Inheritance AOS 4.1.3. - 2016

VCAA - Study Design inheritance: – the nature of chromosomes, alleles, genotype and phenotype – the causes of phenotypic variation: mutations; recombination of parental alleles in sexual reproduction; polygenes; and interactions of environmental factors with genes – continuous and discontinuous variation – patterns of inheritance involving the monohybrid cross: dominance; recessiveness; co-dominance; multiple alleles – dihybrid crosses as independent or linked – pedigree analysis: autosomal and sex-linked inheritance; use of the test cross. http://www.vcaa.vic.edu.au/Documents/vce/biology/BiologySD-2013.pdf

Variation Variation, the small differences that exist between individuals, can be described as being either be; discontinuous continuous

Continuous & Discontinuous Variation that has no limit on the value that can occur within a population. A line graph is used to represent continuous variation. Some examples are height, weight, intelligence, VCAA scores (don’t get me started!!)

Discontinuous Variation individuals fall into a number of distinct classes or categories, and is based on features that cannot be measured across a complete range.

What is a Chromosome? Chromosome is the highly condensed form of DNA Wrapped around histone proteins Wrapped into chromatin fiber Condensed during prophase into the familiar shape Humans have 22 autosomal pairs And one pair of sex chromosomes

Things to remember… Homologous chromosomes are not identical Can have different alleles of genes Sister chromatids are identical Form as cells go through S phase (replication) Attached to each other by centromere Until Anaphase of Mitosis Once separated each is again referred to as a chromosome

Alleles Each of two or more alternative forms of a gene that arise by mutation and are found at the same place (loci) on a chromosome

Genotype & Phenotype Genotype the set of genes in our DNA which is responsible for a particular trait. Phenotype is the physical expression, or characteristics, of that trait

Remember Genotype cannot be changed (generally) Phenotype is affected by the Environment

Variations - Phenotype Variation in the phenotype is caused either by the environment, by genetics, or by a combination of the two Meiosis and sexual reproduction introduces variation Independent assortment of the parental chromosomes; Crossing-over during Prophase I The random fertilisation that forms the zygote.

Mutations Point - single base Frame - gene (more than one base) Chromosome - structure http://www.biotecharticles.com/Genetics-Article/Types-of-Mutations-Frameshift-Chromosomal-and-Point-Mutation-120.html http://vce.bioninja.com.au/aos-3-heredity/molecular-genetics/mutations.html

Mutations

Chromosomal Mutations 5 types of mutations can occur;Five t Inversion, Translocation, Click, watch, answer Nondisjunction, Duplication, Deletion

Gene/Nucleotide Mutations –Point Mutations –Substitutions –Insertions –Deletions –Frameshift Click and GO!!!!

Patterns of Inheritance One man and his peas

……….and then came the flies One man and his peas…… Terms you need to know; Genotype Phenotype Homozygous Heterozygous Monohybrid Dihybrid ……….and then came the flies

Genetics 101 Genetics use letters to represent alleles. uppercase letters represent dominant alleles; lower case represent recessive alleles. An individual’s genotype is is expressed with one letter for each allele. An example, the gene for plant height results in tall or dwarf (short) plants. The allele for tall plant is dominant and is represented by upper case T. The allele for dwarf plant is recessive and assigned a lower case t. Possible genotypes are homozygous dominant ( TT) and heterozygous dominant (Tt) which gives a tall phenotype and homozygous recessive (tt) which presents a short phenotype.

Make sure we got this! TT Tt Rr rr rc

Assigning alleles Do not use letters that are similar shape when they are Capital and Lower case; GOOD Rr, Tt, Bb, Aa BAD Ww, Ss, Pp

Punnets and Probability

PUNNETS

MONOHYBRID CROSS

Parental F1 F2 YOUR GO!

Two traits – Dihybrid Cross Homozygous - Black fur: Long Tail BBTT Heterozygous - Black fur: Long Tail BbTt Homozygous - White fur: Short Tail bbtt

But first the rules

Rules

Two traits – Dihybrid Cross Homozygous - Black fur: Long Tail BBTT Heterozygous - Black fur: Long Tail BbTt Homozygous - White fur: Short Tail bbtt

Practice time Do Answer the questions

Test Cross

Linked Genes Some genes do not assort independently of each other; but rather are inherited together. They are on the same chromosome and are generally inherited together. It is possible to measure the relative position of various linked genes by comparing the ratio of the parental genotypes to recombined genotypes.

Sex linked/X linked A special type of monohybrid inheritance is called sex linkage. Genes carried on either of the chromosomes responsible for sex (X or Y) are said to be sex-linked.

X linked dominant In the case of X linked dominant traits the trait is more common in females than X linked recessive traits. A father will always pass such a trait to his daughters. A heterozygous mother will have a 50% chance of passing the trait to all her children regardless of sex. Hemophillia (H = normal: h = disease) Mum XHXh Dad XHY- (Mum is a carrier) Mother

X linked recessive Hemophilia (H = normal: h = disease) Mum XHXh Dad XhY- Father is affected and mum is a carrier

Pedigree Charts Autosomal Dominant Autosomal Recessive X-linked Dominant X-linked Recessive

Autosomal Dominant