topic 1 classification, variation and...

Topic 1 – Classification, Variation and Inheritance

How are organisms classified?

• Kingdom (Animalia, Plantae, Fungi, Prokaryotae (bacteria), Protoctista)

• Phylum

• Class

• Order

• Family – always ends ‘ae’ or ‘ea’

• Genus – Italicised, capital letter

• Species – Italicised, lower case letter,

How to remember the order

Linnaeus Classification Mnemonic

Kingdom Largest Knowledge

Phylum Plus

Class Careful

Order Observation

Family Frequently

Genus Guarantees

species Smallest success

An American Robin

Turdus migratorious

A British Robin

Erithacus rubecula

These birds both have the common name ROBIN but they are

not from the same species, how do we know?

Binomial classification

The 5 Kingdoms

• Vertebrates = having a backbone or spinal column. (eg cat, human, fish, frog) phylum chordata.

• Invertebrates = Lacking a backbone or spinal column. (eg slug, starfish, insects)

The 5 Classes of Vertebrates Name Main characteristics

Fish Have wet scales and gills, lay eggs in water.

Amphibians Have smooth, moist, permeable skin. Adults have lungs. They lay eggs in water.

Reptiles Have dry, scaly skin. Have lungs They lay leathery shelled eggs.

Mammals Have hair on their body and mammary glands that produce milk. Have lungs. They give birth to live young.

Birds Have feathers and a beak. Have lungs. They lay hard shelled eggs.

Classifying vertebrates Absorbing oxygen?

• Fish and young amphibians = gills

• Mammals, birds, reptiles and adult amphibians = lungs

Reproduction?

• Internal fertilisation – sperm meets egg inside the body = mammals

• External fertilisation – female lays eggs then male releases sperm onto them = fish, amphibians

Maintaining Body temperature?

• Homeotherms – keep body temperature constant by releasing heat to their surroundings = mammals

• Poikilotherms – body temperature changes with surroundings = reptiles

Species Species are organisms that are capable of

interbreeding to produce fertile offspring.

Have Binomial Names eg Homo sapiens Felis catus

Exceptions 1. Hybrids (cross between 2 different species)

eg horse and donkey = mule 2. Ring Species Sometimes there are a chain of

neighbours that can all breed with their neighbour but the ones at either end can’t. These are called a ring species.

Variation Differences within a species. • Environmental – Caused by the environment eg. hair length, sun tan

• Genetic – inherited eg. natural hair colour, eye colour, certain diseases such as cystic fibrosis

• Continuous variation – range from low to high eg height, weight

• Discontinuous variation – distinct categories eg eye colour

Height

Normal Distribution (Bell Shaped) Curve

Natural Selection

Cells and DNA

Alleles

• An allele is an alternative form of a gene (one member of a pair).

• Organisms have two alleles for each characteristic eg hair colour, eye colour.

Gamete (Sperm)

Sexual Reproduction in humans

23 chromosomes 23

chromosomes Gamete (egg)

23 pairs of chromosomes

(one from each gamete)

Normal Body Cell

Punnet squares

• Capital letters show dominant alleles

• Lower case letters show recessive alleles

• The letters in the boxes represent the genotype

• The characteristic you see is called the phenotype e.g red flowers

Complete the punnet square and predict the phenotypes of the next generation.

•The dominant allele for brown eyes is B. •The recessive allele for blue eyes is b. A mother with brown eyes and a genotype Bb reproduces with a father with brown eyes and genotype Bb. What chance does the next generation have of having: Brown eyes? Blue eyes?

BB or bb = homozygous Bb = heterozygous (carriers are hetero)

B b

B BB

(brown) Bb

(Brown)

b Bb

(Brown) bb

(blue)

Ratio = 3 brown:1 blue Probability = 3 in 4 brown 1 in 4 blue Percentage chance = 75% brown 25% blue

Cystic Fibrosis Inherited disease caused by 2 recessive alleles (cc). Dominant allele (C) causes person to be CC – healthy or Cc - carrier. Symptoms thick sticky mucus on lungs coughing bacterial chest infections Breathlessness What chance of having cystic fibrosis from two carrier (Cc) parents?

Cystic Fibrosis

Al

Helen Deb Jack Izzie Gary

Bev

Fred Emma

1a. Which people have the disease?

b. What alleles do they have?

2. Al and Bev have the same alleles – what are they?

3a. Izzie could have 2 combinations of alleles – what could they be.

b. Why can we not tell from this diagram which ones they are?

Dominant – C Recessive - c

Sickle Cell Anaemia

Inherited disease caused by two recessive alleles (ss). Healthy = SS Carrier = Ss Red blood cells become mis shaped so can’t carry as much oxygen. Symptoms •Tiredness •Shortness of breath •Pale skin •Fainting