Science Test 1 Y10 - DNA

gl!! my wording might be confusing for this sorry :,) i'm rushing to make this. I WANNA BE CLEAR ABT THIS PPL HAVE 23 DIFFERENT TYPES OF CHROMOSOMES AND 2 OF EACH TYPE, BOTH GIVING DIFFERENT INFO (idk if that made sense in here)

DNA

Also known as deoxyribonucleic-acid, the basis of inheritance which is made up of nucleotides and is found in the nucleus of all cells that have one. Is in the shape of a double-sided helix

Nucleotide

The building block of DNA, which is made up of phosphate, a deoxyribose sugar, and a nitrogenous base. Connect to others through weak hydrogen bonds formed between bases

Structure of DNA

Made up of two sugar-phosphate backbones (the vertical lines), connected by lines of nitrogenous bases connected by hydrogen bonds (the horizontal)

The Nitrogenous Bases and the Pairing Rule

Four in total, being adenine, thymine, cytosine, and guanine (ATCG). Generally, only the complementary bases are able to pair (adenine with thymine, cytosine with guanine). The order of the bases provide instructions for how certain areas of the body should function (usually just proteins)

Chromosome

A large length of DNA tightly wrapped around proteins, which contains many genes. Usually has 23 different versions in a human body. Extremely information dense in order to make being pulled apart for cell division easier. The amount of these in each organism vary (e.g., 46 in humans)

Gene

A large section of DNA which codes a specific protein or trait, such as skin type or dimples

Cell Division

The process by which a single cell splits into daughter cells. Comes in two forms, mitosis and meiosis. Is important as it provides an exact replica of DNA for a cell in the body. Works due to the complementary base pairing rule, meaning each half of a chromosome be a template for another half

Mitosis

The process by which a cell splits it’s chromosomes in half to create double the amount of chromosomes, in order to create two daughter cells (would be diploid cells represented by 2n). Used for growth, repair and replacing

Meiosis

The process by which a cell splits it’s chromosomes in half to create double the chromosomes, which are then split between 2 daughter cells, then into 4 daughter cells (meaning each has half the amount of chromosomes). These cells are known as gametes, represented as haploid/n, and are for sexual reproduction

Fertilisation

The process in which two gametes with half the number of chromosomes combine to create one cell with the total amount of chromosomes

Process of Cell Division

1. DNA molecule unwinds from chromosome

2. DNA molecule unzips (gets cut in half)

3. Two separate strands form

4. Each side of the DNA acts as a template for new strands using spare nucleotides in the cell

5. Each new side zips up (is put back together)

6. Identical copy of DNA is created

Homologous Chromosomes

Two chromosomes inherited from each parent that have the same purpose (same genes coding same things), and are similar in height, length and centromere location, though having different alleles. Are paired together in a karyotype, and are only not found between and X and Y chromosome

Alleles

Alternative forms of the same gene (e.g., hair colour having brown and blonde)

Purpose of Mitosis

1. For Growth (for a fertilised egg/height)

2. For Repairing (healing wounds, cuts, and broken bones)

3. For Replacing (replacing old, dead, or damaged cells)

Why Meiosis has 2 Divisions

As one division individually splits each chromosome in half, in order to create double the amount of total chromosomes. The second puts half of the total group in one cell, and the other half in another cell

How Genetic Information is From Both Parents

Both parents’ gametes (egg and sperm) are gametes and combine to create a person’s set of 46 chromosomes

Karyotype

A visual display of all of a person’s chromosomes, arranged from longest to shortest in their homologous pairs. Sex chromosomes are found at the end, generally with male karyotypes having XY chromosomes, and female having XX

Amounts of Chromosomes in Other Animals

• Goldfish - 25 types

• Fruit fly - 4 types

• Cat - 19 types

Inheritance

The process by which genetic information is passed down from parents to children

The Contribution to Gregor Mendel to Inheritance

Created three key principles of inheritance, being:

• Inheritance is determines by genes passed onto offspring

• Offspring inherit one gene for each trait

• A trait may not show up in one offspring, but can still appear in the next generation (recessive genes)

Phenotype

How a genetic trait actually looks on the body (e.g., Bb looking like blue eyes). This can be affected by outside factors, such as lack of nutrients or harsh environment

Genotype

The genetic makeup of a specific trait (e.g., blue eyes as Bb). Is communicated as two letters, with capital letters being first and representing the dominant trait, and lowercase being recessive traits

Homozygous

Also known as pure-bred, where a trait is made up of two of the same alleles. Is found in two forms, dominant (having both dominant traits, e.g., BB) and recessive (having both recessive traits, e.g., bb)

Heterozygous

Also known as hybrid, where a trait is made up of a dominant and a recessive allele, e.g., Bb. Will always be displayed as the dominant trait

X-Linked Traits

Traits which are present on the X Chromosome. These traits are more commonly passed onto men as generally they are recessive, and generally men have only one X Chromosome (meaning there can be no dominant gene to overcome the recessive). On the other hand, women generally have two X chromosomes meaning there are more possibilities for a dominant trait to be passed on to overcome the recessive

Notation of Sex-linked Inheritance

X Chromosome is always put before any other chromosomes, and X Chromosomes will have the trait letter in superscript (e.g., XᴬXᵃ). Y will usually have no trait unless it is relevant

Punnet Square

Visualisation of the different possibilities of the passing on of genes. If sexes are known, the male alleles (letters) will be put down the column, while the female alleles will be put across the row

Autosomal vs Sex Linked

Autosomal refers to any chromosomes besides the X and Y chromosomes, while sex-linked refers to only the X and Y