CIE IGCSE Biology Unit 17: Inheritance

Punnett squares

inheritance

the transmission of genetic information from generation to generation

chromosome

a thread-like structure of DNA, carrying genetic information in the form of genes

gene

a length of DNA that codes for a protein

allele

a version of a gene

Describe the inheritance of sex in humans

The difference in sex chromosome between male and female leads to specific inheritance patterns for sex-linked genes

sequence of bases in a gene

the genetic code for putting together amino

acids in the correct order to make a specific

protein

How DNA controls cell functions

controls cell function by controlling the production of proteins (some of which are enzymes), antibodies and receptors for neurotransmitters

Protein synthesis

- the gene coding for the protein remains in

the nucleus

- mRNA molecules carry a copy of the gene

to the cytoplasm

- the mRNA passes through ribosomes

- the ribosome assembles amino acids into

protein molecules

- the specific order of amino acids is

determined by the sequence of bases in

the mRNA

genes not expressed

all body cells in an organism contain the same genes, but many genes in a particular cell are not expressed because the cell only makes the specific proteins it needs

haploid nucleus

a nucleus containing a single set of unpaired

chromosomes, e.g. in gametes

diploid nucleus

a nucleus containing two sets of chromosomes, e.g. in body cells. There are 23 pairs of chromosomes in a human diploid cell

mitosis

nuclear division giving rise to genetically identical cells

Process of mitosis

the exact duplication of chromosomes occurs before mitosis and the copies of chromosomes separate, maintaining the chromosome number

role of mitosis

growth, repair of damaged tissues, replacement of cells and asexual reproduction

stem cells

unspecialised cells that divide by mitosis to produce daughter cells that can become specialised for specific functions

meiosis

reduction division in which the chromosome number is halved from diploid

to haploid resulting in genetically different cells

How meiosis produces variation

by forming new combinations of maternal and

paternal chromosomes

genotype

the genetic make-up of an organism in terms of the alleles present

phenotype

the observable features of an organism

homozygous

having two identical alleles of a particular gene, two identical homozygous individuals that breed together will be pure-breeding

heterozygous

having two different alleles of a particular gene, will not be pure-breeding

dominant

an allele that is expressed if it is present

recessive

an allele that is only expressed when there is no dominant allele of the gene present

genetic diagrams

Finding the possible phenotypic ratio for offsprings

pedigree diagrams

A pedigree chart is a diagram that shows the occurrence and appearance or phenotypes of a particular gene or organism and its ancestors from one generation to the next

punnet square

Finding the possible phenotypic ratio for offsprings

co-dominance

reference to the inheritance of ABO blood groups - phenotypes being A, B, AB and O blood groups and alleles being IA IB and Io

sex-linked characteristic

a characteristic in which the gene responsible

is located on a sex chromosome and that this

makes it more common in one sex than in the

other

colour blindness

An inherited condition in which one or more of the three type of cone cell are unable to respond to coloured light.