Genetics (both topcis)

Chromosome

A long, organized structure of DNA that contains many genes.

46 (23 pairs)

→ 22 pairs = autosomes

→ 1 pair = sex chromosomes

How many chromosomes does humans usually have?

e.g. 🧬 Mum's chromosome 1 + 🧬 Dad's chromosome 1
= homologous pair

Gene

A section of DNA that contains instructions for a particular function or characteristic, such as making a protein.

Allele

A different version of a gene. For example, a gene may influence eye colour, while different alleles contribute to different eye-colour variants.

Trait

A characteristic or feature of an organism, such as blood type or eye colour.

Trait Variant

A different form of a trait. For example, blue vs brown eyes are variants of the eye-colour trait.

Homologous chromosomes

A pair of chromosomes, one inherited from each parent, that carry the same types of genes in the same locations, although they may have different alleles.

Haploid (n)

HAP-loid= HALF the chromosome number → 23

A cell containing one set of chromosomes.

Diploid (2n)

DI-ploid= TWO sets→ 46

A cell containing two sets of chromosomes, one set from each parent.

Autosome

Any chromosome that is not a sex chromosome.

Contain genes for lots of the characteristics and functions of your body that aren't specifically determined by your sex chromosomes.

e.g. blood-related characteristics, metabolism, how cells function, enzymes, physical characteristics, susceptibility to some diseases

1-22 autosomes

How many autosomes does humans have?

Somatic cell

Any body cell that is not a gamete. Usually a diploid

e.g. skin, muscle, liver

Gamete

A sex/reproductive cell: sperm or egg used to make anew organism

They are haploids (23)

Homozygous

Having two identical alleles for a gene.

e.g. AA or aa

Heterozygous

Having two different alleles for a gene

e.g. Aa

Recessive

An allele whose effect is generally masked by a dominant allele in a heterozygous individual. It is usually expressed when two recessive alleles are present (aa).

Dominant

An allele that determines the phenotype when present in a heterozygote. Example: A in Aa.

Karyotype

An organised picture/display of a person's chromosomes, usually arranged in pairs according to size and structure.

Incomplete dominance

Neither allele completely masks the other, so the heterozygote has an intermediate phenotype.

e.g. Red flower × white flower → pink flower

Condominance

Both alleles are fully expressed at the same time in the heterozygote

e.g. Blood type AB → both A and B antigens are expressed.

Multifactorial

A trait influenced by multiple genes AND environmental factors.

e.g. height, body weight, and risk of some diseases.

Mutation

A change in the DNA sequence. Mutations can be harmful, beneficial, or have no noticeable effect.

Single nucleotide polymorphism (SNP)

A common variation involving one nucleotide/base in DNA.

When one DNA letter differs between people at the same position.

e.g.

Person 1:
A — T — C — G — A

Person 2:
A — T — T — G — A
↑
one difference

Carrier

A person who has a recessive disease-associated allele but usually does not show the condition because they have another functioning allele.

Sex-linked

A gene is located on a sex chromosome, usually the X chromosome.

• X-linked = gene is located on the X chromosome.

  Y-linked = gene is located on the Y chromosome.

Independent assortment

During meiosis, homologous chromosome pairs are distributed independently into gametes.

Segregation

The two alleles of a gene separate during meiosis so that each gamete receives one allele.

Genotype

The genetic makeup of an individual for a particular gene.

e.g. AA, Aa or aa

Phenotype

The observable characteristic produced by the interaction of genotype and environment.

Meiosis

The process that makes gametes

Sex chromosomes

• Female → XX

• Male → XY

The pair of chromosomes involved in determining biological sex and also carrying other genes.

SRY gene

A gene located on the Y chromosomes that starts the pathway of typical male sex development.

e.g. hormonal development

DNA

A molecule that stores the genetic information or instructions.

A long chain of nucleotides.

The four bases are: A, T, C, G

Nucleotide

One of the building blocks that makes up DNA

Somatic cells

The cells in your body EXCEPT your gametes (egg or sperm).

Examples include:

• 🧠 Brain cells

• ❤ Heart cells

• 🦴 Bone cells

mRNA

This is the duplicated copy of DNA that leaves the nucleus to transfer to the ribosome.

Ribosome

A structure in the cell that makes proteins.

64

How many codons are possible to be made?

Codons

The sequence of DNA genes.

Example:

• mRNA: AUG | CCU | GAA | UGC or mRNA: AUG | AAA | GCU | UUU

AUG is typically the start codon; tells the ribosome where to begin translating.

Genetic recombination

The process where DNA/alleles from the parents get rearranged into new combinations during meiosis.

It happens during meiosis 1 during cross ober

Cystic Fibrosis

An inherited genetic disorder that affects how cells handle salt and water in the body. This is due to the changes in the CFTR gene.

CFTR gene

Helps control the movement of salt and water across the cell membrane.

The body’s secretions can become thicker and stickier than normal

e.g. 🫁 Lungs → thick mucus can build up and make breathing and infections more difficult.

What happens when CFTR doesn’t work properly?

Achondroplasia

A genetic condition that affects bone growth, particularly the growth of the long bones in the arms and legs.

Autosomal dominant

Xeroderma pigmentosum

A rare genetic condition where the body has difficulty repairing DNA damage caused by ultraviolet (UV) radiation.

Autosomal recessive

Blood typing

A system used to classify blood based on whether your red blood cells have A and/or B antigens on their surface.

A, B, AB, O

The four blood groups

Blood group

Determined by the antigen(s) on your red blood cells.

• Type A → RBCs have A antigen

• Type B → RBCs have B antigen

• Type AB → RBCs have A and B antigens

• Type O → RBCs have neither A nor B antigen

Haemoglobin

A protein inside RBC that carries oxygen

Sickling gene

a variant of the HBB gene, which provides instructions for making beta-globin, a part of haemoglobin.

Beta-globin one of the protein chains that makes up hemoglobin

HBB gene: contains instructions to make HBB gene

Pedigree

A family tree diagram used to track how a genetic trait or condition is passed through generations.

Sex- linked inheritance

A gene responsible for a trait or condition is located on a sex chromosome — usually the X chromosome.

Haemophilia

An inherited bleeding disorder where the blood does not clot properly.

Hemophilia A

factor VIII is missing or doesn't work properly.

Hemophilia B

factor IX is missing or doesn't work properly.