10 Science- Biology

Absoutly no idea ✌🏻

DNA

Deoxyribonucleic Acid is found in the nucleus of every cell. It carries the genetic instructions for the development, functioning and reproduction of all living organisms

How many chromosomes does a human have ?

46 (23 pairs)

What does DNA code for

inherited characteristics - such as eye colour, blood type

DNA replication

Replication copies DNA before cell division so each new cell receives a complete set of genetic instructions

Males chromosomes

XY (one X, one Y chromosome)

side note- X-linked recessive conditions appear more often in males because they have no second X to ‘mask’ the recessive allele

Female chromosomes

XX (two X chromosomes)

Punnett squares

are used to predict the probability of offspring inheriting particular genotypes and phenotypes

Reading Pedigree charts

Squares- males

circles- females

shaded- affected individual

unshaded- unaffected

horizontal line between two individuals- mating pair

vertical lines- offspring

Type of inheritance from a pedigree

If the trait skips a generation- likely recessive

if every generation is affected- likely dominant

if only males are affected- likely X-linked recessive

If both sexes equally affected- likely autosomal

Nucleotide

The structural (building block) unit of DNA. Consists of a deoxyribose sugar + phosphate backbone + one nitrogenous base.

Nitrogenous bases

Adenine (A), Thymine (T), Cytosine (C), Guanine (G). Bases pair specifically: A–T and C–G (complementary base pairing).

DNA

Long molecule made of nucleotides carrying genetic code. Makes up chromosomes

Gene

A specific segment of DNA that codes for a particular trait or protein. A section of DNA on a chromosome

Chromosome

Tightly coiled strands of DNA found in the nucleus. Contains thousands of genes

Two Basic Functions of DNA

•       Carrying genetic information — the sequence of bases stores instructions for all traits

•       Coding to produce proteins — genes direct the production of proteins that control body functions

Helicase

Unwinds and 'unzips' the double helix by breaking hydrogen bonds between base pairs. STEP 1

DNA Polymerase

Reads the template strand and adds complementary nucleotides to build a new strand (A–T, C–G). STEP 2

DNA Ligase

Joins (seals) fragments of newly made DNA together to form a continuous strand. STEP 3

Allele

Different versions of the same gene (e.g. B = brown eyes, b = blue eyes).

Dominant allele

Expressed in the phenotype even when only one copy is present. Written as a CAPITAL letter (e.g. B).

Recessive allele

Only expressed when two copies are present (homozygous recessive). Written in lowercase (e.g. b).

Genotype

The genetic make-up of an organism — the alleles it carries (e.g. BB, Bb, bb).

Phenotype

The physical expression of the genotype — the trait that is visible (e.g. brown eyes).

Homozygous

Two identical alleles (BB or bb).

Heterozygous

Two different alleles (Bb). The dominant trait is expressed.

Autosomal

On non-sex chromosomes (chromosomes 1–22). Cystic fibrosis, freckles. Affects males and females equally

Sex-linked

On the X chromosome (usually). Colour blindness, haemophilia. More common in males (they have only one X)