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Cell Division. Mitosis. The replication of autosomal cells. One cell splits in two creating two identical cells . The cell becomes diploid before splitting into two haploid cells which become diploid again. Video. Meiosis.
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Mitosis • The replication of autosomal cells. • One cell splits in two creating two identical cells. • The cell becomes diploid before splitting into two haploid cells which become diploid again. Video
Meiosis • Similar to mitosis, but the cells divide again to form four haploid cells. • These cells are sex cells or gametes. They become egg and sperm cells which come together to start a baby. • This is why we get half of our DNA from each parent. Video
Mitosis & Meiosis • Go to youtube.com • Watch “Cell Division, Meiosis” by neurocirujo • Watch “Cell division” by dizzo95
Heredity • Genetics
Genes • Gene: a sequence of DNA that codes for a particular characteristic • Allele: different versions of a gene • These different forms are what cause some differences between individuals (other differences are caused by your environment) • All the different genes and alleles that a species has is called the gene pool
Inheritance • 46 chromosomes (23 pairs) • Inherit one set of 23 from your mother, and one set of 23 from your father • Gene: a sequence of DNA that codes for a particular characteristic (eg. hair colour) • Allele: different versions of a gene (eg. brown hair, blonde hair, red hair)
Karyotype • A karyotype is a picture that allows us to see chromosomes arranged in pairs and by number • A karyotype detects the individual’s sex and some genetic disorders • Female (XX) • Male (XY) • Trisomy 21 (Down Syndrome) • The karyotype shows 22 pairs of autosomes (non-sex chromosomes) and 2 sex chromosomes
Mutation • Every difference in an allele is caused by a mutation in the DNA • A mutation in DNA can cause the wrong amino acid to be put into a polypeptide, producing a different protein from the gene • Can lead to cell death, impair important functions, or cause a change in a characteristic • A mutation could affect the colour of skin or hair in an animal. In humans, it could also result in a genetic disease such as removing the ability to digest some foods. Ie/ Lactose intolerance, Gluten intolerance (Celiac) • Sometimes a mutation may have no effect at all, other times it may be of benefit to the individual, but this is rare K. Chamberlain 2008
Heredity • Inheritance of genetic traits
Inheritance A sperm cell and an egg cell each contain a half set of chromosomes. So when they come together to create offspring, the offspring’s genetic material will be made up of half of it’s father’s DNA and half of it’s mother’s DNA. For every pair of chromosome, one will have been inherited from the mother, and the other will have been inherited from the father.
Sex chromosomes • Males: X Y • Females: XX • So a daughter (XX) has inherited one X from her mother and one X from her father • A son (XY) has inherited an X from his mother and a Y from his father
Inheritance • Phenotype: The set of observable characteristics of an individual resulting from the interaction of its genotype with the environment • Genotype: the genetic instructions that cause a produce a particular characteristic or phenotype. • Trait: any characteristic produced by a genotype. Eg. brown hair colour
Mendelian Inheritance • In the 1800‘s Mendel was the first scientist to observe patterns of inheritance • He performed many experiments on garden peas and was able to make conclusion about how certain traits were passed on from parent to offspring
Patterns of inheritance • Dominant traits and alleles - will appear in the offspring if one parent contributes it. They are represented by a capital letter (A, for example) • Eg, if one parent has brown hair and the other light hair, the child will get brown hair, as it is the dominant trait • Recessive traits and alleles - the offspring will only get the trait if both parents contribute the trait. These traits can be carried in the persons genes, without appearing in the person. They are represented by a lower case letter (a, for example) • Eg, a dark-haired person may have one gene for dark hair, which is a dominant trait and one gene for light hair, which is recessive. It is thus possible for two dark-haired parents to have a light-haired child, provided each parent contributes a gene for light hair. K.Chamberlain 2008
Genotypes • Often it is not possible to tell the genotype of the individual by looking at the phenotype • An individual with 2 copies of the same allele is called homozygous. This can also be called pure breeding. • Recessive traits are always homozygous (aa) • Dominant traits can be homozygous (AA) • An individual with 2 different alleles is called heterozygous. An organism with this genotype would be called a hybrid. • Dominant traits can also be heterozygous (Aa) K.Chamberlain 2008
Punnett Squares & Monohybrid Crosses • Punnett squares are used to predict the outcomes of a cross between 2 individuals • The top row has the gametes for 1 individual, and the left column, the gametes for the other individual • In the body of the table, the genotype that could be formed from each gamete combination is written K.Chamberlain 2008
Punnett Squares Sex Linked Autosomal K.Chamberlain 2008
Genetic Disease • Other than things like hair colour and eye colour, diseases can also be inherited from parents. • Eg. Huntingdon’s disease K.Chamberlain 2008
Pedigrees • Pedigrees are family tree diagrams that chart whether a characteristic is present. • They can also help determine if a trait is dominant or recessive. K.Chamberlain 2008
Pedigree Symbols K.Chamberlain 2008
Recessive Autosomal Trait patterns • The trait often skips generations. • • When both parents are affected, all children are affected. • • When both parents are unaffected, they may have affected children. • • Most matings of normal x affected produce all normal children K.Chamberlain 2008
Dominant Autosomal trait patterns • The trait usually occurs in every generation. • At least one parent of an affected child must be affected (no generation skipping). • When both parents are affected, children may be unaffected. K.Chamberlain 2008
Recessive sex-linked trait patterns • As with any X-linked trait, the disease is never passed from father to son. • Males are much more likely to be affected than females. If affected males cannot reproduce, only males will be affected. • All affected males in a family are related through their mothers. • Trait or disease is typically passed from an affected grandfather, through his carrier daughters, to half of his grandsons K.Chamberlain 2008
Dominant sex-linked trait patterns • The trait is never passed from father to son. • All daughters of an affected male and a normal female are affected. All sons of an affected male and a normal female are normal. • Matings of affected females and normal males produce 1/2 the sons affected and 1/2 the daughters affected. K.Chamberlain 2008
Y-linked trait patterns • An affected male can only produce affected sons and normal daughters. • A female can never have the trait K.Chamberlain 2008
Royal Pedigree K.Chamberlain 2008
