Heredity CH 7 PP 1 An introduction Family

Heredity CH 7 – PP 1 An introduction

Family Resemblance

Heredity • The study of inheritance – Genetics • study of mechanism and patterns of inheritance – Gene • Segment of DNA that codes for a specific protein – Genome • Sum of all DNA – Genomics • Study of genomes

Bioinformatics • Using IT to: – Manage large amounts of biological data – Analyse the data • 2003 the Human Genome Project completed mapping the entire human genome – Sequence of base pairs in human DNA – More than three billion pairs

Human Genome Project • Mapped genomes of – Human DNA (a reference genome) – E. Coli – Fruit Fly (Drosophila melanogaster) – Laboratory mouse

Human Genome • 6 billion bases make up your genome – 3 billion pairs – 1 billion codons • 46 chromosomes – 23 pairs

DNA Chromosome • In Eukaryotic organisms, DNA molecules and associated proteins are contained within the nucleus as tangled fibres of chromatin • During division, the long DNA molecules appear as double structures each coiled around histone proteins • In eukaryotes, chromosomes exist as pairs

DNA Chromosome

DNA Chromosome

Shapes of Chromosomes

Chromosome

Chromosome • Telomere – caps the end of the chromatid – Prevents degradation of the DNA – Helps DNA replication

Chromosome • Centromere – Region that divides the chromosome into unequal length arms – Links the two chromatids

Chromosome • Staining chromosomes reveals banding patterns • Pattern is the same in each pair of chromosomes – Homologous chromosomes • Used to manually pair chromosomes

Photos of Human chromosomes

Karyotype • Photographic images of chromosomes are ordered by length, from largest to smallest • Humans have 22 pairs of matched or homologous chromosomes PLUS one pair of sex chromosomes • The number of chromosomes in each somatic (body) cell is called the diploid number 2 n. As chromosomes occurs in pairs, n stands for the number of pairs. Eg Human 2 n =46

Karyotype Autosomes Heterosomes or Sex chromosomes

Karyotype

Numbers of chromosomes • Varies between organisms and is not a measure of the quantity of genetic material – Human 46 (that is 23 pairs) – Chimpanzee 48 – Horse 64 – Dog 78 – Housefly 12 – Cabbage 18 – Potato 48

Sex chromosomes • In humans there is a 50% chance that a sperm carrying a X chromosome OR 50% carrying a Y chromosome will fertilise an egg. • Not always like this in other species • Birds – males are XX, females XY • Some insects females are XX, males XO – only females need matched pair • Bees, females come from fertilised eggs and are diploid, males come from unfertilised eggs and are haploid

Genes • Segment of DNA that directs the formation of a particular structural and functional protein • Vary in size from 8000 to 2 million base pairs • Humans have approx 25, 000 genes • Each gene is found at a particular location on a chromosome called a locus (plural loci)

Inherited Traits

Inherited Traits • Many genes have two or more variations – Alleles • Widow’s Peak has two alleles – Widow’s Peak – Straight hairline

Inherited Traits • You inherit one gene for hairline from each parent • You can inherit – Two genes for Widow’s Peak – Two genes for straight hairline – One gene of each

Inherited Traits • What happens when you inherit one type of allele from each parent? – One allele for straight hairline – One allele for Widow’s Peak

Inherited Traits • What happens when you inherit one type of allele from each parent? e p – One allele for straight hairline ty o – One allele for Widow’s Peak Gen • You have a Widow’s Peak! e p ty o n he P Phenotype = genotype + environmental effects

Inherited Traits • Shorthand way of representing alleles – Widow’s Peak W Straight Hairline w

Inherited Traits Widow’s Peak W Straight Hairline Individual genotypes can be: w Phenotypes WW Widow’s Peak Ww Widow’s Peak ww Straight hairline

Inherited Traits • Widow’s Peak shows up in both W W and W w • Widow’s Peak is said to be Dominant • Straight hairline is said to be Recessive • Having both alleles the same is said to be Homozygous (also called true breeding) • Having both different is said to be Heterozygous (also called a hybrid)

Human Hairline • Widow’s Peak – Autosomal dominant • Straight hairline – Autosomal recessive Explain what this means?

Monohybrid Cross • True breeding Widow’s Peak with straight hairline. P HH X hh H = Widow’s Peak h = straight hairline

Monohybrid Cross • True breeding Widow’s Peak with straight hairline. P F 1 X HH Hh Hh h hh Hh Heterozygous h Hh H H Hh Hh

Monohybrid Cross • Cross two of the F 1 generation F 1 X Hh H Hh h HH Hh Hh hh Genotype ratio HH : Hh : hh 1 : 2 : 1 F 2 HH Hh Hh hh Phenotype ratio Widow’s : Straight 3 : 1

Activitis “Create a Human Karyotype” http: //learn. genetics. utah. edu/content/chromosomes/karyotype/ Then try your hand at diagnosing some genetic diseases on “Diagnose using Karyotypes” http: //www. biology. arizona. edu/human_bio/activities/karyotyping. html Links on Moodle ***plus 9 past exam questions

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