-phosphate backbone with nitrogenous bases (A, T, C and G) attached to the backbone via complementary base pairing.

The backbone of a DNA strand is formed from the deoxyribose sugar of one nucleotide base and the phosphate molecule of the adjacent nucleotide base.

A polymer is a large molecule made up of many repeating subunits, in this case, nucleotides.

Three bases code for one amino acid during protein synthesis.

Protein synthesis is the process by which proteins are made in a cell using the DNA code to code for the correct sequence of amino acids to create the protein

The DNA template (mRNA) is read by the ribosome and carrier molecules (tRNA) bring new amino acids to the ribosome in the correct order to form the protein chain according to the DNA triplet code.

Genetic variants in coding DNA can alter the activity of a protein, potentially changing its function or effectiveness.

Genetic variants in non-coding DNA can alter how genes are expressed, potentially changing when, where, or how much a protein is produced.

When the protein chain is complete it folds up to form a unique shape. This unique shape enables the proteins to do their job as enzymes, hormones or forming structures in the body such as collagen.

A mutation is a change in DNA structure that may result in a change in the protein synthesized by a gene.

False. Most mutations do not alter the protein, or only alter it slightly so that its appearance or function is not changed.

A mutation may code for an altered protein with a different shape, causing an substrate to no longer fit the active site of the enzyme.

Inherited disorders are caused by the inheritance of certain alleles from parents to offspring.

Cystic fibrosis is a genetic disorder of cell membranes that results in the body producing large amounts of thick, sticky mucus in the air passages.

The cystic fibrosis allele is recessive

Polydactyly is a genetic disorder that causes someone to be born with extra fingers or toes.

The polydactyly allele is dominant.

Embryo screening is the process of analysing the genes of an embryo before implantation or while in the womb to detect genetic disorders.

False. Embryo screening raises economic, social, and ethical concerns, such as the potential destruction of embryos with genetic disorders.

Gene therapy is the process of inserting normal alleles into the chromosomes of an individual who carries defective alleles.

One argument for gene therapy is that it can help alleviate suffering in people with genetic disorders.

One argument against gene therapy is that...

There are 46 chromosomes (23 pairs of chromosomes) found in a normal human body cell.

Sex chromosomes are the chromosomes that determine the biological sex of an individual; in humans they are the X and Y chromosomes.

In biological females the sex chromosomes are XX.

In biological males the sex chromosomes are XY.

False. Biological sex is determined by an entire chromosome pair (XX for females, XY for males), not by a single gene.

True. The father determines the biological sex of the child because he can pass on either an X or a Y chromosome.

The probability of a child inheriting two X chromosomes is 1/2 or 50 %.